📄 `prefer-readonly-parameter-types`¶

📊 Analysis Summary¶

Metric	Count
🔧 Functions	2
📦 Imports	9
📑 Type Aliases	2

📚 Table of Contents¶

Default Export
Imports
Functions
Type Aliases

🛠️ File Location:¶

📂 packages/eslint-plugin/src/rules/prefer-readonly-parameter-types.ts

📤 Default Export¶

export default createRule<Options, MessageIds>({ ... })

Property	Value
`name`	'prefer-readonly-parameter-types'
`meta.type`	'suggestion'
`meta.docs.description`	'Require function parameters to be typed as `readonly` to prevent accidental mutation of inputs'
`meta.docs.requiresTypeChecking`	true
`meta.messages.shouldBeReadonly`	'Parameter should be a read only type.'
`meta.schema`	[ { type: 'object', additionalProperties: false, properties: { allow: { ...readonlynessOptionsSchema.properties.allow...
`defaultOptions`	[ { allow: readonlynessOptionsDefaults.allow, checkParameterProperties: true, ignoreInferredTypes: false, treatMethod...

Entry point: create — documented under Functions.

📦 Imports¶

Name	Source
`TSESTree`	`@typescript-eslint/utils`
`AST_NODE_TYPES`	`@typescript-eslint/utils`
`TypeOrValueSpecifier`	`../util`
`createRule`	`../util`
`getParserServices`	`../util`
`isTypeBrandedLiteralLike`	`../util`
`isTypeReadonly`	`../util`
`readonlynessOptionsDefaults`	`../util`
`readonlynessOptionsSchema`	`../util`

Functions¶

`create(context: any, [ { allow, checkParameterProper…: any): { [x: string]: (node: TSESTree.ArrowFunctionExpression | TS…`¶

Parameters:

context any
[ { allow, checkParameterProperties, ignoreInferredTypes, treatMethodsAsReadonly, }, ] any

Returns: { [x: string]: (node: TSESTree.ArrowFunctionExpression | TSESTree.FunctionDeclaration | TSESTree.FunctionExpression | TSESTree.TSCallSignatureDeclaration | TSESTree.TSConstructSignatureDeclaration | TSESTree.TSDeclareFunction | TSESTree.TSEmptyBodyFunctionExpression | TSESTree.TSFunctionType | TSESTree.TSMethodSignature) => void; }

Calls:

getParserServices (from ../util)
services.program.getTypeChecker
services.esTreeNodeToTSNodeMap.get
checker.getTypeFromTypeNode
services.getTypeAtLocation
[ AST_NODE_TYPES.ArrowFunctionExpression, AST_NODE_TYPES.FunctionDeclaration, AST_NODE_TYPES.FunctionExpression, AST_NODE_TYPES.TSCallSignatureDeclaration, AST_NODE_TYPES.TSConstructSignatureDeclaration, AST_NODE_TYPES.TSDeclareFunction, AST_NODE_TYPES.TSEmptyBodyFunctionExpression, AST_NODE_TYPES.TSFunctionType, AST_NODE_TYPES.TSMethodSignature, ].join
getParameterType
isTypeReadonly (from ../util)
isTypeBrandedLiteralLike (from ../util)
context.report

Internal Comments:

// Get type from annotation node to preserve aliasSymbol (x2)

Code

create(
    context,
    [
      {
        allow,
        checkParameterProperties,
        ignoreInferredTypes,
        treatMethodsAsReadonly,
      },
    ],
  ) {
    const services = getParserServices(context);

    function getParameterType(
      actualParam:
        | TSESTree.ArrayPattern
        | TSESTree.AssignmentPattern
        | TSESTree.Identifier
        | TSESTree.ObjectPattern
        | TSESTree.RestElement,
    ): ts.Type {
      if (actualParam.typeAnnotation?.typeAnnotation) {
        // Get type from annotation node to preserve aliasSymbol
        const checker = services.program.getTypeChecker();
        const tsTypeNode = services.esTreeNodeToTSNodeMap.get(
          actualParam.typeAnnotation.typeAnnotation,
        ) as ts.TypeNode;
        return checker.getTypeFromTypeNode(tsTypeNode);
      }
      return services.getTypeAtLocation(actualParam);
    }

    return {
      [[
        AST_NODE_TYPES.ArrowFunctionExpression,
        AST_NODE_TYPES.FunctionDeclaration,
        AST_NODE_TYPES.FunctionExpression,
        AST_NODE_TYPES.TSCallSignatureDeclaration,
        AST_NODE_TYPES.TSConstructSignatureDeclaration,
        AST_NODE_TYPES.TSDeclareFunction,
        AST_NODE_TYPES.TSEmptyBodyFunctionExpression,
        AST_NODE_TYPES.TSFunctionType,
        AST_NODE_TYPES.TSMethodSignature,
      ].join(', ')](
        node:
          | TSESTree.ArrowFunctionExpression
          | TSESTree.FunctionDeclaration
          | TSESTree.FunctionExpression
          | TSESTree.TSCallSignatureDeclaration
          | TSESTree.TSConstructSignatureDeclaration
          | TSESTree.TSDeclareFunction
          | TSESTree.TSEmptyBodyFunctionExpression
          | TSESTree.TSFunctionType
          | TSESTree.TSMethodSignature,
      ): void {
        for (const param of node.params) {
          if (
            !checkParameterProperties &&
            param.type === AST_NODE_TYPES.TSParameterProperty
          ) {
            continue;
          }

          const actualParam =
            param.type === AST_NODE_TYPES.TSParameterProperty
              ? param.parameter
              : param;

          if (ignoreInferredTypes && actualParam.typeAnnotation == null) {
            continue;
          }

          const type = getParameterType(actualParam);
          const isReadOnly = isTypeReadonly(services.program, type, {
            allow,
            treatMethodsAsReadonly: !!treatMethodsAsReadonly,
          });

          if (!isReadOnly && !isTypeBrandedLiteralLike(type)) {
            context.report({
              node: actualParam,
              messageId: 'shouldBeReadonly',
            });
          }
        }
      },
    };
  }

Internal helpers¶

Declared inside another function in this file.

`getParameterType(actualParam: | TSESTree.ArrayPattern | TSESTree.Assi…): ts.Type`¶

Parameters:

actualParam | TSESTree.ArrayPattern | TSESTree.AssignmentPattern | TSESTree.Identifier | TSESTree.ObjectPattern | TSESTree.RestElement

Returns: ts.Type

Calls:

services.program.getTypeChecker
services.esTreeNodeToTSNodeMap.get
checker.getTypeFromTypeNode
services.getTypeAtLocation

Internal Comments:

// Get type from annotation node to preserve aliasSymbol (x2)

Code

function getParameterType(
      actualParam:
        | TSESTree.ArrayPattern
        | TSESTree.AssignmentPattern
        | TSESTree.Identifier
        | TSESTree.ObjectPattern
        | TSESTree.RestElement,
    ): ts.Type {
      if (actualParam.typeAnnotation?.typeAnnotation) {
        // Get type from annotation node to preserve aliasSymbol
        const checker = services.program.getTypeChecker();
        const tsTypeNode = services.esTreeNodeToTSNodeMap.get(
          actualParam.typeAnnotation.typeAnnotation,
        ) as ts.TypeNode;
        return checker.getTypeFromTypeNode(tsTypeNode);
      }
      return services.getTypeAtLocation(actualParam);
    }

Type Aliases¶

`Options`¶

type Options = [
  {
    allow?: TypeOrValueSpecifier[];
    checkParameterProperties?: boolean;
    ignoreInferredTypes?: boolean;
    treatMethodsAsReadonly?: boolean;
  },
];

`MessageIds`¶

type MessageIds = 'shouldBeReadonly';

Generated by Syntax Scribe

📄 prefer-readonly-parameter-types¶