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warn on pointless qualifiers with fixit to remove them #9430

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llvmbot opened this issue Jan 26, 2011 · 5 comments
Closed

warn on pointless qualifiers with fixit to remove them #9430

llvmbot opened this issue Jan 26, 2011 · 5 comments
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bugzilla Issues migrated from bugzilla check-request Request for a new check in clang-tidy clang-tidy

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@llvmbot
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llvmbot commented Jan 26, 2011 •
edited by philnik777
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Bugzilla Link 9058
Version trunk
OS Linux
Reporter LLVM Bugzilla Contributor
CC @chandlerc,@zmodem

Extended Description

We'd like a warning on the qualifier in code like:

  bool const f();
  void f(const int x);

with fixit to remove the dead qualifier. The one use case we want to not break is:

  void f(int *ptr);
  void f(int * const ptr) {
    *ptr++;  // the const prevents the typo "ptr++;"
  }

I'm proposing the warning name -Wpointless-qualifier.
@llvmbot
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llvmbot commented Feb 8, 2011

Part of this is already -Wignored-qualifiers. We should finish off the cases it doesn't catch and add fixits.

In this testcase:

static const const int test1 = 10;
const int test2() { return 10; }
int test3(const int a) { return a + 1; }
int test4(const int const a) { return a + 1; }

Wignored-qualifiers only complains about the return on test2, and without a fixit.

@chandlerc
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The return type cases I believe are fixed in r126321, thanks to Hans.

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 3, 2021
@philnik777
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Retargeting as a clang-tidy check. This does make sense in a definition, so it's only a style choice whether to keep the const in the declaration or not.

@philnik777 philnik777 added clang-tidy check-request Request for a new check in clang-tidy and removed clang:frontend Language frontend issues, e.g. anything involving "Sema" labels Aug 22, 2023
@llvmbot
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llvmbot commented Aug 22, 2023

@llvm/issue-subscribers-clang-tidy

@maflcko
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maflcko commented Jan 15, 2025

This is now fixed, via

  • Wignored-qualifiers:
<source>:1:8: warning: 'const' type qualifier on return type has no effect [-Wignored-qualifiers]
    1 |   bool const f();
      |        ^~~~~
1 warning generated.
  • Wduplicate-decl-specifier:
<source>:3:16: warning: duplicate 'const' declaration specifier [-Wduplicate-decl-specifier]
    3 |   static const const int test1 = 10;
      |                ^~~~~
  • readability-const-return-type:
<source>:1:4: warning: return type 'const bool' is 'const'-qualified at the top level, which may reduce code readability without improving const correctness [readability-const-return-type]
    1 |    const bool f() {return {};};
      |    ^~~~~
  • readability-avoid-const-params-in-decls:
<source>:2:10: warning: parameter 'x' is const-qualified in the function declaration; const-qualification of parameters only has an effect in function definitions [readability-avoid-const-params-in-decls]
    2 |   void f(const int x);
      |          ^~~~~

@maflcko maflcko closed this as completed Jan 15, 2025
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