tint: Make ScopeStack key type generic

The scope stack has potential uses other than mapping from symbols.

Change-Id: I1eaedb9a9c913a7b2cda41bb99a986c552a66110
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/89720
Reviewed-by: Ben Clayton <bclayton@google.com>

src/tint/resolver/dependency_graph.cc

@@ -420,7 +420,7 @@ class DependencyScanner {
     DependencyGraph& graph_;
     DependencyEdges& dependency_edges_;
 
-    ScopeStack<const ast::Node*> scope_stack_;
+    ScopeStack<Symbol, const ast::Node*> scope_stack_;
     Global* current_global_ = nullptr;
 };
 

src/tint/scope_stack.h

@@ -24,7 +24,7 @@ namespace tint {
 
 /// Used to store a stack of scope information.
 /// The stack starts with a global scope which can not be popped.
-template <class T>
+template <class K, class V>
 class ScopeStack {
   public:
     /// Constructor
@@ -47,32 +47,32 @@ class ScopeStack {
     }
 
     /// Assigns the value into the top most scope of the stack.
-    /// @param symbol the symbol of the value
+    /// @param key the key of the value
     /// @param val the value
-    /// @returns the old value if there was an existing symbol at the top of the
+    /// @returns the old value if there was an existing key at the top of the
     /// stack, otherwise the zero initializer for type T.
-    T Set(const Symbol& symbol, T val) {
-        std::swap(val, stack_.back()[symbol]);
+    V Set(const K& key, V val) {
+        std::swap(val, stack_.back()[key]);
         return val;
     }
 
     /// Retrieves a value from the stack
-    /// @param symbol the symbol to look for
+    /// @param key the key to look for
     /// @returns the value, or the zero initializer if the value was not found
-    T Get(const Symbol& symbol) const {
+    V Get(const K& key) const {
         for (auto iter = stack_.rbegin(); iter != stack_.rend(); ++iter) {
             auto& map = *iter;
-            auto val = map.find(symbol);
+            auto val = map.find(key);
             if (val != map.end()) {
                 return val->second;
             }
         }
 
-        return T{};
+        return V{};
     }
 
   private:
-    std::vector<std::unordered_map<Symbol, T>> stack_;
+    std::vector<std::unordered_map<K, V>> stack_;
 };
 
 }  // namespace tint

src/tint/scope_stack_test.cc

@@ -22,7 +22,7 @@ namespace {
 class ScopeStackTest : public ProgramBuilder, public testing::Test {};
 
 TEST_F(ScopeStackTest, Get) {
-    ScopeStack<uint32_t> s;
+    ScopeStack<Symbol, uint32_t> s;
     Symbol a(1, ID());
     Symbol b(3, ID());
     s.Push();
@@ -44,13 +44,13 @@ TEST_F(ScopeStackTest, Get) {
 }
 
 TEST_F(ScopeStackTest, Get_MissingSymbol) {
-    ScopeStack<uint32_t> s;
+    ScopeStack<Symbol, uint32_t> s;
     Symbol sym(1, ID());
     EXPECT_EQ(s.Get(sym), 0u);
 }
 
 TEST_F(ScopeStackTest, Set) {
-    ScopeStack<uint32_t> s;
+    ScopeStack<Symbol, uint32_t> s;
     Symbol a(1, ID());
     Symbol b(2, ID());