Fix #300 - add PossiblyInvalidPropertyFetch

config.xsd

@@ -160,6 +160,7 @@
             <xs:element name="PossiblyInvalidArrayAccess" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="PossiblyInvalidMethodCall" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="PossiblyInvalidPropertyAssignment" type="IssueHandlerType" minOccurs="0" />
+            <xs:element name="PossiblyInvalidPropertyFetch" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="PossiblyNullArgument" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="PossiblyNullArrayAccess" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="PossiblyNullFunctionCall" type="IssueHandlerType" minOccurs="0" />

src/Psalm/Checker/Statements/Expression/FetchChecker.php

@@ -27,6 +27,7 @@ use Psalm\Issue\NullPropertyFetch;
 use Psalm\Issue\NullReference;
 use Psalm\Issue\ParentNotFound;
 use Psalm\Issue\PossiblyInvalidArrayAccess;
+use Psalm\Issue\PossiblyInvalidPropertyFetch;
 use Psalm\Issue\PossiblyNullArrayAccess;
 use Psalm\Issue\PossiblyNullPropertyFetch;
 use Psalm\Issue\PossiblyNullReference;
@@ -167,25 +168,22 @@ class FetchChecker
             return null;
         }
 
+        $invalid_fetch_types = [];
+        $has_valid_fetch_type = false;
+
         foreach ($stmt_var_type->types as $lhs_type_part) {
             if ($lhs_type_part instanceof TNull) {
                 continue;
             }
 
             if (!$lhs_type_part instanceof TNamedObject && !$lhs_type_part instanceof TObject) {
-                if (IssueBuffer::accepts(
+                $invalid_fetch_types[] = (string)$lhs_type_part;
-                    new InvalidPropertyFetch(
-                        'Cannot fetch property on non-object ' . $stmt_var_id . ' of type ' . $lhs_type_part,
-                        new CodeLocation($statements_checker->getSource(), $stmt)
-                    ),
-                    $statements_checker->getSuppressedIssues()
-                )) {
-                    // fall through
-                }
 
                 continue;
             }
 
+            $has_valid_fetch_type = true;
+
             // stdClass and SimpleXMLElement are special cases where we cannot infer the return types
             // but we don't want to throw an error
             // Hack has a similar issue: https://github.com/facebook/hhvm/issues/5164
@@ -365,6 +363,32 @@ class FetchChecker
             }
         }
 
+        if ($invalid_fetch_types) {
+            $lhs_type_part = $invalid_fetch_types[0];
+
+            if ($has_valid_fetch_type) {
+                if (IssueBuffer::accepts(
+                    new PossiblyInvalidPropertyFetch(
+                        'Cannot fetch property on possible non-object ' . $stmt_var_id . ' of type ' . $lhs_type_part,
+                        new CodeLocation($statements_checker->getSource(), $stmt)
+                    ),
+                    $statements_checker->getSuppressedIssues()
+                )) {
+                    // fall through
+                }
+            } else {
+                if (IssueBuffer::accepts(
+                    new InvalidPropertyFetch(
+                        'Cannot fetch property on non-object ' . $stmt_var_id . ' of type ' . $lhs_type_part,
+                        new CodeLocation($statements_checker->getSource(), $stmt)
+                    ),
+                    $statements_checker->getSuppressedIssues()
+                )) {
+                    // fall through
+                }
+            }
+        }
+
         if ($var_id) {
             $context->vars_in_scope[$var_id] = isset($stmt->inferredType) ? $stmt->inferredType : Type::getMixed();
         }

src/Psalm/Issue/PossiblyInvalidPropertyFetch.php

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

tests/PropertyTypeTest.php

@@ -609,6 +609,12 @@ final class B extends A {}',
                     echo $a->foo;',
                 'error_message' => 'InvalidPropertyFetch',
             ],
+            'possiblyBadFetch' => [
+                '<?php
+                    $a = rand(0, 5) > 3 ? "hello" : new stdClass;
+                    echo $a->foo;',
+                'error_message' => 'PossiblyInvalidPropertyFetch',
+            ],
             'mixedPropertyFetch' => [
                 '<?php
                     class Foo {