From 27f90f966100bdfa74d19533ea720cfba92cfa29 Mon Sep 17 00:00:00 2001
From: Connor Peet <connor@peet.io>
Date: Fri, 11 Jul 2025 14:27:55 -0700
Subject: [PATCH] tools: always replace explicit tab in apply_patch insertions
 (#223)

Closes https://github.com/microsoft/vscode/issues/254783
---
 .../extension/tools/node/applyPatch/parser.ts | 12 +++----
 .../tools/test/node/applyPatch/parser.spec.ts | 32 +++++++++++++++++++
 2 files changed, 37 insertions(+), 7 deletions(-)

diff --git a/extensions/copilot/src/extension/tools/node/applyPatch/parser.ts b/extensions/copilot/src/extension/tools/node/applyPatch/parser.ts
index 53478d120c1..b42a11f865e 100644
--- a/extensions/copilot/src/extension/tools/node/applyPatch/parser.ts
+++ b/extensions/copilot/src/extension/tools/node/applyPatch/parser.ts
@@ -408,19 +408,17 @@ export class Parser {
 
 			for (const ch of nextSection.chunks) {
 				ch.origIndex += match.line;
+				ch.insLines = ch.insLines.map(replace_explicit_tabs);
+
 				if (this.fixIndentationDuringMatch) {
 					ch.insLines = ch.insLines.map(ins => isFalsyOrWhitespace(ins) ? ins : additionalIndentation + transformIndentation(ins, srcIndentStyle, targetIndentStyle));
 				}
 
 				if (match.fuzz & Fuzz.NormalizedExplicitTab) {
-					action.chunks.push({
-						delLines: ch.delLines.map(replace_explicit_tabs),
-						insLines: ch.insLines.map(replace_explicit_tabs),
-						origIndex: ch.origIndex,
-					});
-				} else {
-					action.chunks.push(ch);
+					ch.delLines = ch.delLines.map(replace_explicit_tabs);
 				}
+
+				action.chunks.push(ch);
 			}
 			index = match.line + nextSection.nextChunkContext.length;
 			this.index = nextSection.endPatchIndex;
diff --git a/extensions/copilot/src/extension/tools/test/node/applyPatch/parser.spec.ts b/extensions/copilot/src/extension/tools/test/node/applyPatch/parser.spec.ts
index aa310c1402c..16f2699cfb6 100644
--- a/extensions/copilot/src/extension/tools/test/node/applyPatch/parser.spec.ts
+++ b/extensions/copilot/src/extension/tools/test/node/applyPatch/parser.spec.ts
@@ -286,6 +286,38 @@ suite('applyPatch parser', () => {
 		]);
 	});
 
+	it('always normalizes explicit \\t tab chars in replacement', () => {
+		// 4.1 likes to explicitly put tabs as `\\t` in its patches
+		const input = `*** Begin Patch\n*** Update File: a.txt\n@@\n-hello\n+\\t\\tworld\n*** End Patch`;
+
+		expect(text_to_patch(input, {
+			'a.txt': new StringTextDocumentWithLanguageId('hello', 'text/plain')
+		})).toMatchInlineSnapshot(`
+			[
+			  {
+			    "actions": {
+			      "a.txt": {
+			        "chunks": [
+			          {
+			            "delLines": [
+			              "hello",
+			            ],
+			            "insLines": [
+			              "		world",
+			            ],
+			            "origIndex": 0,
+			          },
+			        ],
+			        "movePath": undefined,
+			        "type": "update",
+			      },
+			    },
+			  },
+			  0,
+			]
+		`);
+	});
+
 
 	suite('corpus', () => {
 		const corpusPath = path.join(__dirname, 'corpus');