GitLab

Hannes Siebenhandl pushed to branch wip/fendor/longpath-aware-manifest at Glasgow Haskell Compiler / GHC

Commits:

e23169ef

by Fendor at 2026-03-02T21:37:51+01:00

Add `-fwin-aware-long-paths` to support ling paths on Windows

While Windows supports file paths longer than the MAX_PATH restriction,
it is opt-in, and not enabled by default.

By declaring the binary to be long path aware in the manifest of the
windows executable, the binary opts-in to the new behaviour.

It is up to the developer to make sure they use UNC paths and Win.h
specific functions for filesystem operations to use long paths in their
application.

See
https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation#application-manifest-updates-to-declare-long-path-capability
and https://learn.microsoft.com/en-us/windows/win32/sbscs/application-manifests
for the documentation on the application manifest and long path option.

5 changed files:

compiler/GHC/Driver/DynFlags.hs
compiler/GHC/Driver/Flags.hs
compiler/GHC/Driver/Session.hs
compiler/GHC/Linker/Windows.hs
docs/users_guide/phases.rst

Changes:

compiler/GHC/Driver/DynFlags.hs

@@ -1210,6 +1210,7 @@ defaultFlags settings
    = [ Opt_AutoLinkPackages,
        Opt_DiagnosticsShowCaret,
        Opt_EmbedManifest,
 +      Opt_WinLongPathAware,
        Opt_FamAppCache,
        Opt_GenManifest,
        Opt_GhciHistory,

compiler/GHC/Driver/Flags.hs

@@ -744,6 +744,7 @@ data GeneralFlag
     | Opt_PrintBindContents
     | Opt_GenManifest
     | Opt_EmbedManifest
 +   | Opt_WinLongPathAware
     | Opt_SharedImplib
     | Opt_BuildingCabalPackage
     | Opt_IgnoreDotGhci

compiler/GHC/Driver/Session.hs

@@ -2525,6 +2525,7 @@ fFlagsDeps = [
    flagSpec "eager-blackholing"                Opt_EagerBlackHoling,
    flagSpec "orig-thunk-info"                  Opt_OrigThunkInfo,
    flagSpec "embed-manifest"                   Opt_EmbedManifest,
 +  flagSpec "win-aware-long-paths"             Opt_WinLongPathAware,
    flagSpec "enable-rewrite-rules"             Opt_EnableRewriteRules,
    flagSpec "enable-th-splice-warnings"        Opt_EnableThSpliceWarnings,
    flagSpec "error-spans"                      Opt_ErrorSpans,

compiler/GHC/Linker/Windows.hs

@@ -16,6 +16,7 @@ import System.Directory
  data ManifestOpts = ManifestOpts
    { manifestEmbed :: !Bool    -- ^ Should the manifest be embedded in the binary with Windres
 +  , manifestLongPathAware :: !Bool
    , manifestTempdir :: TempDir
    , manifestWindresConfig :: WindresConfig
    , manifestObjectSuf :: String
@@ -24,6 +25,7 @@ data ManifestOpts = ManifestOpts
  initManifestOpts :: DynFlags -> ManifestOpts
  initManifestOpts dflags = ManifestOpts
    { manifestEmbed = gopt Opt_EmbedManifest dflags
 +  , manifestLongPathAware = gopt Opt_WinLongPathAware dflags
    , manifestTempdir = tmpDir dflags
    , manifestWindresConfig = configureWindres dflags
    , manifestObjectSuf = objectSuf dflags
@@ -37,21 +39,7 @@ maybeCreateManifest
     -> IO [FilePath] -- ^ extra objects to embed, maybe
  maybeCreateManifest logger tmpfs opts exe_filename = do
     let manifest_filename = exe_filename <.> "manifest"
 -       manifest =
 -         "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"yes\"?>\n\
 -         \  <assembly xmlns=\"urn:schemas-microsoft-com:asm.v1\" manifestVersion=\"1.0\">\n\
 -         \  <assemblyIdentity version=\"1.0.0.0\"\n\
 -         \     processorArchitecture=\"X86\"\n\
 -         \     name=\"" ++ dropExtension exe_filename ++ "\"\n\
 -         \     type=\"win32\"/>\n\n\
 -         \  <trustInfo xmlns=\"urn:schemas-microsoft-com:asm.v3\">\n\
 -         \    <security>\n\
 -         \      <requestedPrivileges>\n\
 -         \        <requestedExecutionLevel level=\"asInvoker\" uiAccess=\"false\"/>\n\
 -         \        </requestedPrivileges>\n\
 -         \       </security>\n\
 -         \  </trustInfo>\n\
 -         \</assembly>\n"
 +       manifest = manifestContents (manifestLongPathAware opts) exe_filename
     writeFile manifest_filename manifest
@@ -80,3 +68,36 @@ maybeCreateManifest logger tmpfs opts exe_filename = do
           removeFile manifest_filename
           return [rc_obj_filename]
++
 +manifestContents :: Bool -> FilePath -> String
 +manifestContents longPathAware exe_filename =
 +  unlines $
 +    [ "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"yes\"?>"
 +    , "  <assembly xmlns=\"urn:schemas-microsoft-com:asm.v1\" manifestVersion=\"1.0\">"
 +    , "  <assemblyIdentity version=\"1.0.0.0\""
 +    , "     processorArchitecture=\"X86\""
 +    , "     name=\"" ++ dropExtension exe_filename ++ "\""
 +    , "     type=\"win32\"/>"
 +    , "  <trustInfo xmlns=\"urn:schemas-microsoft-com:asm.v3\">"
 +    , "    <security>"
 +    , "      <requestedPrivileges>"
 +    , "        <requestedExecutionLevel level=\"asInvoker\" uiAccess=\"false\"/>"
 +    , "      </requestedPrivileges>"
 +    , "    </security>"
 +    , "  </trustInfo>"
 +    ]
 +    ++
 +    (
 +      if longPathAware
 +        then
 +          [ "  <application xmlns=\"urn:schemas-microsoft-com:asm.v3\">"
 +          , "    <windowsSettings xmlns:ws2=\"http://schemas.microsoft.com/SMI/2016/WindowsSettings\">"
 +          , "      <ws2:longPathAware>true</ws2:longPathAware>"
 +          , "    </windowsSettings>"
 +          , "  </application>"
 +          ]
 +        else
 +          []
 +    ) ++
 +    [ "  </assembly>"
 +    ]

docs/users_guide/phases.rst

@@ -1430,6 +1430,29 @@ for example).
      See also :ghc-flag:`-pgmwindres ⟨cmd⟩` (:ref:`replacing-phases`) and
      :ghc-flag:`-optwindres ⟨option⟩` (:ref:`forcing-options-through`).
 +.. ghc-flag:: -fwin-aware-long-paths
 +    :shortdesc: Declare the linked binary to be long path aware on Windows.
 +    :reverse: -fno-win-aware-long-paths
 +    :type: dynamic
 +    :category: linking
 +    :since: 9.14.2
++
 +    Declare in the manifest file that GHC generates when linking a binary on Windows
 +    to be aware of long paths.
++
 +    Windows paths usually have a `MAX_PATH <https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation>`__
 +    limit of 260 characters.
 +    This limitation can be lifted by opting into enabling long paths in various
 +    ways, see `Enable long paths in Windows 10 and later`_.
++
 +    To invoke the compiled program with long paths, the Windows manifest needs
 +    to declare that the program is aware of long paths and can handle them
 +    appropriately.
++
 +    :ghc-flag:`-fno-embed-manifest` also implies :ghc-flag:`-fno-win-aware-long-paths`.
++
 +    _Enable long paths in Windows 10 and later: https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation?tabs=registry#enable-long-paths-in-windows-10-version-1607-and-later
++
  .. ghc-flag:: -fno-shared-implib
      :shortdesc: Don't generate an import library for a DLL (Windows only)
      :type: dynamic