flag useless nested template literals

Author: kirkwaiblinger

packages/eslint-plugin/src/rules/no-useless-template-literals.ts

@@ -110,11 +110,12 @@ export default createRule<[], MessageId>({
         }
 
         const fixableExpressions = node.expressions.filter(
-          (expression): expression is TSESTree.Literal | TSESTree.Identifier =>
+          expression =>
             isLiteral(expression) ||
             isUndefinedIdentifier(expression) ||
             isInfinityIdentifier(expression) ||
-            isNaNIdentifier(expression),
+            isNaNIdentifier(expression) ||
+            expression.type === AST_NODE_TYPES.TemplateLiteral,
         );
 
         fixableExpressions.forEach(expression => {
@@ -145,6 +146,19 @@ export default createRule<[], MessageId>({
                 const escapedValue = stringValue.replace(/([`$\\])/g, '\\$1');
 
                 fixes.push(fixer.replaceText(expression, escapedValue));
+              } else if (expression.type === AST_NODE_TYPES.TemplateLiteral) {
+                // Note that some template literals get handled in the previous branch too.
+                // Remove the beginning and trailing backtick characters.
+                fixes.push(
+                  fixer.removeRange([
+                    expression.range[0],
+                    expression.range[0] + 1,
+                  ]),
+                  fixer.removeRange([
+                    expression.range[1] - 1,
+                    expression.range[1],
+                  ]),
+                );
               }
 
               return fixes;

packages/eslint-plugin/tests/rules/no-useless-template-literals.test.ts

@@ -131,6 +131,10 @@ ruleTester.run('no-useless-template-literals', rule, {
     noFormat`
       \`with windows \r new line\`;
     `,
+
+    `
+\`not a useless \${String.raw\`nested interpolation \${a}\`}\`;
+    `,
   ],
 
   invalid: [
@@ -555,5 +559,67 @@ ruleTester.run('no-useless-template-literals', rule, {
         },
       ],
     },
+
+    {
+      code: "`use${'less'}`;",
+      output: '`useless`;',
+      errors: [
+        {
+          messageId: 'noUselessTemplateLiteral',
+          line: 1,
+        },
+      ],
+    },
+
+    {
+      code: `
+declare const nested: string, interpolation: string;
+\`use\${\`less\${nested}\${interpolation}\`}\`;
+      `,
+      output: `
+declare const nested: string, interpolation: string;
+\`useless\${nested}\${interpolation}\`;
+      `,
+      errors: [
+        {
+          messageId: 'noUselessTemplateLiteral',
+        },
+      ],
+    },
+
+    {
+      code: noFormat`
+\`u\${
+  // hopefully this comment is not needed.
+  'se'
+
+}\${
+  \`le\${  \`ss\`  }\`
+}\`;
+      `,
+      output: `
+\`use\${
+  \`less\`
+}\`;
+      `,
+      errors: [
+        {
+          messageId: 'noUselessTemplateLiteral',
+          line: 4,
+        },
+        {
+          messageId: 'noUselessTemplateLiteral',
+          line: 7,
+          column: 3,
+          endLine: 7,
+        },
+        {
+          messageId: 'noUselessTemplateLiteral',
+          line: 7,
+          column: 10,
+          endLine: 7,
+        },
+      ],
+    },
   ],
 });