Flatten ast::Decoration class hierarchy

Remove the decoration groupings (Array, Function, Struct,
StructMember, Type, Variable), such that all *Decoration classes now
subclass ast::Decoration directly. This allows for decorations to be
used in multiple places; for example, builtin decorations are now
valid for both variables and struct members.

Checking that decoration lists only contain decorations that are valid
for the node that they are attached to is now done inside the
validator.

Change-Id: Ie8c0e53e5730a7dedea50a1dec8f26f9e7b00e8d
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/44320
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@chromium.org>

src/transform/emit_vertex_point_size.cc

@@ -47,7 +47,7 @@ Transform::Output EmitVertexPointSize::Run(const Program* in) {
       f32,                                    // type
       false,                                  // is_const
       nullptr,                                // constructor
-      ast::VariableDecorationList{
+      ast::DecorationList{
           out.create<ast::BuiltinDecoration>(Source{},
                                              ast::Builtin::kPointSize),
       });

src/transform/first_index_offset.cc

@@ -101,7 +101,7 @@ Transform::Output FirstIndexOffset::Run(const Program* in) {
 
   CloneContext ctx(&out, in);
   ctx.ReplaceAll([&](ast::Variable* var) -> ast::Variable* {
-    for (ast::VariableDecoration* dec : var->decorations()) {
+    for (ast::Decoration* dec : var->decorations()) {
       if (auto* blt_dec = dec->As<ast::BuiltinDecoration>()) {
         ast::Builtin blt_type = blt_dec->value();
         if (blt_type == ast::Builtin::kVertexIndex) {
@@ -157,7 +157,7 @@ ast::Variable* FirstIndexOffset::State::AddUniformBuffer() {
   ast::StructMemberList members;
   uint32_t offset = 0;
   if (has_vertex_index) {
-    ast::StructMemberDecorationList member_dec;
+    ast::DecorationList member_dec;
     member_dec.push_back(
         dst->create<ast::StructMemberOffsetDecoration>(Source{}, offset));
     members.push_back(dst->create<ast::StructMember>(
@@ -168,7 +168,7 @@ ast::Variable* FirstIndexOffset::State::AddUniformBuffer() {
   }
 
   if (has_instance_index) {
-    ast::StructMemberDecorationList member_dec;
+    ast::DecorationList member_dec;
     member_dec.push_back(
         dst->create<ast::StructMemberOffsetDecoration>(Source{}, offset));
     members.push_back(dst->create<ast::StructMember>(
@@ -178,7 +178,7 @@ ast::Variable* FirstIndexOffset::State::AddUniformBuffer() {
     offset += 4;
   }
 
-  ast::StructDecorationList decos;
+  ast::DecorationList decos;
   decos.push_back(dst->create<ast::StructBlockDecoration>(Source{}));
 
   auto* struct_type = dst->create<type::Struct>(
@@ -192,7 +192,7 @@ ast::Variable* FirstIndexOffset::State::AddUniformBuffer() {
       struct_type,                           // type
       false,                                 // is_const
       nullptr,                               // constructor
-      ast::VariableDecorationList{
+      ast::DecorationList{
           dst->create<ast::BindingDecoration>(Source{}, binding),
           dst->create<ast::GroupDecoration>(Source{}, group),
       });
@@ -227,7 +227,7 @@ ast::VariableDeclStatement* FirstIndexOffset::State::CreateFirstIndexOffset(
       dst->create<type::U32>(),                // type
       true,                                    // is_const
       constructor,                             // constructor
-      ast::VariableDecorationList{});          // decorations
+      ast::DecorationList{});                  // decorations
   return dst->create<ast::VariableDeclStatement>(Source{}, var);
 }
 

src/transform/vertex_pulling.cc

@@ -135,7 +135,7 @@ void VertexPulling::State::FindOrInsertVertexIndexIfUsed() {
       GetI32Type(),                                    // type
       false,                                           // is_const
       nullptr,                                         // constructor
-      ast::VariableDecorationList{
+      ast::DecorationList{
           ctx.dst->create<ast::BuiltinDecoration>(Source{},
                                                   ast::Builtin::kVertexIndex),
       });
@@ -182,7 +182,7 @@ void VertexPulling::State::FindOrInsertInstanceIndexIfUsed() {
       GetI32Type(),                                      // type
       false,                                             // is_const
       nullptr,                                           // constructor
-      ast::VariableDecorationList{
+      ast::DecorationList{
           ctx.dst->create<ast::BuiltinDecoration>(Source{},
                                                   ast::Builtin::kInstanceIndex),
       });
@@ -210,7 +210,7 @@ void VertexPulling::State::ConvertVertexInputVariablesToPrivate() {
             ctx.Clone(v->type()),               // type
             false,                              // is_const
             nullptr,                            // constructor
-            ast::VariableDecorationList{});     // decorations
+            ast::DecorationList{});             // decorations
         location_to_var[location] = replacement;
         location_replacements.emplace_back(LocationReplacement{v, replacement});
         break;
@@ -224,13 +224,13 @@ void VertexPulling::State::AddVertexStorageBuffers() {
   // The array inside the struct definition
   auto* internal_array_type = ctx.dst->create<type::Array>(
       GetU32Type(), 0,
-      ast::ArrayDecorationList{
+      ast::DecorationList{
           ctx.dst->create<ast::StrideDecoration>(Source{}, 4u),
       });
 
   // Creating the struct type
   ast::StructMemberList members;
-  ast::StructMemberDecorationList member_dec;
+  ast::DecorationList member_dec;
   member_dec.push_back(
       ctx.dst->create<ast::StructMemberOffsetDecoration>(Source{}, 0u));
 
@@ -238,7 +238,7 @@ void VertexPulling::State::AddVertexStorageBuffers() {
       Source{}, ctx.dst->Symbols().Register(kStructBufferName),
       internal_array_type, std::move(member_dec)));
 
-  ast::StructDecorationList decos;
+  ast::DecorationList decos;
   decos.push_back(ctx.dst->create<ast::StructBlockDecoration>(Source{}));
 
   auto* struct_type = ctx.dst->create<type::Struct>(
@@ -256,7 +256,7 @@ void VertexPulling::State::AddVertexStorageBuffers() {
         struct_type,                        // type
         false,                              // is_const
         nullptr,                            // constructor
-        ast::VariableDecorationList{
+        ast::DecorationList{
             ctx.dst->create<ast::BindingDecoration>(Source{}, i),
             ctx.dst->create<ast::GroupDecoration>(Source{}, cfg.pulling_group),
         });
@@ -276,11 +276,11 @@ ast::BlockStatement* VertexPulling::State::CreateVertexPullingPreamble() const {
       Source{}, ctx.dst->create<ast::Variable>(
                     Source{},                                         // source
                     ctx.dst->Symbols().Register(kPullingPosVarName),  // symbol
-                    ast::StorageClass::kFunction,     // storage_class
-                    GetI32Type(),                     // type
-                    false,                            // is_const
-                    nullptr,                          // constructor
-                    ast::VariableDecorationList{}));  // decorations
+                    ast::StorageClass::kFunction,  // storage_class
+                    GetI32Type(),                  // type
+                    false,                         // is_const
+                    nullptr,                       // constructor
+                    ast::DecorationList{}));       // decorations
 
   // |kPullingPosVarName| refers to the byte location of the current read. We
   // declare a variable in the shader to avoid having to reuse Expression