Added comments to address @spall's feedback and clang-format

Author: llvm-beanz

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -12707,9 +12707,10 @@ def err_hlsl_param_qualifier_mismatch :
 def err_hlsl_vector_compound_assignment_truncation : Error<
   "left hand operand of type %0 to compound assignment cannot be truncated "
   "when used with right hand operand of type %1">;
-def err_hlsl_builtin_scalar_vector_mismatch : Error<
-  "%select{all|second and third}0 arguments to %1 must be of scalar or "
-  "vector type with matching scalar element type%diff{: $ vs $|}2,3">;
+def err_hlsl_builtin_scalar_vector_mismatch
+    : Error<
+          "%select{all|second and third}0 arguments to %1 must be of scalar or "
+          "vector type with matching scalar element type%diff{: $ vs $|}2,3">;
 
 def warn_hlsl_impcast_vector_truncation : Warning<
   "implicit conversion truncates vector: %0 to %1">, InGroup<Conversion>;

clang/lib/Headers/hlsl/hlsl_detail.h

@@ -97,8 +97,7 @@ constexpr vector<T, L> reflect_vec_impl(vector<T, L> I, vector<T, L> N) {
 #endif
 }
 
-template<typename T>
-struct is_arithmetic {
+template <typename T> struct is_arithmetic {
   static const bool Value = __is_arithmetic(T);
 };
 

clang/test/SemaHLSL/BuiltIns/select-errors.hlsl

@@ -2,16 +2,16 @@
 
 
 int test_select_first_arg_wrong_type(int1 p0, int t0, int f0) {
-  return select(p0, t0, f0);
+  return select(p0, t0, f0); // No diagnostic expected.
 }
 
 int1 test_select_bool_vals_diff_vecs(bool p0, int1 t0, int1 f0) {
-  return select<int1>(p0, t0, f0);
+  return select<int1>(p0, t0, f0); // No diagnostic expected.
 }
 
 int2 test_select_vector_vals_not_vecs(bool2 p0, int t0,
                                                int f0) {
-  return select(p0, t0, f0);
+  return select(p0, t0, f0); // No diagnostic expected.
 }
 
 int1 test_select_vector_vals_wrong_size(bool2 p0, int1 t0, int1 f0) {
@@ -51,12 +51,12 @@ int test_select_builtin_bool_incompatible_args(bool p0, int t0, double f0) {
 
 // if a vector second arg isnt a vector
 int2 test_select_builtin_second_arg_not_vector(bool2 p0, int t0, int2 f0) {
-  return __builtin_hlsl_select(p0, t0, f0);
+  return __builtin_hlsl_select(p0, t0, f0); // No diagnostic expected.
 }
 
 // if a vector third arg isn't a vector
 int2 test_select_builtin_second_arg_not_vector(bool2 p0, int2 t0, int f0) {
-  return __builtin_hlsl_select(p0, t0, f0);
+  return __builtin_hlsl_select(p0, t0, f0); // No diagnostic expected.
 }
 
 // if vector last 2 aren't same type (so both are vectors but wrong type)