[all-commits] [llvm/llvm-project] eaa555: [clang-tidy] misc-unused-parameters: Don't remove ...

[Matthias Gehre via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: eaa55590945a130131a47a4d2b89e3bbdfced79e
      https://github.com/llvm/llvm-project/commit/eaa55590945a130131a47a4d2b89e3bbdfced79e
  Author: Matthias Gehre <gehre.matthias at gmail.com>
  Date:   2020-04-09 (Thu, 09 Apr 2020)

  Changed paths:
    M clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp
    M clang-tools-extra/test/clang-tidy/checkers/misc-unused-parameters.cpp

  Log Message:
  -----------
  [clang-tidy] misc-unused-parameters: Don't remove parameter from lambda

Summary:
Previously, the check would fix
```
using fn = void(int);
void f(fn *);
void test() {
  // CHECK-MESSAGES: :[[@LINE+2]]:12: warning: parameter 'I' is unused
  // CHECK-FIXES: {{^}}  f([](int  /*I*/) {
  f([](int I) { return; });
}
```
into
`f([]() { return; });` which breaks compilation. Now the check is disabled from Lambdas.

The AST is not so easy to use. For
```
    auto l = [](int) {  return;  };
    f(l);
```
one gets
```
 `-CallExpr <line:7:5, col:8> 'void'
      |-ImplicitCastExpr <col:5> 'void (*)(fn *)' <FunctionToPointerDecay>
      | `-DeclRefExpr <col:5> 'void (fn *)' lvalue Function 0x55a91a545e28 'f' 'void (fn *)'
      `-ImplicitCastExpr <col:7> 'void (*)(int)' <UserDefinedConversion>
        `-CXXMemberCallExpr <col:7> 'void (*)(int)'
          `-MemberExpr <col:7> '<bound member function type>' .operator void (*)(int) 0x55a91a546850
            `-ImplicitCastExpr <col:7> 'const (lambda at line:6:14)' lvalue <NoOp>
              `-DeclRefExpr <col:7> '(lambda at line:6:14)':'(lambda at line:6:14)' lvalue Var 0x55a91a5461c0 'l' '(lambda at line:6:14)':'(lambda at line:6:14)'
```
There is no direct use of the `operator()(int I)` of the lambda, so the `!Indexer->getOtherRefs(Function).empty()`
does not fire. In the future, we might be able to use the conversion operator `operator void (*)(int)` to mark
the call operator as having an "other ref".

Reviewers: aaron.ballman, alexfh, hokein, njames93

Subscribers: xazax.hun, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D77680