feat(immutable-data): add option for ignoreNonConstDeclarations to treatParametersAsConst

fix #724

Author: RebeccaStevens

docs/rules/immutable-data.md

@@ -63,7 +63,11 @@ This rule accepts an options object of the following type:
 type Options = {
   ignoreClasses: boolean | "fieldsOnly";
   ignoreImmediateMutation: boolean;
-  ignoreNonConstDeclarations: boolean;
+  ignoreNonConstDeclarations:
+    | boolean
+    | {
+        treatParametersAsConst: boolean;
+      };
   ignoreIdentifierPattern?: string[] | string;
   ignoreAccessorPattern?: string[] | string;
 };
@@ -110,6 +114,10 @@ Note: If a value is referenced by both a `let` and a `const` variable, the `let`
 reference can be modified while the `const` one can't. The may lead to value of
 the `const` variable unexpectedly changing when the `let` one is modified elsewhere.
 
+#### `treatParametersAsConst`
+
+If true, parameters won't be ignored, while other non-const variables will be.
+
 ### `ignoreClasses`
 
 Ignore mutations inside classes.

src/rules/immutable-data.ts

@@ -61,7 +61,11 @@ type Options = [
     IgnoreClassesOption &
     IgnoreIdentifierPatternOption & {
       ignoreImmediateMutation: boolean;
-      ignoreNonConstDeclarations: boolean;
+      ignoreNonConstDeclarations:
+        | boolean
+        | {
+            treatParametersAsConst: boolean;
+          };
     },
 ];
 
@@ -80,7 +84,20 @@ const schema: JSONSchema4[] = [
           type: "boolean",
         },
         ignoreNonConstDeclarations: {
-          type: "boolean",
+          oneOf: [
+            {
+              type: "boolean",
+            },
+            {
+              type: "object",
+              properties: {
+                treatParametersAsConst: {
+                  type: "boolean",
+                },
+              },
+              additionalProperties: false,
+            },
+          ],
         },
       } satisfies JSONSchema4ObjectSchema["properties"],
     ),
@@ -230,11 +247,16 @@ function checkAssignmentExpression(
     };
   }
 
-  if (ignoreNonConstDeclarations) {
+  if (ignoreNonConstDeclarations !== false) {
     const rootIdentifier = findRootIdentifier(node.left.object);
     if (
       rootIdentifier !== undefined &&
-      isDefinedByMutableVariable(rootIdentifier, context)
+      isDefinedByMutableVariable(
+        rootIdentifier,
+        context,
+        ignoreNonConstDeclarations === true ||
+          !ignoreNonConstDeclarations.treatParametersAsConst,
+      )
     ) {
       return {
         context,
@@ -283,11 +305,16 @@ function checkUnaryExpression(
     };
   }
 
-  if (ignoreNonConstDeclarations) {
+  if (ignoreNonConstDeclarations !== false) {
     const rootIdentifier = findRootIdentifier(node.argument.object);
     if (
       rootIdentifier !== undefined &&
-      isDefinedByMutableVariable(rootIdentifier, context)
+      isDefinedByMutableVariable(
+        rootIdentifier,
+        context,
+        ignoreNonConstDeclarations === true ||
+          !ignoreNonConstDeclarations.treatParametersAsConst,
+      )
     ) {
       return {
         context,
@@ -335,11 +362,16 @@ function checkUpdateExpression(
     };
   }
 
-  if (ignoreNonConstDeclarations) {
+  if (ignoreNonConstDeclarations !== false) {
     const rootIdentifier = findRootIdentifier(node.argument.object);
     if (
       rootIdentifier !== undefined &&
-      isDefinedByMutableVariable(rootIdentifier, context)
+      isDefinedByMutableVariable(
+        rootIdentifier,
+        context,
+        ignoreNonConstDeclarations === true ||
+          !ignoreNonConstDeclarations.treatParametersAsConst,
+      )
     ) {
       return {
         context,
@@ -473,18 +505,22 @@ function checkCallExpression(
       !isInChainCallAndFollowsNew(node.callee, context)) &&
     isArrayType(getTypeOfNode(node.callee.object, context))
   ) {
-    if (ignoreNonConstDeclarations) {
-      const rootIdentifier = findRootIdentifier(node.callee.object);
-      if (
-        rootIdentifier === undefined ||
-        !isDefinedByMutableVariable(rootIdentifier, context)
-      ) {
-        return {
-          context,
-          descriptors: [{ node, messageId: "array" }],
-        };
-      }
-    } else {
+    if (ignoreNonConstDeclarations === false) {
+      return {
+        context,
+        descriptors: [{ node, messageId: "array" }],
+      };
+    }
+    const rootIdentifier = findRootIdentifier(node.callee.object);
+    if (
+      rootIdentifier === undefined ||
+      !isDefinedByMutableVariable(
+        rootIdentifier,
+        context,
+        ignoreNonConstDeclarations === true ||
+          !ignoreNonConstDeclarations.treatParametersAsConst,
+      )
+    ) {
       return {
         context,
         descriptors: [{ node, messageId: "array" }],
@@ -507,18 +543,22 @@ function checkCallExpression(
     ) &&
     isObjectConstructorType(getTypeOfNode(node.callee.object, context))
   ) {
-    if (ignoreNonConstDeclarations) {
-      const rootIdentifier = findRootIdentifier(node.callee.object);
-      if (
-        rootIdentifier === undefined ||
-        !isDefinedByMutableVariable(rootIdentifier, context)
-      ) {
-        return {
-          context,
-          descriptors: [{ node, messageId: "object" }],
-        };
-      }
-    } else {
+    if (ignoreNonConstDeclarations === false) {
+      return {
+        context,
+        descriptors: [{ node, messageId: "object" }],
+      };
+    }
+    const rootIdentifier = findRootIdentifier(node.callee.object);
+    if (
+      rootIdentifier === undefined ||
+      !isDefinedByMutableVariable(
+        rootIdentifier,
+        context,
+        ignoreNonConstDeclarations === true ||
+          !ignoreNonConstDeclarations.treatParametersAsConst,
+      )
+    ) {
       return {
         context,
         descriptors: [{ node, messageId: "object" }],

src/utils/tree.ts

@@ -213,6 +213,18 @@ export function isArgument(node: TSESTree.Node): boolean {
   );
 }
 
+/**
+ * Is the given node a parameter?
+ */
+export function isParameter(node: TSESTree.Node): boolean {
+  return (
+    node.parent !== undefined &&
+    isFunctionLike(node.parent) &&
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-argument
+    node.parent.params.includes(node as any)
+  );
+}
+
 /**
  * Is the given node a getter function?
  */
@@ -273,14 +285,27 @@ export function getKeyOfValueInObjectExpression(
  */
 export function isDefinedByMutableVariable<
   Context extends RuleContext<string, BaseOptions>,
->(node: TSESTree.Identifier, context: Context) {
+>(
+  node: TSESTree.Identifier,
+  context: Context,
+  treatParametersAsMutable: boolean,
+): boolean {
   const services = getParserServices(context);
   const symbol = services.getSymbolAtLocation(node);
   const variableDeclaration = symbol?.valueDeclaration;
+
+  if (variableDeclaration === undefined) {
+    return true;
+  }
+  const variableDeclarationNode =
+    services.tsNodeToESTreeNodeMap.get(variableDeclaration);
   if (
-    variableDeclaration === undefined ||
-    !typescript!.isVariableDeclaration(variableDeclaration)
+    variableDeclarationNode !== undefined &&
+    isParameter(variableDeclarationNode)
   ) {
+    return treatParametersAsMutable;
+  }
+  if (!typescript!.isVariableDeclaration(variableDeclaration)) {
     return true;
   }