Golang cmd/compile: spurious undefined identifier warning for invalid identifier

% cat /tmp/x.go
package main

import "fmt"

func main() {
    fmt.Printf☹("hello world")
}
% go build /tmp/x.go
# command-line-arguments
/tmp/x.go:6:6: undefined: fmt.Printf☹
/tmp/x.go:6:12: invalid character U+2639 '☹' in identifier
% 

The first error is irrelevant; the second error is the real problem.

I ran into this in a real program by accidentally typing a non-breaking space (U+00A0), which renders invisibly. That made the first error look even weirder:

/tmp/x.go:6:6: undefined: fmt.Printf 
/tmp/x.go:6:12: invalid character U+00A0 in identifier

If the identifier has an invalid character, that should be diagnosed and there shouldn't be any other errors about it.

/cc @griesemer

Comment From: gabyhelp

Similar Issues

• cmd/compile: inconsistent error message when identifier begins with invalid character #42114
• cmd/compile: bad error message for stray single quote #32133

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Comment From: rsc

Closed #42114 as a duplicate of this one.

Comment From: gopherbot

Change https://go.dev/cl/602476 mentions this issue: types2: avoid spurious "undefined" errors" for invalid identifiers