[clangd] Respect `--sysroot` argument if it is set

Summary:
- Since `--sysroot` is a superset of the `-isysroot` argument, we
  shouldn't add the `-isysroot` if we detect a `--sysroot` flag.

Reviewers: sammccall

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D72415

1 files changed, 3 insertions, 1 deletions

diff --git a/clang-tools-extra/clangd/CompileCommands.cpp b/clang-tools-extra/clangd/CompileCommands.cpp
index b1eca02813b..f11b1236803 100644
--- a/clang-tools-extra/clangd/CompileCommands.cpp
+++ b/clang-tools-extra/clangd/CompileCommands.cpp
@@ -155,7 +155,9 @@ void CommandMangler::adjust(std::vector<std::string> &Cmd) const {
   if (ResourceDir && !Has("-resource-dir"))
     Cmd.push_back(("-resource-dir=" + *ResourceDir));
 
-  if (Sysroot && !Has("-isysroot")) {
+  // Don't set `-isysroot` if it is already set or if `--sysroot` is set.
+  // `--sysroot` is a superset of the `-isysroot` argument.
+  if (Sysroot && !Has("-isysroot") && !Has("--sysroot")) {
     Cmd.push_back("-isysroot");
     Cmd.push_back(*Sysroot);
   }