feat(code-action): add flatten nested attribute set refactor action by takeokunn · Pull Request #757 · nix-community/nixd

takeokunn · 2026-01-04T11:24:49Z

Summary

Adds a new "Flatten nested attribute set" code action that transforms nested attribute sets into dot notation:

# Before
{ foo = { bar = 1; }; }

# After
{ foo.bar = 1; }

This follows the existing pattern established in #756 for code actions.

Changes

File	Description
nixd/lib/Controller/CodeAction.cpp	Add getFlattenableBinds() helper and addFlattenAttrsAction() for the flatten refactoring
nixd/tools/nixd/test/code-action/flatten-attrs.md	Basic test for simple nested attribute flattening
nixd/tools/nixd/test/code-action/flatten-attrs-multi.md	Test for nested sets with multiple bindings
nixd/tools/nixd/test/code-action/flatten-attrs-deep.md	Test for deeply nested attribute paths
nixd/tools/nixd/test/code-action/flatten-attrs-rec.md	Test that rec sets are excluded
nixd/tools/nixd/test/code-action/flatten-attrs-inherit.md	Test that sets with inherit are excluded
nixd/tools/nixd/test/code-action/flatten-attrs-dynamic.md	Test that dynamic ${} names are excluded
nixd/tools/nixd/test/code-action/flatten-attrs-empty.md	Test that empty nested sets are excluded

Behavior

Flatten action offered when:

Cursor is on a binding whose value is an attribute set
All attribute names (outer and inner) are static identifiers
The nested set contains at least one binding

Explicitly excluded:

Recursive attribute sets (rec { ... }): Flattening would change semantics
Inherited bindings (inherit x;): Cannot be represented in dot notation
Dynamic attribute names (${expr}): Cannot be statically flattened
Empty nested sets ({ foo = {}; }): No meaningful transformation

Test Plan

Added 7 lit tests covering positive and negative cases
Tests verify the action is offered only when appropriate
Tests verify correct transformation output for various input shapes
All existing tests pass

In general, we should try to avoid testing redundant content or logic from other PRs within the .md regression tests (though this is sometimes unavoidable). You can use CHECK: patterns to skip over certain sections instead of using CHECK-NEXT:, and you can use CHECK-NOT: to verify the absence of specific structures.

Verify the absence of flatten action using CHECK-NOT directive instead of testing quote action from another PR.

- Remove quote action tests (belongs to different PR) - Use CHECK: instead of CHECK-NEXT: to skip intermediate sections - Focus only on testing flatten action functionality

takeokunn · 2026-01-04T14:01:53Z

@inclyc
Thanks for the review!
I've fixed the part you mentioned in the comments.
I didn't really understand how to write tests, so this was a good learning experience!

Split pack-attrs-siblings-positive.md into two separate test files to fix the CI failure in the nix-build-develop-gcc (undefined, release, false) configuration. The original test contained 2 sequential code action requests followed by an exit notification. Under UBSan, the sanitizer overhead caused a race condition where the second response wasn't fully flushed to stdout before process termination. Following the pattern from PR #757, each test file now contains only ONE code action request, eliminating the race condition. New test files: - pack-attrs-sibling-inherit.md: Tests pack action with inherit sibling - pack-attrs-sibling-different-prefix.md: Tests pack with different prefix

…#758) ## Summary Add a new code action that converts dotted attribute paths to nested attribute sets - the inverse of the "Flatten nested attribute set" action from #757. **Single Pack:** ```nix { foo.bar = 1; } → { foo = { bar = 1; }; } ``` **Bulk Pack** (multiple sibling bindings with same prefix): ```nix { foo.bar = 1; foo.baz = 2; } → { foo = { bar = 1; baz = 2; }; } ``` ## Changes | File | Description | |------|-------------| | nixd/lib/Controller/CodeAction.cpp | Add packAttrs function implementing the pack transformation with single and bulk modes | | **Single Pack Tests** | | | pack-attrs.md | Basic test for dotted path packing | | pack-attrs-deep.md | Test for multi-level dotted paths (packs one level at a time) | | pack-attrs-quoted.md | Test for preserving quoted attribute names | | pack-attrs-multiline.md | Test for multiline attribute set formatting | | pack-attrs-values.md | Test for various value types (empty sets, let expressions, nested sets) | | **Bulk Pack Tests** | | | pack-attrs-bulk.md | Test for bulk pack with sibling bindings | | pack-attrs-bulk-quoted.md | Test for bulk pack with quoted keys requiring proper quoting | | pack-attrs-escape.md | Test for escaping special characters (", \\, $) in quoted keys | | pack-attrs-sibling-inherit.md | Test for pack with inherit sibling (non-conflicting) | | pack-attrs-sibling-different-prefix.md | Test for pack with different prefix siblings | | **Negative Tests** | | | pack-attrs-single.md | Negative test for single-segment paths | | pack-attrs-rec.md | Negative test for recursive attribute sets | | pack-attrs-dynamic.md | Negative test for dynamic interpolation in paths | | pack-attrs-conflict.md | Negative test for non-path binding conflicts (e.g., `{ foo = 1; foo.bar = 2; }`) | | pack-attrs-sibling-dynamic.md | Negative test for dynamic attributes in sibling bindings | | flatten-attrs-deep.md | Updated to verify both Pack and Flatten actions offered together | ## Behavior ### Single Pack Action ("Pack dotted path to nested set") Action is offered when: - Cursor is on a dotted attribute path with 2+ segments (e.g., `foo.bar`) - The attribute is inside a non-recursive attribute set - No sibling bindings share the same first segment prefix ### Bulk Pack Action ("Pack all 'X' bindings to nested set") Action is offered when: - Multiple sibling bindings share the same first segment prefix (e.g., `foo.bar` and `foo.baz`) - All sibling binding paths are static (no dynamic interpolation) - No conflicting non-path binding exists for the prefix Transformation combines all matching siblings: ```nix { foo.bar = 1; foo.baz = 2; foo.qux = 3; } → { foo = { bar = 1; baz = 2; qux = 3; }; } ``` ### Explicitly Excluded - **Single-segment paths** (e.g., `foo = 1`): Nothing to pack - **Recursive attribute sets** (`rec { ... }`): Packing would change semantics - **Dynamic attribute paths** (e.g., `foo.${bar}`): Cannot safely transform interpolated paths - **Conflicting non-path bindings** (e.g., `{ foo = 1; foo.bar = 2; }`): Would create invalid Nix code - **Dynamic sibling attributes**: When any sibling has dynamic interpolation, bulk pack is disabled ### Deep Path Handling Deep paths are packed one level at a time: - `a.b.c = 1` → `a = { b.c = 1; }` (first application) - `a = { b.c = 1; }` → `a = { b = { c = 1; }; }` (second application) ### Key Quoting and Escaping The action correctly handles: - **Quoted keys**: Keys requiring quotes (e.g., `"1foo"`) are properly quoted in output - **Special character escaping**: Characters like `"`, `\`, and `$` are correctly escaped ## Test Plan - ✅ **All CI checks passing** - **16 test files** covering positive and negative cases - **Positive tests** verify correct transformation output for: - Basic single pack - Deep paths (multi-level) - Quoted attribute names - Multiline formatting - Various value types (empty sets, let expressions, nested sets) - Bulk pack with multiple siblings - Bulk pack with special characters in keys - Non-conflicting sibling scenarios (inherit, different prefixes) - **Negative tests** verify action is NOT offered in excluded scenarios: - Single-segment paths - Recursive attribute sets - Dynamic interpolation - Conflicting non-path bindings - Dynamic sibling attributes <img width="876" height="404" alt="CleanShot 2026-01-05 at 22 59 36@2x" src="https://github.com/user-attachments/assets/b32ba748-9ff6-4d40-95d1-8a51e7e82bd3" /> <img width="984" height="412" alt="CleanShot 2026-01-06 at 03 05 10@2x" src="https://github.com/user-attachments/assets/bb69bdc7-9d1f-40b1-8b21-a3ad125c91f2" /> ## Related - Part of #466 - Inverse of #757 (flatten nested attribute set) - Draft PR: #755 (this implements Split 3)

takeokunn added 2 commits January 4, 2026 20:19

test: add tests for flatten nested attribute set code action

4263266

- Add tests for flattening simple, deep, and multi-level attrsets - Add negative tests for dynamic, empty, inherit, and rec attrsets - Verify correct code action offering and ordering in each scenario

takeokunn requested a review from inclyc as a code owner January 4, 2026 11:24

chore(code-action): update CodeAction.cpp without code changes

e7e5a5e

takeokunn mentioned this pull request Jan 4, 2026

[DRAFT] feat(code-action): add refactoring and quickfix actions for Nix code #755

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3 tasks

inclyc added nixd:controller enhancement New feature or request labels Jan 4, 2026

inclyc reviewed Jan 4, 2026

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takeokunn added 4 commits January 4, 2026 22:53

test: use CHECK-NOT for flatten-attrs-dynamic.md

f0223f6

Verify the absence of flatten action using CHECK-NOT directive instead of testing quote action from another PR.

test: use CHECK-NOT for flatten-attrs-empty.md

d7c5141

Verify the absence of flatten action using CHECK-NOT directive instead of testing quote action from another PR.

test: use CHECK-NOT for flatten-attrs-inherit.md

aedf514

Verify the absence of flatten action using CHECK-NOT directive instead of testing quote action from another PR.

test: simplify flatten-attrs-multi.md test

158ea12

- Remove quote action tests (belongs to different PR) - Use CHECK: instead of CHECK-NEXT: to skip intermediate sections - Focus only on testing flatten action functionality

takeokunn requested a review from inclyc January 4, 2026 14:01

inclyc approved these changes Jan 4, 2026

View reviewed changes

takeokunn merged commit 30d15dc into main Jan 4, 2026
19 checks passed

takeokunn deleted the feature/add-code-action-2 branch January 4, 2026 15:07

takeokunn mentioned this pull request Jan 5, 2026

feat(code-action): add pack dotted path to nested set refactor action #758

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feat(code-action): add flatten nested attribute set refactor action#757

feat(code-action): add flatten nested attribute set refactor action#757
takeokunn merged 7 commits into
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takeokunn commented Jan 4, 2026

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takeokunn commented Jan 4, 2026

Summary

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Behavior

Explicitly excluded:

Test Plan

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takeokunn commented Jan 4, 2026

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