feat(prefer-readonly-types): Enforce ReadonlySet over Set and ReadonlyMap over Map

Author: Rebecca Stevens

src/rules/prefer-readonly-types.ts

@@ -71,9 +71,10 @@ const defaultOptions: Options = {
 // The possible error messages.
 const errorMessages = {
   array: "Only readonly arrays allowed.",
-  tuple: "Only readonly tuples allowed.",
   implicit: "Implicitly a mutable array. Only readonly arrays allowed.",
-  property: "A readonly modifier is required."
+  property: "A readonly modifier is required.",
+  tuple: "Only readonly tuples allowed.",
+  type: "Only readonly types allowed."
 } as const;
 
 // The meta data for this rule.
@@ -89,6 +90,11 @@ const meta: RuleMetaData<keyof typeof errorMessages> = {
   schema
 };
 
+const mutableToImmutableTypes: ReadonlyMap<string, string> = new Map<
+  string,
+  string
+>([["Array", "ReadonlyArray"], ["Map", "ReadonlyMap"], ["Set", "ReadonlySet"]]);
+
 /**
  * Check if the given ArrayType or TupleType violates this rule.
  */
@@ -129,21 +135,27 @@ function checkTypeReference(
   context: RuleContext<keyof typeof errorMessages, Options>,
   options: Options
 ): RuleResult<keyof typeof errorMessages, Options> {
-  return {
-    context,
-    descriptors:
-      isIdentifier(node.typeName) &&
-      node.typeName.name === "Array" &&
-      (!options.ignoreReturnType || !isInReturnType(node))
-        ? [
-            {
-              node,
-              messageId: "array",
-              fix: fixer => fixer.insertTextBefore(node, "Readonly")
-            }
-          ]
-        : []
-  };
+  if (isIdentifier(node.typeName)) {
+    const immutableType = mutableToImmutableTypes.get(node.typeName.name);
+    return {
+      context,
+      descriptors:
+        immutableType && (!options.ignoreReturnType || !isInReturnType(node))
+          ? [
+              {
+                node,
+                messageId: "type",
+                fix: fixer => fixer.replaceText(node.typeName, immutableType)
+              }
+            ]
+          : []
+    };
+  } else {
+    return {
+      context,
+      descriptors: []
+    };
+  }
 }
 
 /**

tests/rules/prefer-readonly-types.test.ts

@@ -343,7 +343,41 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "type",
+        type: "TSTypeReference",
+        line: 1,
+        column: 23
+      }
+    ]
+  },
+  {
+    code: dedent`
+      function foo(numbers: Set<number>) {
+      }`,
+    optionsSet: [[]],
+    output: dedent`
+      function foo(numbers: ReadonlySet<number>) {
+      }`,
+    errors: [
+      {
+        messageId: "type",
+        type: "TSTypeReference",
+        line: 1,
+        column: 23
+      }
+    ]
+  },
+  {
+    code: dedent`
+      function foo(numbers: Map<number, string>) {
+      }`,
+    optionsSet: [[]],
+    output: dedent`
+      function foo(numbers: ReadonlyMap<number, string>) {
+      }`,
+    errors: [
+      {
+        messageId: "type",
         type: "TSTypeReference",
         line: 1,
         column: 26
@@ -363,7 +397,7 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 2,
         column: 17
@@ -387,7 +421,7 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 3,
         column: 22
@@ -411,13 +445,13 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 1,
         column: 17
       },
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 3,
         column: 19
@@ -441,13 +475,13 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 1,
         column: 17
       },
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 3,
         column: 19
@@ -499,7 +533,7 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       };`,
     errors: [
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 2,
         column: 12
@@ -624,19 +658,19 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 3,
         column: 19
       },
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 7,
         column: 17
       },
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 11,
         column: 19
@@ -650,7 +684,7 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
     output: `type Foo = ReadonlyArray<string>;`,
     errors: [
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 1,
         column: 12
@@ -674,7 +708,7 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 3,
         column: 19
@@ -694,7 +728,7 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 2,
         column: 14
@@ -718,7 +752,7 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 3,
         column: 19
@@ -732,7 +766,7 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
     output: `const foo: ReadonlyArray<string> = [];`,
     errors: [
       {
-        messageId: "array",
+        messageId: "type",
         type: "TSTypeReference",
         line: 1,
         column: 12