Automatically fold inactive regions

[Colen Garoutte-Carson (Colengms)]

Summary

Adds support for folding inactive preprocessor regions.

• Adds the C/C++: Fold Inactive Regions command for manually folding inactive regions in the active C, C++, or CUDA file.
• Adds the opt-in C_Cpp.autoFoldInactiveRegions setting to fold inactive regions after IntelliSense finishes processing a newly opened editor.
• Keeps folding independent of inactive-region colorization, allowing regions to be folded when C_Cpp.dimInactiveRegions is disabled.
• Leaves existing behavior unchanged by default.

Implementation

Inactive ranges may arrive across multiple IntelliSense result notifications. This change accumulates them per document and waits for a complete IntelliSense pass before folding. This prevents an incomplete result from selecting a nested folding range instead of the surrounding inactive preprocessor branch.

Manual requests made before IntelliSense results are ready remain pending until a complete result arrives. Cached ranges are invalidated when a document changes, opens, or closes, and automatic folding occurs only once per editor instance.

Testing

• Added unit coverage for accumulating complete inactive-region results, replacing and deleting cached results, and producing sorted unique folding lines.
• Added SingleRootProject scenario coverage verifying:
  • Manual folding works with inactive-region dimming disabled.
  • The inactive preprocessor branch is folded instead of a nested function.
  • Inactive regions are automatically folded when the new setting is enabled.
• TypeScript compilation and ESLint pass.
• Focused unit tests: 4 passing.
• SingleRootProject scenario tests: 58 passing.

Fixes #8992

[Copilot]

Copilot review overview

🟡 Changes recommended

URI-scoped folding state is routed through the wrong client in multi-root workspaces, and one-shot folding state has additional gating issues.

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Review effort: Balanced
Findings: 2

Open (2)

• Store folding ranges on the owning workspace client · New
• Require code folding to be enabled before auto-folding · New

What changed in this PR

Adds manual and opt-in automatic folding for inactive preprocessor regions.

Changes:

• Adds inactive-region caching and folding orchestration.
• Registers the command and setting with localized descriptions.
• Adds unit and scenario coverage.

File	Description
Extension/​src/​LanguageServer/​inactiveRegions.ts	Implements inactive-region storage and line selection.
Extension/​src/​LanguageServer/​client.ts	Integrates caching, manual folding, and automatic folding.
Extension/​src/​LanguageServer/​extension.ts	Registers the folding command handler.
Extension/​src/​LanguageServer/​settings.ts	Exposes the automatic-fold setting.
Extension/​package.json	Contributes the command, setting, and command-palette condition.
Extension/​package.nls.json	Adds user-facing command and setting text.
Extension/​test/​unit/​inactiveRegions.test.ts	Tests region accumulation and line generation.
Extension/​test/​scenarios/​SingleRootProject/​tests/​inactiveFolding.test.ts	Tests manual and automatic folding scenarios.

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[Copilot]

Copilot review overview

🔵 Needs a closer look

Manual folding can target a stale workspace client and incorrectly suppress later automatic folding.

Review effort: Balanced
Findings: None

Resolved since last review (2)

• Require code folding to be enabled before auto-folding
• Store folding ranges on the owning workspace client

Previously missed (2)

In code that hasn't changed since last review

Manual folds incorrectly suppress later automatic folding

Extension/​src/​LanguageServer/​client.ts:3018

A manual fold also marks the editor as already auto-folded. If the user manually folds, unfolds, and then enables autoFoldInactiveRegions, the settings-change path will refuse to auto-fold this editor even though no automatic fold occurred. Only record the editor when autoFold is actually true.

Route document command using the current editor URI

Extension/​src/​LanguageServer/​extension.ts:931

Route this document-scoped command from the current editor URI. ClientCollection.didChangeActiveEditor updates ActiveClient only after awaiting the new client's editor-change notification, so invoking this command during a multi-root editor switch can add the pending fold to the previous client; the actual owner receives the ranges and never fulfills that request.

[Copilot]

Copilot review overview

🟢 Approval recommended

The implementation handles result accumulation, lifecycle invalidation, multi-root routing, and configuration behavior with focused coverage.

Review effort: Balanced
Findings: None