Add test for SkSL vector-slice constructors.

SkSL does not support shrinking a vector via casting. Use a swizzle
instead.

Change-Id: Ieba78a05dad9c55f44c765924e28f0c7e1667a67
Bug: skia:12193
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/427198
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>

gn/sksl_tests.gni

@@ -143,6 +143,7 @@ sksl_error_tests = [
   "/sksl/errors/UnscopedVariableInIf.sksl",
   "/sksl/errors/UnscopedVariableInWhile.sksl",
   "/sksl/errors/UsingInvalidValue.sksl",
+  "/sksl/errors/VectorSlice.sksl",
   "/sksl/errors/WhileTypeMismatch.sksl",
 ]
 

resources/sksl/errors/VectorSlice.sksl

@@ -0,0 +1,19 @@
+// Expect 9 errors
+
+// SkSL does not support shrinking a vector via casting.
+// A vector-slice can be performed in SkSL (or GLSL) by using a swizzle instead.
+
+const half4 h4 = half4(0);
+const half3 h3 = half3(h4);
+const half2 h2 = half2(h4);
+const half  h  = half (h4);
+
+const int4  i4 = int4(0);
+const int3  i3 = int3(i4);
+const int2  i2 = int2(i4);
+const int   i  = int (i4);
+
+const bool4 b4 = bool4(false);
+const bool3 b3 = bool3(b4);
+const bool2 b2 = bool2(b4);
+const bool  b  = bool (b4);

tests/sksl/errors/VectorSlice.glsl

@@ -0,0 +1,12 @@
+### Compilation failed:
+
+error: 7: invalid arguments to 'half3' constructor (expected 3 scalars, but found 4)
+error: 8: invalid arguments to 'half2' constructor (expected 2 scalars, but found 4)
+error: 9: invalid argument to 'half' constructor (expected a number or bool, but found 'half4')
+error: 12: invalid arguments to 'int3' constructor (expected 3 scalars, but found 4)
+error: 13: invalid arguments to 'int2' constructor (expected 2 scalars, but found 4)
+error: 14: invalid argument to 'int' constructor (expected a number or bool, but found 'int4')
+error: 17: invalid arguments to 'bool3' constructor (expected 3 scalars, but found 4)
+error: 18: invalid arguments to 'bool2' constructor (expected 2 scalars, but found 4)
+error: 19: invalid argument to 'bool' constructor (expected a number or bool, but found 'bool4')
+9 errors