fix(eslint-plugin): [restrict-plus-operands] consider template literal types as strings (typescript-eslint#3234)

Josh Goldberg · web-flow · commit ccfd68e36539 · 2021-04-04T21:54:19.000-07:00
diff --git a/packages/eslint-plugin/src/rules/restrict-plus-operands.ts b/packages/eslint-plugin/src/rules/restrict-plus-operands.ts
@@ -57,7 +57,10 @@ export default util.createRule<Options, MessageIds>({
       if (type.isNumberLiteral()) {
         return 'number';
       }
-      if (type.isStringLiteral()) {
+      if (
+        type.isStringLiteral() ||
+        util.isTypeFlagSet(type, ts.TypeFlags.TemplateLiteral)
+      ) {
         return 'string';
       }
       // is BigIntLiteral
diff --git a/packages/eslint-plugin/tests/rules/restrict-plus-operands.test.ts b/packages/eslint-plugin/tests/rules/restrict-plus-operands.test.ts
@@ -110,6 +110,12 @@ const x = a + b;
 declare const a: 'string literal' & string;
 declare const b: string;
 const x = a + b;
+    `,
+    `
+function A(s: string) {
+  return \`a\${s}b\` as const;
+}
+const b = A('') + '!';
     `,
     {
       code: `

Original file line number	Diff line number	Diff line change
`@@ -57,7 +57,10 @@ export default util.createRule<Options, MessageIds>({`
`57`	`57`	`if (type.isNumberLiteral()) {`
`58`	`58`	`return 'number';`
`59`	`59`	`}`
`60`		`- if (type.isStringLiteral()) {`
	`60`	`+ if (`
	`61`	`+ type.isStringLiteral() \|\|`
	`62`	`+ util.isTypeFlagSet(type, ts.TypeFlags.TemplateLiteral)`
	`63`	`+ ) {`
`61`	`64`	`return 'string';`
`62`	`65`	`}`
`63`	`66`	`// is BigIntLiteral`