fix(eslint-plugin): [unified-signatures] does not differentiate truly private methods (#10806)

* fix: support private methods

* test: add test

* fix: fix lint

* test: update test

* fix: allow same name for private and non-private methods

* fix: update prefix

Author: y-hsgw

packages/eslint-plugin/src/rules/unified-signatures.ts

@@ -620,7 +620,15 @@ function getOverloadInfo(node: OverloadNode): string {
     default: {
       const { key } = node as MethodDefinition;
 
-      return isIdentifier(key) ? key.name : (key as TSESTree.Literal).raw;
+      if (isPrivateIdentifier(key)) {
+        return `private_identifier_${key.name}`;
+      }
+
+      if (isIdentifier(key)) {
+        return `identifier_${key.name}`;
+      }
+
+      return (key as TSESTree.Literal).raw;
     }
   }
 }
@@ -639,6 +647,12 @@ function isIdentifier(node: TSESTree.Node): node is TSESTree.Identifier {
   return node.type === AST_NODE_TYPES.Identifier;
 }
 
+function isPrivateIdentifier(
+  node: TSESTree.Node,
+): node is TSESTree.PrivateIdentifier {
+  return node.type === AST_NODE_TYPES.PrivateIdentifier;
+}
+
 function isGetterOrSetter(
   node:
     | TSESTree.MethodDefinition

packages/eslint-plugin/tests/rules/unified-signatures.test.ts

@@ -29,6 +29,18 @@ class C {
   a(): void;
   a(a: number, b: number): void;
   a(a?: number, b?: number): void {}
+}
+    `,
+    `
+declare class Example {
+  privateMethod(a: number): void;
+  #privateMethod(a: number, b?: string): void;
+}
+    `,
+    `
+declare class Example {
+  #privateMethod1(a: number): void;
+  #privateMethod2(a: number, b?: string): void;
 }
     `,
     // No error for arity difference greater than 1.
@@ -510,6 +522,25 @@ type T = {
         },
       ],
     },
+    {
+      code: `
+declare class Example {
+  #privateMethod(a: number): void;
+  #privateMethod(a: number, b?: string): void;
+}
+      `,
+      errors: [
+        {
+          column: 29,
+          data: {
+            failureStringStart:
+              'These overloads can be combined into one signature',
+          },
+          line: 4,
+          messageId: 'omittingSingleParameter',
+        },
+      ],
+    },
     {
       // Works for constructor.
       code: `