Add chained swizzle tests (#4699)

Add some additional tests of chained swizzles ending in a single element
swizzle. These are regression tests for the bug caught in:
https://crbug.com/553777974

Author: sudonatalie

src/webgpu/shader/validation/expression/access/vector.spec.ts

@@ -142,6 +142,7 @@ const kConcreteCases = {
   gbra: { wgsl: 'let r : vec4<T> = v.gbra;', ok: (width: number) => width > 3 },
 
   // swizzle chains
+  xy_x: { wgsl: 'let r : T = v.xy.x;', ok: true },
   xy_yx: { wgsl: 'let r : vec2<T> = v.xy.yx;', ok: true },
   xyx_xxy: { wgsl: 'let r : vec3<T> = v.xyx.xxy;', ok: true },
   xyz_zyx: { wgsl: 'let r : vec3<T> = v.xyz.zyx;', ok: (width: number) => width > 2 },
@@ -346,6 +347,7 @@ const kAbstractCases = {
   gbra: { wgsl: 'const r = V.gbra;', result_width: 4, ok: (width: number) => width > 3 },
 
   // swizzle chains
+  xy_x: { wgsl: 'const r = V.xy.x;', result_width: 1, ok: true },
   xy_yx: { wgsl: 'const r = V.xy.yx;', result_width: 2, ok: true },
   xyx_xxy: { wgsl: 'const r = V.xyx.xxy;', result_width: 3, ok: true },
   xyz_zyx: { wgsl: 'const r = V.xyz.zyx;', result_width: 3, ok: (width: number) => width > 2 },
@@ -479,3 +481,35 @@ fn main() {
     const pass = convertible && (typeof c.ok === 'function' ? c.ok(t.params.vector_width) : c.ok);
     t.expectCompileResult(pass, code);
   });
+
+const kChainedSwizzleCases = {
+  // Single-element swizzle of a swizzle
+  xy_x: 'xy.x',
+  // Single-element swizzle of a swizzle with duplicate components
+  xx_x: 'xx.x',
+  // Multi-element swizzle of a swizzle
+  xyy_xy: 'xyy.xy',
+};
+
+g.test('chained_swizzle')
+  .desc('Validate that chained swizzles on memory views succeed during pipeline creation.')
+  .params(u =>
+    u
+      .combine('address_space', ['function', 'private'] as const)
+      .combine('case', keysOf(kChainedSwizzleCases))
+  )
+  .fn(t => {
+    const chain = kChainedSwizzleCases[t.params.case];
+    const code =
+      t.params.address_space === 'private' ? 'var<private> v = vec4f(1.0, 2.0, 3.0, 4.0);' : '';
+    const statements =
+      t.params.address_space === 'function'
+        ? ['var v = vec4f(1.0, 2.0, 3.0, 4.0);', `let a = v.${chain};`, '_ = a;']
+        : [`let a = v.${chain};`, '_ = a;'];
+
+    t.expectPipelineResult({
+      expectedResult: true,
+      code,
+      statements,
+    });
+  });