fix(eslint-plugin): fix no-base-to-string boolean literal check (#1850)

typescript-eslint · Apr 27, 2020 · 2f45e99 · 2f45e99
1 parent ed2bd60
commit 2f45e99
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diff --git a/packages/eslint-plugin/docs/rules/no-base-to-string.md b/packages/eslint-plugin/docs/rules/no-base-to-string.md
@@ -52,6 +52,34 @@ const literalWithToString = {
 `Value: ${literalWithToString}`;
 ```
 
+## Options
+
+```ts
+type Options = {
+  ignoredTypeNames?: string[];
+};
+
+const defaultOptions: Options = {
+  ignoredTypeNames: ['RegExp'],
+};
+```
+
+### `ignoreTypeNames`
+
+A string array of type names to ignore, this is useful for types missing `toString()` (but actually has `toString()`).
+There are some types missing `toString()` in old version TypeScript, like `RegExp`, `URL`, `URLSearchParams` etc.
+
+The following patterns are considered correct with the default options `{ ignoreTypeNames: ["RegExp"] }`:
+
+```ts
+`${/regex/}`;
+'' + /regex/;
+/regex/.toString();
+let value = /regex/;
+value.toString();
+let text = `${value}`;
+```
+
 ## When Not To Use It
 
 If you don't mind `"[object Object]"` in your strings, then you will not need this rule.

diff --git a/packages/eslint-plugin/src/rules/no-base-to-string.ts b/packages/eslint-plugin/src/rules/no-base-to-string.ts
@@ -16,6 +16,7 @@ type Options = [
   {
     /** @deprecated This option is now ignored and treated as always true, it will be removed in 3.0 */
     ignoreTaggedTemplateExpressions?: boolean;
+    ignoredTypeNames?: string[];
   },
 ];
 type MessageIds = 'baseToString';
@@ -42,16 +43,28 @@ export default util.createRule<Options, MessageIds>({
             type: 'boolean',
             default: true,
           },
+          ignoredTypeNames: {
+            type: 'array',
+            items: {
+              type: 'string',
+            },
+          },
         },
         additionalProperties: false,
       },
     ],
     type: 'suggestion',
   },
-  defaultOptions: [{ ignoreTaggedTemplateExpressions: true }],
-  create(context) {
+  defaultOptions: [
+    {
+      ignoreTaggedTemplateExpressions: true,
+      ignoredTypeNames: ['RegExp'],
+    },
+  ],
+  create(context, [option]) {
     const parserServices = util.getParserServices(context);
     const typeChecker = parserServices.program.getTypeChecker();
+    const ignoredTypeNames = option.ignoredTypeNames ?? [];
 
     function checkExpression(node: TSESTree.Expression, type?: ts.Type): void {
       if (node.type === AST_NODE_TYPES.Literal) {
@@ -84,6 +97,15 @@ export default util.createRule<Options, MessageIds>({
         return Usefulness.Always;
       }
 
+      // Patch for old version TypeScript, the Boolean type definition missing toString()
+      if (type.flags & ts.TypeFlags.BooleanLiteral) {
+        return Usefulness.Always;
+      }
+
+      if (ignoredTypeNames.includes(util.getTypeName(typeChecker, type))) {
+        return Usefulness.Always;
+      }
+
       if (
         toString.declarations.every(
           ({ parent }) =>

diff --git a/packages/eslint-plugin/tests/rules/no-base-to-string.test.ts b/packages/eslint-plugin/tests/rules/no-base-to-string.test.ts
@@ -11,39 +11,59 @@ const ruleTester = new RuleTester({
   },
 });
 
+const literalListBasic: string[] = [
+  "''",
+  "'text'",
+  'true',
+  'false',
+  '1',
+  '1n',
+  '[]',
+  '/regex/',
+];
+
+const literalListNeedParen: string[] = [
+  '{}.constructor()',
+  '() => {}',
+  'function() {}',
+];
+
+const literalList = [...literalListBasic, ...literalListNeedParen];
+
+const literalListWrapped = [
+  ...literalListBasic,
+  ...literalListNeedParen.map(i => `(${i})`),
+];
+
 ruleTester.run('no-base-to-string', rule, {
   valid: [
-    "`${''}`;",
-    '`${true}`;',
-    '`${[]}`;',
-    '`${function() {}}`;',
-    "'' + '';",
-    "'' + true;",
-    "'' + [];",
-    'true + true;',
-    "true + '';",
-    'true + [];',
-    '[] + [];',
-    '[] + true;',
-    "[] + '';",
-    '({}.constructor());',
-    "'text'.toString();",
-    'false.toString();',
-    `
-let value = 1;
-value.toString();
-    `,
-    `
-let value = 1n;
-value.toString();
-    `,
+    // template
+    ...literalList.map(i => `\`\${${i}}\`;`),
+
+    // operator + +=
+    ...literalListWrapped
+      .map(l => literalListWrapped.map(r => `${l} + ${r};`))
+      .reduce((pre, cur) => [...pre, ...cur]),
+
+    // toString()
+    ...literalListWrapped.map(i => `${i === '1' ? `(${i})` : i}.toString();`),
+
+    // variable toString() and template
+    ...literalList.map(
+      i => `
+        let value = ${i};
+        value.toString();
+        let text = \`\${value}\`;
+      `,
+    ),
+
     `
 function someFunction() {}
 someFunction.toString();
+let text = \`\${someFunction}\`;
     `,
     'unknownObject.toString();',
     'unknownObject.someOtherMethod();',
-    '(() => {}).toString();',
     `
 class CustomToString {
   toString() {