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go/types: report cause for failing const conversions

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This is a port of CL 360795 to go/types. Error messages were adjusted
accordingly, with a TODO to fix the discrepancy.

Change-Id: Ifd7d8248fa11a31fde391021f3c5f1840877892f
Reviewed-on: https://go-review.googlesource.com/c/go/+/360937
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Robert Findley 2021-11-02 18:42:51 -04:00
parent 2b81b863a2
commit 49a00631b1
2 changed files with 23 additions and 2 deletions
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11
src/go/types/conversions.go
View File

@ -49,8 +49,15 @@ func (check *Checker) conversion(x *operand, T Type) {
// converted.
ok = under(T).(*TypeParam).underIs(func(u Type) bool {
// t is nil if there are no specific type terms
// TODO(gri) add a cause in case of failure
return u != nil && constConvertibleTo(u, nil)
if u == nil {
cause = check.sprintf("%s does not contain specific types", T)
return false
}
if !constConvertibleTo(u, nil) {
cause = check.sprintf("cannot convert %s to %s (in %s)", x, u, T)
return false
}
return true
})
x.mode = value // type parameters are not constants
case x.convertibleTo(check, T, &cause):

14
src/go/types/testdata/spec/conversions.go2 vendored
View File

@ -27,6 +27,20 @@ func _[T ~string]() {
var _ T = 0 // ERROR cannot use .* as T value
}
// failing const conversions of constants to type parameters report a cause
func _[
T1 any,
T2 interface{ m() },
T3 ~int | ~float64 | ~bool,
T4 ~int | ~string,
]() {
// TODO(rfindley): align the error formatting here with types2.
_ = T1(0 /* ERROR cannot convert 0 .* to T1.*T1 does not contain specific types */ )
_ = T2(1 /* ERROR cannot convert 1 .* to T2.*T2 does not contain specific types */ )
_ = T3(2 /* ERROR cannot convert 2 .* to T3.*cannot convert 2 .* to bool \(in T3\) */ )
_ = T4(3.14 /* ERROR cannot convert 3.14 .* to T4.*cannot convert 3.14 .* to int \(in T4\) */ )
}
// "x is assignable to T"
// - tested via assignability tests