Update node_id_map & FindMutators structure

Added function in node_id_map to check a given id is valid and fresh.

Currently, the structure of FindMutators declares node_id_map as const, which causes issues when we want to call `GetFreshId` from the argument that is passed by reference. A simple work around is to pass a non-const node_id_map as argument directly. That way `GetFreshId` function in node_id_map can continue to be non-const and conveniently update next fresh id whenever a fresh id has been taken.

Change-Id: Ia7e1d247cf92dfefd2ef7e7c1b4bf32363d9ce3f
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/61100
Reviewed-by: Paul Thomson <paulthomson@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Paul Thomson <paulthomson@google.com>

fuzzers/tint_ast_fuzzer/mutation_finder.h

@@ -54,7 +54,7 @@ class MutationFinder {
   /// @return all the found mutations.
   virtual MutationList FindMutations(
       const tint::Program& program,
-      const NodeIdMap& node_id_map,
+      NodeIdMap* node_id_map,
       ProbabilityContext* probability_context) const = 0;
 
   /// @brief Compute a probability of applying a single mutation, returned by

fuzzers/tint_ast_fuzzer/mutation_finders/replace_identifiers.cc

@@ -29,7 +29,7 @@ namespace ast_fuzzer {
 
 MutationList MutationFinderReplaceIdentifiers::FindMutations(
     const tint::Program& program,
-    const NodeIdMap& node_id_map,
+    NodeIdMap* node_id_map,
     ProbabilityContext* probability_context) const {
   MutationList result;
 
@@ -61,8 +61,8 @@ MutationList MutationFinderReplaceIdentifiers::FindMutations(
               candidate_variables)];
 
       result.push_back(std::make_unique<MutationReplaceIdentifier>(
-          node_id_map.GetId(user->Declaration()),
-          node_id_map.GetId(replacement->Declaration())));
+          node_id_map->GetId(user->Declaration()),
+          node_id_map->GetId(replacement->Declaration())));
     }
   }
 

fuzzers/tint_ast_fuzzer/mutation_finders/replace_identifiers.h

@@ -29,7 +29,7 @@ class MutationFinderReplaceIdentifiers : public MutationFinder {
  public:
   MutationList FindMutations(
       const tint::Program& program,
-      const NodeIdMap& node_id_map,
+      NodeIdMap* node_id_map,
       ProbabilityContext* probability_context) const override;
   uint32_t GetChanceOfApplyingMutation(
       ProbabilityContext* probability_context) const override;

fuzzers/tint_ast_fuzzer/mutator.cc

@@ -141,7 +141,7 @@ tint::Program Mutate(tint::Program program,
     // Get all applicable mutations from some mutation finder.
     const auto& mutation_finder =
         finders[probability_context->GetRandomIndex(finders)];
-    auto mutations = mutation_finder->FindMutations(program, node_id_map,
+    auto mutations = mutation_finder->FindMutations(program, &node_id_map,
                                                     probability_context);
 
     const auto old_applied_mutations = applied_mutations;

fuzzers/tint_ast_fuzzer/node_id_map.cc

@@ -40,17 +40,21 @@ const ast::Node* NodeIdMap::GetNode(IdType id) const {
 
 void NodeIdMap::Add(const ast::Node* node, IdType id) {
   assert(!node_to_id_.count(node) && "The node already exists in the map");
-  assert(!id_to_node_.count(id) && "Id already exists in the map");
+  assert(IdIsFreshAndValid(id) && "Id already exists in the map or Id is zero");
   assert(node && "`node` can't be a nullptr");
-  assert(id && "`id` can't be equal to 0");
 
   node_to_id_[node] = id;
   id_to_node_[id] = node;
+
   if (id >= fresh_id_) {
     fresh_id_ = id + 1;
   }
 }
 
+bool NodeIdMap::IdIsFreshAndValid(IdType id) {
+  return id && !id_to_node_.count(id);
+}
+
 NodeIdMap::IdType NodeIdMap::TakeFreshId() {
   assert(fresh_id_ != 0 && "`NodeIdMap` id has overflowed");
   return fresh_id_++;

fuzzers/tint_ast_fuzzer/node_id_map.h

@@ -67,6 +67,13 @@ class NodeIdMap {
   /// @param id - may not be 0 and can't be present in this map.
   void Add(const ast::Node* node, IdType id);
 
+  /// @brief Returns whether the id is fresh by checking if it exists in
+  /// the id map and the id is not 0.
+  /// @param id - an id that is used to check in the map.
+  /// @return true the given id is fresh and valid (non-zero).
+  /// @return false otherwise.
+  bool IdIsFreshAndValid(IdType id);
+
   /// @brief Returns an id that is guaranteed to be unoccupied in this map.
   ///
   /// This will effectively increase the counter. This means that two