fix(prefer-readonly-types): Give tuples their own error message.

Author: Rebecca Stevens

src/rules/prefer-readonly-types.ts

@@ -23,6 +23,7 @@ import {
   isTSArrayType,
   isTSIndexSignature,
   isTSParameterProperty,
+  isTSTupleType,
   isTSTypeOperator
 } from "../util/typeguard";
 
@@ -70,6 +71,7 @@ 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."
 } as const;
@@ -105,7 +107,7 @@ function checkArrayOrTupleType(
         ? [
             {
               node,
-              messageId: "array",
+              messageId: isTSTupleType(node) ? "tuple" : "array",
               fix:
                 node.parent && isTSArrayType(node.parent)
                   ? fixer => [

src/util/typeguard.ts

@@ -166,6 +166,12 @@ export function isTSPropertySignature(
   return node.type === AST_NODE_TYPES.TSPropertySignature;
 }
 
+export function isTSTupleType(
+  node: TSESTree.Node
+): node is TSESTree.TSTupleType {
+  return node.type === AST_NODE_TYPES.TSTupleType;
+}
+
 export function isTSTypeAliasDeclaration(
   node: TSESTree.Node
 ): node is TSESTree.TSTypeAliasDeclaration {

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

@@ -517,7 +517,7 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "tuple",
         type: "TSTupleType",
         line: 1,
         column: 21
@@ -534,13 +534,13 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "tuple",
         type: "TSTupleType",
         line: 1,
         column: 21
       },
       {
-        messageId: "array",
+        messageId: "tuple",
         type: "TSTupleType",
         line: 1,
         column: 38
@@ -557,7 +557,7 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "tuple",
         type: "TSTupleType",
         line: 1,
         column: 47
@@ -574,7 +574,7 @@ const invalid: ReadonlyArray<InvalidTestCase> = [
       }`,
     errors: [
       {
-        messageId: "array",
+        messageId: "tuple",
         type: "TSTupleType",
         line: 1,
         column: 21