Add ability to generate typedefs from dawn.json

Can be used to help with deprecation during simple struct renames.

Includes typedefs for VertexAttributeDescriptor -> VertexAttribute and
VertexBufferLayoutDescriptor -> VertexBufferLayout as specified by the
latest RenderPipelineDescriptor changes.

Bug: dawn:642
Change-Id: Iab3d74d179884499540e813b0e66859713031ccb
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/40581
Commit-Queue: Brandon Jones <bajones@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>

dawn.json

@@ -954,7 +954,7 @@
         "extensible": true,
         "members": []
     },
-    "vertex attribute descriptor": {
+    "vertex attribute": {
         "category": "structure",
         "extensible": false,
         "members": [
@@ -963,23 +963,31 @@
             {"name": "shader location", "type": "uint32_t"}
         ]
     },
-    "vertex buffer layout descriptor": {
+    "vertex attribute descriptor": {
+        "category": "typedef",
+        "type": "vertex attribute"
+    },
+    "vertex buffer layout": {
         "category": "structure",
         "extensible": false,
         "members": [
             {"name": "array stride", "type": "uint64_t"},
             {"name": "step mode", "type": "input step mode", "default": "vertex"},
             {"name": "attribute count", "type": "uint32_t"},
-            {"name": "attributes", "type": "vertex attribute descriptor", "annotation": "const*", "length": "attribute count"}
+            {"name": "attributes", "type": "vertex attribute", "annotation": "const*", "length": "attribute count"}
         ]
     },
+    "vertex buffer layout descriptor": {
+        "category": "typedef",
+        "type": "vertex buffer layout"
+    },
     "vertex state descriptor": {
         "category": "structure",
         "extensible": true,
         "members": [
             {"name": "index format", "type": "index format", "default": "undefined"},
             {"name": "vertex buffer count", "type": "uint32_t", "default": 0},
-            {"name": "vertex buffers", "type": "vertex buffer layout descriptor", "annotation": "const*", "length": "vertex buffer count"}
+            {"name": "vertex buffers", "type": "vertex buffer layout", "annotation": "const*", "length": "vertex buffer count"}
         ]
     },
     "input step mode": {

generator/dawn_json_generator.py

@@ -128,6 +128,12 @@ class CallbackType(Type):
         self.arguments = []
 
 
+class TypedefType(Type):
+    def __init__(self, name, json_data):
+        Type.__init__(self, name, json_data)
+        self.type = None
+
+
 class NativeType(Type):
     def __init__(self, name, json_data):
         Type.__init__(self, name, json_data, native=True)
@@ -271,6 +277,10 @@ def link_callback(callback, types):
                                                types)
 
 
+def link_typedef(typedef, types):
+    typedef.type = types[typedef.json_data['type']]
+
+
 # Sort structures so that if struct A has struct B as a member, then B is
 # listed before A.
 #
@@ -321,6 +331,7 @@ def parse_json(json):
         'callback': CallbackType,
         'object': ObjectType,
         'structure': StructureType,
+        'typedef': TypedefType,
     }
 
     types = {}
@@ -346,6 +357,9 @@ def parse_json(json):
     for callback in by_category['callback']:
         link_callback(callback, types)
 
+    for typedef in by_category['typedef']:
+        link_typedef(typedef, types)
+
     for category in by_category.keys():
         by_category[category] = sorted(
             by_category[category], key=lambda typ: typ.name.canonical_case())

generator/templates/dawn_native/wgpu_structs.h

@@ -64,6 +64,10 @@ namespace dawn_native {
 
     {% endfor %}
 
+    {% for typeDef in by_category["typedef"] %}
+        using {{as_cppType(typeDef.name)}} = {{as_cppType(typeDef.type.name)}};
+    {% endfor %}
+
 } // namespace dawn_native
 
 #endif  // DAWNNATIVE_WGPU_STRUCTS_H_

generator/templates/webgpu.h

@@ -117,6 +117,13 @@ typedef struct WGPUChainedStruct {
 
 {% endfor %}
 
+{% for typeDef in by_category["typedef"] %}
+    // {{as_cType(typeDef.name)}} is deprecated.
+    // Use {{as_cType(typeDef.type.name)}} instead.
+    typedef {{as_cType(typeDef.type.name)}} {{as_cType(typeDef.name)}};
+
+{% endfor %}
+
 #ifdef __cplusplus
 extern "C" {
 #endif

generator/templates/webgpu_cpp.h

@@ -63,6 +63,13 @@ namespace wgpu {
         struct {{as_cppType(type.name)}};
     {% endfor %}
 
+    {% for typeDef in by_category["typedef"] %}
+        // {{as_cppType(typeDef.name)}} is deprecated.
+        // Use {{as_cppType(typeDef.type.name)}} instead.
+        using {{as_cppType(typeDef.name)}} = {{as_cppType(typeDef.type.name)}};
+
+    {% endfor %}
+
     template<typename Derived, typename CType>
     class ObjectBase {
       public: