[clang] [Clang] [Diagnostics] Simplify filenames that contain '..' (PR #143520)

[Corentin Jabot via cfe-commits]

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@@ -2403,3 +2403,75 @@ SourceManagerForFile::SourceManagerForFile(StringRef FileName,
   assert(ID.isValid());
   SourceMgr->setMainFileID(ID);
 }
+
+StringRef
+SourceManager::getNameForDiagnostic(StringRef Filename,
+                                    const DiagnosticOptions &Opts) const {
+  OptionalFileEntryRef File = getFileManager().getOptionalFileRef(Filename);
+  if (!File)
+    return Filename;
+
+  bool SimplifyPath = [&] {
+    if (Opts.AbsolutePath)
+      return true;
+
+    // Try to simplify paths that contain '..' in any case since paths to
+    // standard library headers especially tend to get quite long otherwise.
+    // Only do that for local filesystems though to avoid slowing down
+    // compilation too much.
+    if (!File->getName().contains(".."))
+      return false;
+
+    // If we're not on Windows, check if we're on a network file system and
+    // avoid simplifying the path in that case since that can be slow. On
+    // Windows, the check for a local filesystem is already slow, so skip it.
+#ifndef _WIN32
+    if (!llvm::sys::fs::is_local(File->getName()))
+      return false;
+#endif
+
+    return true;
+  }();
+
+  if (!SimplifyPath)
+    return Filename;
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cor3ntin wrote:

I wonder if it would be more efficient to check the map first

https://github.com/llvm/llvm-project/pull/143520