CloneContext: Don't create named symbols from unnamed

Registering a new Symbol with the NameFor() of the source symbol creates
a new *named* symbol. When mixing these with unnamed symbols we can have
collisions.

Update CloneContext::Clone(Symbol) to properly clone unnamed symbols.

Update (most) the transforms to ctx.Clone() the symbols instead of
registering the names directly.

Fix up the tests where the symbol IDs have changed.

Note: We can still have symbol collisions if a program is authored with
identifiers like 'tint_symbol_3'. This will be fixed up in a later
change.

Change-Id: I0ce559644da3d60e1060f2eef185fa55ae284521
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/46866
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>

src/utils/get_or_create.h

@@ -0,0 +1,44 @@
+// 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_UTILS_GET_OR_CREATE_H_
+#define SRC_UTILS_GET_OR_CREATE_H_
+
+#include <unordered_map>
+
+namespace tint {
+namespace utils {
+
+/// GetOrCreate is a utility function for lazily adding to an unordered map.
+/// If the map already contains the key `key` then this is returned, otherwise
+/// `create()` is called and the result is added to the map and is returned.
+/// @param map the unordered_map
+/// @param key the map key of the item to query or add
+/// @param create a callable function-like object with the signature `V()`
+/// @return the value of the item with the given key, or the newly created item
+template <typename K, typename V, typename CREATE, typename H>
+V GetOrCreate(std::unordered_map<K, V, H>& map, K key, CREATE&& create) {
+  auto it = map.find(key);
+  if (it != map.end()) {
+    return it->second;
+  }
+  V value = create();
+  map.emplace(key, value);
+  return value;
+}
+
+}  // namespace utils
+}  // namespace tint
+
+#endif  //  SRC_UTILS_GET_OR_CREATE_H_

src/utils/get_or_create_test.cc

@@ -0,0 +1,49 @@
+// 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/utils/get_or_create.h"
+
+#include <unordered_map>
+
+#include "gtest/gtest.h"
+
+namespace tint {
+namespace utils {
+namespace {
+
+TEST(GetOrCreateTest, NewKey) {
+  std::unordered_map<int, int> map;
+  EXPECT_EQ(GetOrCreate(map, 1, [&] { return 2; }), 2);
+  EXPECT_EQ(map.size(), 1u);
+  EXPECT_EQ(map[1], 2);
+}
+
+TEST(GetOrCreateTest, ExistingKey) {
+  std::unordered_map<int, int> map;
+  map[1] = 2;
+  bool called = false;
+  EXPECT_EQ(GetOrCreate(map, 1,
+                        [&] {
+                          called = true;
+                          return -2;
+                        }),
+            2);
+  EXPECT_EQ(called, false);
+  EXPECT_EQ(map.size(), 1u);
+  EXPECT_EQ(map[1], 2);
+}
+
+}  // namespace
+}  // namespace utils
+}  // namespace tint