[Bug c++/90475] New: Diagnostic for designated initializer could be a lot better

[barry.revzin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90475

            Bug ID: 90475
           Summary: Diagnostic for designated initializer could be a lot
                    better
           Product: gcc
           Version: 9.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: barry.revzin at gmail dot com
  Target Milestone: ---

gcc 8 and 9 have made dramatic improvements in diagnostics, but here's a case
where it could be a lot better: the "oops, I typoed my designated initializer"
case:

struct X { int i, j; };

X f() { return {.i=42, .k=17}; }

emits:

<source>: In function 'X f()':
<source>:3:29: error: could not convert '{42, 17}' from '<brace-enclosed
initializer list>' to 'X'
    3 | X f() { return {.i=42, .k=17}; }
      |                             ^
      |                             |
      |                             <brace-enclosed initializer list>
Compiler returned: 1

Similarly:

struct X { int i, j; };

void g(X );
void h() {
    g({.i=42, .k=17});
}

emits:

<source>: In function 'void h()':
<source>:5:21: error: could not convert '{42, 17}' from '<brace-enclosed
initializer list>' to 'X'
    5 |     g({.i=42, .k=17});
      |                     ^
      |                     |
      |                     <brace-enclosed initializer list>
Compiler returned: 1

Would be very cool if the diagnostic could somehow point to the "k"
initializer, rather than basically "I dunno what is this thing??"

(obviously not the most high priority thing, just a nice to have)