Fix completions for contextually constrained types in JSDoc

[DanielRosenwasser]

Basically we had a missing symbol because we were navigating the "original" syntax tree, and we were not grabbing the reparsed node. Unfortunately, that's not sufficient because not every JSDoc type node will have a corresponding reparsed node - in some cases, JSDoc nodes will never be re-attached to the resulting tree.

The code is resilient to these edge-cases and checks for an actual symbol, but tries to use the name of a syntax node as a fallback.

Fixes #3010.

[Copilot]

Pull request overview

Fixes a crash in the language service when requesting completions for contextual type-argument constraints inside JSDoc object types (nil symbol on a PropertySignature), and adds coverage to prevent regressions.

Changes:

• Update getConstraintOfTypeArgumentProperty to prefer a reparsed (JSDoc-cloned) node’s symbol when available, with a fallback to the property’s declared name.
• Add a new fourslash test that exercises the two reported JSDoc scenarios (with and without an attachable declaration) and verifies string-literal completions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
internal/ls/completions.go	Avoids nil dereference by using the reparsed node’s symbol (or property name text) to look up the contextual property type for constraint-based completions.
internal/fourslash/tests/completionsForContextualConstraintTypeInJsDoc_test.go	Adds regression coverage for contextual-constraint completions in JSDoc object type arguments.

[Copilot]

CompletionsExpectedItemDefaults.EditRange is left as nil here, which will assert that the server returns a nil CompletionItemDefaults.EditRange. For type-literal completions the server typically sets an edit range; this test should set EditRange to Ignored (or assert the exact range) to avoid a hard failure.

Suggested change

	ItemDefaults: &fourslash.CompletionsExpectedItemDefaults{CommitCharacters: &[]string{".", ",", ";"}},
	ItemDefaults: &fourslash.CompletionsExpectedItemDefaults{
	CommitCharacters: &[]string{".", ",", ";"},
	EditRange: fourslash.Ignored,
	},

[DanielRosenwasser]

Hard failure? What?

I do wonder if we need to specify any of these ItemDefaults though.