cmd/compile: failure to diagnose invalid conversion to complex64

[dvyukov]

gc successfully compiles the following program:

package a
var a = complex64(6)/774516156475830989403545856475830078125

while both gccgo and go/types reject it with:

error: complex real part overflow
774516156475830989403545856475830078125 (untyped int constant) overflows complex64

go version devel +40a1516 Fri Jul 3 03:08:40 2015 +0000 linux/amd64

[dvyukov]

@griesemer

[griesemer]

I don't believe this is a gc bug. First of all, the conversion is not illegal - an untyped int constant can be converted into a complex value. The complaints are about overflow. But the value 774516156475830989403545856475830078125 is converted into a float64 w/o problem:

package a
var x float64 = 774516156475830989403545856475830078125

Making this a go/types bug.

[griesemer]

Never mind - my bad! It's complex64 - not complex128! (I hate these names).

Indeed, "var _ float32 = 774516156475830989403545856475830078125" is not valid because the number is too large for any float32, and thus too large for any complex64 component.

gc should not accept this. Changing back to gc bug. Sorry.

[rsc]

CL forthcoming.