From 39c992c255ecaa065ba02aa25b9d4b9408d98a0d Mon Sep 17 00:00:00 2001
From: Bruce Weirdan <weirdan@gmail.com>
Date: Tue, 14 Feb 2023 02:25:46 -0400
Subject: [PATCH] Emit issues for calls to `is_a(string, class-string, false)`

Fixes vimeo/psalm#4092
---
 .../Call/NamedFunctionCallHandler.php         | 36 ++++++++++++++
 tests/FunctionCallTest.php                    | 48 +++++++++++++++++++
 2 files changed, 84 insertions(+)

diff --git a/src/Psalm/Internal/Analyzer/Statements/Expression/Call/NamedFunctionCallHandler.php b/src/Psalm/Internal/Analyzer/Statements/Expression/Call/NamedFunctionCallHandler.php
index 79196cc1d..39cf5dd95 100644
--- a/src/Psalm/Internal/Analyzer/Statements/Expression/Call/NamedFunctionCallHandler.php
+++ b/src/Psalm/Internal/Analyzer/Statements/Expression/Call/NamedFunctionCallHandler.php
@@ -514,6 +514,42 @@ class NamedFunctionCallHandler
                 }
             }
         }
+
+        if ($first_arg
+            && $function_id === 'is_a'
+            // assertion reconsiler already emits relevant (but different) issues
+            && !$context->inside_conditional
+        ) {
+            $first_arg_type = $statements_analyzer->node_data->getType($first_arg->value);
+
+            if ($first_arg_type && $first_arg_type->isString()) {
+                $third_arg = $stmt->getArgs()[2] ?? null;
+                if ($third_arg) {
+                    $third_arg_type = $statements_analyzer->node_data->getType($third_arg->value);
+                } else {
+                    $third_arg_type = Type::getFalse();
+                }
+
+                if ($third_arg_type
+                    && $third_arg_type->isSingle()
+                    && $third_arg_type->isFalse()
+                ) {
+                    if ($first_arg_type->from_docblock) {
+                        IssueBuffer::maybeAdd(new RedundantFunctionCallGivenDocblockType(
+                            'Call to is_a always return false when first argument is string '
+                            . 'unless third argument is true',
+                            new CodeLocation($statements_analyzer, $function_name),
+                        ));
+                    } else {
+                        IssueBuffer::maybeAdd(new RedundantFunctionCall(
+                            'Call to is_a always return false when first argument is string '
+                            . 'unless third argument is true',
+                            new CodeLocation($statements_analyzer, $function_name),
+                        ));
+                    }
+                }
+            }
+        }
     }
 
     private static function handleDependentTypeFunction(
diff --git a/tests/FunctionCallTest.php b/tests/FunctionCallTest.php
index 41916337e..6c0a4f8a6 100644
--- a/tests/FunctionCallTest.php
+++ b/tests/FunctionCallTest.php
@@ -2693,6 +2693,54 @@ class FunctionCallTest extends TestCase
                 ',
                 'error_message' => 'InvalidArgument',
             ],
+            'is_a_withAStringAndNoThirdArg' => [
+                'code' => '<?php
+                    is_a("Foo", Exception::class);
+                ',
+                'error_message' => 'RedundantFunctionCall',
+            ],
+            'is_a_withAStringAndFalseThirdArg' => [
+                'code' => '<?php
+                    is_a("Foo", Exception::class, false);
+                ',
+                'error_message' => 'RedundantFunctionCall',
+            ],
+            'is_a_withAUnionOfStringsAndNoThirdArg' => [
+                'code' => '<?php
+                    is_a(rand(0, 1) ? "Foo" : "Bar", Exception::class);
+                ',
+                'error_message' => 'RedundantFunctionCall',
+            ],
+            'is_a_withAUnionOfStringsAndFalseThirdArg' => [
+                'code' => '<?php
+                    is_a(rand(0, 1) ? "Foo" : "Bar", Exception::class, false);
+                ',
+                'error_message' => 'RedundantFunctionCall',
+            ],
+            'is_a_withAClassStringAndNoThirdArg' => [
+                'code' => '<?php
+                    is_a(InvalidArgumentException::class, Exception::class);
+                ',
+                'error_message' => 'RedundantFunctionCall',
+            ],
+            'is_a_withAClassStringAndFalseThirdArg' => [
+                'code' => '<?php
+                    is_a(InvalidArgumentException::class, Exception::class, false);
+                ',
+                'error_message' => 'RedundantFunctionCall',
+            ],
+            'is_a_withAUnionOfClassStringsAndNoThirdArg' => [
+                'code' => '<?php
+                    is_a(rand(0, 1) ? InvalidArgumentException::class : RuntimeException::class, Exception::class);
+                ',
+                'error_message' => 'RedundantFunctionCall',
+            ],
+            'is_a_withAUnionOfClassStringsAndFalseThirdArg' => [
+                'code' => '<?php
+                    is_a(rand(0, 1) ? InvalidArgumentException::class : RuntimeException::class, Exception::class, false);
+                ',
+                'error_message' => 'RedundantFunctionCall',
+            ],
         ];
     }