fix #321 - feat: Implement volar-service-json for JSON language support

[fantonangeli]

Closes #321

Description

Implement the JSON language service component for the @openworkflowspec/language-servicei nee package. This service wraps vscode-json-languageservice and provides JSON-specific authoring assistance for Open Workflow documents.

Motivation

Providing robust JSON language support enables developers to author Open Workflow documents with confidence through schema-driven completions and real-time validation

How to test:

Only with this until we don't have the text-editor integration.

pnpm --filter @openworkflowspec/language-service build:prod

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[Copilot]

🟡 Changes recommended

Five moderate issues remain involving language filtering, completion ranges, schema workarounds, and diagnostic coverage.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Implements Volar-based JSON language support for Open Workflow documents.

Changes:

• Adds schema validation, completions, and CodeLens support.
• Integrates Volar JSON service dependencies and exports.
• Adds tests, documentation, and release metadata.

File summaries

File	Summary
pnpm-workspace.yaml	Adds shared dependency catalog entries.
pnpm-lock.yaml	Locks new dependencies.
packages/language-service/vite.config.ts	Externalizes runtime dependencies.
packages/language-service/tests/volar/json/createJsonSchemaLanguageServicePlugin.test.ts	Tests schema completions.
packages/language-service/tests/volar/json/createJsonLanguageServicePlugins.test.ts	Tests plugin composition.
packages/language-service/tests/volar/json/createJsonCompletionsPlugin.test.ts	Tests custom completions.
packages/language-service/tests/volar/json/createJsonCodeLensesPlugin.test.ts	Tests CodeLens behavior.
packages/language-service/tests/testUtils.ts	Adds shared test utilities.
packages/language-service/src/volar/json/schema.ts	Configures schema validation; moderate issues remain regarding schema workarounds and diagnostic coverage (1 and 2 votes).
packages/language-service/src/volar/json/completions.ts	Adds Hello World completion; moderate issues remain regarding language-ID filtering (2 votes) and whitespace edit ranges (1 vote).
packages/language-service/src/volar/json/code-lenses.ts	Adds workflow CodeLens support; a moderate language-ID filtering issue remains (2 votes).
packages/language-service/src/volar/index.ts	Exports JSON plugins.
packages/language-service/src/utils.ts	Adds empty-workflow detection.
packages/language-service/src/samples/hello-world.ts	Defines sample workflow content.
packages/language-service/README.md	Documents the JSON language-service API.
packages/language-service/package.json	Declares package dependencies.
.changeset/json-language-service-completions.md	Records the package release change.

Review details

Files not reviewed (1)

• pnpm-lock.yaml: Generated file

Suppressed comments (2)

packages/language-service/src/volar/json/completions.ts:49

• Because isEmptyWorkflow also returns true for whitespace-only documents, a completion requested after leading whitespace receives a text-edit range at (0, 0) that does not contain the requested position. LSP clients may reject or mishandle such an item; accept the completion position and use a zero-length range at that position (or another valid single-line range containing it).

                textEdit: { range: EMPTY_RANGE, newText: HELLO_WORLD_SAMPLE },

packages/language-service/src/volar/json/schema.ts:31

• Using the SDK schema directly reintroduces validation diagnostics that this repository currently has to strip: specWorkarounds.ts documents that the bundled SDK schema is ahead of the published specification for the URI-template and emit.event.with.source rules, and removes those false errors before they reach users. volar-service-json will report those same schema failures as editor diagnostics, so apply the existing workaround to this diagnostic path or provide a corrected schema before exposing it here.

            schema: workflowSchema,

• Files reviewed: 16/17 changed files
• Comments generated: 3
• Review effort level: Lite

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[fantonangeli]

Suppressed Copilot comments:

Whitespace completion range:
I don't think this is a real issue for this foundation PR. A document containing:
" "
would become :
"{...hello world...} "
after accepting the completion.
Since Hello World is only a temporary demo, I'd keep this out of scope for this PR.

Schema workaround:
This is a known temporary workaround tracked by #267 and currently belongs to the Diagram Editor.
I would avoid Language Service depending on the Diagram Editor or duplicating that logic here.

[Copilot]

🟡 Changes recommended

Schema compatibility and document-scoping issues remain unresolved.

Get a fresh assessment by requesting another Copilot review.

Review details

Files not reviewed (1)

• pnpm-lock.yaml: Generated file

Suppressed comments (1)

packages/language-service/src/volar/json/schema.ts:30

• This association is matched against the document URI, so *.json does not match unsaved/in-memory JSON documents such as untitled: or Monaco's inmemory:// models. In the target editor, schema diagnostics and schema-driven completions will therefore be missing until the workflow is saved; restrict the Volar selector to json and associate the schema with all documents handled by that selector (or explicitly cover the host's unsaved URI patterns), and add an unsaved-document test.

            fileMatch: ["*.json"],

• Files reviewed: 16/17 changed files
• Comments generated: 2
• Review effort level: Lite

[fantonangeli]

Suppressed comments (1)

packages/language-service/src/volar/json/schema.ts:30

* This association is matched against the document URI, so `*.json` does not match unsaved/in-memory JSON documents such as `untitled:` or Monaco's `inmemory://` models. In the target editor, schema diagnostics and schema-driven completions will therefore be missing until the workflow is saved; restrict the Volar selector to `json` and associate the schema with all documents handled by that selector (or explicitly cover the host's unsaved URI patterns), and add an unsaved-document test.

            fileMatch: ["*.json"],

It would be better to create a model, from the Text Editor, with a URI like inmemory://open-workflow/workflow.json and keep fileMatch: ["*.json"], instead of setting a generic fileMatch: ["*"]