fix-big-sur.patch

diff --git a/compiler/ghci/Linker.hs b/compiler/ghci/Linker.hs
index dbe71cd9ab048bd5cc9b2774dd30faeecbdd84fb..da18c019461bdffd62e06bd0441742786109c08c 100644
--- a/compiler/ghci/Linker.hs
+++ b/compiler/ghci/Linker.hs
@@ -1676,6 +1676,38 @@ addEnvPaths name list
 -- ----------------------------------------------------------------------------
 -- Loading a dynamic library (dlopen()-ish on Unix, LoadLibrary-ish on Win32)
 
+{-
+Note [macOS Big Sur dynamic libraries]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+macOS Big Sur makes the following change to how frameworks are shipped
+with the OS:
+
+> New in macOS Big Sur 11 beta, the system ships with a built-in
+> dynamic linker cache of all system-provided libraries.  As part of
+> this change, copies of dynamic libraries are no longer present on
+> the filesystem.  Code that attempts to check for dynamic library
+> presence by looking for a file at a path or enumerating a directory
+> will fail.  Instead, check for library presence by attempting to
+> dlopen() the path, which will correctly check for the library in the
+> cache. (62986286)
+
+(https://developer.apple.com/documentation/macos-release-notes/macos-big-sur-11_0_1-release-notes/)
+
+Therefore, the previous method of checking whether a library exists
+before attempting to load it makes GHC.Runtime.Linker.loadFramework
+fail to find frameworks installed at /System/Library/Frameworks.
+Instead, any attempt to load a framework at runtime, such as by
+passing -framework OpenGL to runghc or running code loading such a
+framework with GHCi, fails with a 'not found' message.
+
+GHC.Runtime.Linker.loadFramework now opportunistically loads the
+framework libraries without checking for their existence first,
+failing only if all attempts to load a given framework from any of the
+various possible locations fail.  See also #18446, which this change
+addresses.
+-}
+
 -- Darwin / MacOS X only: load a framework
 -- a framework is a dynamic library packaged inside a directory of the same
 -- name. They are searched for in different paths than normal libraries.
@@ -1686,17 +1718,29 @@ loadFramework hsc_env extraPaths rootname
                                   Left _ -> []
                                   Right dir -> [dir </> "Library/Frameworks"]
               ps = extraPaths ++ homeFrameworkPath ++ defaultFrameworkPaths
-        ; mb_fwk <- findFile ps fwk_file
-        ; case mb_fwk of
-            Just fwk_path -> loadDLL hsc_env fwk_path
-            Nothing       -> return (Just "not found") }
-                -- Tried all our known library paths, but dlopen()
-                -- has no built-in paths for frameworks: give up
+        ; errs <- findLoadDLL ps []
+        ; return $ fmap (intercalate ", ") errs
+        }
    where
      fwk_file = rootname <.> "framework" </> rootname
-        -- sorry for the hardcoded paths, I hope they won't change anytime soon:
+
+     -- sorry for the hardcoded paths, I hope they won't change anytime soon:
      defaultFrameworkPaths = ["/Library/Frameworks", "/System/Library/Frameworks"]
 
+     -- Try to call loadDLL for each candidate path.
+     --
+     -- See Note [macOS Big Sur dynamic libraries]
+     findLoadDLL [] errs =
+       -- Tried all our known library paths, but dlopen()
+       -- has no built-in paths for frameworks: give up
+       return $ Just errs
+     findLoadDLL (p:ps) errs =
+       do { dll <- loadDLL hsc_env (p </> fwk_file)
+          ; case dll of
+              Nothing  -> return Nothing
+              Just err -> findLoadDLL ps ((p ++ ": " ++ err):errs)
+          }
+
 {- **********************************************************************
 
                 Helper functions