Warn on semicolons immediately following "else"

[llvmbot]

Bugzilla Link	35319
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@dwblaikie,@DougGregor,@rnk,@Weverything
Fixed by commit(s)	r318456

Extended Description

clang version 6.0.0 (trunk 317263)

This code:

    int main(int argc, char** argv) {
      if (argc > 4);   // <-- Note semicolon!
      return 0;
    }

Gives:

    eraseme.cc:2:16: warning: if statement has empty body [-Wempty-body]
      if (argc > 4);
                   ^
    eraseme.cc:2:16: note: put the semicolon on a separate line to silence this
          warning
    1 warning generated.

This is good! And it also works for else if cases. But I just did the same bug and put a semicolon after a bare else:

    int main(int argc, char** argv) {
      if (argc > 4)
        return 1;
      else;  // <- Semicolon
        return 2;
      return 0;
    }

And there is no warning. This was pretty tricky to find and it seems like the same rule for if semicolons should just also be applied to else.

[rnk]

Thanks, should be fixed by r318456.

[rnk]

This was reverted.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (llvmbot)

| | | | --- | --- | | Bugzilla Link | [35319](https://llvm.org/bz35319) | | Version | trunk | | OS | Linux | | Reporter | LLVM Bugzilla Contributor | | CC | @dwblaikie,@DougGregor,@rnk,@Weverything | | Fixed by commit(s) | r318456 |

Extended Description

clang version 6.0.0 (trunk 317263)

This code:

int main(int argc, char** argv) {
  if (argc > 4);   // <-- Note semicolon!
  return 0;
}

Gives:

eraseme.cc:2:16: warning: if statement has empty body [-Wempty-body]
  if (argc > 4);
               ^
eraseme.cc:2:16: note: put the semicolon on a separate line to silence this
      warning
1 warning generated.

This is good! And it also works for "else if" cases. But I just did the same bug and put a semicolon after a bare else:

int main(int argc, char** argv) {
  if (argc > 4)
    return 1;
  else;  // <- Semicolon
    return 2;
  return 0;
}

And there is no warning. This was pretty tricky to find and it seems like the same rule for "if" semicolons should just also be applied to "else".

[wheatman]

confirming that this is still the case in post 17 trunk(5a56f00)
https://godbolt.org/z/nqoqWeExb

code

int main(int argc, char** argv) {
  if (argc > 4)
    return 1;
  else;  // <- Semicolon
    return 2;
  return 0;
}

no warning given for clang

[shafik]

Commit that attempted to fix this: adefb76

Commit that revert it says it was reverted it: 59ad150

says:

This caused warnings also when the if or else comes from macros.

So someone can likely pick up the original fix and needs to add tests for macros to make sure this does not break likely existing code.

[shafik]

Also see 9541975 for an example for when the original fix that was reverted failed on.