Add reverse-agreement rebase for NES cache behind experiment flag by ulugbekna · Pull Request #310793 · microsoft/vscode

ulugbekna · 2026-04-16T16:36:40Z

When the user types more text than the model predicted at the same position (e.g., model predicts `{`, user types `{\n\t`), the rebase engine now recognizes that the model's edit is consumed by the user's typing and offers the remaining unconsumed model edits as rebased suggestions.

Changes

editRebase.ts: Added a reverse-agreement branch in `tryRebaseEdits` that iterates through model edits consumed by the user's typing, emitting only the unconsumed remainder. Guarded by `nesConfigs.reverseAgreement`.
configurationService.ts: Added `InlineEditsReverseAgreement` experiment-based config key (`chat.advanced.inlineEdits.reverseAgreement`, default: `false`).
nextEditCache.ts: Wired `reverseAgreement` config into `_getNesRebaseConfigs()`.
rebaseResult.ts: Updated diagnostic output to include `reverseAgreement` in generated test cases.
editRebase.spec.ts: Added 10 unit tests covering positive, negative, and edge cases.
nextEditCacheRebase.spec.ts: Integration test for the Fibonacci scenario with the flag enabled.

Key design decisions

Uses `ourEdit.replaceRange.equals(baseEdit.replaceRange)` (not `containsRange`) to avoid false positives when user replacements extend beyond the model edit range.
Applies the same `maxAgreementOffset`/`maxImperfectAgreementLength` strict-mode limits as the forward agreement path.
Trailing gap check verifies original content preservation via `startsWith`, allowing extra user typing after consumed model edits.

Copilot

Pull request overview

Adds an experiment-guarded “reverse agreement” path to the inline-edits rebase engine so cached/model edits can be rebased when the user types more than the model predicted at the same location, preserving and offering only the unconsumed remainder.

Changes:

Add reverseAgreement handling to tryRebaseEdits (guarded by nesConfigs.reverseAgreement) and propagate the config from NextEditCache.
Introduce chat.advanced.inlineEdits.reverseAgreement as an experiment-based TeamInternal setting (default false) and include it in rebase failure diagnostics.
Add unit + integration coverage for reverse-agreement scenarios (including a Fibonacci regression test).

Show a summary per file

File	Description
extensions/copilot/src/extension/inlineEdits/common/editRebase.ts	Implements reverse-agreement rebase branch behind config flag.
extensions/copilot/src/platform/configuration/common/configurationService.ts	Adds TeamInternal experiment-based config key for reverse agreement.
extensions/copilot/src/extension/inlineEdits/node/nextEditCache.ts	Wires reverse-agreement config into `NesRebaseConfigs` passed to rebase.
extensions/copilot/src/extension/inlineEdits/node/rebaseResult.ts	Includes `reverseAgreement` in auto-generated failure test output.
extensions/copilot/src/extension/inlineEdits/test/common/editRebase.spec.ts	Adds reverse-agreement unit tests (positive/negative/edge cases).
extensions/copilot/src/extension/inlineEdits/test/node/nextEditCacheRebase.spec.ts	Adds integration regression test for cache rebase with the flag enabled.
extensions/copilot/.esbuild.ts	Changes watch-mode rebuild strategy to use `ctx.watch()` per context.

Copilot's findings

Comments suppressed due to low confidence (1)

extensions/copilot/src/extension/inlineEdits/test/node/nextEditCacheRebase.spec.ts:132

The test hard-codes a user-specific absolute path (/Users/ulugbekna/...). This is non-portable and can be problematic on Windows/CI. Use a generic test path (e.g. /test/nodeTypesDefinitionProvider.ts) or construct a temp path instead.

		// Initialize workspace doc with the CURRENT document state
		// (so checkEditConsistency(documentBeforeEdit + userEditSince = currentDoc) passes)

Files reviewed: 7/7 changed files
Comments generated: 4

Copilot · 2026-04-16T16:46:48Z

+	// Document states at different points in time
+	const docAtRequest18 = docPrefix + 'class Fibonacci ';     // offset 1944 → "class Fibonacci " ends at 1960
+	const currentDoc = docPrefix + 'class Fibonacci {\n\t';    // offset 1944 → "class Fibonacci {\n\t" ends at 1963
+
+	function makeSource(): NextEditFetchRequest {
+		const logContext = new InlineEditRequestLogContext('test', 0, undefined);
+		return new NextEditFetchRequest(generateUuid(), logContext, undefined, false);
+	}
+
+	beforeEach(() => {
+		configService = new InMemoryConfigurationService(new DefaultsOnlyConfigurationService());
+		configService.setConfig(ConfigKey.TeamInternal.InlineEditsReverseAgreement, true);
+		obsWorkspace = new MutableObservableWorkspace();
+		logService = new LogServiceImpl([]);
+		expService = new NullExperimentationService();
+
+		docId = DocumentId.create(URI.file('/Users/ulugbekna/code/tsq/src/nodeTypesDefinitionProvider.ts').toString());
+		// Initialize workspace doc with the CURRENT document state
+		// (so checkEditConsistency(documentBeforeEdit + userEditSince = currentDoc) passes)
+		obsWorkspace.addDocument({ id: docId, initialValue: currentDoc });
+
+		cache = new NextEditCache(obsWorkspace, logService, configService, expService);
+	});
+
+	it('rebases cached edit when model predicted class Fibonacci { and user typed the same', () => {
+		// Scenario from real usage:
+		//   documentBeforeEdit (at cache time): ...class Fibonacci \n (ends at offset 1960)
+		//   Model's edit: replace [1944,1960) "class Fibonacci " → "class Fibonacci {"
+		//   Model also has a 2nd edit: insert at 1961 → class body
+		//   User then typed "{\n\t" → userEditSince: [1944,1960) → "class Fibonacci {\n\t"
+		//
+		// The user's typing is a superset of the model's first edit (model: "{", user: "{\n\t"),
+		// so rebase should succeed and the 2nd edit (class body) should be offered.
+		const cachedEdit = cache.setKthNextEdit(
+			docId,
+			new StringText(docAtRequest18),
+			new OffsetRange(1944, 1960), // editWindow
+			new StringReplacement(new OffsetRange(1944, 1960), 'class Fibonacci {'),
+			0,


This test relies on hard-coded offsets (e.g. 1944/1960/1961/1963). That makes the test brittle if docPrefix changes. Consider computing these offsets from docPrefix.length (and/or indexOf) so the scenario remains correct even if the prefix text is edited.

This issue also appears on line 131 of the same file.

Copilot · 2026-04-16T16:46:49Z

-		rebuild();
+		for (const ctx of contexts) {
+			await ctx.watch();
+		}


This PR’s description is focused on NES reverse-agreement rebase, but this hunk changes the Copilot extension esbuild watch implementation (removing the repo-level watcher/debounce and switching to ctx.watch()). If this change is intentional, please update the PR description/scope; otherwise, consider splitting it into a separate PR to keep review and risk contained.

Copilot · 2026-04-16T16:46:49Z

+	const docAtRequest18 = docPrefix + 'class Fibonacci ';     // offset 1944 → "class Fibonacci " ends at 1960
+	const currentDoc = docPrefix + 'class Fibonacci {\n\t';    // offset 1944 → "class Fibonacci {\n\t" ends at 1963


docAtRequest6 is declared but never used. With noUnusedLocals/linting enabled this will fail the build; please remove it (or use it in the test).

Copilot · 2026-04-16T16:46:49Z

+	beforeEach(() => {
+		configService = new InMemoryConfigurationService(new DefaultsOnlyConfigurationService());
+		configService.setConfig(ConfigKey.TeamInternal.InlineEditsReverseAgreement, true);


InMemoryConfigurationService.setConfig(...) returns a Promise. Please await it in beforeEach (or prefix with void) to avoid a floating promise lint violation and to ensure the config is applied before NextEditCache is constructed.

Suggested change

beforeEach(() => {

configService = new InMemoryConfigurationService(new DefaultsOnlyConfigurationService());

configService.setConfig(ConfigKey.TeamInternal.InlineEditsReverseAgreement, true);

beforeEach(async () => {

configService = new InMemoryConfigurationService(new DefaultsOnlyConfigurationService());

await configService.setConfig(ConfigKey.TeamInternal.InlineEditsReverseAgreement, true);

When the user types more text than the model predicted at the same position (e.g., model: '{', user: '{\n\t'), the rebase engine now recognizes that the model's edit is consumed by the user's typing and offers the remaining unconsumed model edits as rebased suggestions. The new behavior is gated behind the 'reverseAgreement' experiment flag in NesRebaseConfigs (config key: chat.advanced.inlineEdits.reverseAgreement, default: false). Adds 10 unit tests covering positive, negative, and edge cases.

github-actions · 2026-04-16T16:55:59Z

Screenshot Changes

Base: df871147 Current: 941de6ca

Changed (3)

chat/aiCustomizations/aiCustomizationManagementEditor/McpBrowseMode/Dark

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chat/aiCustomizations/aiCustomizationManagementEditor/McpBrowseMode/Light

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editor/inlineCompletions/other/JumpToHint/Dark

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Copilot AI review requested due to automatic review settings April 16, 2026 16:36

ulugbekna enabled auto-merge (squash) April 16, 2026 16:37

Copilot started reviewing on behalf of ulugbekna April 16, 2026 16:37 View session

ulugbekna disabled auto-merge April 16, 2026 16:37

ulugbekna enabled auto-merge (squash) April 16, 2026 16:37

vs-code-engineering Bot assigned ulugbekna Apr 16, 2026

Copilot AI reviewed Apr 16, 2026

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microsoft deleted a comment from github-actions Bot Apr 16, 2026

ulugbekna added 4 commits April 16, 2026 18:50

nes: cache: add a test to show how rebasing fails

2ee31a4

remove unused var

e4e41df

address review: computed offsets, await setConfig, generic path

9b1a83d

ulugbekna force-pushed the ulugbekna/social-partridge branch from 88e8618 to 9b1a83d Compare April 16, 2026 16:52

Yoyokrazy approved these changes Apr 16, 2026

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ulugbekna merged commit f563e5b into main Apr 16, 2026
26 checks passed

ulugbekna deleted the ulugbekna/social-partridge branch April 16, 2026 17:20

vs-code-engineering Bot added this to the 1.117.0 milestone Apr 16, 2026

vs-code-engineering Bot mentioned this pull request Apr 28, 2026

[Error] [GitHub.copilot-chat] unhandlederror-No cached edit #313047

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Add reverse-agreement rebase for NES cache behind experiment flag#310793

Add reverse-agreement rebase for NES cache behind experiment flag#310793
ulugbekna merged 4 commits intomainfrom
ulugbekna/social-partridge

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		const docAtRequest18 = docPrefix + 'class Fibonacci '; // offset 1944 → "class Fibonacci " ends at 1960
		const currentDoc = docPrefix + 'class Fibonacci {\n\t'; // offset 1944 → "class Fibonacci {\n\t" ends at 1963

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ulugbekna commented Apr 16, 2026

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