[PATCH] D72041: [clangd] Handle go-to-definition in macro invocations where the target appears in the expansion multiple times

[Sam McCall via Phabricator via cfe-commits]

sammccall accepted this revision.
sammccall added a comment.
This revision is now accepted and ready to land.

Awesome, thanks for fixing this!



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Comment at: clang-tools-extra/clangd/Selection.cpp:261
+      // consider it selected.
+      if (!SeenMacroCalls.insert(ArgStart).second) {
+        return NoTokens;
----------------
nridge wrote:
> sammccall wrote:
> > sammccall wrote:
> > > Given the following program:
> > > ```
> > > #define SQUARE(x) x * x;
> > > int four = [[SQUARE(2)]];
> > > ```
> > > We're going to now report the binary operator and one of the operands as selected and not the other, which doesn't seem desirable.
> > > 
> > > I think we want to accept macro-selected || arg-selected, so probably doing the current "non-argument macro expansion" first unconditionally or factoring it out into a function.
> > > 
> > > This will change the behavior of `int four = [[SQUARE]](2)` to consider the literal children selected too, I think this is fine.
> > I don't think it's a good idea to add hidden state and side-effects to testChunk() - it breaks a lot of assumptions that help reason about the code, and using `mutable` hides the violation of them.
> > (And a possible source of bugs - this is first in traversal order rather than first in source order - these are mostly but IIRC not always the same).
> > 
> > Instead I think you can do this statelessly: from the top-level spelling location, walk down with `SM.getMacroArgExpandedLocation` until you hit the target FileID (this is the first-expansion of first-expansion of first-expansion...) or the FileID stops changing (you've reached the innermost macro invocation, and your target location was on a different branch).
> I agree that adding state is not great. I thought it was icky as I was writing it, I just couldn't think of an alternative. Thank you for suggesting one!
> 
> I implemented what you suggested, and it seems to work. I did want to ask a clarifying question to make sure I understand correctly: when an argument occurs multiple times in a macro exapnsion, the occurrences will have distinct `FileID`s (as opposed just different offsets in the same macro `FileID`)?
That's right. My mental model is:
 - a TU is a sequence of expanded (i.e. post-PP) tokens
 - a FileID always corresponds to a single subrange of these expanded tokens...
 - ...with holes in it for child FileIDs. Parents/children nest properly.

One of the things I really like about the syntax::TokenBuffer API is that it exposes this structure.


================
Comment at: clang-tools-extra/clangd/Selection.cpp:166
+    if (SM.getFileID(Next) == SM.getFileID(Prev)) {
+      break;
+    }
----------------
nit: return false directly?


================
Comment at: clang-tools-extra/clangd/Selection.cpp:287
     if (SM.getFileID(ArgStart) == SelFile) {
-      SourceLocation ArgEnd = SM.getTopMacroCallerLoc(Batch.back().location());
-      return testTokenRange(SM.getFileOffset(ArgStart),
-                            SM.getFileOffset(ArgEnd));
+      if (isFirstExpansion(FID, ArgStart, SM)) {
+        SourceLocation ArgEnd =
----------------
when false is the fallthrough to handling as if part of the macro body deliberate?

Thinking about it I suppose either that or returning NoTokens works, but please document it, e.g. `} else { /* fall through and treat as part of the macro body */}`


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  https://reviews.llvm.org/D72041/new/

https://reviews.llvm.org/D72041