writer/msl: Emit const on array and ptr parameters

This fixes issues with passing constant arrays to functions.

Change-Id: I6e2f1c3f64df836c0b6a55ab925cf3c2bc317733
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/51861
Auto-Submit: James Price <jrprice@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/writer/msl/generator_impl.cc

@@ -1311,7 +1311,9 @@ bool GeneratorImpl::EmitFunctionInternal(ast::Function* func,
 
     auto* type = program_->Sem().Get(v)->Type();
 
-    if (!EmitType(type, program_->Symbols().NameFor(v->symbol()))) {
+    std::string param_name =
+        "const " + program_->Symbols().NameFor(v->symbol());
+    if (!EmitType(type, param_name)) {
       return false;
     }
     // Parameter name is output as part of the type for arrays and pointers.

src/writer/msl/generator_impl_function_test.cc

@@ -770,7 +770,7 @@ TEST_F(MslGeneratorImplTest, Emit_Function_WithArrayParams) {
   EXPECT_EQ(gen.result(), R"(#include <metal_stdlib>
 
 using namespace metal;
-  void my_func(float a[5]) {
+  void my_func(float const a[5]) {
     return;
   }
 

test/ptr_ref/load/param/ptr.spvasm.expected.msl

@@ -1,7 +1,7 @@
 #include <metal_stdlib>
 
 using namespace metal;
-int func(int value, thread int* pointer) {
+int func(int value, thread int* const pointer) {
   int const x_9 = *(pointer);
   return (value + x_9);
 }

test/ptr_ref/load/param/ptr.wgsl.expected.msl

@@ -1,7 +1,7 @@
 #include <metal_stdlib>
 
 using namespace metal;
-int func(int value, thread int* pointer) {
+int func(int value, thread int* const pointer) {
   return (value + *(pointer));
 }
 

test/ptr_ref/store/param/ptr.spvasm.expected.msl

@@ -1,7 +1,7 @@
 #include <metal_stdlib>
 
 using namespace metal;
-void func(int value, thread int* pointer) {
+void func(int value, thread int* const pointer) {
   *(pointer) = value;
   return;
 }

test/ptr_ref/store/param/ptr.wgsl.expected.msl

@@ -1,7 +1,7 @@
 #include <metal_stdlib>
 
 using namespace metal;
-void func(int value, thread int* pointer) {
+void func(int value, thread int* const pointer) {
   *(pointer) = value;
 }
 

test/types/parameters.wgsl.expected.msl

@@ -4,7 +4,7 @@ using namespace metal;
 struct S {
 };
 
-void foo(bool param_bool, int param_i32, uint param_u32, float param_f32, int2 param_v2i32, uint3 param_v3u32, float4 param_v4f32, float2x3 param_m2x3, float param_arr[4], S param_struct, thread float* param_ptr_f32, thread float4* param_ptr_vec, thread float (*param_ptr_arr)[4]) {
+void foo(bool param_bool, int param_i32, uint param_u32, float param_f32, int2 param_v2i32, uint3 param_v3u32, float4 param_v4f32, float2x3 param_m2x3, float const param_arr[4], S param_struct, thread float* const param_ptr_f32, thread float4* const param_ptr_vec, thread float (*const param_ptr_arr)[4]) {
 }
 
 kernel void tint_symbol() {