[Bug c++/106330] New: Unknown type leads to error messages about missing lambda capture

[Bug c++/106330] New: Unknown type leads to error messages about missing lambda capture

[drahflow at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106330

            Bug ID: 106330
           Summary: Unknown type leads to error messages about missing
                    lambda capture
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: drahflow at gmx dot de
  Target Milestone: ---

Running g++ on

void unhelpful(int i) {
    Unknown u;
    u.distract();

    for(auto &i: u) {
        [i]() {
            unhelpful(i);
        };
    }
}

outputs

test.c++: In function 'void unhelpful(int)':
test.c++:2:5: error: 'Unknown' was not declared in this scope
    2 |     Unknown u;
      |     ^~~~~~~
test.c++:3:5: error: 'u' was not declared in this scope
    3 |     u.distract();
      |     ^
test.c++: In lambda function:
test.c++:7:23: error: 'i' is not captured
    7 |             unhelpful(i);
      |                       ^
test.c++:6:11: note: the lambda has no capture-default
    6 |         [i]() {
      |           ^
test.c++:5:15: note: '<typeprefixerror>i' declared here
    5 |     for(auto &i: u) {
      |               ^
Compiler returned: 1

The error message for line 7 together with the two notes are quite unhelpful.
(Of course the example where I encountered the problem had a lot more code
between u.distract() and for(auto &i: u) ... )