bind-gen: Optimize rendering of TextNode and introduce EmptyNode

Bug: 839389
Change-Id: I583f47fc7f065489fb4f5a2473898fb95c9c7bb8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1980604
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728404}

third_party/blink/renderer/bindings/scripts/bind_gen/code_node.py

@@ -339,10 +339,21 @@ class CodeNode(object):
             symbol_node, set()).add(symbol_scope_chain)
 
 
+class EmptyNode(CodeNode):
+    """Represents the zero-length text and renders nothing."""
+
+    def __init__(self):
+        CodeNode.__init__(self)
+
+    def _render(self, renderer, last_render_state):
+        pass
+
+
 class LiteralNode(CodeNode):
     """
     Represents a literal text, which will be rendered as is without any template
-    magic applied.
+    magic applied.  The given literal text object will be stringified on each
+    rendering.
     """
 
     def __init__(self, literal_text):
@@ -358,7 +369,28 @@ class LiteralNode(CodeNode):
             renderer.pop_caller()
 
 
-class TextNode(CodeNode):
+def TextNode(template_text):
+    """
+    Represents a template text node.
+
+    TextNode is designed to be a leaf node of a code node tree.  TextNode
+    represents a template text while LiteralNode represents a literal text.
+    All template magics will be applied to |template_text|.
+
+    This function is pretending to be a CodeNode subclass and instantiates one
+    of text-ish code node subclass depending on the content of |template_text|.
+    """
+    assert isinstance(template_text, str)
+
+    if "$" in template_text or "%" in template_text:
+        return _TextNode(template_text)
+    elif template_text:
+        return LiteralNode(template_text)
+    else:
+        return EmptyNode()
+
+
+class _TextNode(CodeNode):
     """
     Represents a template text node.
 

third_party/blink/renderer/bindings/scripts/bind_gen/codegen_utils.py

@@ -7,6 +7,7 @@ import web_idl
 from . import name_style
 from .clang_format import clang_format
 from .code_node import CodeNode
+from .code_node import EmptyNode
 from .code_node import LiteralNode
 from .code_node import SequenceNode
 from .codegen_accumulator import CodeGenAccumulator
@@ -69,9 +70,9 @@ def enclose_with_header_guard(code_node, header_guard):
     return SequenceNode([
         LiteralNode("#ifndef {}".format(header_guard)),
         LiteralNode("#define {}".format(header_guard)),
-        LiteralNode(""),
+        EmptyNode(),
         code_node,
-        LiteralNode(""),
+        EmptyNode(),
         LiteralNode("#endif  // {}".format(header_guard)),
     ])
 
@@ -82,9 +83,9 @@ def enclose_with_namespace(code_node, namespace):
 
     return SequenceNode([
         LiteralNode("namespace {} {{".format(namespace)),
-        LiteralNode(""),
+        EmptyNode(),
         code_node,
-        LiteralNode(""),
+        EmptyNode(),
         LiteralNode("}}  // namespace {}".format(namespace)),
     ])