Iterated array in foreach body is never empty

psalm-baseline.xml

@@ -379,9 +379,6 @@
     </RedundantCondition>
   </file>
   <file src="src/Psalm/Internal/PhpVisitor/Reflector/FunctionLikeDocblockScanner.php">
-    <PossiblyInvalidArrayOffset>
-      <code>$fixed_type_tokens[$i - 1]</code>
-    </PossiblyInvalidArrayOffset>
     <PossiblyUndefinedArrayOffset>
       <code>$source_param_string</code>
     </PossiblyUndefinedArrayOffset>

psalm.xml.dist

@@ -54,6 +54,7 @@
     </plugins>
 
     <issueHandlers>
+        <Trace errorLevel="error"/>
         <PossiblyNullOperand errorLevel="suppress"/>
 
         <DeprecatedMethod>

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

@@ -21,6 +21,7 @@
 use Psalm\Internal\Analyzer\StatementsAnalyzer;
 use Psalm\Internal\FileManipulation\FileManipulationBuffer;
 use Psalm\Internal\Scope\LoopScope;
+use Psalm\Internal\Type\AssertionReconciler;
 use Psalm\Internal\Type\Comparator\AtomicTypeComparator;
 use Psalm\Internal\Type\TypeExpander;
 use Psalm\Issue\ImpureMethodCall;
@@ -36,6 +37,7 @@
 use Psalm\IssueBuffer;
 use Psalm\Node\Expr\VirtualMethodCall;
 use Psalm\Node\VirtualIdentifier;
+use Psalm\Storage\Assertion;
 use Psalm\Type;
 use Psalm\Type\Atomic;
 use Psalm\Type\Atomic\Scalar;
@@ -268,6 +270,19 @@ public static function analyze(
             $foreach_context->vars_in_scope[$context_var_id] = $context_type;
         }
 
+        if ($var_id && $foreach_context->hasVariable($var_id)) {
+            // refine the type of the array variable we iterate over
+            // if we entered loop body, the array cannot be empty
+            $foreach_context->vars_in_scope[$var_id] = AssertionReconciler::reconcile(
+                new Assertion\NonEmpty(),
+                $foreach_context->vars_in_scope[$var_id],
+                null,
+                $statements_analyzer,
+                true, // inside loop ?
+                $statements_analyzer->getTemplateTypeMap() ?? [],
+            );
+        }
+
         $foreach_context->inside_loop = true;
         $foreach_context->break_types[] = 'loop';
 

src/Psalm/Internal/PhpVisitor/Reflector/FunctionLikeDocblockScanner.php

@@ -489,7 +489,8 @@ private static function getConditionalSanitizedTypeTokens(
 
                         // spaces are allowed before $foo in get(string $foo) magic method
                         // definitions, but we want to remove them in this instance
-                        if (isset($fixed_type_tokens[$i - 1])
+                        if ($i > 0
+                            && isset($fixed_type_tokens[$i - 1])
                             && $fixed_type_tokens[$i - 1][0][0] === ' '
                         ) {
                             unset($fixed_type_tokens[$i - 1]);

tests/Loop/ForeachTest.php

@@ -1159,6 +1159,18 @@ function foo(array $files): void
                         }
                     }',
             ],
+            'arrayIsNotEmptyInForeachLoop' => [
+                'code' => <<<'PHP'
+                    <?php
+                    /** @return non-empty-array */
+                    function f(array $a): array {
+                        foreach ($a as $_) {
+                            return $a;
+                        }
+                        throw new RuntimeException;
+                    }
+                    PHP,
+            ],
         ];
     }
 
@@ -1373,6 +1385,18 @@ function foo(array $a) : void {
                     if ($a) {}',
                 'error_message' => 'RedundantCondition',
             ],
+            'arrayCanBeEmptyOutsideTheLoop' => [
+                'code' => <<<'PHP'
+                    <?php
+                    /** @return non-empty-array */
+                    function f(array $a): array {
+                        foreach ($a as $_) {
+                        }
+                        return $a;
+                    }
+                    PHP,
+                'error_message' => 'LessSpecificReturnStatement',
+            ],
         ];
     }
 }