Description
The Go 1.21 compiler implements significantly more powerful and precise type inference than Go 1.20. One of the improvements made is for untyped constants (#58671). That change was implemented based on the language version: -lang must be >= go1.21.
func f[P any](...P) {}
func main() {
f(1, 2.0)
}produces an error (default type float64 of 2.0 does not match inferred type int for P) with -lang=go1.20 but runs fine with -lang >= go1.21.
However, there are plenty of other inference improvements that that were made for 1.21 which are accessible even if -lang < go1.21. For instance:
package main
func f[T any](interface{ m(T) }) {}
type S struct{}
func (S) m(int) {}
func main() {
f(S{})
}In this case the change and error is not fundamentally different from above: in Go 1.20 we couldn't infer a type argument and now we can. In both these cases one can provide explicit type arguments and make the code compile. Also, all inference improvements are fully backwards-compatible.
I propose that we remove the -lang check for the more lenient constant handling for consistency with the other inference improvements. (Making all improvements -lang dependent is not practical.)