Odd/incorrect error message with @as in function with type parameter

[euclidianAce]

Zig Version

0.10.0-dev.74+426679574

Steps to Reproduce

try to zig run the following programs

// a.zig
pub fn main() void {
    const x: i32 = 4;
    const y = @as(f32, x) * 1.75;
    const z: i32 = @as(i32, y);
    @import("std").log.debug("x={}, y={}, z={}", .{ x, y, z });
}

// b.zig
pub fn main() void {
    const z = scale(4, f32, 1.75);
    @import("std").log.debug("z={}", .{z});
}

fn scale(n: i32, comptime Factor: type, factor: Factor) Factor {
    // first attempt was:
    //   return @intCast(i32, @as(Factor, n) * factor)
    // attempting to split it up like so results in the same error
    var new = @as(Factor, n);
    new *= factor;
    return @as(i32, new);
}

Expected Behavior

Both of the above programs to compile and run, logging the same value for z

Actual Behavior

a.zig runs fine, b.zig has a compile error:

$ zig run b.zig
.\b.zig:11:27: error: expected type 'f32', found 'i32'
    var new = @as(Factor, n);
                          ^
.\b.zig:3:20: note: called from here
    const z = scale(4, f32, 1.75);
                   ^
.\b.zig:2:20: note: called from here
pub fn main() void {
                   ^

After messing around, I think it could have something to do with the fact that @as doesn't like certain float to int conversions (hence the existence of @intToFloat and @floatToInt), and the error reporting gets confused and reports this as expected <destination type>, found <actual argument type> rather than something like unable to cast value of type <type>, to type <type>.

I've adapted the actual program to check at compile time whether Factor is integral or floating point and done the appropriate @intToFloat/@floatToInt, but this error message through me for a loop

[Vexu]

Self-hosted also gets this wrong:

a.zig:41:5: error: expected type 'f32', found 'i32'
    var new = @as(Factor, n);
    ^~~~~~~~~~~~~~~~~~~~~~~~

[mlugg]

Is it defined that the compiler will allow any int<->float conversion with @as when they're comptime-known to be safe? If not, it's actually a bug that a.zig compiles here. (But yes the error message could definitely be improved)

[Vexu]

Is it defined that the compiler will allow any int<->float conversion with @as when they're comptime-known to be safe

Yes.

[nektro]

this test isnt happening at comptime

[mlugg]

this test isnt happening at comptime

No, but in a.zig, x is comptime-known when y is defined, whereas in b.zig it's not (due to being a function parameter).