Tolerant parsing: continue parsing when a Glimmer syntax is invalid

packages/@glimmer/syntax/lib/parser.ts

@@ -58,15 +58,18 @@ export abstract class Parser {
     >
   > = null;
   public tokenizer: EventedTokenizer;
+  protected continueOnError: boolean;
 
   constructor(
     source: src.Source,
     entityParser = new EntityParser(namedCharRefs),
-    mode: 'precompile' | 'codemod' = 'precompile'
+    mode: 'precompile' | 'codemod' = 'precompile',
+    continueOnError = false,
   ) {
     this.source = source;
     this.lines = source.source.split(/\r\n?|\n/u);
     this.tokenizer = new EventedTokenizer(this, entityParser, mode);
+    this.continueOnError = continueOnError;
   }
 
   offset(): src.SourceOffset {

packages/@glimmer/syntax/lib/parser/handlebars-node-visitors.ts

@@ -355,7 +355,15 @@ export abstract class HandlebarsNodeVisitors extends Parser {
     return comment;
   }
 
-  PartialStatement(partial: HBS.PartialStatement): never {
+  PartialStatement(partial: HBS.PartialStatement): ASTv1.ErrorNode {
+    if(this.continueOnError) {
+      let error = b.error({
+        loc: this.source.spanFor(partial.loc),
+        message: `Handlebars partials are not supported`
+      });
+      appendChild(this.currentElement(), error);
+      return error;
+    }
     throw generateSyntaxError(
       `Handlebars partials are not supported`,
       this.source.spanFor(partial.loc)

packages/@glimmer/syntax/lib/parser/tokenizer-event-handlers.ts

@@ -716,6 +716,7 @@ export interface PreprocessOptions {
     escaping/unescaping of HTML entity codes.
    */
   mode?: 'codemod' | 'precompile' | undefined;
+  continueOnError?: boolean | undefined;
 }
 
 export interface Syntax {
@@ -786,7 +787,7 @@ export function preprocess(
     end: offsets.endPosition,
   };
 
-  let template = new TokenizerEventHandlers(source, entityParser, mode).parse(
+  let template = new TokenizerEventHandlers(source, entityParser, mode, options.continueOnError).parse(
     ast,
     options.locals ?? []
   );

packages/@glimmer/syntax/lib/v1/handlebars-ast.ts

@@ -18,7 +18,7 @@ export interface NodeMap {
   Decorator: { input: Decorator; output: never };
   BlockStatement: { input: BlockStatement; output: ASTv1.BlockStatement | void };
   DecoratorBlock: { input: DecoratorBlock; output: never };
-  PartialStatement: { input: PartialStatement; output: never };
+  PartialStatement: { input: PartialStatement; output: ASTv1.ErrorNode };
   PartialBlockStatement: { input: PartialBlockStatement; output: never };
   ContentStatement: { input: ContentStatement; output: void };
   CommentStatement: { input: CommentStatement; output: ASTv1.MustacheCommentStatement | null };

packages/@glimmer/syntax/lib/v1/nodes-v1.ts

@@ -135,6 +135,7 @@ export type StatementName =
   | 'BlockStatement'
   | 'MustacheCommentStatement'
   | 'TextNode'
+  | 'ErrorNode'
   | 'ElementNode';
 
 export interface AttrNode extends BaseNode {
@@ -288,6 +289,11 @@ export interface HashPair extends BaseNode {
   value: Expression;
 }
 
+export interface ErrorNode extends BaseNode {
+  type: 'ErrorNode';
+  message: string;
+}
+
 export interface StripFlags {
   open: boolean;
   close: boolean;
@@ -318,6 +324,8 @@ export type Nodes = {
 
   Hash: Hash;
   HashPair: HashPair;
+
+  ErrorNode: ErrorNode;
 };
 
 export type NodeType = keyof Nodes;

packages/@glimmer/syntax/lib/v1/parser-builders.ts

@@ -434,6 +434,14 @@ class Builders {
   }): T {
     return buildLegacyLiteral({ type, value, loc });
   }
+
+  error({ message, loc }: { message: string; loc: SourceSpan }): ASTv1.ErrorNode {
+    return {
+      type: 'ErrorNode',
+      message,
+      loc,
+    };
+  }
 }
 
 const b = new Builders();

packages/@glimmer/syntax/lib/v1/public-builders.ts

@@ -483,6 +483,13 @@ function buildLoc(
   }
 }
 
+function buildError(message = '', loc?: SourceLocation): ASTv1.ErrorNode {
+  return b.error({
+    message,
+    loc: buildLoc(loc || null),
+  });
+}
+
 export default {
   mustache: buildMustache,
   block: buildBlock,
@@ -503,6 +510,7 @@ export default {
   template: buildTemplate,
   loc: buildLoc,
   pos: buildPosition,
+  error: buildError,
 
   path: buildPath,
 

packages/@glimmer/syntax/test/parser-node-test.ts

@@ -35,6 +35,15 @@ test('various html element paths', () => {
   }
 });
 
+test('continue parsing after an error', () => {
+  let t = '<img id="one">{{> face}}<img id="two">';
+  astEqual(t, b.template([
+    element('img', ['attrs', ['id', 'one']]),
+    b.error('Handlebars partials are not supported'),
+    element('img', ['attrs', ['id', 'two']])
+  ]), undefined, { continueOnError: true });
+});
+
 test('elements can have empty attributes', () => {
   let t = '<img id="">';
   astEqual(t, b.template([element('img', ['attrs', ['id', '']])]));