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// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
// See the Mustachio README at tool/mustachio/ for high-level
// documentation.
import 'dart:collection';
import 'dart:convert' show htmlEscape;
import 'package:analyzer/file_system/file_system.dart';
import 'package:meta/meta.dart';
import 'parser.dart';
// TODO(devoncarew): See is we can make this synchronous.
/// The signature of a partial resolver function.
typedef PartialResolver = Future<File> Function(String uri);
/// The signature of a generated render function.
typedef RenderFunction<T> = String Function(T context, Template template);
/// A parsed Mustache template.
/// This container includes Templates for all partials parsed in the template
/// file.
class Template {
/// The parsed Mustache syntax tree.
final List<MustachioNode> ast;
/// A mapping of partial keys to partial [File]s.
/// This may appear redundant with [partialTemplates], the mapping of partial
/// files to partial templates. The reason for two mappings is that
/// [partialTemplates] functions as a cache, so that each [File] containing a
/// partial template is only parsed once, and also so that partial templates
/// can reference themselves, or otherwise recurse. The cache is passed down
/// from template to partial. Mapping a partial key to a partial [File],
/// however, cannot be shared between templates and partials because they
/// typically contain relative file paths. Each partial file path is given
/// relative to the template or partial making the reference.
// TODO(srawlins): Resolving partials from the Parser rather than
// [Template.parse] would allow the [File] to be stored on the [Partial] node,
// removing the need for this mapping.
final Map<String, File> partials;
/// A mapping of partial [File]s to parsed Mustache templates.
final Map<File, Template> partialTemplates;
{required this.ast,
required this.partials,
required this.partialTemplates});
/// Parses [file] as a Mustache template, returning a [Template].
/// A [partialResolver] can be passed if custom partial resolution is required
/// (for example, to load any partial from a single directory, and to append a
/// particular suffix).
/// By default, a partial key is resolved as a file path which is either
/// absolute, or relative to the directory containing the template which
/// references the partial.
/// For example, if the Mustache template at `/foo/template.html` includes a
/// Partial node, `{{>partials/p1.html}}`, then the partial file path is
/// resolved as `/foo/partials/p1.html`. If this template includes a Partial
/// node, `{{>p2.html}}`, then this partial file path is resolved (relative to
/// the directory containing `p1.html`, not relative to the top-level
/// template), as `/foo/partials/p2.html`.
static Future<Template> parse(File file,
{PartialResolver? partialResolver,
@internal Map<File, Template>? partialTemplates}) async {
partialTemplates ??= <File, Template>{};
if (partialResolver == null) {
var pathContext = file.provider.pathContext;
// By default, resolve partials as absolute file paths, or as relative
// file paths, relative to the template directory from which they are
// referenced.
partialResolver = (String path) async {
var partialPath = pathContext.isAbsolute(path)
? path
: pathContext.join(file.parent.path, path);
var partialFile =
return partialFile;
// If we fail to read [file], and an exception is thrown, one of two
// things happen:
// 1) In the case of a reference from a partial, the exception is caught
// below, when parsing partials, and rethrown with information about the
// template with the reference.
// 2) In the case of a reference from a top-level template, user code has
// called [Template.parse], and the user is responsible for handling the
// exception.
var ast = MustachioParser(file.readAsStringSync(), file.toUri()).parse();
var nodeQueue = Queue.of(ast);
var partials = <String, File>{};
// Walk the Mustache syntax tree, looking for Partial nodes.
while (nodeQueue.isNotEmpty) {
var node = nodeQueue.removeFirst();
if (node is Text) {
// Nothing to do.
} else if (node is Variable) {
// Nothing to do.
} else if (node is Section) {
} else if (node is Partial) {
var key = node.key;
if (!partials.containsKey(key)) {
partials[key] = await partialResolver(key);
var partialFile = partials[key]!;
if (!partialTemplates.containsKey(partialFile)) {
try {
var partialTemplate = await Template.parse(partialFile,
partialResolver: partialResolver,
partialTemplates: {...partialTemplates});
partialTemplates[partialFile] = partialTemplate;
} on FileSystemException catch (e) {
throw MustachioResolutionError(node.span.message(
'FileSystemException (${e.message}) when reading partial:'));
return Template._(
ast: ast, partials: partials, partialTemplates: partialTemplates);
/// The base class for a generated Mustache renderer.
abstract class RendererBase<T extends Object?> {
/// The context object which this renderer can render.
final T context;
/// The renderer of the parent context, if any, otherwise `null`.
final RendererBase<Object?>? parent;
/// The current template being rendered.
/// When rendering a partial, the [context] object, and hence the
/// [RendererBase] does not change, only this current template.
Template _template;
/// The output buffer into which [context] is rendered, using a template.
final StringSink sink;
final Set<String> _invisibleGetters;
this.sink, {
Set<String> invisibleGetters = const {},
}) : _invisibleGetters = invisibleGetters;
Template get template => _template;
void write(String text) => sink.write(text);
String get contextChainString =>
parent == null ? '$T' : '${parent!.contextChainString} > $T';
/// Returns the [Property] on this renderer named [name].
/// If no property named [name] exists for this renderer, `null` is returned.
Property<T>? getProperty(String key);
/// Resolves [names] into one or more field accesses, returning the result as
/// a String.
/// [names] may have multiple dot-separate names, and [names] may not be a
/// valid property of _this_ context type, in which the [parent] renderer is
/// referenced.
String getFields(Variable node) {
var names = node.key;
if (names.length == 1 && names.single == '.') {
return context.toString();
var firstName = names.first;
try {
var property = getProperty(firstName);
var remainingNames = [...names.skip(1)];
if (property != null) {
try {
return property.renderVariable(context, property, remainingNames);
// ignore: avoid_catching_errors
} on PartialMustachioResolutionError catch (e) {
// The error thrown by [Property.renderVariable] does not have all of
// the names required for a decent error. We throw a new error here.
throw MustachioResolutionError(node.keySpan.message(
"Failed to resolve '${}' on ${e.contextType} while "
'resolving $remainingNames as a property chain on any types in '
'the context chain: $contextChainString, after first resolving '
"'$firstName' to a property on $T"));
// ignore: avoid_catching_errors
} on _MustachioResolutionErrorWithoutSpan catch (e) {
throw MustachioResolutionError(node.keySpan.message(e.message));
final parent = this.parent;
if (parent != null) {
return parent.getFields(node);
} else {
throw MustachioResolutionError(node.keySpan.message(
"Failed to resolve '${names.first}' as a property on any types in "
'the context chain: $contextChainString'));
/// Renders a block of Mustache template, the [ast], into [sink].
void renderBlock(List<MustachioNode> ast) {
for (var node in ast) {
if (node is Text) {
} else if (node is Variable) {
var content = getFields(node);
if (node.escape) {
} else {
} else if (node is Section) {
} else if (node is Partial) {
void section(Section node) {
var key = node.key.first;
var property = getProperty(key);
if (property == null) {
final parent = this.parent;
if (parent == null) {
throw MustachioResolutionError(node.keySpan.message(
"Failed to resolve '$key' as a property on any types in the "
'current context'));
} else {
return parent.section(node);
var getBool = property.getBool;
if (getBool != null) {
var boolResult = getBool(context);
if ((boolResult && !node.invert) || (!boolResult && node.invert)) {
var renderIterable = property.renderIterable;
if (renderIterable != null) {
var renderedIterable = renderIterable(context, this, node.children, sink);
if (node.invert && renderedIterable.isEmpty) {
// An inverted section is rendered with the current context.
} else if (!node.invert && renderedIterable.isNotEmpty) {
renderedIterable.toList(growable: false);
// Otherwise, render nothing.
// If this section is not a conditional or repeated section, it is a value
// section, regardless of type.
if (node.invert && property.isNullValue(context)) {
} else if (!node.invert && !property.isNullValue(context)) {
property.renderValue!(context, this, node.children, sink);
void partial(Partial node) {
var key = node.key;
var partialFile = template.partials[key];
var partialTemplate = template.partialTemplates[partialFile]!;
var outerTemplate = _template;
_template = partialTemplate;
_template = outerTemplate;
String renderSimple(Object? context, List<MustachioNode> ast, Template template,
StringSink sink,
{required RendererBase<Object> parent, required Set<String> getters}) {
var renderer = SimpleRenderer(context, parent, template, sink, getters);
return renderer.sink.toString();
class SimpleRenderer extends RendererBase<Object?> {
RendererBase<Object> super.parent,
Set<String> invisibleGetters,
) : super(invisibleGetters: invisibleGetters);
Property<Object>? getProperty(String key) {
if (_invisibleGetters.contains(key)) {
throw MustachioResolutionError(_failedKeyVisibilityMessage(key));
} else {
return null;
String getFields(Variable node) {
var names = node.key;
var firstName = node.key.first;
if (names.length == 1 && firstName == '.') {
return context.toString();
} else if (_invisibleGetters.contains(firstName)) {
throw MustachioResolutionError(_failedKeyVisibilityMessage(firstName));
} else if (parent != null) {
return parent!.getFields(node);
} else {
return 'null';
String _failedKeyVisibilityMessage(String name) {
var type = context.runtimeType;
return '[$name] is a getter on $type, which is not visible to Mustache. '
'To render [$name] on $type, make it visible to Mustache via the '
'`visibleTypes` parameter on `@Renderer`; to render [$name] on a '
'different type up in the context stack, perhaps provide [$name] via '
'a different name.';
/// An individual property of objects of type [T], including functions for
/// rendering various types of Mustache nodes.
class Property<T extends Object?> {
/// Gets the value of this property on the object [context].
final Object? Function(T context) getValue;
final String Function(T, Property<T>, List<String>) renderVariable;
/// Gets the bool value (true or false, never null) of this property on the
/// object [context].
final bool Function(T context)? getBool;
final Iterable<void> Function(
T, RendererBase<T>, List<MustachioNode>, StringSink)? renderIterable;
final bool Function(T) isNullValue;
final void Function(T, RendererBase<T>, List<MustachioNode>, StringSink)?
{required this.getValue,
required this.renderVariable,
// TODO(jcollins-g): consider making this required or emitting warnings
// if called on a non-nullable?
bool Function(T)? isNullValue,
: isNullValue = (isNullValue ?? (_) => false);
String renderSimpleVariable(
T c, List<String> remainingNames, String typeString) {
if (remainingNames.isEmpty) {
return getValue(c).toString();
} else {
throw MustachioResolutionError(
_simpleResolveErrorMessage(remainingNames, typeString));
static String _simpleResolveErrorMessage(List<String> key, String type) =>
'Failed to resolve $key property chain on $type using a simple renderer; '
'expose the properties of $type by adding it to the @Renderer '
"annotation's 'visibleTypes' list";
/// An error indicating that a renderer failed to resolve a key.
class MustachioResolutionError extends Error {
final String message;
String toString() => 'MustachioResolutionError: $message';
/// An error indicating that a renderer failed to resolve a follow-on name in a
/// multi-name key.
class PartialMustachioResolutionError extends Error {
final String name;
final Type contextType;
PartialMustachioResolutionError(, this.contextType);
/// A Mustachio resolution error which is thrown in a position where the AST
/// node is not known.
/// This error should be caught and "re-thrown" as a [MustachioResolutionError]
/// with a message derived from a [SourceSpan].
class _MustachioResolutionErrorWithoutSpan extends Error {
final String message;
extension MapExtensions<T> on Map<String, Property<T>> {
Property<T> getValue(String name) {
if (containsKey(name)) {
return this[name]!;
} else {
throw PartialMustachioResolutionError(name, T);