cmd/compile: assignment errors have become overly verbose

[griesemer]

Some of the assignment errors have become overly verbose. Examples:

package p

func f(int) (int, string) { return 0, "foo" }

func _() {
	f("foo")            // ERROR: cannot use "foo" (untyped string constant) as int value in argument to f
	var _, _ int = f(0) // ERROR: cannot use 2nd function result (value of type string) as int value in multiple assignment
}

We should produce more concise errors.
See also #78884 for some examples and former (1.16) error messages.

[gabyhelp]

Related Issues

• cmd/compile: confusing error in multiple assignment #78884
• cmd/compile: = and := errors are unnecessarily different #48558 (closed)
• cmd/compile: assignment error messages #48585
• go/types: provide better error message for errors in n:1 init assignment #15783
• cmd/compile: awkward wording of count mismatch error #22159 (closed)
• cmd/compile: regressed and non-informative error messages when return call site doesn't match return signature #48834 (closed)
• cmd/compile: incorrect pluralization in error message #45369 (closed)
• go/types, types2: remove discrepancy between type-checker and compiler error messages #55326 (closed)
• cmd/compile: regressed and non-informative error messages when wrong arguments/counts are passed into a function call #48835 (closed)

Related Code Changes

• cmd/compile: improve assignment count mismatch error message

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[AbhinavMir]

Me likey.

some ideas?

cannot convert x (int) to string , unknown field foo in T, drop references to <type> value, just <type> makes sense. Is there active work on this? I can pick it up if we do the hard work of deciding what's the right new standard haha. or I can open a draft PR and we can discuss there.

[griesemer]

Thanks @AbhinavMir, for the offer, but somebody in the compiler team should probably do this unless you're prepared to go through possibly many code review revisions which may not be accepted in the end. It's subtle because error messages around assignments (and elsewhere) are constructed and assembled in different places and have to fit together.
Nobody is working on this yet, it's not high priority.

[AbhinavMir]

That's fair! Hope it gets thru at some point! Would love to see it live