From 51bfb3666b0059782f4ae815d6af9ae199e2eb4b Mon Sep 17 00:00:00 2001
From: Brown <github@muglug.com>
Date: Tue, 25 Aug 2020 11:24:57 -0400
Subject: [PATCH] Fix #4052 - foreach over an iterable is impure

---
 .../Statements/Block/ForeachAnalyzer.php      | 25 +++++++++++++++++++
 tests/PureAnnotationTest.php                  | 19 ++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/src/Psalm/Internal/Analyzer/Statements/Block/ForeachAnalyzer.php b/src/Psalm/Internal/Analyzer/Statements/Block/ForeachAnalyzer.php
index 662085d99..62544c7c7 100644
--- a/src/Psalm/Internal/Analyzer/Statements/Block/ForeachAnalyzer.php
+++ b/src/Psalm/Internal/Analyzer/Statements/Block/ForeachAnalyzer.php
@@ -16,6 +16,7 @@ use Psalm\Internal\FileManipulation\FileManipulationBuffer;
 use Psalm\CodeLocation;
 use Psalm\Context;
 use Psalm\Exception\DocblockParseException;
+use Psalm\Issue\ImpureMethodCall;
 use Psalm\Issue\InvalidDocblock;
 use Psalm\Issue\InvalidIterator;
 use Psalm\Issue\NullIterator;
@@ -563,6 +564,30 @@ class ForeachAnalyzer
                 }
 
                 $has_valid_iterator = true;
+
+                if (!$context->pure) {
+                    $project_analyzer = $statements_analyzer->getProjectAnalyzer();
+
+                    if ($codebase->alter_code
+                        && (isset($project_analyzer->getIssuesToFix()['MissingPureAnnotation'])
+                            || isset($project_analyzer->getIssuesToFix()['MissingImmutableAnnotation']))
+                        && $statements_analyzer->getSource()
+                            instanceof \Psalm\Internal\Analyzer\FunctionLikeAnalyzer
+                    ) {
+                        $statements_analyzer->getSource()->inferred_has_mutation = true;
+                        $statements_analyzer->getSource()->inferred_impure = true;
+                    }
+                } else {
+                    if (IssueBuffer::accepts(
+                        new ImpureMethodCall(
+                            'Cannot call a possibly-mutating Traversable::getIterator from a pure context',
+                            new CodeLocation($statements_analyzer, $stmt)
+                        ),
+                        $statements_analyzer->getSuppressedIssues()
+                    )) {
+                        // fall through
+                    }
+                }
             } elseif ($iterator_atomic_type instanceof Type\Atomic\TNamedObject) {
                 if ($iterator_atomic_type->value !== 'Traversable' &&
                     $iterator_atomic_type->value !== $statements_analyzer->getClassName()
diff --git a/tests/PureAnnotationTest.php b/tests/PureAnnotationTest.php
index 7c1c82ccc..048b556c0 100644
--- a/tests/PureAnnotationTest.php
+++ b/tests/PureAnnotationTest.php
@@ -732,6 +732,25 @@ class PureAnnotationTest extends TestCase
                     }',
                 'error_message' => 'ImpureVariable',
             ],
+            'iterableIsNotPure' => [
+                '<?php
+                    namespace Test;
+
+                    /**
+                     * @param iterable<string> $pieces
+                     *
+                     * @psalm-pure
+                     */
+                    function foo(iterable $pieces): string
+                    {
+                        foreach ($pieces as $piece) {
+                            return $piece;
+                        }
+
+                        return "jello";
+                    }',
+                'error_message' => 'ImpureMethodCall',
+            ],
         ];
     }
 }