fix: preserve cursor position when applying diffs

- Check if file is already active editor before calling showTextDocument
- Skip showTextDocument call when file is already open to preserve viewport
- Add tests for the new behavior to ensure viewport preservation
- Fixes #6853

src/integrations/editor/DiffViewProvider.ts

@@ -207,7 +207,13 @@ export class DiffViewProvider {
 			await updatedDocument.save()
 		}
 
-		await vscode.window.showTextDocument(vscode.Uri.file(absolutePath), { preview: false, preserveFocus: true })
+		// Only show the document if it's not already the active editor
+		// This preserves the viewport position when the file is already open
+		const activeEditor = vscode.window.activeTextEditor
+		const fileUri = vscode.Uri.file(absolutePath)
+		if (!activeEditor || !arePathsEqual(activeEditor.document.uri.fsPath, absolutePath)) {
+			await vscode.window.showTextDocument(fileUri, { preview: false, preserveFocus: true })
+		}
 		await this.closeAllDiffViews()
 
 		// Getting diagnostics before and after the file edit is a better approach than
@@ -661,11 +667,17 @@ export class DiffViewProvider {
 		// Open the document to ensure diagnostics are loaded
 		// When openFile is false (PREVENT_FOCUS_DISRUPTION enabled), we only open in memory
 		if (openFile) {
-			// Show the document in the editor
-			await vscode.window.showTextDocument(vscode.Uri.file(absolutePath), {
-				preview: false,
-				preserveFocus: true,
-			})
+			// Only show the document if it's not already the active editor
+			// This preserves the viewport position when the file is already open
+			const activeEditor = vscode.window.activeTextEditor
+			const fileUri = vscode.Uri.file(absolutePath)
+			if (!activeEditor || !arePathsEqual(activeEditor.document.uri.fsPath, absolutePath)) {
+				// Show the document in the editor
+				await vscode.window.showTextDocument(fileUri, {
+					preview: false,
+					preserveFocus: true,
+				})
+			}
 		} else {
 			// Just open the document in memory to trigger diagnostics without showing it
 			const doc = await vscode.workspace.openTextDocument(vscode.Uri.file(absolutePath))

src/integrations/editor/__tests__/DiffViewProvider.spec.ts

@@ -362,6 +362,8 @@ describe("DiffViewProvider", () => {
 			// Mock vscode functions
 			vi.mocked(vscode.window.showTextDocument).mockResolvedValue({} as any)
 			vi.mocked(vscode.languages.getDiagnostics).mockReturnValue([])
+			// Mock activeTextEditor as null by default
+			vi.mocked(vscode.window).activeTextEditor = null as any
 		})
 
 		it("should write content directly to file without opening diff view", async () => {
@@ -390,6 +392,26 @@ describe("DiffViewProvider", () => {
 			expect(result.finalContent).toBe("new content")
 		})
 
+		it("should not call showTextDocument when file is already active editor", async () => {
+			// Mock active editor with the same file
+			vi.mocked(vscode.window).activeTextEditor = {
+				document: {
+					uri: { fsPath: `${mockCwd}/test.ts` },
+				},
+			} as any
+
+			vi.mocked(vscode.window.showTextDocument).mockClear()
+
+			await diffViewProvider.saveDirectly("test.ts", "new content", true, true, 1000)
+
+			// Verify file was written
+			const fs = await import("fs/promises")
+			expect(fs.writeFile).toHaveBeenCalledWith(`${mockCwd}/test.ts`, "new content", "utf-8")
+
+			// Verify showTextDocument was NOT called since file is already active
+			expect(vscode.window.showTextDocument).not.toHaveBeenCalled()
+		})
+
 		it("should not open file when openWithoutFocus is false", async () => {
 			await diffViewProvider.saveDirectly("test.ts", "new content", false, true, 1000)
 
@@ -456,6 +478,8 @@ describe("DiffViewProvider", () => {
 			// Mock vscode functions
 			vi.mocked(vscode.window.showTextDocument).mockResolvedValue({} as any)
 			vi.mocked(vscode.languages.getDiagnostics).mockReturnValue([])
+			// Mock activeTextEditor as null by default
+			vi.mocked(vscode.window).activeTextEditor = null as any
 		})
 
 		it("should apply diagnostic delay when diagnosticsEnabled is true", async () => {
@@ -516,5 +540,48 @@ describe("DiffViewProvider", () => {
 			expect(mockDelay).toHaveBeenCalledWith(5000)
 			expect(vscode.languages.getDiagnostics).toHaveBeenCalled()
 		})
+
+		it("should not call showTextDocument when file is already active editor", async () => {
+			// Mock active editor with the same file
+			vi.mocked(vscode.window).activeTextEditor = {
+				document: {
+					uri: { fsPath: `${mockCwd}/test.ts` },
+				},
+			} as any
+
+			// Mock closeAllDiffViews
+			;(diffViewProvider as any).closeAllDiffViews = vi.fn().mockResolvedValue(undefined)
+
+			vi.mocked(vscode.window.showTextDocument).mockClear()
+
+			await diffViewProvider.saveChanges(true, 1000)
+
+			// Verify showTextDocument was NOT called since file is already active
+			expect(vscode.window.showTextDocument).not.toHaveBeenCalled()
+			// Verify closeAllDiffViews was still called
+			expect((diffViewProvider as any).closeAllDiffViews).toHaveBeenCalled()
+		})
+
+		it("should call showTextDocument when active editor is different file", async () => {
+			// Mock active editor with a different file
+			vi.mocked(vscode.window).activeTextEditor = {
+				document: {
+					uri: { fsPath: `${mockCwd}/different.ts` },
+				},
+			} as any
+
+			// Mock closeAllDiffViews
+			;(diffViewProvider as any).closeAllDiffViews = vi.fn().mockResolvedValue(undefined)
+
+			vi.mocked(vscode.window.showTextDocument).mockClear()
+
+			await diffViewProvider.saveChanges(true, 1000)
+
+			// Verify showTextDocument WAS called since active editor is different file
+			expect(vscode.window.showTextDocument).toHaveBeenCalledWith(
+				expect.objectContaining({ fsPath: `${mockCwd}/test.ts` }),
+				{ preview: false, preserveFocus: true },
+			)
+		})
 	})
 })