cmd/compile, go/types: fix checking of bad type switch
Consider the following program:
package p
func f() {
x := 1
v := 2
switch v.(type) {
case int:
println(x)
println(x / 0)
case 1:
}
}
Before this CL, the compiler prints:
x.go:4:2: x declared but not used
x.go:6:9: v (variable of type int) is not an interface
x is in fact used, and other errors in the switch go undiagnosed.
This commit fixes that problem by processing the switch statement
even when the 'not an interface' error is reported.
Now the compiler drops the spurious 'declared but not used'
and adds two previously undiagnosed problems:
x.go:6:9: v (variable of type int) is not an interface
x.go:9:15: invalid operation: division by zero
x.go:10:7: 1 is not a type
go/types was printing roughly the same thing the compiler did before,
and now still prints roughly the same thing the compiler does after.
(The only differences are in the exact reported columns.)