error message regression: "no resolution found"

[nrc]

"resolution"/"resolve" is compiler jargon and shouldn't be present in user-facing messages. Could be replaced by "declaration" or "definition", though I suspect we might be able to craft a better message than that.

cc @jseyfried @jonathandturner @GuillaumeGomez

[petrochenkov]

"resolution"/"resolve" is compiler jargon and shouldn't be present in user-facing messages.

This is news for me, the change was certainly intended.
Previously "unresolved" was used in patterns in struct expressions, #38154 unified error messages and now it's used everywhere.
There's also an independent error about "unresolved import"s.

Now "unresolved"/"resolution" is used twice in non-import paths - in the basic error message (unresolved <struct> <A::B>) and in the fallback label (no resolution found) when we can't say anything more useful.

Alternatives:
"undefined"
"undeclared"
"unknown"
"not in scope"
"can't find"

EDIT: for comparison, errors from clang and gcc:

// clang
main.cpp:2:14: error: use of undeclared identifier 'b'
    auto a = b;    
             ^

// gcc
main.cpp: In function 'int main()':
main.cpp:2:14: error: 'b' was not declared in this scope
     auto a = b;
              ^

[jseyfried]

How about something like this?

use foo::bar; //~ ERROR no module `foo` in the crate root
//  ^^^^^^^^ `foo` undeclared
//  ^^^ undeclared (pending better span info)

mod baz {}
use baz::bar; //~ ERROR no item `bar` in `baz`
//       ^^^ undeclared

fn main() {
    foo; //~ ERROR no value `foo` in scope
//  ^^^ not in scope
}

[GuillaumeGomez]

@jseyfried: I like your examples!
@nrc: it'd be more clear, indeed.

[nrc]

@petrochenkov I think I feel better with "resolved"/"unresolved" as verbs/adverbs than I do with "resolution" as a noun. I like your other suggestions (and @jseyfried's) better.

I would prefer more 'wordy' error messages (similar to the GCC/Clang) examples, rather than the shorter, note-like ones @jseyfried suggested, e.g., "bar is undeclared" rather than just "undeclared" or "'foo' was not declared in this scope" rather than "not in scope".

[jseyfried]

@nrc

the shorter, note-like ones @jseyfried suggested

To be clear, I was only suggesting the shorter ones for the span_labels, e.g.

error: no value `foo` in scope
 --> <anon>:2:5
  |
2 |     foo;
  |     ^^^ not in scope