[clangd] Don't traverse the AST within uninteresting files during indexing

Summary:
We already skip function bodies from these files while parsing, and drop symbols
found in them. However, traversing their ASTs still takes a substantial amount
of time.

Non-scientific benchmark on my machine:
  background-indexing llvm-project (llvm+clang+clang-tools-extra), wall time
  before: 7:46
  after: 5:13
  change: -33%

Indexer.cpp libclang should be updated too, I'm less familiar with that code,
and it's doing tricky things with the ShouldSkipFunctionBody callback, so it
needs to be done separately.

Reviewers: kadircet

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D80296

1 files changed, 3 insertions, 0 deletions

diff --git a/clang/lib/Index/IndexDecl.cpp b/clang/lib/Index/IndexDecl.cpp
index 68160bc5..2ba323e 100644
--- a/clang/lib/Index/IndexDecl.cpp
+++ b/clang/lib/Index/IndexDecl.cpp
@@ -765,6 +765,9 @@ bool IndexingContext::indexTopLevelDecl(const Decl *D) {
   if (isa<ObjCMethodDecl>(D))
     return true; // Wait for the objc container.
 
+  if (IndexOpts.ShouldTraverseDecl && !IndexOpts.ShouldTraverseDecl(D))
+    return true; // skip
+
   return indexDecl(D);
 }