[clangd] Support passing a relative path to -compile-commands-dir

[DaanDeMeyer]

Summary

This is useful when using clangd with CMake based projects in Visual Studio Code since when using CMake the compile_commands.json file is usually located in a build subdirectory which isn't a parent directory of the source files. Allowing passing relative paths to -compile-commands-dir allows specifying clangd.arguments = ["-compile-commands-dir=build"] in VSCode's settings file and having it work for each CMake based project that uses the build subdirectory as the build directory (instead of having to specify the absolute path to the compile commands directory for each separate project in VSCode's settings).

[sammccall]

Thanks for the fix!

clangd/tool/ClangdMain.cpp

261 ↗

(On Diff #170338)

This comment echoes the code, but doesn't say *why*.
Consider replacing with
// clangd changes working directory a lot, so we need an absolute path.

263 ↗

(On Diff #170338)

it's fine to call make_absolute on an absolute path, it's a no-op.
You can do that here to avoid a special case.

267 ↗

(On Diff #170338)

nit: we tend to inline this as if (std::error_code EC = sys::fs...)

272 ↗

(On Diff #170338)

This is a no-op (as are the existing ones on 255 and 259...)

[DaanDeMeyer]

Updated diff according to comments.

[sammccall]

It looks like these are your first couple of LLVM patches.
So, welcome :-) And do you want me to commit them for you?

Typically your first few patches get landed by someone else, and then you ask for commit access: https://llvm.org/docs/DeveloperPolicy.html#obtaining-commit-access

[DaanDeMeyer]

You can commit them. Thanks for all the quick responses!

clang-tools-extra/trunk/clangd/tool/ClangdMain.cpp

int main(int argc, char *argv[]) {
   // stream can cause significant (non-deterministic) latency for the logger.
   errs().SetBuffered();
   StreamLogger Logger(errs(), LogLevel);
   clangd::LoggingSession LoggingSession(Logger);
 
   // If --compile-commands-dir arg was invoked, check value and override default
   // path.
   Optional<Path> CompileCommandsDirPath;
-  if (CompileCommandsDir.empty()) {
-    CompileCommandsDirPath = None;
-  } else if (!sys::path::is_absolute(CompileCommandsDir) ||
-             !sys::fs::exists(CompileCommandsDir)) {
-    errs() << "Path specified by --compile-commands-dir either does not "
-              "exist or is not an absolute "
-              "path. The argument will be ignored.\n";
-    CompileCommandsDirPath = None;
+  if (!CompileCommandsDir.empty()) {
+    if (sys::fs::exists(CompileCommandsDir)) {
+      // We support passing both relative and absolute paths to the
+      // --compile-commands-dir argument, but we assume the path is absolute in
+      // the rest of clangd so we make sure the path is absolute before
+      // continuing.
+      SmallString<128> Path(CompileCommandsDir);
+      if (std::error_code EC = sys::fs::make_absolute(Path)) {
+        errs() << "Error while converting the relative path specified by "
+                  "--compile-commands-dir to an absolute path: "
+               << EC.message() << ". The argument will be ignored.\n";
       } else {
-    CompileCommandsDirPath = CompileCommandsDir;
+        CompileCommandsDirPath = Path.str();
+      }
+    } else {
+      errs() << "Path specified by --compile-commands-dir does not exist. The "
+                "argument will be ignored.\n";
+    }
   }
 
   ClangdServer::Options Opts;
   switch (PCHStorage) {
   case PCHStorageFlag::Memory:
     Opts.StorePreamblesInMemory = true;
     break;
   case PCHStorageFlag::Disk: