[PATCH] D95726: clang-tidy: modernize-use-nullptr mistakenly fixes rewritten spaceship operator comparisons - hasGrandparent version

[Conrad Poelman via Phabricator via cfe-commits]

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As in https://reviews.llvm.org/D95714, `clang-tidy -std=c++20` with `modernize-use-nullptr` mistakenly inserts `nullptr` in place of the comparison operator if the comparison internally expands in the AST to a rewritten spaceship operator. This can be reproduced by running the new `modernize-use-nullptr-cxx20.cpp` test without applying the supplied patch to UseNullptrCheck.cpp; the current clang-tidy will mistakenly replace:

  result = (a1 < a2);

with

  result = (a1 nullptr a2);

Oops!

The supplied patch fixes this by adding just one comment and one line of code to UseNullptrCheck.cpp:

  // Skip implicit casts to 0 generated by operator<=> rewrites.
  unless(hasGrandparent(cxxRewrittenBinaryOperator())),

It also adds the new `hasGrandparent` matcher, which is necessary as opposed to `hasAncestor` to properly convert:

  result = (a1 > (ptr == 0 ? a1 : a2));

to

  result = (a1 > (ptr == nullptr ? a1 : a2));

In this case the AST has an "ancestor" that is a rewritten binary operator, but not a direct grandparent.

This is an alternative to https://reviews.llvm.org/D95714.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D95726

Files:
  clang-tools-extra/clang-tidy/modernize/UseNullptrCheck.cpp
  clang-tools-extra/test/clang-tidy/checkers/modernize-use-nullptr-cxx20.cpp
  clang/include/clang/ASTMatchers/ASTMatchers.h
  clang/include/clang/ASTMatchers/ASTMatchersInternal.h
  clang/lib/ASTMatchers/ASTMatchFinder.cpp

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