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

• Publish @eslint/json

Phase 8: Create @eslint/markdown package

• Convert to @eslint/markdown markdown#260

Phase 9: Ecosystem Updates

• Document how to create languages
• Update @types/eslint with language type definitions
• Publish Code Explorer
• Publish blog post announcing Markdown/JSON and Code Explorer

Phase 10: Removal of old APIs (v10.0.0)

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