[clangd] Include insertion: require header guards, drop other heuristics, treat .def like .inc.

Summary:
We do have some reports of include insertion behaving badly in some
codebases. Requiring header guards both makes sense in principle, and is
likely to disable this "nice-to-have" feature in codebases where headers don't
follow the expected pattern.

With this we can drop some other heuristics, such as looking at file
extensions to detect known non-headers - implementation files have no guards.

One wrinkle here is #import - objc headers may not have guards because
they're intended to be used via #import. If the header is the main file
or is #included, we won't collect locations - merge should take care of
this if we see the file #imported somewhere. Seems likely to be OK.

Headers which have a canonicalization (stdlib, IWYU) are exempt from this check.
*.inc files continue to be handled by looking up to the including file.
This patch also adds *.def here - tablegen wants this pattern too.

In terms of code structure, the division between SymbolCollector and
CanonicalIncludes has shifted: SymbolCollector is responsible for more.
This is because SymbolCollector has all the SourceManager/HeaderSearch access
needed for checking for guards, and we interleave these checks with the *.def
checks in a loop (potentially).
We could hand all the info into CanonicalIncludes and put the logic there
if that's preferable.

Reviewers: ioeric

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D60316

llvm-svn: 358571

0 files changed, 0 insertions, 0 deletions