readability-const-return-type identifies the wrong `const` token that qualifies the return type

[llvmbot]

Bugzilla Link	44326
Resolution	FIXED
Resolved on	Jan 04, 2020 14:45
Version	unspecified
OS	All
Reporter	LLVM Bugzilla Contributor
CC	@JonasToth

Extended Description

For the following code located in const-ret-type.cpp:

const int* const volatile foo() {}

The following invocation of clang-tidy produces the following output:

$ clang-tidy -checks=-*,readability-const-return-type const-ret-type.cpp
2 warnings generated.
const-ret-type.cpp:1:1: warning: return type 'const int const volatile' is 'const'-qualified at the top level, ...
const int const volatile foo() {}
^~~~~~
Suppressed 1 warnings (1 with check filters).

While the expected diagnostic should be:

const int* const volatile foo() {}
^~~~~~

The readability-const-return-type checker incorrectly flags the first const token, but it's actually the other const token that precedes volatile that qualifies the return type. Applying the suggested fixit can result in a miscompilation. The culprit is in the implementation of the utils::lexer::getConstQualifyingToken function. I have a patch ready and I plan to submit it for review shortly.

[llvmbot]

A fix is up for a review: https://reviews.llvm.org/D71666

[JonasToth]

fixede with https://reviews.llvm.org/rGf58f39137c6e5a324ef684b1d72bddae244aa94d

Thank you for the patch!