Add PossiblyInvalidCast for more refined checks

assets/config_levels/5.xml

@@ -65,6 +65,7 @@
         <PossiblyInvalidArrayAccess errorLevel="info" />
         <PossiblyInvalidArrayAssignment errorLevel="info" />
         <PossiblyInvalidArrayOffset errorLevel="info" />
+        <PossiblyInvalidCast errorLevel="info" />
         <PossiblyInvalidFunctionCall errorLevel="info" />
         <PossiblyInvalidIterator errorLevel="info" />
         <PossiblyInvalidMethodCall errorLevel="info" />

assets/config_levels/6.xml

@@ -65,6 +65,7 @@
         <PossiblyInvalidArrayAccess errorLevel="info" />
         <PossiblyInvalidArrayAssignment errorLevel="info" />
         <PossiblyInvalidArrayOffset errorLevel="info" />
+        <PossiblyInvalidCast errorLevel="info" />
         <PossiblyInvalidFunctionCall errorLevel="info" />
         <PossiblyInvalidIterator errorLevel="info" />
         <PossiblyInvalidMethodCall errorLevel="info" />

assets/config_levels/7.xml

@@ -65,6 +65,7 @@
         <PossiblyInvalidArrayAccess errorLevel="info" />
         <PossiblyInvalidArrayAssignment errorLevel="info" />
         <PossiblyInvalidArrayOffset errorLevel="info" />
+        <PossiblyInvalidCast errorLevel="info" />
         <PossiblyInvalidFunctionCall errorLevel="info" />
         <PossiblyInvalidIterator errorLevel="info" />
         <PossiblyInvalidMethodCall errorLevel="info" />

assets/config_levels/8.xml

@@ -65,6 +65,7 @@
         <PossiblyInvalidArrayAccess errorLevel="info" />
         <PossiblyInvalidArrayAssignment errorLevel="info" />
         <PossiblyInvalidArrayOffset errorLevel="info" />
+        <PossiblyInvalidCast errorLevel="info" />
         <PossiblyInvalidFunctionCall errorLevel="info" />
         <PossiblyInvalidIterator errorLevel="info" />
         <PossiblyInvalidMethodCall errorLevel="info" />

config.xsd

@@ -261,6 +261,7 @@
             <xs:element name="PossiblyInvalidArrayAccess" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="PossiblyInvalidArrayAssignment" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="PossiblyInvalidArrayOffset" type="IssueHandlerType" minOccurs="0" />
+            <xs:element name="PossiblyInvalidCast" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="PossiblyInvalidFunctionCall" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="PossiblyInvalidIterator" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="PossiblyInvalidMethodCall" type="IssueHandlerType" minOccurs="0" />

docs/issues.md

@@ -1464,6 +1464,20 @@ $arr = rand(0, 1) ? 5 : [4, 3, 2, 1];
 $arr[0] = "hello";
 ```
 
+### PossiblyInvalidCast
+
+Emitted when attempting to cast a value that may not be castable
+
+```php
+class A {}
+class B {
+    public function __toString() {
+        return 'hello';
+    }
+}
+$c = (string) (rand(0, 1) ? new A() : new B());
+```
+
 ### PossiblyInvalidArrayOffset
 
 Emitted when it’s possible that the array offset is not applicable to the value you’re trying to access.

src/Psalm/Config.php

@@ -990,7 +990,7 @@ class Config
 
         $fq_class_name = reset($declared_classes);
 
-        if (!$codebase->classExtends(
+        if (!$codebase->classlikes->classExtends(
             $fq_class_name,
             $must_extend
         )

src/Psalm/Internal/Analyzer/Statements/ExpressionAnalyzer.php

@@ -35,6 +35,7 @@ use Psalm\Issue\ForbiddenCode;
 use Psalm\Issue\InvalidCast;
 use Psalm\Issue\InvalidClone;
 use Psalm\Issue\InvalidDocblock;
+use Psalm\Issue\PossiblyInvalidCast;
 use Psalm\Issue\PossiblyUndefinedVariable;
 use Psalm\Issue\UndefinedConstant;
 use Psalm\Issue\UndefinedVariable;
@@ -1473,6 +1474,9 @@ class ExpressionAnalyzer
             return;
         }
 
+        $has_valid_cast = false;
+        $invalid_casts = [];
+
         foreach ($stmt->inferredType->getTypes() as $atomic_type) {
             if (!$atomic_type instanceof TMixed
                 && !$atomic_type instanceof Type\Atomic\TResource
@@ -1487,9 +1491,27 @@ class ExpressionAnalyzer
                 )
                 && !$has_scalar_match
             ) {
+                $invalid_casts[] = $atomic_type->getId();
+            } else {
+                $has_valid_cast = true;
+            }
+        }
+
+        if ($invalid_casts) {
+            if ($has_valid_cast) {
+                if (IssueBuffer::accepts(
+                    new PossiblyInvalidCast(
+                        $invalid_casts[0] . ' cannot be cast to string',
+                        new CodeLocation($statements_analyzer->getSource(), $stmt)
+                    ),
+                    $statements_analyzer->getSuppressedIssues()
+                )) {
+                    // fall through
+                }
+            } else {
                 if (IssueBuffer::accepts(
                     new InvalidCast(
-                        $atomic_type->getId() . ' cannot be cast to string',
+                        $invalid_casts[0] . ' cannot be cast to string',
                         new CodeLocation($statements_analyzer->getSource(), $stmt)
                     ),
                     $statements_analyzer->getSuppressedIssues()

src/Psalm/Issue/PossiblyInvalidCast.php

@@ -0,0 +1,6 @@
+<?php
+namespace Psalm\Issue;
+
+class PossiblyInvalidCast extends CodeIssue
+{
+}

tests/ToStringTest.php

@@ -193,7 +193,7 @@ class ToStringTest extends TestCase
                         $a = [];
                     }
                     $b = (string) $a;',
-                'error_message' => 'InvalidCast',
+                'error_message' => 'PossiblyInvalidCast',
             ],
             'cannotCastInsideString' => [
                 '<?php