fix: clamp completion range when scanner crosses tag boundary

src/parser/htmlScanner.ts

@@ -139,7 +139,7 @@ class MultiLineStream {
 }
 const _BNG = '!'.charCodeAt(0);
 const _MIN = '-'.charCodeAt(0);
-const _LAN = '<'.charCodeAt(0);
+export const _LAN = '<'.charCodeAt(0);
 const _RAN = '>'.charCodeAt(0);
 const _FSL = '/'.charCodeAt(0);
 const _EQS = '='.charCodeAt(0);

src/services/htmlCompletion.ts

@@ -4,7 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { HTMLDocument, Node } from '../parser/htmlParser.js';
-import { createScanner } from '../parser/htmlScanner.js';
+import { createScanner, _LAN } from '../parser/htmlScanner.js';
 import {
 	CompletionConfiguration, ICompletionParticipant, ScannerState, TokenType, LanguageServiceOptions, DocumentContext,
 	Position, CompletionList, CompletionItemKind, Range, TextEdit, InsertTextFormat, CompletionItem, MarkupKind, TextDocument
@@ -293,7 +293,19 @@ export class HTMLCompletion {
 				let valueContentEnd = valueEnd;
 				// valueEnd points to the char after quote, which encloses the replace range
 				if (valueEnd > valueStart && text[valueEnd - 1] === text[valueStart]) {
-					valueContentEnd--;
+					// Even when a matching quote is found, the scanner may have latched
+					// onto an unrelated later quote across HTML tag boundaries. If any
+					// `<` appears between the cursor and the alleged closing quote,
+					// treat the value as unclosed and clamp so the completion cannot
+					// delete subsequent markup. See microsoft/vscode#273226.
+					let crossesTagBoundary = false;
+					for (let i = offset; i < valueEnd - 1; i++) {
+						if (text.charCodeAt(i) === _LAN) {
+							crossesTagBoundary = true;
+							break;
+						}
+					}
+					valueContentEnd = crossesTagBoundary ? offset : valueContentEnd - 1;
 				} else {
 					// unclosed quote: clamp the end to the cursor position so that
 					// the replace range does not extend into subsequent HTML content

src/test/completion.test.ts

@@ -172,6 +172,18 @@ suite('HTML Completion', () => {
 		testCompletionFor('<th><input type="che|</th><td></td>', {
 			items: [{ label: 'checkbox', resultText: '<th><input type="checkbox</th><td></td>' }]
 		});
+		// unclosed quote with a stray quote later in the document (scanner would
+		// otherwise latch onto the stray quote and blow away the markup between
+		// the cursor and that quote). See microsoft/vscode#273226.
+		testCompletionFor('<th><input type="che|</th><p title="later"></p>', {
+			items: [{ label: 'checkbox', resultText: '<th><input type="checkbox</th><p title="later"></p>' }]
+		});
+		testCompletionFor('<th><input type="che|</th>\n<p title="later"></p>', {
+			items: [{ label: 'checkbox', resultText: '<th><input type="checkbox</th>\n<p title="later"></p>' }]
+		});
+		testCompletionFor('<th><input type="che|\n</th>', {
+			items: [{ label: 'checkbox', resultText: '<th><input type="checkbox\n</th>' }]
+		});
 
 		testCompletionFor('<div dir=|></div>', {
 			items: [