Unused lambda capture source ranges are slightly off

[tbaederr]

See: https://godbolt.org/z/MKjzsYb9b

int main() {

    int a = 0, b = 0;

    auto F = [&a, &b]() {

    };
}

The output is:

<source>:7:16: warning: lambda capture 'a' is not used [-Wunused-lambda-capture]
    7 |     auto F = [&a, &b]() {
      |               ~^~
<source>:7:20: warning: lambda capture 'b' is not used [-Wunused-lambda-capture]
    7 |     auto F = [&a, &b]() {
      |                 ~~~^
<source>:7:10: warning: unused variable 'F' [-Wunused-variable]
    7 |     auto F = [&a, &b]() {
      |          ^

1) The source range for &a includes the comma after it 2) The source range for &b includes both the comma and the whitespace between that and the capture

The second point is especially fun when inserting some useless whitespace:

    auto F = [&a,         

     &b]() {

    };

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Timm Baeder (tbaederr)

See: https://godbolt.org/z/MKjzsYb9b ```c++ int main() { int a = 0, b = 0; auto F = [&a, &b]() { }; } ``` The output is: ```console <source>:7:16: warning: lambda capture 'a' is not used [-Wunused-lambda-capture] 7 | auto F = [&a, &b]() { | ~^~ <source>:7:20: warning: lambda capture 'b' is not used [-Wunused-lambda-capture] 7 | auto F = [&a, &b]() { | ~~~^ <source>:7:10: warning: unused variable 'F' [-Wunused-variable] 7 | auto F = [&a, &b]() { | ^ ``` 1) The source range for `&a` includes the comma after it 2) The source range for `&b` includes both the comma and the whitespace between that and the capture The second point is especially fun when inserting some useless whitespace: ```c++ auto F = [&a, &b]() { }; ```

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

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3. Fix the issue locally.
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[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Timm Baeder (tbaederr)

See: https://godbolt.org/z/MKjzsYb9b ```c++ int main() { int a = 0, b = 0; auto F = [&a, &b]() { }; } ``` The output is: ```console <source>:7:16: warning: lambda capture 'a' is not used [-Wunused-lambda-capture] 7 | auto F = [&a, &b]() { | ~^~ <source>:7:20: warning: lambda capture 'b' is not used [-Wunused-lambda-capture] 7 | auto F = [&a, &b]() { | ~~~^ <source>:7:10: warning: unused variable 'F' [-Wunused-variable] 7 | auto F = [&a, &b]() { | ^ ``` 1) The source range for `&a` includes the comma after it 2) The source range for `&b` includes both the comma and the whitespace between that and the capture The second point is especially fun when inserting some useless whitespace: ```c++ auto F = [&a, &b]() { }; ```

[shafik]

Note the source range for a does not include the comma after it if you have whitespace: https://godbolt.org/z/sGEYPaThs

[c8ef]

Hi, I would like to work on this.

[c8ef]

I believe the issue was introduced in https://github.com/llvm/llvm-project/commit/832f49b90a4907a0bc2b34b688c32f3c9613aab0. Interpreting the source range as the fix-it range rather than the diagnostic range actually makes some kind of sense.

[c8ef]

So I’m wondering if this is the intended behavior. If we want to fix it, where should the changes be made? From the perspective of the fix-it suggestion, the comma still needs to be bound to a variable, either the former or the latter.

[tbaederr]

Right, those aren't just ranges, but delete ranges from the fixme. In that case, I'm not sure what to do. :upside_down_face:

[jhendle2]

For https://godbolt.org/z/8zdKPxY6K

int main() {

    int a = 0, b = 0;

    auto F = [&a, &b]() {

    };
}

The output is:

<source>:11:16: warning: lambda capture 'a' is not used [-Wunused-lambda-capture]
   11 |     auto F = [&a, &b]() {
      |               ~^~
<source>:11:20: warning: lambda capture 'b' is not used [-Wunused-lambda-capture]
   11 |     auto F = [&a, &b]() {
      |                 ~~~^
<source>:11:10: warning: unused variable 'F' [-Wunused-variable]
   11 |     auto F = [&a, &b]() {
      |          ^

So, I assume the third warning output should be:

<source>:11:20: warning: lambda capture 'b' is not used [-Wunused-lambda-capture]
   11 |     auto F = [&a, &b]() {
      |                   ~^

Because this matches the behavior for a lambda with a single unsued capture?

<source>:11:16: warning: lambda capture 'a' is not used [-Wunused-lambda-capture]
   11 |     auto F = [&a]() {
      |               ~^

[tbaederr]

Kinda, yes. But the output is already correct as it is, when we consider that the source ranges aren't supposed to just highlight the unused parameter. They are fix-it hints that will remove the underlined text when applied.

[jhendle2]

Hi, can this ticket be assigned to me?