fix(eslint-plugin): [no-base-to-string] handle intersection types

packages/eslint-plugin/src/rules/no-base-to-string.ts

@@ -112,6 +112,24 @@ export default util.createRule<Options, MessageIds>({
         return Usefulness.Always;
       }
 
+      if (type.isIntersection()) {
+        let someSubtypeUseful = false;
+
+        for (const subType of type.types) {
+          const subtypeUsefulness = collectToStringCertainty(subType);
+
+          if (subtypeUsefulness === Usefulness.Always) {
+            return Usefulness.Always;
+          }
+
+          if (subtypeUsefulness !== Usefulness.Never) {
+            someSubtypeUseful = true;
+          }
+        }
+
+        return someSubtypeUseful ? Usefulness.Sometimes : Usefulness.Never;
+      }
+
       if (!type.isUnion()) {
         return Usefulness.Never;
       }

packages/eslint-plugin/tests/rules/no-base-to-string.test.ts

@@ -107,6 +107,12 @@ tag\`\${{}}\`;
       function tag() {}
       tag\`\${{}}\`;
     `,
+    `
+      interface Brand {}
+      function test(v: string & Brand): string {
+        return v + '';
+      }
+    `,
   ],
   invalid: [
     {
@@ -217,5 +223,23 @@ tag\`\${{}}\`;
         },
       ],
     },
+    {
+      code: `
+        interface A {}
+        interface B {}
+        function test(intersection: A & B): string {
+          return intersection + '';
+        }
+      `,
+      errors: [
+        {
+          data: {
+            certainty: 'will',
+            name: 'intersection',
+          },
+          messageId: 'baseToString',
+        },
+      ],
+    },
   ],
 });