JSON language features broken. TreeSitter `grammar.json`. no error

[RedCMD]

Trying to open a TreeSitter grammar.json file freezes all JSON language features without error
https://github.com/RedCMD/Lag-Syntax-Highlighter/blob/main/_test/grammar.json

Steps to Reproduce:

1. Create new file
2. Assign JSON
3. Copy-paste code snippet
4. notice once the schema loads, all JSON language features stop working
   Hover, format, intellisense, diagnostics etc

{
	"$schema": "https://tree-sitter.github.io/tree-sitter/assets/schemas/grammar.schema.json",
	"name": "laggy-schema",
	"rules": {
		"json": {
			"type": "REPEAT",
			"content": {
				"type": "REPEAT",
				"content": {
					"type": "REPEAT",
					"content": {
						"type": "REPEAT",
						"content": {
							"type": "REPEAT",
							"content": {
								"type": "REPEAT",
								"content": {
									"type": "REPEAT",
									"content": {
										"type": "REPEAT",
										"content": {
											"type": "REPEAT",
											"content": {
												"type": "REPEAT",
												"content": {
													"type": "REPEAT",
													"content": {
														"type": "REPEAT",
														"content": {
															"type": "REPEAT",
															"content": {
																"type": "REPEAT",
																"content": {
																	"type": "REPEAT",
																	"content": {
																		"type": "REPEAT",
																		"content": {
																			"type": "BLANK"
																		}
																	}
																}
															}
														}
													}
												}
											}
										}
									}
								}
							}
						}
					}
				}
			}
		}
	}
}

Does this issue occur when all extensions are disabled?: Yes

• VS Code Version: 1.102.0 https://insiders.vscode.dev/
• OS Version: Windows 11

[RedCMD]

I should have made this in https://github.com/microsoft/vscode-json-languageservice

@aeschli are you able to transfer it please?

[Mayank-Maurya]

Hi @aeschli , I noticed this issue has been open for a while, and I'd love to help get it resolved. With my hands-on Typescript experience, I'm ready to dive straight in and start working on a PR. If your plate is full right now, would you be open to assigning this to me?

[aeschli]

@Mayank-Maurya If you have to to have a look, that would be great!

[Mayank-Maurya]

Hi @aeschli
I've opened a PR with a patch that resolves this freeze natively in the language service.

What was happening: The VS Code JSON parser contains an internal optimization method (_tryDiscriminatorOptimization) designed to protect against exponential backtracking inside deep anyOf / oneOf blocks. However, it was strictly looking at discriminator schemas that used the

const
keyword. Because the TreeSitter schema designates its node definitions via enum arrays (e.g. type: { enum: ["STRING", "PATTERN"] }), the optimization engine was aborting. This caused the document's validation to evaluate every single structural combination across 18 levels of depth which completely hangs the CPU.

The fix: I've expanded the optimization logic so enum variants are indexed as cleanly as

const
statements. The validation correctly shortcuts to the single proper branch, and resolving the grammar schema now takes just a couple of milliseconds.
#320