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
The `Value.eql` function has to test for value equality *as-if* the lhs
value parameter is coerced into the type of the rhs. For tagged unions,
there was a problematic case when the lhs was an anonymous struct,
because in such case the value is empty_struct_value and the type
contains all the value information. But the only type available in the
function was the rhs type.
So the fix involved making `Value.eqlAdvanced` also accept the lhs type,
and then enhancing the logic to handle the case of the `.anon_struct` tag.
closes#12418
Tests run locally:
* test-behavior
* test-cases
Previously we would assign the error message to Sema and then never
clear it even when destroying the error message, which caused memory
corruption.
Closes#12437
Sema: insert an error return trace frame when appropriate when analyzing
ret_load. Also optimize the instructions to avoid an unnecessary block
sent to the backends.
AstGen: always emit a dbg_stmt for return expressions, in between the
defer instructions and the return instruction.
This improves the following test case:
```zig
pub fn main() !void {
return foo();
}
fn foo() !void {
return error.Bad;
}
```
The error return trace now points to the return token instead of
pointing to the foo() function call, matching stage1.
stage2 was adding bogus error return trace frames when an error was not
being returned. This commit makes several improvements:
* Make a runtime check if necessary to only emit a frame into the error
return trace when an actual error is returned.
* Use the `analyzeIsNonErrComptimeOnly` machinery to avoid runtime
checks when it is compile-time-known that the value is an error, or a
non-error.
* Make std.builtin.returnError take a non-optional stack trace pointer.
closes#12174
Piggybacking on 40f8f0134f5da9baaefd0fdab529d5585fa46199, remainder
division, modulus, and `%` syntax no longer emit safety checks for a
comptime-known denominator.
