Fix: Support enum discriminators to prevent exponential validation freeze (#284)

[Mayank-Maurya]

Fixes #284 - JSON Language service freezes (CPU 100%) when validating Tree-sitter grammar

Description: This PR resolves a severe performance bottleneck where deeply nested, recursive JSON schemas (such as the Tree-sitter grammar.schema.json) cause the validation thread to freeze due to catastrophic backtracking in array combinations.

Root Cause: The language service employs

_tryDiscriminatorOptimization
to avoid exhaustively testing every anyOf/oneOf branch. However, it previously only mapped properties declared with

const
. Because Tree-sitter's schema differentiates its branches using enum identifiers (e.g. type: { enum: ["TOKEN", "IMMEDIATE_TOKEN"] }), the optimization function aborted. This forced the AST validator to fall back into a full

O(A^N)
combinatorial evaluation.

Changes:

Enhanced Discriminator Extraction: Expanded

_tryDiscriminatorOptimization
in

src/parser/jsonParser.ts
to correctly map schema.enum arrays alongside schema.const.
Updated Completion Tests: Refined outdated assertions in

src/test/completion.test.ts
. Before this fix, the parser failed to discriminate type: "1" properties declared via enum arrays, incorrectly offering autocomplete suggestions from multiple branches. It now accurately isolates exactly the correct branch and only returns relevant completions.
Regression Testing: Added a dedicated regression test to

src/test/parser.test.ts
using an enum-based recursive schema. The parsing test limits out to < 100ms (where without this patch, the same minimal depth takes over 5,000ms entirely bottlenecking Node).

[Mayank-Maurya]

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[aeschli]

@Mayank-Maurya Thanks a lot for the analysis and the fix. Very appreciated!