Fix symlink resolution in GetCanonicalPath

[DaanDeMeyer]

Summary

https://github.com/llvm/llvm-project/commit/dd67793c0c549638cd93cad1142d324b979ba682 removed file path symlink resolution in GetCanonicalPath. This revision adds the file path symlink resolution back to GetCanonicalPath. This is needed so that clangd always navigates us to the original file instead of a symlink.

See https://github.com/clangd/clangd/issues/197 for an extended discussion.

(It would be great if this can still make it in the 10.0.0 release)

[DaanDeMeyer]

Abandoning this since clangd shouldn't be forced to deal with the outrageous build system that I'm forced to use. I'm currently just building clangd from source with these changes which works fine.

clang-tools-extra/clangd/SourceCode.cpp

     }
   }
 
+  SmallString<128> RealPath;
+  if (SourceMgr.getFileManager().getVirtualFileSystem().getRealPath(FilePath,
+                                                                    RealPath)) {
+    log("Could not compute real path: {0}", FilePath);
+    return FilePath.str().str();
+  }
+
   // Handle the symbolic link path case where the current working directory
   // (getCurrentWorkingDirectory) is a symlink. We always want to the real
   // file path (instead of the symlink path) for the  C++ symbols.

   //  The file path of Symbol is "/project/src/foo.h" instead of
   //  "/tmp/build/foo.h"
   if (auto Dir = SourceMgr.getFileManager().getDirectory(
-          llvm::sys::path::parent_path(FilePath))) {
-    llvm::SmallString<128> RealPath;
+          llvm::sys::path::parent_path(RealPath))) {
+    llvm::SmallString<128> DirRealPath;
     llvm::StringRef DirName = SourceMgr.getFileManager().getCanonicalName(*Dir);
-    llvm::sys::path::append(RealPath, DirName,
-                            llvm::sys::path::filename(FilePath));
-    return RealPath.str().str();
+    llvm::sys::path::append(DirRealPath, DirName,
+                            llvm::sys::path::filename(RealPath));
+    return DirRealPath.str().str();
   }
 
-  return FilePath.str().str();
+  return RealPath.str().str();
 }
 
 TextEdit toTextEdit(const FixItHint &FixIt, const SourceManager &M,