tint/resolver: Add `DataType<T>::ElementType` typedef

To point to the element type of T. Helpful for tests.

Change-Id: I41b5ad0923375e11509acf67959a849da3d1ebcf
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/91421
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>

src/tint/resolver/resolver_test_helper.h

@@ -189,6 +189,9 @@ struct DataType<void> {
 /// Helper for building bool types and expressions
 template <>
 struct DataType<bool> {
+    /// The element type
+    using ElementType = bool;
+
     /// false as bool is not a composite type
     static constexpr bool is_composite = false;
 
@@ -211,6 +214,9 @@ struct DataType<bool> {
 /// Helper for building i32 types and expressions
 template <>
 struct DataType<i32> {
+    /// The element type
+    using ElementType = i32;
+
     /// false as i32 is not a composite type
     static constexpr bool is_composite = false;
 
@@ -233,6 +239,9 @@ struct DataType<i32> {
 /// Helper for building u32 types and expressions
 template <>
 struct DataType<u32> {
+    /// The element type
+    using ElementType = u32;
+
     /// false as u32 is not a composite type
     static constexpr bool is_composite = false;
 
@@ -255,6 +264,9 @@ struct DataType<u32> {
 /// Helper for building f32 types and expressions
 template <>
 struct DataType<f32> {
+    /// The element type
+    using ElementType = f32;
+
     /// false as f32 is not a composite type
     static constexpr bool is_composite = false;
 
@@ -277,6 +289,9 @@ struct DataType<f32> {
 /// Helper for building f16 types and expressions
 template <>
 struct DataType<f16> {
+    /// The element type
+    using ElementType = f16;
+
     /// false as f16 is not a composite type
     static constexpr bool is_composite = false;
 
@@ -299,6 +314,9 @@ struct DataType<f16> {
 /// Helper for building abstract float types and expressions
 template <>
 struct DataType<AFloat> {
+    /// The element type
+    using ElementType = AFloat;
+
     /// false as AFloat is not a composite type
     static constexpr bool is_composite = false;
 
@@ -320,6 +338,9 @@ struct DataType<AFloat> {
 /// Helper for building abstract integer types and expressions
 template <>
 struct DataType<AInt> {
+    /// The element type
+    using ElementType = AInt;
+
     /// false as AFloat is not a composite type
     static constexpr bool is_composite = false;
 
@@ -341,6 +362,9 @@ struct DataType<AInt> {
 /// Helper for building vector types and expressions
 template <uint32_t N, typename T>
 struct DataType<vec<N, T>> {
+    /// The element type
+    using ElementType = T;
+
     /// true as vectors are a composite type
     static constexpr bool is_composite = true;
 
@@ -381,6 +405,9 @@ struct DataType<vec<N, T>> {
 /// Helper for building matrix types and expressions
 template <uint32_t N, uint32_t M, typename T>
 struct DataType<mat<N, M, T>> {
+    /// The element type
+    using ElementType = T;
+
     /// true as matrices are a composite type
     static constexpr bool is_composite = true;
 
@@ -423,6 +450,9 @@ struct DataType<mat<N, M, T>> {
 /// Helper for building alias types and expressions
 template <typename T, int ID>
 struct DataType<alias<T, ID>> {
+    /// The element type
+    using ElementType = T;
+
     /// true if the aliased type is a composite type
     static constexpr bool is_composite = DataType<T>::is_composite;
 
@@ -466,6 +496,9 @@ struct DataType<alias<T, ID>> {
 /// Helper for building pointer types and expressions
 template <typename T>
 struct DataType<ptr<T>> {
+    /// The element type
+    using ElementType = T;
+
     /// true if the pointer type is a composite type
     static constexpr bool is_composite = false;
 
@@ -496,6 +529,9 @@ struct DataType<ptr<T>> {
 /// Helper for building array types and expressions
 template <uint32_t N, typename T>
 struct DataType<array<N, T>> {
+    /// The element type
+    using ElementType = T;
+
     /// true as arrays are a composite type
     static constexpr bool is_composite = true;