WebUI: Allow specifying additional imports in Lit HTML template files.
This is necessary to allow Lit HTML templates to refer to things that
don't exist on the corresponding `this` element. For example importing
the sentinel "nothing" value [1] or other built-in directives [2]
directly into the template's scope.
[1] https://lit.dev/docs/api/templates/#nothing
[2] https://lit.dev/docs/templates/directives/
Bug: 1503223
Change-Id: I9ae74976d71bd7700c431ea4e83d12d4e18697c3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5157592
Reviewed-by: Rebekah Potter <[email protected]>
Commit-Queue: Demetrios Papadopoulos <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1242802}
diff --git a/tools/polymer/html_to_wrapper.py b/tools/polymer/html_to_wrapper.py
index 749fb6d..c32f109 100644
--- a/tools/polymer/html_to_wrapper.py
+++ b/tools/polymer/html_to_wrapper.py
@@ -20,6 +20,7 @@
import argparse
import io
+import re
import shutil
import sys
import tempfile
@@ -47,7 +48,7 @@
# Template for Lit component HTML templates.
_LIT_ELEMENT_TEMPLATE = """import {html} from '%(scheme)s//resources/lit/v3_0/lit.rollup.js';
import type {%(class_name)s} from './%(file_name)s.js';
-
+%(imports)s
export function getHtml(this: %(class_name)s) {
return html`<!--_html_template_start_-->%(content)s<!--_html_template_end_-->`;
}"""
@@ -86,6 +87,44 @@
return 'native'
+_IMPORTS_START_REGEX = '^<!-- #html_wrapper_imports_start$'
+_IMPORTS_END_REGEX = '^#html_wrapper_imports_end -->$'
+
+
+# Extract additional imports to carry over to the HTML wrapper file.
+def _extract_import_metadata(file, minify):
+ start_line = -1
+ end_line = -1
+
+ with io.open(file, encoding='utf-8', mode='r') as f:
+ lines = f.read().splitlines()
+
+ for i, line in enumerate(lines):
+ if start_line == -1:
+ if re.search(_IMPORTS_START_REGEX, line):
+ assert end_line == -1
+ start_line = i
+ else:
+ assert end_line == -1
+
+ if re.search(_IMPORTS_END_REGEX, line):
+ assert start_line > -1
+ end_line = i
+ break
+
+ if start_line == -1 or end_line == -1:
+ assert start_line == -1
+ assert end_line == -1
+ return None
+
+ return {
+ # Strip metadata from content, unless minification is used, which will
+ # strip any HTML comments anyway.
+ 'content': None if minify else '\n'.join(lines[end_line + 1:]),
+ 'imports': '\n'.join(lines[start_line + 1:end_line]) + '\n',
+ }
+
+
def main(argv):
parser = argparse.ArgumentParser()
parser.add_argument('--in_folder', required=True)
@@ -173,6 +212,15 @@
substitutions['class_name'] = class_name
substitutions['file_name'] = basename
+ # Extracting import metadata from original non-minified template.
+ import_metadata = _extract_import_metadata(
+ path.join(args.in_folder, in_file), args.minify)
+ substitutions['imports'] = \
+ '' if import_metadata is None else import_metadata['imports']
+ if import_metadata is not None and not args.minify:
+ # Remove metadata lines from content.
+ substitutions['content'] = import_metadata['content']
+
wrapper = TEMPLATE_MAP[template_type] % substitutions
out_folder_for_file = path.join(out_folder, path.dirname(in_file))
