[clangd] Always use preamble (even stale) for code completion
Summary:
This improves performance of code completion, because we avoid stating
the files from the preamble and never attempt to parse the files
without using the preamble if it's provided.
However, the change comes at a cost of sometimes providing incorrect
results when doing code completion after making actually considerable
changes to the files used in the preamble or the preamble itself.
Eventually the preamble will get rebuilt and code completion will
be providing the correct results.
Reviewers: bkramer, sammccall, jkorous-apple
Reviewed By: sammccall
Subscribers: klimek, cfe-commits
Differential Revision: https://reviews.llvm.org/D41991
llvm-svn: 322854
diff --git a/clang-tools-extra/clangd/CodeComplete.cpp b/clang-tools-extra/clangd/CodeComplete.cpp
index 73acc0c..fe74dbd 100644
--- a/clang-tools-extra/clangd/CodeComplete.cpp
+++ b/clang-tools-extra/clangd/CodeComplete.cpp
@@ -517,14 +517,18 @@
std::unique_ptr<llvm::MemoryBuffer> ContentsBuffer =
llvm::MemoryBuffer::getMemBufferCopy(Contents, FileName);
- // Attempt to reuse the PCH from precompiled preamble, if it was built.
+ // We reuse the preamble whether it's valid or not. This is a
+ // correctness/performance tradeoff: building without a preamble is slow, and
+ // completion is latency-sensitive.
if (Preamble) {
auto Bounds =
ComputePreambleBounds(*CI->getLangOpts(), ContentsBuffer.get(), 0);
- if (!Preamble->CanReuse(*CI, ContentsBuffer.get(), Bounds, VFS.get()))
- Preamble = nullptr;
+ // FIXME(ibiryukov): Remove this call to CanReuse() after we'll fix
+ // clients relying on getting stats for preamble files during code
+ // completion.
+ // Note that results of CanReuse() are ignored, see the comment above.
+ Preamble->CanReuse(*CI, ContentsBuffer.get(), Bounds, VFS.get());
}
-
auto Clang = prepareCompilerInstance(
std::move(CI), Preamble, std::move(ContentsBuffer), std::move(PCHs),
std::move(VFS), DummyDiagsConsumer);