feat(language-server): clear diagnostic for nested parallel blocks by farhan523 · Pull Request #2985 · likec4/likec4

farhan523 · 2026-05-25T06:05:26Z

Checklist

I've thoroughly read the latest contribution guidelines.
I've rebased my branch onto main before creating this PR.
I've added tests to cover my changes (if applicable).
I've verified pnpm typecheck and pnpm test.
I've added changesets.
My change requires documentation updates. (no — internal grammar/validator change, no public DSL semantics shift)
I've updated the documentation accordingly. (N/A)

Summary

Resolves #988 (originally from @susliko in discussion #816).

Today parallel { parallel { ... } } in a dynamic view produces a cryptic parser error like Expecting token of type --> RightCurly <-- but found --> 'parallel' <--. The grammar simply forbids the nested form structurally, so users get the raw parser error.

This PR:

Loosens the grammar so a DynamicViewParallelSteps can appear as a step inside another DynamicViewParallelSteps. The parser accepts the form now, instead of rejecting it.
Adds a dynamicViewParallelSteps validator that walks steps and emits a clear error — Nested parallel blocks are not allowed — on any nested DynamicViewParallelSteps. The diagnostic is attached to the inner block so the squiggle lines up with the offending parallel/par keyword.

Net behaviour: same outcome (the model is rejected), much better message.

Files

Grammar — like-c4.langium: (steps+=(DynamicViewParallelSteps | DynamicViewStep))*.
Validator — validation/dynamic-view.ts: new dynamicViewParallelSteps check.
Registration — validation/index.ts: wired under the DynamicViewParallelSteps key.
Parser — model/parser/ViewsParser.ts: parseDynamicParallelSteps now filters out nested ParallelSteps before calling parseDynamicStep (the validator has already errored on them; this keeps the c4-model side narrow and avoids a confusing internal type error).

Test plan

New tests in dynamic-view.spec.ts:

A single, non-nested parallel block — no errors.
parallel { parallel { ... } } — reports Nested parallel blocks are not allowed.
par { par { ... } } (the par alias) — same diagnostic.

Local: pnpm test packages/language-server/src/validation/dynamic-view.spec.ts → 12/12 passing, pnpm --filter @likec4/language-server typecheck → clean, pnpm lint:errors-only → 0 errors.

Generated parser artifacts (packages/language-server/src/generated/) are git-ignored, so CI's pnpm generate step will produce the updated parser from the new grammar.

Nested `parallel { parallel { ... } }` in dynamic views previously`produced a cryptic parser error because the grammar rejected the form`outright. The grammar now accepts `DynamicViewParallelSteps` as a step`inside another `DynamicViewParallelSteps`, and a new validator emits`a clear `Nested parallel blocks are not allowed` error on the inner`block. `ViewsParser` filters nested ParallelSteps when building the c4 model`(the validator already errors on them) to keep the parser side narrow. Resolves likec4#988

changeset-bot · 2026-05-25T06:05:33Z

🦋 Changeset detected

Latest commit: e98fbe1

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 22 packages

Name	Type
@likec4/language-server	Patch
@likec4/playground	Patch
@likec4/language-services	Patch
likec4	Patch
@likec4/lsp	Patch
@likec4/mcp	Patch
likec4-vscode	Patch
@likec4/vite-plugin	Patch
@likec4/spa	Patch
@likec4/docs-astro	Patch
@likec4/style-preset	Patch
@likec4/styles	Patch
@likec4/config	Patch
@likec4/core	Patch
@likec4/diagram	Patch
@likec4/generators	Patch
@likec4/layouts	Patch
@likec4/leanix-bridge	Patch
@likec4/log	Patch
@likec4/react	Patch
@likec4/tsconfig	Patch
@likec4/vscode-preview	Patch

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coderabbitai · 2026-05-25T06:12:47Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 544f9654-0131-461f-97c5-9a04e00ea548

📥 Commits

Reviewing files that changed from the base of the PR and between c18fa00 and e98fbe1.

📒 Files selected for processing (6)

.changeset/lsp-nested-parallel-diagnostic.md
packages/language-server/src/like-c4.langium
packages/language-server/src/model/parser/ViewsParser.ts
packages/language-server/src/validation/dynamic-view.spec.ts
packages/language-server/src/validation/dynamic-view.ts
packages/language-server/src/validation/index.ts

📝 Walkthrough

Walkthrough

This PR improves error reporting for nested parallel blocks in LikeC4 dynamic views by loosening the grammar to allow parsing nested structures, adding a validation check that detects and reports them as errors, and adjusting the parser to filter them before processing.

Changes

Nested Parallel Block Detection

Layer / File(s)	Summary
Grammar and validation infrastructure `packages/language-server/src/like-c4.langium`, `packages/language-server/src/validation/dynamic-view.ts`, `packages/language-server/src/validation/index.ts`	`DynamicViewParallelSteps` grammar rule is updated to parse nested parallel blocks alongside steps. New validation check `dynamicViewParallelSteps` detects and reports nested blocks as errors. Validation check is registered in the core registry.
Parser filtering of nested blocks `packages/language-server/src/model/parser/ViewsParser.ts`	`parseDynamicParallelSteps` filters out nested `DynamicViewParallelSteps` blocks before mapping steps, preventing internal parsing errors for structures already flagged by validation.
Tests and documentation `packages/language-server/src/validation/dynamic-view.spec.ts`, `.changeset/lsp-nested-parallel-diagnostic.md`	Test suite covers acceptance of non-nested parallel blocks, rejection of nested blocks with the diagnostic "Nested parallel blocks are not allowed", and rejection via the `par` alias. Changeset documents the patch release.

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: adding a clear diagnostic message for nested parallel blocks in the language server.
Description check	✅ Passed	The description is comprehensive and complete, covering all checklist items, explaining the problem and solution clearly, detailing file changes, and documenting test coverage and verification steps.
Linked Issues check	✅ Passed	The PR fully addresses issue `#988` by implementing the requested feature: providing a clear diagnostic for nested parallel blocks instead of cryptic parser errors.
Out of Scope Changes check	✅ Passed	All changes are directly related to resolving issue `#988`: grammar loosening, validator implementation, parser filtering, test coverage, and validation registration are all in scope.

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davydkov

Great improvement, thank you!

davydkov approved these changes Jun 2, 2026

View reviewed changes

davydkov enabled auto-merge (squash) June 2, 2026 20:39

davydkov merged commit e2ad89e into likec4:main Jun 2, 2026
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likec4-ci Bot mentioned this pull request Jun 2, 2026

release: v1.58.0 #2981

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feat(language-server): clear diagnostic for nested parallel blocks#2985

feat(language-server): clear diagnostic for nested parallel blocks#2985
davydkov merged 1 commit into
likec4:mainfrom
farhan523:feat/lsp-nested-parallel-diagnostic

farhan523 commented May 25, 2026

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farhan523 commented May 25, 2026

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Files

Test plan

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