[PATCH] D83508: [clangd][Hover] Don't use Decl if it is not related with tokens under cursor.

[Sam McCall via Phabricator via cfe-commits]

sammccall added inline comments.


================
Comment at: clang-tools-extra/clangd/Selection.cpp:227
         continue;
+      // Ignore tokens in disabled preprocessor sections.
+      if (Buf.expandedTokens(SM.getMacroArgExpandedLocation(T->location()))
----------------
ArcsinX wrote:
> sammccall wrote:
> > I think this is more work than we'd like to do in this loop (the whole file could be selected!) and it's also not obviously correct - it relies on the assumption that any token that doesn't expand to something by itself, isn't a macro argument or macro name, is part of an ignored region. (That may or may not be correct, but it's a nontrivial assumption to make here).
> > 
> > I think the API we need is something like `vector<TokenBuffer::Expansion> TokenBuffer::expansionsOverlapping(ArrayRef<Token> Spelled)`.
> > This requires a couple of binary searches on the TokenBuffer side to compute, and on this side we can just look at the spelled token ranges for empty expansions and mark them in a bitmap.
> > 
> > I'm happy to try to put together a TokenBuffer patch if this is too much of a yak-shave, though.
> >  it relies on the assumption that any token that doesn't expand to something by itself, isn't a macro argument or macro name, is part of an ignored region. (That may or may not be correct, but it's a nontrivial assumption to make here).
> 
> Example `#define FOO BAR`.
> Expanded tokens:
> Spelled tokens: `#`, `define`, `FOO`, `BAR`
> 
> I think we could ignore all except `FOO` in this case. Also I found similar check in XRefs.cpp `bool tokenSpelledAt(SourceLocation SpellingLoc, const syntax::TokenBuffer &TB)`
> 
> How to judge should we skip token or not if we do not have expanded tokens for it? Do you have any advice here?
I'm not following, because I think we can ignore *all* those tokens. We care about macro names when the macros are *used* (tokens expanded from macro bodies are associated from the macro name at the expansion point). But not where they're defined.

> Also I found similar check in XRefs.cpp
Yes, there are a few restrictions there though:
 - it's only used for identifiers, so there are fewer cases to consider
 - performance doesn't matter at all, as it runs in response to an explicit action and runs on ~2 tokens

> How to judge should we skip token or not if we do not have expanded tokens for it? Do you have any advice here?
I think we should just always skip in this case, let me try this out...


Repository:
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CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D83508/new/

https://reviews.llvm.org/D83508