End an unclosed block in {% liquid %} at its last line

.changeset/liquid-unclosed-block-end.md

@@ -0,0 +1,5 @@
+---
+'@shopify/liquid-html-parser': patch
+---
+
+Fix the end of an unclosed block in `{% liquid %}`. It ended past the end of the template, as if its end tag came after the last line. It now ends where the last line does, as an unclosed block outside `{% liquid %}` does.

packages/liquid-html-parser/src/document/liquid-lines.ts

@@ -153,19 +153,15 @@ export function parseLineBlockTag(
     reason = e instanceof Error ? e.message : 'unknown error';
   }
 
-  const endTagLength = 3 + envelope.tagName.length; // 'end' + tagName
-
   if (def.branches.length === 0) {
-    const { children, endNameOffset } = parseLineBlockBody(parser, envelope.tagName, ctx);
-    const endPosition: Position = { start: endNameOffset, end: endNameOffset + endTagLength };
+    const { children, endPosition } = parseLineBlockBody(parser, envelope.tagName, ctx);
     if (markupParsed) {
       return makeLiquidTagNamed(envelope, markup, children, endPosition, { start: '', end: '' });
     }
     return makeLiquidTagBaseCase(envelope, children, endPosition, { start: '', end: '' }, reason);
   }
 
-  const { branches, endNameOffset } = parseLineBranchedBody(parser, envelope.tagName, def, ctx);
-  const endPosition: Position = { start: endNameOffset, end: endNameOffset + endTagLength };
+  const { branches, endPosition } = parseLineBranchedBody(parser, envelope.tagName, def, ctx);
   if (markupParsed) {
     return makeLiquidTagNamed(envelope, markup, branches, endPosition, { start: '', end: '' });
   }
@@ -282,24 +278,26 @@ export function parseLineBlockBody(
   parser: LineParserDelegate,
   parentName: string,
   ctx: LiquidLineContext,
-): { children: LiquidStatement[]; endNameOffset: number } {
+): { children: LiquidStatement[]; endPosition: Position } {
   const children: LiquidStatement[] = [];
 
   while (ctx.index < ctx.lines.length) {
     const line = ctx.lines[ctx.index];
 
     if (line.tagName === `end${parentName}`) {
       ctx.index++;
-      return { children, endNameOffset: line.nameOffset };
+      const endPosition = { start: line.nameOffset, end: line.nameOffset + line.tagName.length };
+      return { children, endPosition };
     }
 
     ctx.index++;
     children.push(parseLiquidStatement(parser, line.tagName, line.markup, line.markupOffset, ctx));
   }
 
   if (parser.lineAllowUnclosedDocumentNode) {
-    const endNameOffset = ctx.lines.length > 0 ? ctx.lines[ctx.lines.length - 1].lineEnd : 0;
-    return { children, endNameOffset };
+    // An unclosed block ends where its last line does, as at the top level.
+    const end = ctx.lines.length > 0 ? ctx.lines[ctx.lines.length - 1].lineEnd : 0;
+    return { children, endPosition: { start: end, end } };
   }
 
   throw new LiquidHTMLASTParsingError(
@@ -316,7 +314,7 @@ export function parseLineBranchedBody(
   parentName: string,
   def: TagDefinitionBlock,
   ctx: LiquidLineContext,
-): { branches: LiquidBranch[]; endNameOffset: number } {
+): { branches: LiquidBranch[]; endPosition: Position } {
   const branches: LiquidBranch[] = [];
   const bodyStart = ctx.index > 0 ? ctx.lines[ctx.index - 1].lineEnd : 0;
   let currentBranch: LiquidBranchUnnamed | LiquidBranchNamed = makeLiquidBranchUnnamed(
@@ -338,7 +336,8 @@ export function parseLineBranchedBody(
       );
       branches.push(currentBranch);
       ctx.index++;
-      return { branches, endNameOffset: line.nameOffset };
+      const endPosition = { start: line.nameOffset, end: line.nameOffset + line.tagName.length };
+      return { branches, endPosition };
     }
 
     if (isBranchName(line.tagName) && def.branches.includes(line.tagName)) {
@@ -371,16 +370,16 @@ export function parseLineBranchedBody(
   }
 
   if (parser.lineAllowUnclosedDocumentNode) {
-    const endNameOffset = ctx.lines.length > 0 ? ctx.lines[ctx.lines.length - 1].lineEnd : 0;
+    const end = ctx.lines.length > 0 ? ctx.lines[ctx.lines.length - 1].lineEnd : 0;
     finalizeBranch(
       currentBranch,
       currentChildren,
-      endNameOffset,
+      end,
       parser.getSource(),
       parser.lineParseHtml ? ChildFilterMode.StripEdges : ChildFilterMode.Syntactic,
     );
     branches.push(currentBranch);
-    return { branches, endNameOffset };
+    return { branches, endPosition: { start: end, end } };
   }
 
   throw new LiquidHTMLASTParsingError(

packages/liquid-html-parser/src/document/parser.test.ts

@@ -183,6 +183,9 @@ describe('Unit: document-parser', () => {
       // Verify inner structure is properly parsed (not base case fallback)
       expectPath(ast, 'children.0.markup.0.name').to.eql('assign');
       expectPath(ast, 'children.0.markup.1.name').to.eql('if');
+      // It ends where its last line does, since there's no endif.
+      expectPosition(ast, 'children.0.markup.1').toEqual('if use_variant\n    assign var2 = var1');
+      expectPath(ast, 'children.0.markup.1.blockEndPosition').to.eql({ start: 74, end: 74 });
     });
 
     it('should parse raw Liquid tags normally (doc, comment, raw)', () => {