create a separate issue type

config.xsd

@@ -427,6 +427,7 @@
             <xs:element name="ReferenceReusedFromConfusingScope" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="ReservedWord" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="RiskyCast" type="IssueHandlerType" minOccurs="0" />
+            <xs:element name="RiskyTruthyFalsyComparison" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="StringIncrement" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="TaintedCallable" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="TaintedCookie" type="IssueHandlerType" minOccurs="0" />

docs/running_psalm/error_levels.md

@@ -173,6 +173,7 @@ Level 5 and above allows a more non-verifiable code, and higher levels are even
 - [TooManyArguments](issues/TooManyArguments.md)
 - [TypeDoesNotContainNull](issues/TypeDoesNotContainNull.md)
 - [TypeDoesNotContainType](issues/TypeDoesNotContainType.md)
+- [RiskyTruthyFalsyComparison](issues/RiskyTruthyFalsyComparison.md)
 - [UndefinedMagicMethod](issues/UndefinedMagicMethod.md)
 - [UndefinedMagicPropertyAssignment](issues/UndefinedMagicPropertyAssignment.md)
 - [UndefinedMagicPropertyFetch](issues/UndefinedMagicPropertyFetch.md)

docs/running_psalm/issues.md

@@ -229,6 +229,7 @@
  - [ReferenceReusedFromConfusingScope](issues/ReferenceReusedFromConfusingScope.md)
  - [ReservedWord](issues/ReservedWord.md)
  - [RiskyCast](issues/RiskyCast.md)
+ - [RiskyTruthyFalsyComparison](issues/RiskyTruthyFalsyComparison.md)
  - [StringIncrement](issues/StringIncrement.md)
  - [TaintedCallable](issues/TaintedCallable.md)
  - [TaintedCookie](issues/TaintedCookie.md)

docs/running_psalm/issues/RiskyTruthyFalsyComparison.md

@@ -0,0 +1,29 @@
+# RiskyTruthyFalsyComparison
+
+Emitted when comparing a value with multiple types that can both contain truthy and falsy values.
+
+```php
+<?php
+
+/**
+ * @param array|null $arg
+ * @return void
+ */
+function foo($arg) {
+    if ($arg) {
+        // this is risky, bc the empty array and null case are handled together
+    }
+    
+    if (!$arg) {
+        // this is risky, bc the empty array and null case are handled together  
+    }
+}
+```
+
+## Why this is bad
+
+The truthy/falsy type of one variable is often forgotten and not handled explicitly causing hard to track down errors.
+
+## How to fix
+
+Explicitly validate the variable with strict comparison.

src/Psalm/Internal/Analyzer/Statements/Block/IfConditionalAnalyzer.php

@@ -15,6 +15,7 @@ use Psalm\Internal\Scope\IfScope;
 use Psalm\Issue\DocblockTypeContradiction;
 use Psalm\Issue\RedundantCondition;
 use Psalm\Issue\RedundantConditionGivenDocblockType;
+use Psalm\Issue\RiskyTruthyFalsyComparison;
 use Psalm\Issue\TypeDoesNotContainType;
 use Psalm\IssueBuffer;
 use Psalm\Type\Atomic\TBool;
@@ -388,13 +389,13 @@ final class IfConditionalAnalyzer
                 if ($has_both) {
                     $both_types = $both_types->freeze();
                     IssueBuffer::maybeAdd(
-                        new TypeDoesNotContainType(
+                        new RiskyTruthyFalsyComparison(
                             'Operand of type ' . $type->getId() . ' contains ' .
                             'type' . (count($both_types->getAtomicTypes()) > 1 ? 's' : '') . ' ' .
                             $both_types->getId() . ', which can be falsy and truthy. ' .
                             'This can cause possibly unexpected behavior. Use strict comparison instead.',
                             new CodeLocation($statements_analyzer, $stmt),
-                            $type->getId() . ' truthy-falsy',
+                            $type->getId(),
                         ),
                         $statements_analyzer->getSuppressedIssues(),
                     );

src/Psalm/Internal/Analyzer/Statements/Expression/BooleanNotAnalyzer.php

@@ -7,7 +7,7 @@ use Psalm\CodeLocation;
 use Psalm\Context;
 use Psalm\Internal\Analyzer\Statements\ExpressionAnalyzer;
 use Psalm\Internal\Analyzer\StatementsAnalyzer;
-use Psalm\Issue\TypeDoesNotContainType;
+use Psalm\Issue\RiskyTruthyFalsyComparison;
 use Psalm\IssueBuffer;
 use Psalm\Type;
 use Psalm\Type\Atomic\TBool;
@@ -63,13 +63,13 @@ final class BooleanNotAnalyzer
                 if ($has_both) {
                     $both_types = $both_types->freeze();
                     IssueBuffer::maybeAdd(
-                        new TypeDoesNotContainType(
+                        new RiskyTruthyFalsyComparison(
                             'Operand of type ' . $expr_type->getId() . ' contains ' .
                             'type' . (count($both_types->getAtomicTypes()) > 1 ? 's' : '') . ' ' .
                             $both_types->getId() . ', which can be falsy and truthy. ' .
                             'This can cause possibly unexpected behavior. Use strict comparison instead.',
                             new CodeLocation($statements_analyzer, $stmt),
-                            $expr_type->getId() . ' truthy-falsy',
+                            $expr_type->getId(),
                         ),
                         $statements_analyzer->getSuppressedIssues(),
                     );

src/Psalm/Internal/Analyzer/Statements/Expression/EmptyAnalyzer.php

@@ -8,7 +8,7 @@ use Psalm\Context;
 use Psalm\Internal\Analyzer\StatementsAnalyzer;
 use Psalm\Issue\ForbiddenCode;
 use Psalm\Issue\InvalidArgument;
-use Psalm\Issue\TypeDoesNotContainType;
+use Psalm\Issue\RiskyTruthyFalsyComparison;
 use Psalm\IssueBuffer;
 use Psalm\Type;
 use Psalm\Type\Atomic\TBool;
@@ -82,13 +82,13 @@ final class EmptyAnalyzer
                 if ($has_both) {
                     $both_types = $both_types->freeze();
                     IssueBuffer::maybeAdd(
-                        new TypeDoesNotContainType(
+                        new RiskyTruthyFalsyComparison(
                             'Operand of type ' . $expr_type->getId() . ' contains ' .
                             'type' . (count($both_types->getAtomicTypes()) > 1 ? 's' : '') . ' ' .
                             $both_types->getId() . ', which can be falsy and truthy. ' .
                             'This can cause possibly unexpected behavior. Use strict comparison instead.',
                             new CodeLocation($statements_analyzer, $stmt),
-                            $expr_type->getId() . ' truthy-falsy',
+                            $expr_type->getId(),
                         ),
                         $statements_analyzer->getSuppressedIssues(),
                     );

src/Psalm/Issue/RiskyTruthyFalsyComparison.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace Psalm\Issue;
+
+use Psalm\CodeLocation;
+
+final class RiskyTruthyFalsyComparison extends CodeIssue
+{
+    public const ERROR_LEVEL = 4;
+    public const SHORTCODE = 356;
+
+    public function __construct(string $message, CodeLocation $code_location, ?string $dupe_key)
+    {
+        parent::__construct($message, $code_location);
+        $this->dupe_key = $dupe_key;
+    }
+}

tests/TypeReconciliation/ConditionalTest.php

@@ -3528,7 +3528,7 @@ class ConditionalTest extends TestCase
 						if ($arg) {
 						}
 					}',
-                'error_message' => 'TypeDoesNotContainType',
+                'error_message' => 'RiskyTruthyFalsyComparison',
             ],
             'nonStrictConditionTruthyFalsyNegated' => [
                 'code' => '<?php
@@ -3540,7 +3540,7 @@ class ConditionalTest extends TestCase
 						if (!$arg) {
 						}
 					}',
-                'error_message' => 'TypeDoesNotContainType',
+                'error_message' => 'RiskyTruthyFalsyComparison',
             ],
             'nonStrictConditionTruthyFalsyFuncCall' => [
                 'code' => '<?php
@@ -3558,7 +3558,7 @@ class ConditionalTest extends TestCase
 					 * @return array|null
 					 */
 					function bar($arg) {}',
-                'error_message' => 'TypeDoesNotContainType',
+                'error_message' => 'RiskyTruthyFalsyComparison',
             ],
             'nonStrictConditionTruthyFalsyFuncCallNegated' => [
                 'code' => '<?php
@@ -3576,7 +3576,7 @@ class ConditionalTest extends TestCase
 					 * @return array|null
 					 */
 					function bar($arg) {}',
-                'error_message' => 'TypeDoesNotContainType',
+                'error_message' => 'RiskyTruthyFalsyComparison',
             ],
             'redundantConditionForNonEmptyString' => [
                 'code' => '<?php