[naga wgsl-in] Implement abstract types for consts, constructors.

Author: jimblandy

CHANGELOG.md

@@ -102,8 +102,44 @@ Passing an owned value `window` to `Surface` will return a `Surface<'static>`. S
 - Introduce a new `Scalar` struct type for use in Naga's IR, and update all frontend, middle, and backend code appropriately. By @jimblandy in [#4673](https://github.com/gfx-rs/wgpu/pull/4673).
 - Add more metal keywords. By @fornwall in [#4707](https://github.com/gfx-rs/wgpu/pull/4707).
 
-- Implement WGSL abstract types (by @jimblandy):
-  - Add a new `naga::Literal` variant, `I64`, for signed 64-bit literals. [#4711](https://github.com/gfx-rs/wgpu/pull/4711)
+-   Add partial support for WGSL abstract types (@jimblandy in [#4743](https://github.com/gfx-rs/wgpu/pull/4743)).
+
+    Abstract types make numeric literals easier to use, by
+    automatically converting literals and other constant expressions
+    from abstract numeric types to concrete types when safe and
+    necessary. For example, to build a vector of floating-point
+    numbers, Naga previously made you write:
+
+        vec3<f32>(1.0, 2.0, 3.0)
+
+    With this change, you can now simply write:
+
+        vec3<f32>(1, 2, 3)
+
+    Even though the literals are abstract integers, Naga recognizes
+    that it is safe and necessary to convert them to `f32` values in
+    order to build the vector. You can also use abstract values as
+    initializers for global constants, like this:
+
+        const unit_x: vec2<f32> = vec2(1, 0);
+
+    The literals `1` and `0` are abstract integers, and the expression
+    `vec2(1, 0)` is an abstract vector. However, Naga recognizes that
+    it can convert that to the concrete type `vec2<f32>` to satisfy
+    the given type of `unit_x`.
+
+    The WGSL specification permits abstract integers and
+    floating-point values in almost all contexts, but Naga's support
+    for this is still incomplete. Many WGSL operators and builtin
+    functions are specified to produce abstract results when applied
+    to abstract inputs, but for now Naga simply concretizes them all
+    before applying the operation. We will expand Naga's abstract type
+    support in subsequent pull requests.
+
+    As part of this work, the public types `naga::ScalarKind` and
+    `naga::Literal` now have new variants, `AbstractInt` and `AbstractFloat`.
+
+- Add a new `naga::Literal` variant, `I64`, for signed 64-bit literals. [#4711](https://github.com/gfx-rs/wgpu/pull/4711)
 
 - Emit and init `struct` member padding always. By @ErichDonGubler in [#4701](https://github.com/gfx-rs/wgpu/pull/4701).
 

naga/Cargo.toml

@@ -31,7 +31,7 @@ deserialize = ["serde", "bitflags/serde", "indexmap/serde"]
 arbitrary = ["dep:arbitrary", "bitflags/arbitrary", "indexmap/arbitrary"]
 spv-in = ["petgraph", "spirv"]
 spv-out = ["spirv"]
-wgsl-in = ["hexf-parse", "unicode-xid"]
+wgsl-in = ["hexf-parse", "unicode-xid", "compact"]
 wgsl-out = []
 hlsl-out = []
 compact = []

naga/src/front/wgsl/error.rs

@@ -251,6 +251,12 @@ pub enum Error<'a> {
     ExpectedPositiveArrayLength(Span),
     MissingWorkgroupSize(Span),
     ConstantEvaluatorError(ConstantEvaluatorError, Span),
+    AutoConversion {
+        dest_span: Span,
+        dest_type: String,
+        source_span: Span,
+        source_type: String,
+    },
 }
 
 impl<'a> Error<'a> {
@@ -712,6 +718,20 @@ impl<'a> Error<'a> {
                 )],
                 notes: vec![],
             },
+            Error::AutoConversion { dest_span, ref dest_type, source_span, ref source_type } => ParseError {
+                message: format!("automatic conversions cannot convert `{source_type}` to `{dest_type}`"),
+                labels: vec![
+                    (
+                        dest_span,
+                        format!("a value of type {dest_type} is required here").into(),
+                    ),
+                    (
+                        source_span,
+                        format!("this expression has type {source_type}").into(),
+                    )
+                ],
+                notes: vec![],
+            }
         }
     }
 }