Merge pull request #7392 from hasufell/hasufell/PR/issue-7390/fix-ghc-pkg-guesses

Prefer canonicalized path when guessing tools from GHC path

Cabal/src/Distribution/Simple/GHC.hs

@@ -240,10 +240,11 @@ guessToolFromGhcPath tool ghcProg verbosity searchpath
                              | otherwise = [guessGhcVersioned dir suf,
                                             guessVersioned dir suf,
                                             guessNormal dir]
-           guesses = mkGuesses given_dir given_suf ++
-                            if real_path == given_path
-                                then []
-                                else mkGuesses real_dir real_suf
+           -- order matters here, see https://github.com/haskell/cabal/issues/7390
+           guesses = (if real_path == given_path
+                        then []
+                        else mkGuesses real_dir real_suf)
+                     ++ mkGuesses given_dir given_suf
        info verbosity $ "looking for tool " ++ toolname
          ++ " near compiler in " ++ given_dir
        debug verbosity $ "candidate locations: " ++ show guesses

cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectory/setup.cabal.out

 # Setup configure
 Configuring SameDirectory-0.1.0.0...
-cabal: Version mismatch between ghc and ghc-pkg: <ROOT>/./ghc is version <GHCVER> <ROOT>/./ghc-pkg is version 9999999
+cabal: Version mismatch between ghc and ghc-pkg: <ROOT>/./ghc is version <GHCVER> <ROOT>/ghc-pkg is version 9999999

cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectory/setup.out

 # Setup configure
 Configuring SameDirectory-0.1.0.0...
-setup: Version mismatch between ghc and ghc-pkg: <ROOT>/./ghc is version <GHCVER> <ROOT>/./ghc-pkg is version 9999999
+setup: Version mismatch between ghc and ghc-pkg: <ROOT>/./ghc is version <GHCVER> <ROOT>/ghc-pkg is version 9999999

cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectoryGhcVersion/setup.cabal.out

 # Setup configure
 Configuring SameDirectory-0.1.0.0...
-cabal: Version mismatch between ghc and ghc-pkg: <ROOT>/./ghc-7.10 is version <GHCVER> <ROOT>/./ghc-pkg-ghc-7.10 is version 9999999
+cabal: Version mismatch between ghc and ghc-pkg: <ROOT>/./ghc-7.10 is version <GHCVER> <ROOT>/ghc-pkg-ghc-7.10 is version 9999999

cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectoryGhcVersion/setup.out

 # Setup configure
 Configuring SameDirectory-0.1.0.0...
-setup: Version mismatch between ghc and ghc-pkg: <ROOT>/./ghc-7.10 is version <GHCVER> <ROOT>/./ghc-pkg-ghc-7.10 is version 9999999
+setup: Version mismatch between ghc and ghc-pkg: <ROOT>/./ghc-7.10 is version <GHCVER> <ROOT>/ghc-pkg-ghc-7.10 is version 9999999

cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectoryVersion/setup.cabal.out

 # Setup configure
 Configuring SameDirectory-0.1.0.0...
-cabal: Version mismatch between ghc and ghc-pkg: <ROOT>/./ghc-7.10 is version <GHCVER> <ROOT>/./ghc-pkg-7.10 is version 9999999
+cabal: Version mismatch between ghc and ghc-pkg: <ROOT>/./ghc-7.10 is version <GHCVER> <ROOT>/ghc-pkg-7.10 is version 9999999

cabal-testsuite/PackageTests/GhcPkgGuess/SameDirectoryVersion/setup.out

 # Setup configure
 Configuring SameDirectory-0.1.0.0...
-setup: Version mismatch between ghc and ghc-pkg: <ROOT>/./ghc-7.10 is version <GHCVER> <ROOT>/./ghc-pkg-7.10 is version 9999999
+setup: Version mismatch between ghc and ghc-pkg: <ROOT>/./ghc-7.10 is version <GHCVER> <ROOT>/ghc-pkg-7.10 is version 9999999

changelog.d/pr-7392

+synopsis: Prefer canonicalized path when guessing tools from GHC path
+packages: Cabal
+prs: #7392
+issues: #7390
+
+description: {
+
+Motivation
+----------
+Often times, the user facing `ghc` binary is
+symlinked by other forces, such as the package manager,
+tooling like ghcup etc. As such, the naming convention
+(version suffix in particular) may not align with the
+assumptions made in Cabal and it may find an incorrect ghc-pkg.
+
+See:
+  - https://github.com/haskell/cabal/issues/7390
+  - https://gitlab.haskell.org/ghc/ghc/-/issues/18807
+  - https://gitlab.haskell.org/haskell/ghcup-hs/-/issues/73
+
+Solution
+--------
+Guessing the ghc-pkg path is already a hack and will be solved
+more appropriately in the future, see
+  - https://gitlab.haskell.org/ghc/ghc/-/merge_requests/4214
+  - https://gitlab.haskell.org/ghc/ghc/-/snippets/2710
+These patches will solve the issue for future GHC versions.
+
+As such, this patch provides a workaround for
+older, already existing GHC versions by first always
+following the symbolic link of the ghc binary (if it is one)
+and prefering its target directory as the guess lookup
+location.
+
+Rationale
+---------
+The canonicalized path of the ghc binary usually points to the
+bin/ directory unpacked from a bindist, which is less likely to be
+tampered with by distributions and tools. As such, prefering the
+canoncialized path should get us more robust results.
+
+}
+
+