Previously, implicit padding members of `struct`s were suppressed from
structure definitions in Metal output if they had a binding specified
for them (i.e., `@location(0)`). This padding is, however, is necessary
for correct access of member fields passed into shaders by uniform and
storage buffers. Unconditionally emit padding members for `struct`s.
Resolves
[`gfx-rs/wgpu`#4701](https://github.com/gfx-rs/wgpu/pull/4701).
Following Rust convention, let `naga::front::wgsl::ParseError`'s
methods `emit_to_stderr_with_path` and `emit_to_string_with_path`
accept any `AsRef<Path>` argument as the path.
Pass input paths in snapshot tests, so that failures processing
shaders name the input file being processed.
Change the WGSL code in the `function_returns_void` test in
`tests/wgsl-errors.rs` so that the construction expression types
correctly. Subsequent iterations of the WGSL front end will be doing
some type checking earlier, to support WGSL's automatic conversions,
and without this fix, this test will stop checking what it is intended
to check.
Let `naga::TypeInner::Matrix` hold a full `Scalar`, with a kind and
byte width, not merely a byte width, to make it possible to represent
matrices of AbstractFloats for WGSL.
When asked to evaluate an `Expression::As` cast applied to a `Splat`
expression, change `ConstantEvaluator::cast` to preserve the `Splat`,
rather than expanding it out to a `Compose` expression.
Introduce a new struct type, `Scalar`, combining a `ScalarKind` and a
`Bytes` width, and use this whenever such pairs of values are passed
around.
In particular, use `Scalar` in `TypeInner` variants `Scalar`, `Vector`,
`Atomic`, and `ValuePointer`.
Introduce associated `Scalar` constants `I32`, `U32`, `F32`, `BOOL`
and `F64`, for common cases.
Introduce a helper function `Scalar::float` for constructing `Float`
scalars of a given width, for dealing with `TypeInner::Matrix`, which
only supplies the scalar width of its elements, not a kind.
Introduce helper functions on `Literal` and `TypeInner`, to produce
the `Scalar` describing elements' values.
Use `Scalar` in `wgpu_core::validation::NumericType` as well.
When an error snapshot test fails and we generate a diff comparing the
expected output with the actual output, treat the expected output as
the diff "from", and the actual output as the diff "to" - not the
reverse.
