Implement Language Plugins

[nzakas]

This issue describes the implementation plan for eslint/rfcs#99, which will take place in several phases:

Phase 1: Implement external changes

• Allow for custom node type keys estools/esquery#139
• External class resolve estools/esquery#140
• Update eslint-scope ScopeManager to expose isNodejsScope() as public method

Phase 2: Implement backward-compatible changes

• Implement SourceCode#getInlineConfig()
• Implement SourceCode#getDisableDirectives()
• Implement SourceCode#traverse()
• Copy context.getAncestors() to SourceCode feat: Move getDeclaredVariables and getAncestors to SourceCode #17059
• Copy context.getDeclaredVariables() to SourceCode feat: Move getDeclaredVariables and getAncestors to SourceCode #17059
• Copy context.getScope() to SourceCode feat: Copy getScope() to SourceCode #17004
• Copy context.markVariableAsUsed() to SourceCode feat: Implement SourceCode#markVariableAsUsed() #17086
• Copy parserServices to SourceCode feat: Move parserServices to SourceCode #17311
• Create context.cwd to replace context.getCwd() feat: add cwd to rule context #17106
• Create context.sourceCode to replace context.getSourceCode() feat: add sourceCode property to the rule context #17107
• Create context.filename to replace context.getFilename() feat: add filename to the rule context #17108
• Create context.physicalFilename to replace context.getPhysicalFilename() feat: add physicalFilename property to the rule context #17111
• Blog post encouraging people to switch to the new APIs

Phase 4: Deprecation of old APIs (v8.0.0)

• Update RuleTester to warn about context.getAncestors()
• Update RuleTester to warn about context.getDeclaredVariables()
• Update RuleTester to warn about context.getScope()
• Update RuleTester to warn about context.parserServices
• Update RuleTester to warn about context.getCwd()
• Update RuleTester to warn about context.getSourceCode()
• Update RuleTester to warn about context.getFilename()
• Update RuleTester to warn about context.getPhysicalFilename()

Phase 5: Removal of old APIs (v9.0.0)

• Remove context.getAncestors()
• Remove context.getDeclaredVariables()
• Remove context.getScope()
• Remove context.markVariableAsUsed()
• Remove context.parserServices

Phase 6: Create JS language object

• Create JS language object with parse() and createSourceCode()
• Update flat config to have language option (also update default config to use JS language object)
• Update Linter to call language object for parsing (fallback to JS language for eslintrc)
• Update Linter to use SourceCode#getInlineConfig()
• Update Linter to use SourceCode#getDisableDirectives()
• Update Linter to use SourceCode#traverse()

Phase 7: Create @eslint/json package

TBD

Phase 8: Create @eslint/markdown package

TBD

Phase 9: Removal of old APIs (v10.0.0)

• Remove context.getCwd()
• Remove context.getSourceCode()
• Remove context.getFilename()
• Remove context.getPhysicalFilename()

[snitin315]

I can also help with phase 2, I can start with Copy context.markVariableAsUsed() to SourceCode. @nzakas Let me know if that's ok.

[nzakas]

@snitin315 markVariableAsUsed() is a bit complicated, so I'd prefer to keep that one. If you could do the next few items (cwd, sourceCode, filename, and physicalFilename) that would be a huge help.

[amareshsm]

@nzakas I can also help with some items (any of CWD, sourceCode, filename, and physicalFilename) if possible. Can you pls give some context?

[nzakas]

@amareshsm if you'd like to take a look at those four, this is the part of the code involved:

eslint/lib/linter/linter.js

Lines 979 to 1000 in 9d1b8fc

	const sharedTraversalContext = Object.freeze(
	Object.assign(
	Object.create(BASE_TRAVERSAL_CONTEXT),
	{
	getAncestors: () => sourceCode.getAncestors(currentNode),
	getDeclaredVariables: node => sourceCode.getDeclaredVariables(node),
	getCwd: () => cwd,
	getFilename: () => filename,
	getPhysicalFilename: () => physicalFilename || filename,
	getScope: () => sourceCode.getScope(currentNode),
	getSourceCode: () => sourceCode,
	markVariableAsUsed: name => markVariableAsUsed(sourceCode, currentNode, languageOptions, name),
	parserOptions: {
	...languageOptions.parserOptions
	},
	parserPath: parserName,
	languageOptions,
	parserServices: sourceCode.parserServices,
	settings
	}
	)
	);

Basically, we want to create properties where there are currently methods, and then update all of the rules to use the properties instead of the methods.

[ollie-iterators]

Phase 1 is finished!!!

[ollie-iterators]

With #17086 merged, Copy context.markVariableAsUsed() to SourceCode should be checked off

[mdjermanovic]

I'll work on parserServices.

[ollie-iterators]

With #17107 merged, Create context.sourceCode to replace context.getSourceCode() should be checked off

[nzakas]

@ollie-iterators it seems like you enjoy tracking our tasks, do you have any interest in becoming more involved with the project?

[nzakas]

I'm working on getInlineConfig next.

Edit: Okay, this is a lot more complicated than I realized initially. This may take a while and require some design changes.

[ollie-iterators]

@ollie-iterators it seems like you enjoy tracking our tasks, do you have any interest in becoming more involved with the project?

I haven't thought about that. I might be interested in that.

[nzakas]

@ollie-iterators cool. If you want to discuss, swing by Discord and we'd be happy to chat.

[mdjermanovic]

• Copy parserServices to SourceCode

I'm working on this now.

parserServices actually already exists on SourceCode, so the task is only to update documentation and tests.