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Sema: error on ambiguous coercion of comptime float and ints

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The following, from the documentation as of the time of writing, illustrates
the problem:

```zig
// Compile time coercion of float to int
test "implicit cast to comptime_int" {
    var f: f32 = 54.0 / 5;
    _ = f;
}
```

It is not clear how to unify the types of 54.0 and 5 to perform the
division. We can either

 - cast 54.0 to comptime_int resulting in @as(comptime_int, 10), which is
   casted to @as(f32, 10), or
 - cast 5 to comptime_float resulting in @as(comptime_float, 10.8), which
   is casted to @as(f32, 10.8)

Since the two resulting values are different, a compiler error is appropriate.

If we know that casting to either type will result in the same value we
don't need to error.  For instance, 10.0 / 2 is okay, as is 10 / 2.0.

Fixes: #12364
This commit is contained in:
Martin Hafskjold Thoresen 2022-08-10 23:32:02 +02:00 committed by Andrew Kelley
parent 070282a96e
commit 07f64a2e13
2 changed files with 20 additions and 4 deletions
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16
src/Sema.zig
View File

@ -11202,6 +11202,22 @@ fn zirDiv(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Ins
const maybe_lhs_val = try sema.resolveMaybeUndefValIntable(block, lhs_src, casted_lhs);
const maybe_rhs_val = try sema.resolveMaybeUndefValIntable(block, rhs_src, casted_rhs);
if ((lhs_ty.tag() == .comptime_float and rhs_ty.tag() == .comptime_int) or
(lhs_ty.tag() == .comptime_int and rhs_ty.tag() == .comptime_float))
{
// If it makes a difference whether we coerce to ints or floats before doing the division, error.
// If lhs % rhs is 0, it doesn't matter.
var lhs_val = maybe_lhs_val orelse unreachable;
var rhs_val = maybe_rhs_val orelse unreachable;
var rem = lhs_val.floatRem(rhs_val, resolved_type, sema.arena, target) catch unreachable;
var float_rem = rem.toFloat(f32);
if (float_rem != 0.0) {
return sema.fail(block, src, "ambiguous coercion of division operands: '{s}' and '{s}': division has non-zero reminder: {d}", .{
@tagName(lhs_ty.tag()), @tagName(rhs_ty.tag()), float_rem,
});
}
}
// TODO: emit compile error when .div is used on integers and there would be an
// ambiguous result between div_floor and div_trunc.

8
test/behavior/floatop.zig
View File

@ -194,8 +194,8 @@ fn testSin() !void {
const eps = epsForType(ty);
try expect(@sin(@as(ty, 0)) == 0);
try expect(math.approxEqAbs(ty, @sin(@as(ty, std.math.pi)), 0, eps));
try expect(math.approxEqAbs(ty, @sin(@as(ty, std.math.pi / 2)), 1, eps));
try expect(math.approxEqAbs(ty, @sin(@as(ty, std.math.pi / 4)), 0.7071067811865475, eps));
try expect(math.approxEqAbs(ty, @sin(@as(ty, std.math.pi / 2.0)), 1, eps));
try expect(math.approxEqAbs(ty, @sin(@as(ty, std.math.pi / 4.0)), 0.7071067811865475, eps));
}
{
@ -228,8 +228,8 @@ fn testCos() !void {
const eps = epsForType(ty);
try expect(@cos(@as(ty, 0)) == 1);
try expect(math.approxEqAbs(ty, @cos(@as(ty, std.math.pi)), -1, eps));
try expect(math.approxEqAbs(ty, @cos(@as(ty, std.math.pi / 2)), 0, eps));
try expect(math.approxEqAbs(ty, @cos(@as(ty, std.math.pi / 4)), 0.7071067811865475, eps));
try expect(math.approxEqAbs(ty, @cos(@as(ty, std.math.pi / 2.0)), 0, eps));
try expect(math.approxEqAbs(ty, @cos(@as(ty, std.math.pi / 4.0)), 0.7071067811865475, eps));
}
{