as_bind_group.rs

use bevy_macro_utils::{get_lit_bool, get_lit_str, BevyManifest, Symbol};
use proc_macro::TokenStream;
use proc_macro2::{Ident, Span};
use quote::{quote, ToTokens};
use syn::{
    parenthesized,
    parse::{Parse, ParseStream},
    punctuated::Punctuated,
    token::{Comma, DotDot},
    Data, DataStruct, Error, Fields, LitInt, LitStr, Meta, MetaList, Result,
};

const UNIFORM_ATTRIBUTE_NAME: Symbol = Symbol("uniform");
const TEXTURE_ATTRIBUTE_NAME: Symbol = Symbol("texture");
const STORAGE_TEXTURE_ATTRIBUTE_NAME: Symbol = Symbol("storage_texture");
const SAMPLER_ATTRIBUTE_NAME: Symbol = Symbol("sampler");
const STORAGE_ATTRIBUTE_NAME: Symbol = Symbol("storage");
const BIND_GROUP_DATA_ATTRIBUTE_NAME: Symbol = Symbol("bind_group_data");
const BINDLESS_ATTRIBUTE_NAME: Symbol = Symbol("bindless");
const DATA_ATTRIBUTE_NAME: Symbol = Symbol("data");
const BINDING_ARRAY_MODIFIER_NAME: Symbol = Symbol("binding_array");
const LIMIT_MODIFIER_NAME: Symbol = Symbol("limit");
const INDEX_TABLE_MODIFIER_NAME: Symbol = Symbol("index_table");
const RANGE_MODIFIER_NAME: Symbol = Symbol("range");
const BINDING_MODIFIER_NAME: Symbol = Symbol("binding");

#[derive(Copy, Clone, Debug)]
enum BindingType {
    Uniform,
    Texture,
    StorageTexture,
    Sampler,
    Storage,
}

#[derive(Clone)]
enum BindingState<'a> {
    Free,
    Occupied {
        binding_type: BindingType,
        ident: &'a Ident,
    },
    OccupiedConvertedUniform,
    OccupiedMergeableUniform {
        uniform_fields: Vec<&'a syn::Field>,
    },
}

enum BindlessSlabResourceLimitAttr {
    Auto,
    Limit(LitInt),
}

// The `bindless(index_table(range(M..N)))` attribute.
struct BindlessIndexTableRangeAttr {
    start: LitInt,
    end: LitInt,
}

pub fn derive_as_bind_group(ast: syn::DeriveInput) -> Result<TokenStream> {
    let manifest = BevyManifest::shared();
    let render_path = manifest.get_path("bevy_render");
    let image_path = manifest.get_path("bevy_image");
    let asset_path = manifest.get_path("bevy_asset");
    let ecs_path = manifest.get_path("bevy_ecs");

    let mut binding_states: Vec<BindingState> = Vec::new();
    let mut binding_impls = Vec::new();
    let mut bindless_binding_layouts = Vec::new();
    let mut non_bindless_binding_layouts = Vec::new();
    let mut bindless_resource_types = Vec::new();
    let mut bindless_buffer_descriptors = Vec::new();
    let mut attr_prepared_data_ident = None;
    // After the first attribute pass, this will be `None` if the object isn't
    // bindless and `Some` if it is.
    let mut attr_bindless_count = None;
    let mut attr_bindless_index_table_range = None;
    let mut attr_bindless_index_table_binding = None;

    // `actual_bindless_slot_count` holds the actual number of bindless slots
    // per bind group, taking into account whether the current platform supports
    // bindless resources.
    let actual_bindless_slot_count = Ident::new("actual_bindless_slot_count", Span::call_site());
    let bind_group_layout_entries = Ident::new("bind_group_layout_entries", Span::call_site());

    // The `BufferBindingType` and corresponding `BufferUsages` used for
    // uniforms. We need this because bindless uniforms don't exist, so in
    // bindless mode we must promote uniforms to storage buffers.
    let uniform_binding_type = Ident::new("uniform_binding_type", Span::call_site());
    let uniform_buffer_usages = Ident::new("uniform_buffer_usages", Span::call_site());

    // Read struct-level attributes, first pass.
    for attr in &ast.attrs {
        if let Some(attr_ident) = attr.path().get_ident() {
            if attr_ident == BIND_GROUP_DATA_ATTRIBUTE_NAME {
                if let Ok(prepared_data_ident) =
                    attr.parse_args_with(|input: ParseStream| input.parse::<Ident>())
                {
                    attr_prepared_data_ident = Some(prepared_data_ident);
                }
            } else if attr_ident == BINDLESS_ATTRIBUTE_NAME {
                attr_bindless_count = Some(BindlessSlabResourceLimitAttr::Auto);
                if let Meta::List(_) = attr.meta {
                    // Parse bindless features.
                    attr.parse_nested_meta(|submeta| {
                        if submeta.path.is_ident(&LIMIT_MODIFIER_NAME) {
                            let content;
                            parenthesized!(content in submeta.input);
                            let lit: LitInt = content.parse()?;

                            attr_bindless_count = Some(BindlessSlabResourceLimitAttr::Limit(lit));
                            return Ok(());
                        }

                        if submeta.path.is_ident(&INDEX_TABLE_MODIFIER_NAME) {
                            submeta.parse_nested_meta(|subsubmeta| {
                                if subsubmeta.path.is_ident(&RANGE_MODIFIER_NAME) {
                                    let content;
                                    parenthesized!(content in subsubmeta.input);
                                    let start: LitInt = content.parse()?;
                                    content.parse::<DotDot>()?;
                                    let end: LitInt = content.parse()?;
                                    attr_bindless_index_table_range =
                                        Some(BindlessIndexTableRangeAttr { start, end });
                                    return Ok(());
                                }

                                if subsubmeta.path.is_ident(&BINDING_MODIFIER_NAME) {
                                    let content;
                                    parenthesized!(content in subsubmeta.input);
                                    let lit: LitInt = content.parse()?;

                                    attr_bindless_index_table_binding = Some(lit);
                                    return Ok(());
                                }

                                Err(Error::new_spanned(
                                    attr,
                                    "Expected `range(M..N)` or `binding(N)`",
                                ))
                            })?;
                            return Ok(());
                        }

                        Err(Error::new_spanned(
                            attr,
                            "Expected `limit` or `index_table`",
                        ))
                    })?;
                }
            }
        }
    }

    // Read struct-level attributes, second pass.
    for attr in &ast.attrs {
        if let Some(attr_ident) = attr.path().get_ident()
            && (attr_ident == UNIFORM_ATTRIBUTE_NAME || attr_ident == DATA_ATTRIBUTE_NAME)
        {
            let UniformBindingAttr {
                binding_type,
                binding_index,
                converted_shader_type,
                binding_array: binding_array_binding,
            } = get_uniform_binding_attr(attr)?;
            match binding_type {
                UniformBindingAttrType::Uniform => {
                    binding_impls.push(quote! {{
                            use #render_path::render_resource::AsBindGroupShaderType;
                            let mut buffer = #render_path::render_resource::encase::UniformBuffer::new(Vec::new());
                            let converted: #converted_shader_type = self.as_bind_group_shader_type(&images);
                            buffer.write(&converted).unwrap();
                            (
                                #binding_index,
                                #render_path::render_resource::OwnedBindingResource::Buffer(render_device.create_buffer_with_data(
                                    &#render_path::render_resource::BufferInitDescriptor {
                                        label: None,
                                        usage: #uniform_buffer_usages,
                                        contents: buffer.as_ref(),
                                    },
                                ))
                            )
                        }});

                    match (&binding_array_binding, &attr_bindless_count) {
                        (&None, &Some(_)) => {
                            return Err(Error::new_spanned(
                                attr,
                                "Must specify `binding_array(...)` with `#[uniform]` if the \
                                    object is bindless",
                            ));
                        }
                        (&Some(_), &None) => {
                            return Err(Error::new_spanned(
                                attr,
                                "`binding_array(...)` with `#[uniform]` requires the object to \
                                    be bindless",
                            ));
                        }
                        _ => {}
                    }

                    let binding_array_binding = binding_array_binding.unwrap_or(0);
                    bindless_binding_layouts.push(quote! {
                            #bind_group_layout_entries.push(
                                #render_path::render_resource::BindGroupLayoutEntry {
                                    binding: #binding_array_binding,
                                    visibility: #render_path::render_resource::ShaderStages::FRAGMENT | #render_path::render_resource::ShaderStages::VERTEX | #render_path::render_resource::ShaderStages::COMPUTE,
                                    ty: #render_path::render_resource::BindingType::Buffer {
                                        ty: #uniform_binding_type,
                                        has_dynamic_offset: false,
                                        min_binding_size: Some(<#converted_shader_type as #render_path::render_resource::ShaderType>::min_size()),
                                    },
                                    count: #actual_bindless_slot_count,
                                }
                            );
                        });

                    add_bindless_resource_type(
                        &render_path,
                        &mut bindless_resource_types,
                        binding_index,
                        quote! { #render_path::render_resource::BindlessResourceType::Buffer },
                    );
                }

                UniformBindingAttrType::Data => {
                    binding_impls.push(quote! {{
                            use #render_path::render_resource::AsBindGroupShaderType;
                            use #render_path::render_resource::encase::{ShaderType, internal::WriteInto};
                            let mut buffer: Vec<u8> = Vec::new();
                            let converted: #converted_shader_type = self.as_bind_group_shader_type(&images);
                            converted.write_into(
                                &mut #render_path::render_resource::encase::internal::Writer::new(
                                    &converted,
                                    &mut buffer,
                                    0,
                                ).unwrap(),
                            );
                            let min_size = <#converted_shader_type as #render_path::render_resource::ShaderType>::min_size().get() as usize;
                            while buffer.len() < min_size {
                                buffer.push(0);
                            }
                            (
                                #binding_index,
                                #render_path::render_resource::OwnedBindingResource::Data(
                                    #render_path::render_resource::OwnedData(buffer)
                                )
                            )
                        }});

                    let binding_array_binding = binding_array_binding.unwrap_or(0);
                    bindless_binding_layouts.push(quote! {
                            #bind_group_layout_entries.push(
                                #render_path::render_resource::BindGroupLayoutEntry {
                                    binding: #binding_array_binding,
                                    visibility: #render_path::render_resource::ShaderStages::FRAGMENT | #render_path::render_resource::ShaderStages::VERTEX | #render_path::render_resource::ShaderStages::COMPUTE,
                                    ty: #render_path::render_resource::BindingType::Buffer {
                                        ty: #uniform_binding_type,
                                        has_dynamic_offset: false,
                                        min_binding_size: Some(<#converted_shader_type as #render_path::render_resource::ShaderType>::min_size()),
                                    },
                                    count: None,
                                }
                            );
                        });

                    add_bindless_resource_type(
                        &render_path,
                        &mut bindless_resource_types,
                        binding_index,
                        quote! { #render_path::render_resource::BindlessResourceType::DataBuffer },
                    );
                }
            }

            // Push the non-bindless binding layout.

            non_bindless_binding_layouts.push(quote!{
                    #bind_group_layout_entries.push(
                        #render_path::render_resource::BindGroupLayoutEntry {
                            binding: #binding_index,
                            visibility: #render_path::render_resource::ShaderStages::FRAGMENT | #render_path::render_resource::ShaderStages::VERTEX | #render_path::render_resource::ShaderStages::COMPUTE,
                            ty: #render_path::render_resource::BindingType::Buffer {
                                ty: #uniform_binding_type,
                                has_dynamic_offset: false,
                                min_binding_size: Some(<#converted_shader_type as #render_path::render_resource::ShaderType>::min_size()),
                            },
                            count: None,
                        }
                    );
                });

            bindless_buffer_descriptors.push(quote! {
                #render_path::render_resource::BindlessBufferDescriptor {
                    // Note that, because this is bindless, *binding
                    // index* here refers to the index in the
                    // bindless index table (`bindless_index`), and
                    // the actual binding number is the *binding
                    // array binding*.
                    binding_number: #render_path::render_resource::BindingNumber(
                        #binding_array_binding
                    ),
                    bindless_index:
                        #render_path::render_resource::BindlessIndex(#binding_index),
                            size: Some(
                                <
                                    #converted_shader_type as
                                    #render_path::render_resource::ShaderType
                                >::min_size().get() as usize
                            ),
                }
            });

            let required_len = binding_index as usize + 1;
            if required_len > binding_states.len() {
                binding_states.resize(required_len, BindingState::Free);
            }
            binding_states[binding_index as usize] = BindingState::OccupiedConvertedUniform;
        }
    }

    let fields = match &ast.data {
        Data::Struct(DataStruct {
            fields: Fields::Named(fields),
            ..
        }) => &fields.named,
        _ => {
            return Err(Error::new_spanned(
                ast,
                "Expected a struct with named fields",
            ));
        }
    };

    // Count the number of sampler fields needed. We might have to disable
    // bindless if bindless arrays take the GPU over the maximum number of
    // samplers.
    let mut sampler_binding_count: u32 = 0;

    // Read field-level attributes
    for field in fields {
        // Search ahead for texture attributes so we can use them with any
        // corresponding sampler attribute.
        let mut tex_attrs = None;
        for attr in &field.attrs {
            let Some(attr_ident) = attr.path().get_ident() else {
                continue;
            };
            if attr_ident == TEXTURE_ATTRIBUTE_NAME {
                let (_binding_index, nested_meta_items) = get_binding_nested_attr(attr)?;
                tex_attrs = Some(get_texture_attrs(nested_meta_items)?);
            }
        }

        for attr in &field.attrs {
            let Some(attr_ident) = attr.path().get_ident() else {
                continue;
            };

            let binding_type = if attr_ident == UNIFORM_ATTRIBUTE_NAME {
                BindingType::Uniform
            } else if attr_ident == TEXTURE_ATTRIBUTE_NAME {
                BindingType::Texture
            } else if attr_ident == STORAGE_TEXTURE_ATTRIBUTE_NAME {
                BindingType::StorageTexture
            } else if attr_ident == SAMPLER_ATTRIBUTE_NAME {
                BindingType::Sampler
            } else if attr_ident == STORAGE_ATTRIBUTE_NAME {
                BindingType::Storage
            } else {
                continue;
            };

            let (binding_index, nested_meta_items) = get_binding_nested_attr(attr)?;

            let field_name = field.ident.as_ref().unwrap();
            let required_len = binding_index as usize + 1;
            if required_len > binding_states.len() {
                binding_states.resize(required_len, BindingState::Free);
            }

            match &mut binding_states[binding_index as usize] {
                value @ BindingState::Free => {
                    *value = match binding_type {
                        BindingType::Uniform => BindingState::OccupiedMergeableUniform {
                            uniform_fields: vec![field],
                        },
                        _ => {
                            // only populate bind group entries for non-uniforms
                            // uniform entries are deferred until the end
                            BindingState::Occupied {
                                binding_type,
                                ident: field_name,
                            }
                        }
                    }
                }
                BindingState::Occupied {
                    binding_type,
                    ident: occupied_ident,
                } => {
                    return Err(Error::new_spanned(
                        attr,
                        format!("The '{field_name}' field cannot be assigned to binding {binding_index} because it is already occupied by the field '{occupied_ident}' of type {binding_type:?}.")
                    ));
                }
                BindingState::OccupiedConvertedUniform => {
                    return Err(Error::new_spanned(
                        attr,
                        format!("The '{field_name}' field cannot be assigned to binding {binding_index} because it is already occupied by a struct-level uniform binding at the same index.")
                    ));
                }
                BindingState::OccupiedMergeableUniform { uniform_fields } => match binding_type {
                    BindingType::Uniform => {
                        uniform_fields.push(field);
                    }
                    _ => {
                        return Err(Error::new_spanned(
                                attr,
                                format!("The '{field_name}' field cannot be assigned to binding {binding_index} because it is already occupied by a {:?}.", BindingType::Uniform)
                            ));
                    }
                },
            }

            match binding_type {
                BindingType::Uniform => {
                    if attr_bindless_count.is_some() {
                        return Err(Error::new_spanned(
                            attr,
                            "Only structure-level `#[uniform]` attributes are supported in \
                             bindless mode",
                        ));
                    }

                    // uniform codegen is deferred to account for combined uniform bindings
                }

                BindingType::Storage => {
                    let StorageAttrs {
                        visibility,
                        binding_array: binding_array_binding,
                        read_only,
                        buffer,
                    } = get_storage_binding_attr(nested_meta_items)?;
                    let visibility =
                        visibility.hygienic_quote(&quote! { #render_path::render_resource });

                    let field_name = field.ident.as_ref().unwrap();

                    if buffer {
                        binding_impls.push(quote! {
                            (
                                #binding_index,
                                #render_path::render_resource::OwnedBindingResource::Buffer({
                                    self.#field_name.clone()
                                })
                            )
                        });
                    } else {
                        binding_impls.push(quote! {
                        (
                            #binding_index,
                            #render_path::render_resource::OwnedBindingResource::Buffer({
                                let handle: &#asset_path::Handle<#render_path::storage::ShaderStorageBuffer> = (&self.#field_name);
                                storage_buffers.get(handle).ok_or_else(|| #render_path::render_resource::AsBindGroupError::RetryNextUpdate)?.buffer.clone()
                            })
                        )
                        });
                    }

                    non_bindless_binding_layouts.push(quote! {
                        #bind_group_layout_entries.push(
                            #render_path::render_resource::BindGroupLayoutEntry {
                                binding: #binding_index,
                                visibility: #visibility,
                                ty: #render_path::render_resource::BindingType::Buffer {
                                    ty: #render_path::render_resource::BufferBindingType::Storage { read_only: #read_only },
                                    has_dynamic_offset: false,
                                    min_binding_size: None,
                                },
                                count: #actual_bindless_slot_count,
                            }
                        );
                    });

                    if let Some(binding_array_binding) = binding_array_binding {
                        // Add the storage buffer to the `BindlessResourceType` list
                        // in the bindless descriptor.
                        let bindless_resource_type = quote! {
                            #render_path::render_resource::BindlessResourceType::Buffer
                        };
                        add_bindless_resource_type(
                            &render_path,
                            &mut bindless_resource_types,
                            binding_index,
                            bindless_resource_type,
                        );

                        // Push the buffer descriptor.
                        bindless_buffer_descriptors.push(quote! {
                            #render_path::render_resource::BindlessBufferDescriptor {
                                // Note that, because this is bindless, *binding
                                // index* here refers to the index in the bindless
                                // index table (`bindless_index`), and the actual
                                // binding number is the *binding array binding*.
                                binding_number: #render_path::render_resource::BindingNumber(
                                    #binding_array_binding
                                ),
                                bindless_index:
                                    #render_path::render_resource::BindlessIndex(#binding_index),
                                size: None,
                            }
                        });

                        // Declare the binding array.
                        bindless_binding_layouts.push(quote!{
                            #bind_group_layout_entries.push(
                                #render_path::render_resource::BindGroupLayoutEntry {
                                    binding: #binding_array_binding,
                                    visibility: #render_path::render_resource::ShaderStages::FRAGMENT | #render_path::render_resource::ShaderStages::VERTEX | #render_path::render_resource::ShaderStages::COMPUTE,
                                    ty: #render_path::render_resource::BindingType::Buffer {
                                        ty: #render_path::render_resource::BufferBindingType::Storage {
                                            read_only: #read_only
                                        },
                                        has_dynamic_offset: false,
                                        min_binding_size: None,
                                    },
                                    count: #actual_bindless_slot_count,
                                }
                            );
                        });
                    }
                }

                BindingType::StorageTexture => {
                    if attr_bindless_count.is_some() {
                        return Err(Error::new_spanned(
                            attr,
                            "Storage textures are unsupported in bindless mode",
                        ));
                    }

                    let StorageTextureAttrs {
                        dimension,
                        image_format,
                        access,
                        visibility,
                    } = get_storage_texture_binding_attr(nested_meta_items)?;

                    let visibility =
                        visibility.hygienic_quote(&quote! { #render_path::render_resource });

                    let fallback_image = get_fallback_image(&render_path, dimension);

                    // insert fallible texture-based entries at 0 so that if we fail here, we exit before allocating any buffers
                    binding_impls.insert(0, quote! {
                        ( #binding_index,
                          #render_path::render_resource::OwnedBindingResource::TextureView(
                                #render_path::render_resource::#dimension,
                                {
                                    let handle: Option<&#asset_path::Handle<#image_path::Image>> = (&self.#field_name).into();
                                    if let Some(handle) = handle {
                                        images.get(handle).ok_or_else(|| #render_path::render_resource::AsBindGroupError::RetryNextUpdate)?.texture_view.clone()
                                    } else {
                                        #fallback_image.texture_view.clone()
                                    }
                                }
                            )
                        )
                    });

                    non_bindless_binding_layouts.push(quote! {
                        #bind_group_layout_entries.push(
                            #render_path::render_resource::BindGroupLayoutEntry {
                                binding: #binding_index,
                                visibility: #visibility,
                                ty: #render_path::render_resource::BindingType::StorageTexture {
                                    access: #render_path::render_resource::StorageTextureAccess::#access,
                                    format: #render_path::render_resource::TextureFormat::#image_format,
                                    view_dimension: #render_path::render_resource::#dimension,
                                },
                                count: #actual_bindless_slot_count,
                            }
                        );
                    });
                }

                BindingType::Texture => {
                    let TextureAttrs {
                        dimension,
                        sample_type,
                        multisampled,
                        visibility,
                    } = tex_attrs.as_ref().unwrap();

                    let visibility =
                        visibility.hygienic_quote(&quote! { #render_path::render_resource });

                    let fallback_image = get_fallback_image(&render_path, *dimension);

                    // insert fallible texture-based entries at 0 so that if we fail here, we exit before allocating any buffers
                    binding_impls.insert(0, quote! {
                        (
                            #binding_index,
                            #render_path::render_resource::OwnedBindingResource::TextureView(
                                #render_path::render_resource::#dimension,
                                {
                                    let handle: Option<&#asset_path::Handle<#image_path::Image>> = (&self.#field_name).into();
                                    if let Some(handle) = handle {
                                        images.get(handle).ok_or_else(|| #render_path::render_resource::AsBindGroupError::RetryNextUpdate)?.texture_view.clone()
                                    } else {
                                        #fallback_image.texture_view.clone()
                                    }
                                }
                            )
                        )
                    });

                    sampler_binding_count += 1;

                    non_bindless_binding_layouts.push(quote! {
                        #bind_group_layout_entries.push(
                            #render_path::render_resource::BindGroupLayoutEntry {
                                binding: #binding_index,
                                visibility: #visibility,
                                ty: #render_path::render_resource::BindingType::Texture {
                                    multisampled: #multisampled,
                                    sample_type: #render_path::render_resource::#sample_type,
                                    view_dimension: #render_path::render_resource::#dimension,
                                },
                                count: #actual_bindless_slot_count,
                            }
                        );
                    });

                    let bindless_resource_type = match *dimension {
                        BindingTextureDimension::D1 => {
                            quote! {
                                #render_path::render_resource::BindlessResourceType::Texture1d
                            }
                        }
                        BindingTextureDimension::D2 => {
                            quote! {
                                #render_path::render_resource::BindlessResourceType::Texture2d
                            }
                        }
                        BindingTextureDimension::D2Array => {
                            quote! {
                                #render_path::render_resource::BindlessResourceType::Texture2dArray
                            }
                        }
                        BindingTextureDimension::Cube => {
                            quote! {
                                #render_path::render_resource::BindlessResourceType::TextureCube
                            }
                        }
                        BindingTextureDimension::CubeArray => {
                            quote! {
                                #render_path::render_resource::BindlessResourceType::TextureCubeArray
                            }
                        }
                        BindingTextureDimension::D3 => {
                            quote! {
                                #render_path::render_resource::BindlessResourceType::Texture3d
                            }
                        }
                    };

                    // Add the texture to the `BindlessResourceType` list in the
                    // bindless descriptor.
                    add_bindless_resource_type(
                        &render_path,
                        &mut bindless_resource_types,
                        binding_index,
                        bindless_resource_type,
                    );
                }

                BindingType::Sampler => {
                    let SamplerAttrs {
                        sampler_binding_type,
                        visibility,
                        ..
                    } = get_sampler_attrs(nested_meta_items)?;
                    let TextureAttrs { dimension, .. } = tex_attrs
                        .as_ref()
                        .expect("sampler attribute must have matching texture attribute");

                    let visibility =
                        visibility.hygienic_quote(&quote! { #render_path::render_resource });

                    let fallback_image = get_fallback_image(&render_path, *dimension);

                    let expected_samplers = match sampler_binding_type {
                        SamplerBindingType::Filtering => {
                            quote!( [#render_path::render_resource::TextureSampleType::Float { filterable: true }] )
                        }
                        SamplerBindingType::NonFiltering => quote!([
                            #render_path::render_resource::TextureSampleType::Float { filterable: false },
                            #render_path::render_resource::TextureSampleType::Sint,
                            #render_path::render_resource::TextureSampleType::Uint,
                        ]),
                        SamplerBindingType::Comparison => {
                            quote!( [#render_path::render_resource::TextureSampleType::Depth] )
                        }
                    };

                    // insert fallible texture-based entries at 0 so that if we fail here, we exit before allocating any buffers
                    binding_impls.insert(0, quote! {
                        (
                            #binding_index,
                            #render_path::render_resource::OwnedBindingResource::Sampler(
                                // TODO: Support other types.
                                #render_path::render_resource::WgpuSamplerBindingType::Filtering,
                                {
                                let handle: Option<&#asset_path::Handle<#image_path::Image>> = (&self.#field_name).into();
                                if let Some(handle) = handle {
                                    let image = images.get(handle).ok_or_else(|| #render_path::render_resource::AsBindGroupError::RetryNextUpdate)?;

                                    let Some(sample_type) = image.texture_format.sample_type(None, Some(render_device.features())) else {
                                        return Err(#render_path::render_resource::AsBindGroupError::InvalidSamplerType(
                                            #binding_index,
                                            "None".to_string(),
                                            format!("{:?}", #expected_samplers),
                                        ));
                                    };

                                    let valid = #expected_samplers.contains(&sample_type);

                                    if !valid {
                                        return Err(#render_path::render_resource::AsBindGroupError::InvalidSamplerType(
                                            #binding_index,
                                            format!("{:?}", sample_type),
                                            format!("{:?}", #expected_samplers),
                                        ));
                                    }
                                    image.sampler.clone()
                                } else {
                                    #fallback_image.sampler.clone()
                                }
                            })
                        )
                    });

                    sampler_binding_count += 1;

                    non_bindless_binding_layouts.push(quote!{
                        #bind_group_layout_entries.push(
                            #render_path::render_resource::BindGroupLayoutEntry {
                                binding: #binding_index,
                                visibility: #visibility,
                                ty: #render_path::render_resource::BindingType::Sampler(#render_path::render_resource::#sampler_binding_type),
                                count: #actual_bindless_slot_count,
                            }
                        );
                    });

                    // Add the sampler to the `BindlessResourceType` list in the
                    // bindless descriptor.
                    //
                    // TODO: Support other types of samplers.
                    add_bindless_resource_type(
                        &render_path,
                        &mut bindless_resource_types,
                        binding_index,
                        quote! {
                            #render_path::render_resource::BindlessResourceType::SamplerFiltering
                        },
                    );
                }
            }
        }
    }

    // Produce impls for fields with uniform bindings
    let struct_name = &ast.ident;
    let struct_name_literal = struct_name.to_string();
    let struct_name_literal = struct_name_literal.as_str();
    let mut field_struct_impls = Vec::new();

    let uniform_binding_type_declarations = match attr_bindless_count {
        Some(_) => {
            quote! {
                let (#uniform_binding_type, #uniform_buffer_usages) =
                    if Self::bindless_supported(render_device) && !force_no_bindless {
                        (
                            #render_path::render_resource::BufferBindingType::Storage { read_only: true },
                            #render_path::render_resource::BufferUsages::STORAGE,
                        )
                    } else {
                        (
                            #render_path::render_resource::BufferBindingType::Uniform,
                            #render_path::render_resource::BufferUsages::UNIFORM,
                        )
                    };
            }
        }
        None => {
            quote! {
                let (#uniform_binding_type, #uniform_buffer_usages) = (
                    #render_path::render_resource::BufferBindingType::Uniform,
                    #render_path::render_resource::BufferUsages::UNIFORM,
                );
            }
        }
    };

    for (binding_index, binding_state) in binding_states.iter().enumerate() {
        let binding_index = binding_index as u32;
        if let BindingState::OccupiedMergeableUniform { uniform_fields } = binding_state {
            // single field uniform bindings for a given index can use a straightforward binding
            if uniform_fields.len() == 1 {
                let field = &uniform_fields[0];
                let field_name = field.ident.as_ref().unwrap();
                let field_ty = &field.ty;
                binding_impls.push(quote! {{
                    let mut buffer = #render_path::render_resource::encase::UniformBuffer::new(Vec::new());
                    buffer.write(&self.#field_name).unwrap();
                    (
                        #binding_index,
                        #render_path::render_resource::OwnedBindingResource::Buffer(render_device.create_buffer_with_data(
                            &#render_path::render_resource::BufferInitDescriptor {
                                label: None,
                                usage: #uniform_buffer_usages,
                                contents: buffer.as_ref(),
                            },
                        ))
                    )
                }});

                non_bindless_binding_layouts.push(quote!{
                    #bind_group_layout_entries.push(
                        #render_path::render_resource::BindGroupLayoutEntry {
                            binding: #binding_index,
                            visibility: #render_path::render_resource::ShaderStages::FRAGMENT | #render_path::render_resource::ShaderStages::VERTEX | #render_path::render_resource::ShaderStages::COMPUTE,
                            ty: #render_path::render_resource::BindingType::Buffer {
                                ty: #uniform_binding_type,
                                has_dynamic_offset: false,
                                min_binding_size: Some(<#field_ty as #render_path::render_resource::ShaderType>::min_size()),
                            },
                            count: #actual_bindless_slot_count,
                        }
                    );
                });
            // multi-field uniform bindings for a given index require an intermediate struct to derive ShaderType
            } else {
                let uniform_struct_name = Ident::new(
                    &format!("_{struct_name}AsBindGroupUniformStructBindGroup{binding_index}"),
                    Span::call_site(),
                );

                let field_name = uniform_fields.iter().map(|f| f.ident.as_ref().unwrap());
                let field_type = uniform_fields.iter().map(|f| &f.ty);
                field_struct_impls.push(quote! {
                    #[derive(#render_path::render_resource::ShaderType)]
                    struct #uniform_struct_name<'a> {
                        #(#field_name: &'a #field_type,)*
                    }
                });

                let field_name = uniform_fields.iter().map(|f| f.ident.as_ref().unwrap());
                binding_impls.push(quote! {{
                    let mut buffer = #render_path::render_resource::encase::UniformBuffer::new(Vec::new());
                    buffer.write(&#uniform_struct_name {
                        #(#field_name: &self.#field_name,)*
                    }).unwrap();
                    (
                        #binding_index,
                        #render_path::render_resource::OwnedBindingResource::Buffer(render_device.create_buffer_with_data(
                            &#render_path::render_resource::BufferInitDescriptor {
                                label: None,
                                usage: #uniform_buffer_usages,
                                contents: buffer.as_ref(),
                            },
                        ))
                    )
                }});

                non_bindless_binding_layouts.push(quote!{
                    #bind_group_layout_entries.push(#render_path::render_resource::BindGroupLayoutEntry {
                        binding: #binding_index,
                        visibility: #render_path::render_resource::ShaderStages::FRAGMENT | #render_path::render_resource::ShaderStages::VERTEX | #render_path::render_resource::ShaderStages::COMPUTE,
                        ty: #render_path::render_resource::BindingType::Buffer {
                            ty: #uniform_binding_type,
                            has_dynamic_offset: false,
                            min_binding_size: Some(<#uniform_struct_name as #render_path::render_resource::ShaderType>::min_size()),
                        },
                        count: #actual_bindless_slot_count,
                    });
                });
            }
        }
    }

    let generics = ast.generics;
    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();

    let (prepared_data, get_prepared_data) = if let Some(prepared) = attr_prepared_data_ident {
        let get_prepared_data = quote! { self.into() };
        (quote! {#prepared}, get_prepared_data)
    } else {
        let prepared_data = quote! { () };
        (prepared_data.clone(), prepared_data)
    };

    // Calculate the number of samplers that we need, so that we don't go over
    // the limit on certain platforms. See
    // https://github.com/bevyengine/bevy/issues/16988.
    let bindless_count_syntax = match attr_bindless_count {
        Some(BindlessSlabResourceLimitAttr::Auto) => {
            quote! { #render_path::render_resource::AUTO_BINDLESS_SLAB_RESOURCE_LIMIT }
        }
        Some(BindlessSlabResourceLimitAttr::Limit(ref count)) => {
            quote! { #count }
        }
        None => quote! { 0 },
    };

    // Calculate the actual bindless index table range, taking the
    // `#[bindless(index_table(range(M..N)))]` attribute into account.
    let bindless_index_table_range = match attr_bindless_index_table_range {
        None => {
            let resource_count = bindless_resource_types.len() as u32;
            quote! {
                #render_path::render_resource::BindlessIndex(0)..
                #render_path::render_resource::BindlessIndex(#resource_count)
            }
        }
        Some(BindlessIndexTableRangeAttr { start, end }) => {
            quote! {
                #render_path::render_resource::BindlessIndex(#start)..
                #render_path::render_resource::BindlessIndex(#end)
            }
        }
    };

    // Calculate the actual binding number of the bindless index table, taking
    // the `#[bindless(index_table(binding(B)))]` into account.
    let bindless_index_table_binding_number = match attr_bindless_index_table_binding {
        None => quote! { #render_path::render_resource::BindingNumber(0) },
        Some(binding_number) => {
            quote! { #render_path::render_resource::BindingNumber(#binding_number) }
        }
    };

    // Calculate the actual number of bindless slots, taking hardware
    // limitations into account.
    let (bindless_slot_count, actual_bindless_slot_count_declaration, bindless_descriptor_syntax) =
        match attr_bindless_count {
            Some(ref bindless_count) => {
                let bindless_supported_syntax = quote! {
                        fn bindless_supported(
                            render_device: &#render_path::renderer::RenderDevice
                        ) -> bool {
                            render_device.features().contains(
                                #render_path::settings::WgpuFeatures::BUFFER_BINDING_ARRAY |
                                #render_path::settings::WgpuFeatures::TEXTURE_BINDING_ARRAY
                            ) &&
                            render_device.limits().max_storage_buffers_per_shader_stage > 0 &&
                                render_device.limits().max_samplers_per_shader_stage >=
                                    (#sampler_binding_count * #bindless_count_syntax)
                        }
                };
                let actual_bindless_slot_count_declaration = quote! {
                    let #actual_bindless_slot_count = if Self::bindless_supported(render_device) &&
                            !force_no_bindless {
                        ::core::num::NonZeroU32::new(#bindless_count_syntax)
                    } else {
                        None
                    };
                };
                let bindless_slot_count_declaration = match bindless_count {
                    BindlessSlabResourceLimitAttr::Auto => {
                        quote! {
                            fn bindless_slot_count() -> Option<
                                #render_path::render_resource::BindlessSlabResourceLimit
                            > {
                                Some(#render_path::render_resource::BindlessSlabResourceLimit::Auto)
                            }
                        }
                    }
                    BindlessSlabResourceLimitAttr::Limit(lit) => {
                        quote! {
                            fn bindless_slot_count() -> Option<
                                #render_path::render_resource::BindlessSlabResourceLimit
                            > {
                                Some(#render_path::render_resource::BindlessSlabResourceLimit::Custom(#lit))
                            }
                        }
                    }
                };

                let bindless_buffer_descriptor_count = bindless_buffer_descriptors.len();

                // We use `LazyLock` so that we can call `min_size`, which isn't
                // a `const fn`.
                let bindless_descriptor_syntax = quote! {
                    static RESOURCES: &[#render_path::render_resource::BindlessResourceType] = &[
                        #(#bindless_resource_types),*
                    ];
                    static BUFFERS: ::std::sync::LazyLock<[
                        #render_path::render_resource::BindlessBufferDescriptor;
                        #bindless_buffer_descriptor_count
                    ]> = ::std::sync::LazyLock::new(|| {
                        [#(#bindless_buffer_descriptors),*]
                    });
                    static INDEX_TABLES: &[
                        #render_path::render_resource::BindlessIndexTableDescriptor
                    ] = &[
                        #render_path::render_resource::BindlessIndexTableDescriptor {
                            indices: #bindless_index_table_range,
                            binding_number: #bindless_index_table_binding_number,
                        }
                    ];
                    Some(#render_path::render_resource::BindlessDescriptor {
                        resources: ::std::borrow::Cow::Borrowed(RESOURCES),
                        buffers: ::std::borrow::Cow::Borrowed(&*BUFFERS),
                        index_tables: ::std::borrow::Cow::Borrowed(&*INDEX_TABLES),
                    })
                };

                (
                    quote! {
                        #bindless_slot_count_declaration
                        #bindless_supported_syntax
                    },
                    actual_bindless_slot_count_declaration,
                    bindless_descriptor_syntax,
                )
            }
            None => (
                TokenStream::new().into(),
                quote! { let #actual_bindless_slot_count: Option<::core::num::NonZeroU32> = None; },
                quote! { None },
            ),
        };

    Ok(TokenStream::from(quote! {
        #(#field_struct_impls)*

        impl #impl_generics #render_path::render_resource::AsBindGroup for #struct_name #ty_generics #where_clause {
            type Data = #prepared_data;

            type Param = (
                #ecs_path::system::lifetimeless::SRes<#render_path::render_asset::RenderAssets<#render_path::texture::GpuImage>>,
                #ecs_path::system::lifetimeless::SRes<#render_path::texture::FallbackImage>,
                #ecs_path::system::lifetimeless::SRes<#render_path::render_asset::RenderAssets<#render_path::storage::GpuShaderStorageBuffer>>,
            );

            #bindless_slot_count

            fn label() -> Option<&'static str> {
                Some(#struct_name_literal)
            }

            fn unprepared_bind_group(
                &self,
                layout: &#render_path::render_resource::BindGroupLayout,
                render_device: &#render_path::renderer::RenderDevice,
                (images, fallback_image, storage_buffers): &mut #ecs_path::system::SystemParamItem<'_, '_, Self::Param>,
                force_no_bindless: bool,
            ) -> Result<#render_path::render_resource::UnpreparedBindGroup, #render_path::render_resource::AsBindGroupError> {
                #uniform_binding_type_declarations

                let bindings = #render_path::render_resource::BindingResources(vec![#(#binding_impls,)*]);

                Ok(#render_path::render_resource::UnpreparedBindGroup {
                    bindings,
                })
            }

            #[allow(clippy::unused_unit)]
            fn bind_group_data(&self) -> Self::Data {
                #get_prepared_data
            }

            fn bind_group_layout_entries(
                render_device: &#render_path::renderer::RenderDevice,
                force_no_bindless: bool
            ) -> Vec<#render_path::render_resource::BindGroupLayoutEntry> {
                #actual_bindless_slot_count_declaration
                #uniform_binding_type_declarations

                let mut #bind_group_layout_entries = Vec::new();
                match #actual_bindless_slot_count {
                    Some(bindless_slot_count) => {
                        let bindless_index_table_range = #bindless_index_table_range;
                        #bind_group_layout_entries.extend(
                            #render_path::render_resource::create_bindless_bind_group_layout_entries(
                                bindless_index_table_range.end.0 -
                                    bindless_index_table_range.start.0,
                                bindless_slot_count.into(),
                                #bindless_index_table_binding_number,
                            ).into_iter()
                        );
                        #(#bindless_binding_layouts)*;
                    }
                    None => {
                        #(#non_bindless_binding_layouts)*;
                    }
                };
                #bind_group_layout_entries
            }

            fn bindless_descriptor() -> Option<#render_path::render_resource::BindlessDescriptor> {
                #bindless_descriptor_syntax
            }
        }
    }))
}

/// Adds a bindless resource type to the `BindlessResourceType` array in the
/// bindless descriptor we're building up.
///
/// See the `bevy_render::render_resource::bindless::BindlessResourceType`
/// documentation for more information.
fn add_bindless_resource_type(
    render_path: &syn::Path,
    bindless_resource_types: &mut Vec<proc_macro2::TokenStream>,
    binding_index: u32,
    bindless_resource_type: proc_macro2::TokenStream,
) {
    // If we need to grow the array, pad the unused fields with
    // `BindlessResourceType::None`.
    if bindless_resource_types.len() < (binding_index as usize + 1) {
        bindless_resource_types.resize_with(binding_index as usize + 1, || {
            quote! { #render_path::render_resource::BindlessResourceType::None }
        });
    }

    // Assign the `BindlessResourceType`.
    bindless_resource_types[binding_index as usize] = bindless_resource_type;
}

fn get_fallback_image(
    render_path: &syn::Path,
    dimension: BindingTextureDimension,
) -> proc_macro2::TokenStream {
    quote! {
        match #render_path::render_resource::#dimension {
            #render_path::render_resource::TextureViewDimension::D1 => &fallback_image.d1,
            #render_path::render_resource::TextureViewDimension::D2 => &fallback_image.d2,
            #render_path::render_resource::TextureViewDimension::D2Array => &fallback_image.d2_array,
            #render_path::render_resource::TextureViewDimension::Cube => &fallback_image.cube,
            #render_path::render_resource::TextureViewDimension::CubeArray => &fallback_image.cube_array,
            #render_path::render_resource::TextureViewDimension::D3 => &fallback_image.d3,
        }
    }
}

/// Represents the arguments for the `uniform` binding attribute.
///
/// If parsed, represents an attribute
/// like `#[uniform(LitInt, Ident)]`
struct UniformBindingMeta {
    lit_int: LitInt,
    ident: Ident,
    binding_array: Option<LitInt>,
}

/// The parsed structure-level `#[uniform]` or `#[data]` attribute.
///
/// The corresponding syntax is `#[uniform(BINDING_INDEX, CONVERTED_SHADER_TYPE,
/// binding_array(BINDING_ARRAY)]`, optionally replacing `uniform` with `data`.
struct UniformBindingAttr {
    /// Whether the declaration is `#[uniform]` or `#[data]`.
    binding_type: UniformBindingAttrType,
    /// The binding index.
    binding_index: u32,
    /// The uniform data type.
    converted_shader_type: Ident,
    /// The binding number of the binding array, if this is a bindless material.
    binding_array: Option<u32>,
}

/// Whether a structure-level shader type declaration is `#[uniform]` or
/// `#[data]`.
enum UniformBindingAttrType {
    /// `#[uniform]`: i.e. in bindless mode, we need a separate buffer per data
    /// instance.
    Uniform,
    /// `#[data]`: i.e. in bindless mode, we concatenate all instance data into
    /// a single buffer.
    Data,
}

/// Represents the arguments for any general binding attribute.
///
/// If parsed, represents an attribute
/// like `#[foo(LitInt, ...)]` where the rest is optional [`Meta`].
enum BindingMeta {
    IndexOnly(LitInt),
    IndexWithOptions(BindingIndexOptions),
}

/// Represents the arguments for an attribute with a list of arguments.
///
/// This represents, for example, `#[texture(0, dimension = "2d_array")]`.
struct BindingIndexOptions {
    lit_int: LitInt,
    _comma: Comma,
    meta_list: Punctuated<Meta, Comma>,
}

impl Parse for BindingMeta {
    fn parse(input: ParseStream) -> Result<Self> {
        if input.peek2(Comma) {
            input.parse().map(Self::IndexWithOptions)
        } else {
            input.parse().map(Self::IndexOnly)
        }
    }
}

impl Parse for BindingIndexOptions {
    fn parse(input: ParseStream) -> Result<Self> {
        Ok(Self {
            lit_int: input.parse()?,
            _comma: input.parse()?,
            meta_list: input.parse_terminated(Meta::parse, Comma)?,
        })
    }
}

impl Parse for UniformBindingMeta {
    // Parse syntax like `#[uniform(0, StandardMaterial, binding_array(10))]`.
    fn parse(input: ParseStream) -> Result<Self> {
        let lit_int = input.parse()?;
        input.parse::<Comma>()?;
        let ident = input.parse()?;

        // Look for a `binding_array(BINDING_NUMBER)` declaration.
        let mut binding_array: Option<LitInt> = None;
        if input.parse::<Comma>().is_ok() {
            if input
                .parse::<syn::Path>()?
                .get_ident()
                .is_none_or(|ident| *ident != BINDING_ARRAY_MODIFIER_NAME)
            {
                return Err(Error::new_spanned(ident, "Expected `binding_array`"));
            }
            let parser;
            parenthesized!(parser in input);
            binding_array = Some(parser.parse()?);
        }

        Ok(Self {
            lit_int,
            ident,
            binding_array,
        })
    }
}

/// Parses a structure-level `#[uniform]` attribute (not a field-level
/// `#[uniform]` attribute).
fn get_uniform_binding_attr(attr: &syn::Attribute) -> Result<UniformBindingAttr> {
    let attr_ident = attr
        .path()
        .get_ident()
        .expect("Shouldn't be here if we didn't have an attribute");

    let uniform_binding_meta = attr.parse_args_with(UniformBindingMeta::parse)?;

    let binding_index = uniform_binding_meta.lit_int.base10_parse()?;
    let ident = uniform_binding_meta.ident;
    let binding_array = match uniform_binding_meta.binding_array {
        None => None,
        Some(binding_array) => Some(binding_array.base10_parse()?),
    };

    Ok(UniformBindingAttr {
        binding_type: if attr_ident == UNIFORM_ATTRIBUTE_NAME {
            UniformBindingAttrType::Uniform
        } else {
            UniformBindingAttrType::Data
        },
        binding_index,
        converted_shader_type: ident,
        binding_array,
    })
}

fn get_binding_nested_attr(attr: &syn::Attribute) -> Result<(u32, Vec<Meta>)> {
    let binding_meta = attr.parse_args_with(BindingMeta::parse)?;

    match binding_meta {
        BindingMeta::IndexOnly(lit_int) => Ok((lit_int.base10_parse()?, Vec::new())),
        BindingMeta::IndexWithOptions(BindingIndexOptions {
            lit_int,
            _comma: _,
            meta_list,
        }) => Ok((lit_int.base10_parse()?, meta_list.into_iter().collect())),
    }
}

#[derive(Default)]
enum ShaderStageVisibility {
    #[default]
    All,
    None,
    Flags(VisibilityFlags),
}

#[derive(Default)]
struct VisibilityFlags {
    vertex: bool,
    fragment: bool,
    compute: bool,
}

impl ShaderStageVisibility {
    fn vertex_fragment() -> Self {
        Self::Flags(VisibilityFlags::vertex_fragment())
    }

    fn compute() -> Self {
        Self::Flags(VisibilityFlags::compute())
    }
}

impl VisibilityFlags {
    fn vertex_fragment() -> Self {
        Self {
            vertex: true,
            fragment: true,
            ..Default::default()
        }
    }

    fn compute() -> Self {
        Self {
            compute: true,
            ..Default::default()
        }
    }
}

impl ShaderStageVisibility {
    fn hygienic_quote(&self, path: &proc_macro2::TokenStream) -> proc_macro2::TokenStream {
        match self {
            ShaderStageVisibility::All => quote! {
                if cfg!(feature = "webgpu") {
                    todo!("Please use a more specific shader stage: https://github.com/gfx-rs/wgpu/issues/7708")
                } else {
                    #path::ShaderStages::all()
                }
            },
            ShaderStageVisibility::None => quote! { #path::ShaderStages::NONE },
            ShaderStageVisibility::Flags(flags) => {
                let mut quoted = Vec::new();

                if flags.vertex {
                    quoted.push(quote! { #path::ShaderStages::VERTEX });
                }
                if flags.fragment {
                    quoted.push(quote! { #path::ShaderStages::FRAGMENT });
                }
                if flags.compute {
                    quoted.push(quote! { #path::ShaderStages::COMPUTE });
                }

                quote! { #(#quoted)|* }
            }
        }
    }
}

const VISIBILITY: Symbol = Symbol("visibility");
const VISIBILITY_VERTEX: Symbol = Symbol("vertex");
const VISIBILITY_FRAGMENT: Symbol = Symbol("fragment");
const VISIBILITY_COMPUTE: Symbol = Symbol("compute");
const VISIBILITY_ALL: Symbol = Symbol("all");
const VISIBILITY_NONE: Symbol = Symbol("none");

fn get_visibility_flag_value(meta_list: &MetaList) -> Result<ShaderStageVisibility> {
    let mut flags = Vec::new();

    meta_list.parse_nested_meta(|meta| {
        flags.push(meta.path);
        Ok(())
    })?;

    if flags.is_empty() {
        return Err(Error::new_spanned(
            meta_list,
            "Invalid visibility format. Must be `visibility(flags)`, flags can be `all`, `none`, or a list-combination of `vertex`, `fragment` and/or `compute`."
        ));
    }

    if flags.len() == 1
        && let Some(flag) = flags.first()
    {
        if flag == VISIBILITY_ALL {
            return Ok(ShaderStageVisibility::All);
        } else if flag == VISIBILITY_NONE {
            return Ok(ShaderStageVisibility::None);
        }
    }

    let mut visibility = VisibilityFlags::default();

    for flag in flags {
        if flag == VISIBILITY_VERTEX {
            visibility.vertex = true;
        } else if flag == VISIBILITY_FRAGMENT {
            visibility.fragment = true;
        } else if flag == VISIBILITY_COMPUTE {
            visibility.compute = true;
        } else {
            return Err(Error::new_spanned(
                flag,
                "Not a valid visibility flag. Must be `all`, `none`, or a list-combination of `vertex`, `fragment` and/or `compute`."
            ));
        }
    }

    Ok(ShaderStageVisibility::Flags(visibility))
}

// Returns the `binding_array(10)` part of a field-level declaration like
// `#[storage(binding_array(10))]`.
fn get_binding_array_flag_value(meta_list: &MetaList) -> Result<u32> {
    meta_list
        .parse_args_with(|input: ParseStream| input.parse::<LitInt>())?
        .base10_parse()
}

#[derive(Clone, Copy, Default)]
enum BindingTextureDimension {
    D1,
    #[default]
    D2,
    D2Array,
    Cube,
    CubeArray,
    D3,
}

enum BindingTextureSampleType {
    Float { filterable: bool },
    Depth,
    Sint,
    Uint,
}

impl ToTokens for BindingTextureDimension {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        tokens.extend(match self {
            BindingTextureDimension::D1 => quote! { TextureViewDimension::D1 },
            BindingTextureDimension::D2 => quote! { TextureViewDimension::D2 },
            BindingTextureDimension::D2Array => quote! { TextureViewDimension::D2Array },
            BindingTextureDimension::Cube => quote! { TextureViewDimension::Cube },
            BindingTextureDimension::CubeArray => quote! { TextureViewDimension::CubeArray },
            BindingTextureDimension::D3 => quote! { TextureViewDimension::D3 },
        });
    }
}

impl ToTokens for BindingTextureSampleType {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        tokens.extend(match self {
            BindingTextureSampleType::Float { filterable } => {
                quote! { TextureSampleType::Float { filterable: #filterable } }
            }
            BindingTextureSampleType::Depth => quote! { TextureSampleType::Depth },
            BindingTextureSampleType::Sint => quote! { TextureSampleType::Sint },
            BindingTextureSampleType::Uint => quote! { TextureSampleType::Uint },
        });
    }
}

struct TextureAttrs {
    dimension: BindingTextureDimension,
    sample_type: BindingTextureSampleType,
    multisampled: bool,
    visibility: ShaderStageVisibility,
}

impl Default for BindingTextureSampleType {
    fn default() -> Self {
        BindingTextureSampleType::Float { filterable: true }
    }
}

impl Default for TextureAttrs {
    fn default() -> Self {
        Self {
            dimension: Default::default(),
            sample_type: Default::default(),
            multisampled: true,
            visibility: Default::default(),
        }
    }
}

struct StorageTextureAttrs {
    dimension: BindingTextureDimension,
    // Parsing of the image_format parameter is deferred to the type checker,
    // which will error if the format is not member of the TextureFormat enum.
    image_format: proc_macro2::TokenStream,
    // Parsing of the access parameter is deferred to the type checker,
    // which will error if the access is not member of the StorageTextureAccess enum.
    access: proc_macro2::TokenStream,
    visibility: ShaderStageVisibility,
}

impl Default for StorageTextureAttrs {
    fn default() -> Self {
        Self {
            dimension: Default::default(),
            image_format: quote! { Rgba8Unorm },
            access: quote! { ReadWrite },
            visibility: ShaderStageVisibility::compute(),
        }
    }
}

fn get_storage_texture_binding_attr(metas: Vec<Meta>) -> Result<StorageTextureAttrs> {
    let mut storage_texture_attrs = StorageTextureAttrs::default();

    for meta in metas {
        use syn::Meta::{List, NameValue};
        match meta {
            // Parse #[storage_texture(0, dimension = "...")].
            NameValue(m) if m.path == DIMENSION => {
                let value = get_lit_str(DIMENSION, &m.value)?;
                storage_texture_attrs.dimension = get_texture_dimension_value(value)?;
            }
            // Parse #[storage_texture(0, format = ...))].
            NameValue(m) if m.path == IMAGE_FORMAT => {
                storage_texture_attrs.image_format = m.value.into_token_stream();
            }
            // Parse #[storage_texture(0, access = ...))].
            NameValue(m) if m.path == ACCESS => {
                storage_texture_attrs.access = m.value.into_token_stream();
            }
            // Parse #[storage_texture(0, visibility(...))].
            List(m) if m.path == VISIBILITY => {
                storage_texture_attrs.visibility = get_visibility_flag_value(&m)?;
            }
            NameValue(m) => {
                return Err(Error::new_spanned(
                    m.path,
                    "Not a valid name. Available attributes: `dimension`, `image_format`, `access`.",
                ));
            }
            _ => {
                return Err(Error::new_spanned(
                    meta,
                    "Not a name value pair: `foo = \"...\"`",
                ));
            }
        }
    }

    Ok(storage_texture_attrs)
}

const DIMENSION: Symbol = Symbol("dimension");
const IMAGE_FORMAT: Symbol = Symbol("image_format");
const ACCESS: Symbol = Symbol("access");
const SAMPLE_TYPE: Symbol = Symbol("sample_type");
const FILTERABLE: Symbol = Symbol("filterable");
const MULTISAMPLED: Symbol = Symbol("multisampled");

// Values for `dimension` attribute.
const DIM_1D: &str = "1d";
const DIM_2D: &str = "2d";
const DIM_3D: &str = "3d";
const DIM_2D_ARRAY: &str = "2d_array";
const DIM_CUBE: &str = "cube";
const DIM_CUBE_ARRAY: &str = "cube_array";

// Values for sample `type` attribute.
const FLOAT: &str = "float";
const DEPTH: &str = "depth";
const S_INT: &str = "s_int";
const U_INT: &str = "u_int";

fn get_texture_attrs(metas: Vec<Meta>) -> Result<TextureAttrs> {
    let mut dimension = Default::default();
    let mut sample_type = Default::default();
    let mut multisampled = Default::default();
    let mut filterable = None;
    let mut filterable_ident = None;

    let mut visibility = ShaderStageVisibility::vertex_fragment();

    for meta in metas {
        use syn::Meta::{List, NameValue};
        match meta {
            // Parse #[texture(0, dimension = "...")].
            NameValue(m) if m.path == DIMENSION => {
                let value = get_lit_str(DIMENSION, &m.value)?;
                dimension = get_texture_dimension_value(value)?;
            }
            // Parse #[texture(0, sample_type = "...")].
            NameValue(m) if m.path == SAMPLE_TYPE => {
                let value = get_lit_str(SAMPLE_TYPE, &m.value)?;
                sample_type = get_texture_sample_type_value(value)?;
            }
            // Parse #[texture(0, multisampled = "...")].
            NameValue(m) if m.path == MULTISAMPLED => {
                multisampled = get_lit_bool(MULTISAMPLED, &m.value)?;
            }
            // Parse #[texture(0, filterable = "...")].
            NameValue(m) if m.path == FILTERABLE => {
                filterable = get_lit_bool(FILTERABLE, &m.value)?.into();
                filterable_ident = m.path.into();
            }
            // Parse #[texture(0, visibility(...))].
            List(m) if m.path == VISIBILITY => {
                visibility = get_visibility_flag_value(&m)?;
            }
            NameValue(m) => {
                return Err(Error::new_spanned(
                    m.path,
                    "Not a valid name. Available attributes: `dimension`, `sample_type`, `multisampled`, or `filterable`."
                ));
            }
            _ => {
                return Err(Error::new_spanned(
                    meta,
                    "Not a name value pair: `foo = \"...\"`",
                ));
            }
        }
    }

    // Resolve `filterable` since the float
    // sample type is the one that contains the value.
    if let Some(filterable) = filterable {
        let path = filterable_ident.unwrap();
        match sample_type {
            BindingTextureSampleType::Float { filterable: _ } => {
                sample_type = BindingTextureSampleType::Float { filterable }
            }
            _ => {
                return Err(Error::new_spanned(
                    path,
                    "Type must be `float` to use the `filterable` attribute.",
                ));
            }
        };
    }

    Ok(TextureAttrs {
        dimension,
        sample_type,
        multisampled,
        visibility,
    })
}

fn get_texture_dimension_value(lit_str: &LitStr) -> Result<BindingTextureDimension> {
    match lit_str.value().as_str() {
        DIM_1D => Ok(BindingTextureDimension::D1),
        DIM_2D => Ok(BindingTextureDimension::D2),
        DIM_2D_ARRAY => Ok(BindingTextureDimension::D2Array),
        DIM_3D => Ok(BindingTextureDimension::D3),
        DIM_CUBE => Ok(BindingTextureDimension::Cube),
        DIM_CUBE_ARRAY => Ok(BindingTextureDimension::CubeArray),

        _ => Err(Error::new_spanned(
            lit_str,
            "Not a valid dimension. Must be `1d`, `2d`, `2d_array`, `3d`, `cube` or `cube_array`.",
        )),
    }
}

fn get_texture_sample_type_value(lit_str: &LitStr) -> Result<BindingTextureSampleType> {
    match lit_str.value().as_str() {
        FLOAT => Ok(BindingTextureSampleType::Float { filterable: true }),
        DEPTH => Ok(BindingTextureSampleType::Depth),
        S_INT => Ok(BindingTextureSampleType::Sint),
        U_INT => Ok(BindingTextureSampleType::Uint),

        _ => Err(Error::new_spanned(
            lit_str,
            "Not a valid sample type. Must be `float`, `depth`, `s_int` or `u_int`.",
        )),
    }
}

#[derive(Default)]
struct SamplerAttrs {
    sampler_binding_type: SamplerBindingType,
    visibility: ShaderStageVisibility,
}

#[derive(Default)]
enum SamplerBindingType {
    #[default]
    Filtering,
    NonFiltering,
    Comparison,
}

impl ToTokens for SamplerBindingType {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        tokens.extend(match self {
            SamplerBindingType::Filtering => quote! { SamplerBindingType::Filtering },
            SamplerBindingType::NonFiltering => quote! { SamplerBindingType::NonFiltering },
            SamplerBindingType::Comparison => quote! { SamplerBindingType::Comparison },
        });
    }
}

const SAMPLER_TYPE: Symbol = Symbol("sampler_type");

const FILTERING: &str = "filtering";
const NON_FILTERING: &str = "non_filtering";
const COMPARISON: &str = "comparison";

fn get_sampler_attrs(metas: Vec<Meta>) -> Result<SamplerAttrs> {
    let mut sampler_binding_type = Default::default();
    let mut visibility = ShaderStageVisibility::vertex_fragment();

    for meta in metas {
        use syn::Meta::{List, NameValue};
        match meta {
            // Parse #[sampler(0, sampler_type = "..."))].
            NameValue(m) if m.path == SAMPLER_TYPE => {
                let value = get_lit_str(DIMENSION, &m.value)?;
                sampler_binding_type = get_sampler_binding_type_value(value)?;
            }
            // Parse #[sampler(0, visibility(...))].
            List(m) if m.path == VISIBILITY => {
                visibility = get_visibility_flag_value(&m)?;
            }
            NameValue(m) => {
                return Err(Error::new_spanned(
                    m.path,
                    "Not a valid name. Available attributes: `sampler_type`.",
                ));
            }
            _ => {
                return Err(Error::new_spanned(
                    meta,
                    "Not a name value pair: `foo = \"...\"`",
                ));
            }
        }
    }

    Ok(SamplerAttrs {
        sampler_binding_type,
        visibility,
    })
}

fn get_sampler_binding_type_value(lit_str: &LitStr) -> Result<SamplerBindingType> {
    match lit_str.value().as_str() {
        FILTERING => Ok(SamplerBindingType::Filtering),
        NON_FILTERING => Ok(SamplerBindingType::NonFiltering),
        COMPARISON => Ok(SamplerBindingType::Comparison),

        _ => Err(Error::new_spanned(
            lit_str,
            "Not a valid dimension. Must be `filtering`, `non_filtering`, or `comparison`.",
        )),
    }
}

#[derive(Default)]
struct StorageAttrs {
    visibility: ShaderStageVisibility,
    binding_array: Option<u32>,
    read_only: bool,
    buffer: bool,
}

const READ_ONLY: Symbol = Symbol("read_only");
const BUFFER: Symbol = Symbol("buffer");

fn get_storage_binding_attr(metas: Vec<Meta>) -> Result<StorageAttrs> {
    let mut visibility = ShaderStageVisibility::vertex_fragment();
    let mut binding_array = None;
    let mut read_only = false;
    let mut buffer = false;

    for meta in metas {
        use syn::Meta::{List, Path};
        match meta {
            // Parse #[storage(0, visibility(...))].
            List(m) if m.path == VISIBILITY => {
                visibility = get_visibility_flag_value(&m)?;
            }
            // Parse #[storage(0, binding_array(...))] for bindless mode.
            List(m) if m.path == BINDING_ARRAY_MODIFIER_NAME => {
                binding_array = Some(get_binding_array_flag_value(&m)?);
            }
            Path(path) if path == READ_ONLY => {
                read_only = true;
            }
            Path(path) if path == BUFFER => {
                buffer = true;
            }
            _ => {
                return Err(Error::new_spanned(
                    meta,
                    "Not a valid attribute. Available attributes: `read_only`, `visibility`",
                ));
            }
        }
    }

    Ok(StorageAttrs {
        visibility,
        binding_array,
        read_only,
        buffer,
    })
}