From c7154bf71cdceab97133898ac3347d2e6119eb3c Mon Sep 17 00:00:00 2001
From: James Garbutt <43081j@users.noreply.github.com>
Date: Fri, 3 Jan 2025 18:40:58 +0000
Subject: [PATCH] chore(eslint-plugin): use `getConstraintInfo` in
 no-unnecessary-template-expression (#10578)

Switches the `no-unnecessary-template-expression` rule to use
`getConstraintInfo` internally.

Related #10569
---
 .../no-unnecessary-template-expression.ts     | 22 +++++++++++++------
 ...no-unnecessary-template-expression.test.ts |  5 +++++
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-template-expression.ts b/packages/eslint-plugin/src/rules/no-unnecessary-template-expression.ts
index 90ad42fb0169..8556c51191dc 100644
--- a/packages/eslint-plugin/src/rules/no-unnecessary-template-expression.ts
+++ b/packages/eslint-plugin/src/rules/no-unnecessary-template-expression.ts
@@ -5,7 +5,7 @@ import * as ts from 'typescript';
 
 import {
   createRule,
-  getConstrainedTypeAtLocation,
+  getConstraintInfo,
   getMovedNodeCode,
   getParserServices,
   isTypeFlagSet,
@@ -51,21 +51,29 @@ export default createRule<[], MessageId>({
     function isUnderlyingTypeString(
       expression: TSESTree.Expression,
     ): expression is TSESTree.Identifier | TSESTree.StringLiteral {
-      const type = getConstrainedTypeAtLocation(services, expression);
+      const checker = services.program.getTypeChecker();
+      const { constraintType } = getConstraintInfo(
+        checker,
+        services.getTypeAtLocation(expression),
+      );
+
+      if (constraintType == null) {
+        return false;
+      }
 
       const isString = (t: ts.Type): boolean => {
         return isTypeFlagSet(t, ts.TypeFlags.StringLike);
       };
 
-      if (type.isUnion()) {
-        return type.types.every(isString);
+      if (constraintType.isUnion()) {
+        return constraintType.types.every(isString);
       }
 
-      if (type.isIntersection()) {
-        return type.types.some(isString);
+      if (constraintType.isIntersection()) {
+        return constraintType.types.some(isString);
       }
 
-      return isString(type);
+      return isString(constraintType);
     }
 
     function isLiteral(
diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-template-expression.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-template-expression.test.ts
index 6043b2b8b50d..eb87d7f3755d 100644
--- a/packages/eslint-plugin/tests/rules/no-unnecessary-template-expression.test.ts
+++ b/packages/eslint-plugin/tests/rules/no-unnecessary-template-expression.test.ts
@@ -1142,6 +1142,11 @@ this code has trailing whitespace: \${'    '}
   // intentional comment after
 }\`;
     `,
+    `
+      function getTpl<T>(input: T) {
+        return \`\${input}\`;
+      }
+    `,
   ],
 
   invalid: [