Add ast::DisableValidationDecoration

An [[internal]] decoration that specifically disables certain validation checks.
Begin with a single kFunctionHasNoBody mode.
Migrate the Resolver to using this instead of allowing any InternalDecoration to disable the checks for no-body.

Bug: tint:797
Change-Id: I213b9a6844a456775ede06d60e456d9f77a449d0
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/50741
Auto-Submit: Ben Clayton <bclayton@google.com>
Reviewed-by: James Price <jrprice@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>

src/ast/disable_validation_decoration.cc

@@ -0,0 +1,46 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/ast/disable_validation_decoration.h"
+#include "src/clone_context.h"
+#include "src/program_builder.h"
+
+TINT_INSTANTIATE_TYPEINFO(tint::ast::DisableValidationDecoration);
+
+namespace tint {
+namespace ast {
+
+DisableValidationDecoration::DisableValidationDecoration(
+    ProgramID program_id,
+    DisabledValidation validation)
+    : Base(program_id), validation_(validation) {}
+
+DisableValidationDecoration::~DisableValidationDecoration() = default;
+
+std::string DisableValidationDecoration::Name() const {
+  switch (validation_) {
+    case DisabledValidation::kFunctionHasNoBody:
+      return "disable_validation__function_has_no_body";
+  }
+  return "<invalid>";
+}
+
+DisableValidationDecoration* DisableValidationDecoration::Clone(
+    CloneContext* ctx) const {
+  return ctx->dst->ASTNodes().Create<DisableValidationDecoration>(
+      ctx->dst->ID(), validation_);
+}
+
+}  // namespace ast
+}  // namespace tint

src/ast/disable_validation_decoration.h

@@ -0,0 +1,67 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_AST_DISABLE_VALIDATION_DECORATION_H_
+#define SRC_AST_DISABLE_VALIDATION_DECORATION_H_
+
+#include <string>
+
+#include "src/ast/internal_decoration.h"
+
+namespace tint {
+namespace ast {
+
+/// Enumerator of validation features that can be disabled with a
+/// DisableValidationDecoration decoration.
+enum class DisabledValidation {
+  /// When applied to a function, the validator will not complain there is no
+  /// body to a function.
+  kFunctionHasNoBody,
+};
+
+/// An internal decoration used to tell the validator to ignore specific
+/// violations. Typically generated by transforms that need to produce ASTs that
+/// would otherwise cause validation errors.
+class DisableValidationDecoration
+    : public Castable<DisableValidationDecoration, InternalDecoration> {
+ public:
+  /// Constructor
+  /// @param program_id the identifier of the program that owns this node
+  /// @param validation the validation to disable
+  explicit DisableValidationDecoration(ProgramID program_id,
+                                       DisabledValidation validation);
+
+  /// Destructor
+  ~DisableValidationDecoration() override;
+
+  /// @return the validation that this decoration disables
+  DisabledValidation Validation() const { return validation_; }
+
+  /// @return a short description of the internal decoration which will be
+  /// displayed in WGSL as `[[internal(<name>)]]` (but is not parsable).
+  std::string Name() const override;
+
+  /// Performs a deep clone of this object using the CloneContext `ctx`.
+  /// @param ctx the clone context
+  /// @return the newly cloned object
+  DisableValidationDecoration* Clone(CloneContext* ctx) const override;
+
+ private:
+  DisabledValidation const validation_;
+};
+
+}  // namespace ast
+}  // namespace tint
+
+#endif  // SRC_AST_DISABLE_VALIDATION_DECORATION_H_

src/ast/internal_decoration.h

@@ -25,7 +25,6 @@ namespace ast {
 /// A decoration used to indicate that a function is tint-internal.
 /// These decorations are not produced by generators, but instead are usually
 /// created by transforms for consumption by a particular backend.
-/// Functions annotated with this decoration will have relaxed validation.
 class InternalDecoration : public Castable<InternalDecoration, Decoration> {
  public:
   /// Constructor