Right now a node's .parent property is loosely typed as TESTree.Node. This is pretty sucky as it means that users need to either add unnecessary logic or explicit casts to refine types in some cases.

There are a number of nodes wherein we know exactly what the parent node will always be due to the defined structure of the AST.
For example, we know that a VariableDeclarator will always have a VariableDeclaration parent.

We should define some of these simpler relationships in our types to improve the experience of consuming the AST types.

Some cases we can define:

• AccessorProperty has parent ClassBody (feat(ast-spec): add parent property to AccessorProperty node types #9487)
• CatchClause has parent TryStatement
• ClassBody has parent ClassDeclaration | ClassExpression | TSAbstractClassDeclaration
• ExportSpecifier has parent ExportNamedDeclaration
• ImportAttribute has parent ImportDeclaration | ImportExpression
• ImportDefaultSpecifier has parent ImportDeclaration
• ImportNamespaceSpecifier has parent ImportDeclaration
• ImportSpecifier has parent ExportAllDeclaration | ExportNamedDeclaration | ImportDeclaration
• JSXAttribute has parent JSXOpeningElement
• JSXClosingElement has parent JSXElement
• JSXClosingFragment has parent JSXFragment
• JSXOpeningElement has parent JSXElement
• JSXOpeningFragment has parent JSXFragment
• JSXSpreadAttribute has parent JSXOpeningElement
• MethodDefinition has parent ClassBody
• Property has parent ObjectExpression | ObjectPattern
• PropertyDefinition has parent ClassBody
• SpreadElement has parent ArrayExpression | CallExpression | ObjectExpression
• StaticBlock has parent ClassBody
• SwitchCase has parent SwitchStatement
• TemplateElement has parent TemplateLiteral | TSTemplateLiteralType
• TSAbstractAccessorProperty has parent ClassBody
• TSAbstractMethodDefinition has parent ClassBody
• TSAbstractPropertyDefinition has parent ClassBody
• TSCallSignatureDeclaration has parent TSInterfaceBody | TSTypeLiteral
• TSConstructSignatureDeclaration has parent TSInterfaceBody | TSTypeLiteral
• TSClassImplements has parent ClassDeclaration | ClassExpression
• TSEnumMember has parent TSEnumDeclaration
• TSIndexSignature has parent ClassBody | TSInterfaceBody | TSTypeLiteral
• TSInterfaceBody has parent TSInterfaceDeclaration
• TSInterfaceHeritage has parent TSInterfaceBody
• TSMethodSignature has parent TSInterfaceBody | TSTypeLiteral
• TSModuleBlock has parent TSModuleDeclaration
• TSParameterProperty has parent FunctionLike
• TSPropertySignature has parent TSInterfaceBody | TSTypeLiteral
• TSTypeParameter has parent TSInferType | TSTypeParameterDeclaration | TSMappedType
• VariableDeclarator has parent VariableDeclaration (feat(typescript-estree): restrict variable declarator definite/init combinations #9228)

Note: the implementor should double check that I've written these correctly by comparing them against the AST types.

The import thing to note is that we shouldn't define all of the relationships that exist - just a subset of them that we can easily statically define and maintain. I'd probably put a rule around ~3 parent types being the maximum.