Avoid unnecessary Target canonicalisation in Session setup

ghcide/session-loader/Development/IDE/Session.hs

@@ -553,11 +553,11 @@ fromTargetId is exts (GHC.TargetModule mod) env dep = do
               , i <- is
               , boot <- ["", "-boot"]
               ]
-    locs <- mapM (fmap toNormalizedFilePath' . canonicalizePath) fps
+    let locs = map toNormalizedFilePath' fps
     return [TargetDetails (TargetModule mod) env dep locs]
 -- For a 'TargetFile' we consider all the possible module names
 fromTargetId _ _ (GHC.TargetFile f _) env deps = do
-    nf <- toNormalizedFilePath' <$> canonicalizePath f
+    let nf = toNormalizedFilePath' f
     return [TargetDetails (TargetFile nf) env deps [nf]]
 
 toFlagsMap :: TargetDetails -> [(NormalizedFilePath, (IdeResult HscEnvEq, DependencyInfo))]

ghcide/test/data/symlink/hie.yaml

@@ -0,0 +1,10 @@
+
+cradle:
+  direct:
+    arguments:
+      - -i
+      - -isrc
+      - -iother_loc/
+      - other_loc/Sym.hs
+      - src/Foo.hs
+      - -Wall

ghcide/test/data/symlink/some_loc/Sym.hs

@@ -0,0 +1,4 @@
+module Sym where
+
+foo :: String
+foo = ""

ghcide/test/data/symlink/src/Foo.hs

@@ -0,0 +1,4 @@
+module Foo where
+
+import Sym
+

ghcide/test/exe/Main.hs

@@ -164,6 +164,7 @@ main = do
     , pluginParsedResultTests
     , preprocessorTests
     , thTests
+    , symlinkTests
     , safeTests
     , unitTests
     , haddockTests
@@ -4055,6 +4056,18 @@ thTests =
     expectDiagnostics [ ( cPath, [(DsWarning, (3, 0), "Top-level binding with no type signature: a :: A")] ) ]
     ]
 
+-- | Tests for projects that use symbolic links one way or another
+symlinkTests :: TestTree
+symlinkTests =
+  testGroup "Projects using Symlinks"
+    [ testCase "Module is symlinked" $ runWithExtraFiles "symlink" $ \dir -> do
+        liftIO $ createFileLink (dir </> "some_loc" </> "Sym.hs") (dir </> "other_loc" </> "Sym.hs")
+        let fooPath = dir </> "src" </> "Foo.hs"
+        _ <- openDoc fooPath "haskell"
+        expectDiagnosticsWithTags  [("src" </> "Foo.hs", [(DsWarning, (2, 0), "The import of 'Sym' is redundant", Just DtUnnecessary)])]
+        pure ()
+    ]
+
 -- | test that TH is reevaluated on typecheck
 thReloadingTest :: Bool -> TestTree
 thReloadingTest unboxed = testCase name $ runWithExtraFiles dir $ \dir -> do