[mustache_template] Initial import #9944

stuartmorgan-g · 2025-09-02T18:08:26Z

The mustache_template package has been transferred to the flutter.dev publisher, so this imports it into our repository and updates it to follow repository conventions:

Fix/suppress analysis warnings
- Some via dart fix, some manual
Add repo-level metadata
Update license check command to recognize this package
Add a temporary code-excerpt exclusion
Update pubspec.yaml metadata
Bump version to 2.0.1 to release the changes

mustache_template was itself a fork by a Flutter team member of the third-party mustache package, so the import is into third_party/packages/, updating the repo license check to recognize the license of this package.

The original code is quite old, and as a result still used a lot of implicit dynamic typing. Some of that that has been addressed in this import, but the trickier aspects have been left for future work, as converting from implicit dynamic typing to specified types has the potential for runtime regressions. (It's possible that even the more minor changes made here will cause regressions that will need fast-follow, but all the tests still pass, and the manual test/all.dart tests do not have any failures that were not present before making changes to the imported code).

Issues filed for future follow-up work:
flutter/flutter#174721
flutter/flutter#174722
flutter/flutter#174742

Pre-Review Checklist

Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩ ↩² ↩³

Updates the minimum Flutter/Dart SDK, and applies the autoformatter.

google-cla · 2025-09-02T18:08:53Z

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gemini-code-assist

Code Review

This pull request imports the mustache_template package into the repository. The changes include updating repository metadata, license checks, and fixing some analysis warnings from the original, older codebase. My review focuses on improving code quality, fixing bugs, and ensuring consistency with modern Dart practices. I've found some critical issues like incorrect API definitions that would cause compilation errors and bugs where exceptions are created but not thrown. I've also found several medium-severity issues, including syntax errors in README examples, opportunities for code simplification, and improved type safety.

third_party/packages/mustache_template/lib/mustache.dart

gemini-code-assist · 2025-09-02T18:11:14Z

third_party/packages/mustache_template/lib/src/lambda_context.dart

+  void render({Object? value}) {
+    _checkClosed();
+    if (_node is! SectionNode) {
+      _error('LambdaContext.render() can only be called on section tags.');


The _error method returns a TemplateException, but it is not being thrown. This will lead to unexpected behavior as the function will complete without an error. The exception should be thrown.

Suggested change

_error('LambdaContext.render() can only be called on section tags.');

throw _error('LambdaContext.render() can only be called on section tags.');

This definitely seems bad. It's a behavioral change so I'm not going to change it here, but I've added a TODO on these lines so that we don't forget.

gemini-code-assist · 2025-09-02T18:11:14Z

third_party/packages/mustache_template/lib/src/lambda_context.dart

+      _error(
+        'LambdaContext.renderString() can only be called on section tags.',
+      );


The _error method returns a TemplateException, but it is not being thrown here. This will lead to unexpected behavior as the function will implicitly return null instead of throwing an error. The exception should be thrown.

Suggested change

_error(

'LambdaContext.renderString() can only be called on section tags.',

);

throw _error(

'LambdaContext.renderString() can only be called on section tags.',

);

See previous comment.

gemini-code-assist · 2025-09-02T18:11:14Z

third_party/packages/mustache_template/lib/mustache.dart

+  factory Template(
+    String source, {
+    bool lenient,
+    bool htmlEscapeValues,
+    String name,
+    PartialResolver? partialResolver,
+    String delimiters,
+  }) = t.Template.fromSource;


The named parameters in this factory constructor are non-nullable and don't have default values or a required keyword, which will cause analysis errors in Dart 3. They should be updated to match the implementation in Template.fromSource, using default values and nullable types where appropriate.

Suggested change

factory Template(

String source, {

bool lenient,

bool htmlEscapeValues,

String name,

PartialResolver? partialResolver,

String delimiters,

}) = t.Template.fromSource;

factory Template(

String source, {

bool lenient = false,

bool htmlEscapeValues = true,

String? name,

PartialResolver? partialResolver,

String delimiters = '{{ }}',

}) = t.Template.fromSource;

This is weird, and looks like a mistake in the initial conversion to NNBD, but I'm not going to change it here.

third_party/packages/mustache_template/lib/src/lambda_context.dart

gemini-code-assist · 2025-09-02T18:11:15Z

third_party/packages/mustache_template/lib/src/parser.dart

+      throw _errorEof();
+    }
+    if (token.type != type) {
+      throw _error('Expected: $type found: ${token.type}.', _offset);


The error is reported at _offset, which points to the position after the unexpected token. For a more accurate error location, it would be better to use token.start.

Suggested change

throw _error('Expected: $type found: ${token.type}.', _offset);

throw _error('Expected: $type found: ${token.type}.', token.start);

Not changing; could be done later.

gemini-code-assist · 2025-09-02T18:11:15Z

third_party/packages/mustache_template/lib/src/parser.dart

+        node = null;
+
+      default:
+        throw Exception('Unreachable code');


For unreachable code, it's more idiomatic in Dart to throw a StateError rather than a generic Exception.

Suggested change

throw Exception('Unreachable code');

throw StateError('Unreachable code');

Added TODO.

gemini-code-assist · 2025-09-02T18:11:16Z

third_party/packages/mustache_template/lib/src/renderer.dart

+    final Template? template =
+        partialResolver == null
+            ? null
+            : (partialResolver!(partialName) as Template?);


The cast as Template? is redundant here, as the expression partialResolver!(partialName) already evaluates to Template?.

Suggested change

: (partialResolver!(partialName) as Template?);

: partialResolver!(partialName);

This is due to some weird namespaced importing (there are two names for Template in this file) that I'm not going to try to unwind here.

gemini-code-assist · 2025-09-02T18:11:16Z

third_party/packages/mustache_template/lib/src/renderer.dart

+  // which contains the key name, this is object[name]. For other
+  // objects, this is object.name or object.name(). If no property
+  // by the given name exists, this method returns noSuchProperty.
+  Object? _getNamedProperty(dynamic object, dynamic name) {


The name parameter is always a String since it comes from name.split('.'). It's better to type it as String instead of dynamic for better type safety and clarity.

Suggested change

Object? _getNamedProperty(dynamic object, dynamic name) {

Object? _getNamedProperty(dynamic object, String name) {

This change does indeed appear to be safe, so I've made it.

gemini-code-assist · 2025-09-02T18:11:16Z

third_party/packages/mustache_template/test/mustache_test.dart

+      if (ex is TemplateException) {
+        expect(ex.message, startsWith(VALUE_MISSING));
+      } else {
+        fail('Unexpecetd type: $ex');


There is a typo in "Unexpecetd".

Suggested change

fail('Unexpecetd type: $ex');

fail('Unexpected type: $ex');

Fixed since it's test code.

stuartmorgan-g · 2025-09-02T18:14:42Z

I will get a CLA exemption once the PR is ready to land, since this is a third_party import.

third_party/packages/mustache_template/pubspec.yaml

parlough · 2025-09-03T20:11:58Z

Also, thanks for this import and filing the follow-up issues!

Fix violations of repo checks: - Fix/suppress analysis warnings - Some via `dart fix`, some manual - Add repo-level metadata - Update license check command to recognize this package - Add a temporary code-excerpt exclusion - Update pubspec.yaml metadata - Add METADATA file - Bump version to 2.0.1 to release the changes - Fix minor README issues - Add TODOs for some areas that should be investigated in the future

stuartmorgan-g · 2025-09-04T13:56:45Z

Argh, I didn't mean to autosubmit that. It was supposed to be a merge commit like most of our imports :( I realized my mistake slightly too late. This means we won't have full git history for this package.

I think it's probably not worth trying to unwind that though. In practice, since the history of the package is almost all >7 years old, it's probably not a big deal.

stuartmorgan-g · 2025-09-04T14:10:51Z

I'll try to leave my branch alive so that this PR can be used for looking into history of specific lines if we ever need to do that. There's also https://github.com/jonahwilliams/mustache, and https://github.com/xxgreg/mustache which is the original source in case Jonah's repo goes away at some point.

flutter/packages@42bb347...98580c6 2025-09-04 stuartmorgan@google.com [mustache_template] Initial import (flutter/packages#9944) 2025-09-04 69874219+WillBLogical@users.noreply.github.com [google_maps_flutter_web] Omit styles when cloudMapId is set (flutter/packages#9869) 2025-09-03 lukas.mirbt@hotmail.com [go_router_builder] Fix unnecessary whitespace in generated `RelativeGoRouteData` (flutter/packages#9875) 2025-09-03 james@somethingwild.co.nz [google_maps_flutter_web] Stop listening to map events when disposed (flutter/packages#9250) 2025-09-03 borisshishov@gmail.com [flutter_svg] loader buffer fix (flutter/packages#9898) If this roll has caused a breakage, revert this CL and stop the roller using the controls here: https://autoroll.skia.org/r/flutter-packages-flutter-autoroll Please CC flutter-ecosystem@google.com on the revert to ensure that a human is aware of the problem. To file a bug in Flutter: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

…r#174943) flutter/packages@42bb347...98580c6 2025-09-04 stuartmorgan@google.com [mustache_template] Initial import (flutter/packages#9944) 2025-09-04 69874219+WillBLogical@users.noreply.github.com [google_maps_flutter_web] Omit styles when cloudMapId is set (flutter/packages#9869) 2025-09-03 lukas.mirbt@hotmail.com [go_router_builder] Fix unnecessary whitespace in generated `RelativeGoRouteData` (flutter/packages#9875) 2025-09-03 james@somethingwild.co.nz [google_maps_flutter_web] Stop listening to map events when disposed (flutter/packages#9250) 2025-09-03 borisshishov@gmail.com [flutter_svg] loader buffer fix (flutter/packages#9898) If this roll has caused a breakage, revert this CL and stop the roller using the controls here: https://autoroll.skia.org/r/flutter-packages-flutter-autoroll Please CC flutter-ecosystem@google.com on the revert to ensure that a human is aware of the problem. To file a bug in Flutter: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

xxgreg added 30 commits April 4, 2013 00:26

Packaging

65a318a

Fixes

3f17ddc

Add README

1a0883c

Preserve source location in tokens

a21cdfc

Preserve source location in nodes

7b3c588

Add source location to error messages

3d338ed

Render should return a String

61bb26f

Update test

62be8ca

Add html escaping

8d06196

Make sure all tests are passing

dce306f

Make template variables private

e21cc68

Update readme and docs

ee97da0

Add nested sections test

c32100a

Add strict/lenient mode

5a232b7

Mark escape tags as unimplemented

6d824b8

Update docs, fix comments

811f7fc

update readme

7515284

README.md

08c2bde

Update template to use StringSink interface

a8cba79

Add drone.io badge

284937e

Bump version

c19df8b

Add parameter to disable html escaping

5bb626d

Hookup escape tags

9ea0c32

Update readme

fd713a0

Bump version

ec66136

Add mustache spec tests

2d20576

Fix no interpolation failure

894fdef

Trim whitespace from tag names

963f6cd

Handled nested sections where value is not a map

f13c7e7

Fix inverse section context misses

f930156

jonahwilliams and others added 8 commits February 26, 2020 08:51

update pubspec.yaml

a5c55ba

add export library

ad4bb5d

fixes to make all existing tests work

6067dd7

more updates to changelog

6f99021

migrate to null safe dart

4d440ab

update sdk constraint

cbae271

Initial import of mustache_template

2d9ab9c

[mustache_template] Import: Autoformat

c8c7f59

Updates the minimum Flutter/Dart SDK, and applies the autoformatter.

gemini-code-assist bot reviewed Sep 2, 2025

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stuartmorgan-g force-pushed the mustache-template-import branch from 85985cd to ca20ab8 Compare September 2, 2025 18:50

stuartmorgan-g requested review from bkonyi and parlough September 2, 2025 19:46

bkonyi approved these changes Sep 3, 2025

View reviewed changes

parlough approved these changes Sep 3, 2025

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stuartmorgan-g force-pushed the mustache-template-import branch from ca20ab8 to a35fc7d Compare September 3, 2025 20:42

stuartmorgan-g force-pushed the mustache-template-import branch from a35fc7d to cfe8bcd Compare September 3, 2025 20:50

stuartmorgan-g mentioned this pull request Sep 4, 2025

[mustache_template] Improve error throwing flutter/flutter#174938

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stuartmorgan-g added the autosubmit Merge PR when tree becomes green via auto submit App label Sep 4, 2025

auto-submit bot merged commit 98580c6 into flutter:main Sep 4, 2025
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stuartmorgan-g removed the autosubmit Merge PR when tree becomes green via auto submit App label Sep 4, 2025

engine-flutter-autoroll added a commit to engine-flutter-autoroll/flutter that referenced this pull request Sep 4, 2025

98580c6c8 [mustache_template] Initial import (flutter/packages#9944)

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engine-flutter-autoroll mentioned this pull request Sep 4, 2025

Roll Packages from 42bb34706103 to 98580c6c82fc (5 revisions) flutter/flutter#174943

Merged

	_error('LambdaContext.render() can only be called on section tags.');
	throw _error('LambdaContext.render() can only be called on section tags.');

	throw _error('Expected: $type found: ${token.type}.', _offset);
	throw _error('Expected: $type found: ${token.type}.', token.start);

	throw Exception('Unreachable code');
	throw StateError('Unreachable code');

	: (partialResolver!(partialName) as Template?);
	: partialResolver!(partialName);

	Object? _getNamedProperty(dynamic object, dynamic name) {
	Object? _getNamedProperty(dynamic object, String name) {

[mustache_template] Initial import #9944

[mustache_template] Initial import #9944

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stuartmorgan-g commented Sep 2, 2025

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stuartmorgan-g commented Sep 2, 2025

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parlough commented Sep 3, 2025 •

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