From 4a38ab165fc83bd69e6a99839a9e70a819aeb901 Mon Sep 17 00:00:00 2001
From: Matthew Brown <github@muglug.com>
Date: Sat, 31 Aug 2019 10:02:11 -0400
Subject: [PATCH] Fix erroneous marking of external-mutation-free method as
 unused

---
 .../Expression/Call/MethodCallAnalyzer.php    |  3 ++-
 .../Expression/Call/NewAnalyzer.php           |  2 ++
 .../Visitor/CheckTrivialExprVisitor.php       |  2 +-
 tests/UnusedCodeTest.php                      | 22 +++++++++++++++++++
 4 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/Psalm/Internal/Analyzer/Statements/Expression/Call/MethodCallAnalyzer.php b/src/Psalm/Internal/Analyzer/Statements/Expression/Call/MethodCallAnalyzer.php
index eaa5f7a3d47..b9611b18f19 100644
--- a/src/Psalm/Internal/Analyzer/Statements/Expression/Call/MethodCallAnalyzer.php
+++ b/src/Psalm/Internal/Analyzer/Statements/Expression/Call/MethodCallAnalyzer.php
@@ -1250,7 +1250,8 @@ function (PhpParser\Node\Arg $arg) {
                                     // fall through
                                 }
                             } elseif (($method_storage->mutation_free
-                                    || $method_pure_compatible)
+                                    || ($method_storage->external_mutation_free
+                                        && (isset($stmt->var->external_mutation_free) || isset($stmt->var->pure))))
                                 && $codebase->find_unused_variables
                                 && !$context->inside_conditional
                                 && !$context->inside_unset
diff --git a/src/Psalm/Internal/Analyzer/Statements/Expression/Call/NewAnalyzer.php b/src/Psalm/Internal/Analyzer/Statements/Expression/Call/NewAnalyzer.php
index c0aab8d4581..ad742f686a1 100644
--- a/src/Psalm/Internal/Analyzer/Statements/Expression/Call/NewAnalyzer.php
+++ b/src/Psalm/Internal/Analyzer/Statements/Expression/Call/NewAnalyzer.php
@@ -475,6 +475,8 @@ public static function analyze(
                 }
 
                 if ($storage->external_mutation_free) {
+                    /** @psalm-suppress UndefinedPropertyAssignment */
+                    $stmt->external_mutation_free = true;
                     $stmt->inferredType->external_mutation_free = true;
                 }
             }
diff --git a/src/Psalm/Internal/Visitor/CheckTrivialExprVisitor.php b/src/Psalm/Internal/Visitor/CheckTrivialExprVisitor.php
index e009ebff296..c9ce2fc631a 100644
--- a/src/Psalm/Internal/Visitor/CheckTrivialExprVisitor.php
+++ b/src/Psalm/Internal/Visitor/CheckTrivialExprVisitor.php
@@ -46,7 +46,7 @@ private function checkNonTrivialExpr(PhpParser\Node\Expr $node)
                 return false;
             }
 
-            if ($node instanceof PhpParser\Node\Expr\New_ && !empty($node->inferredType->external_mutation_free)) {
+            if ($node instanceof PhpParser\Node\Expr\New_ && isset($node->external_mutation_free)) {
                 return false;
             }
 
diff --git a/tests/UnusedCodeTest.php b/tests/UnusedCodeTest.php
index 7e89b6d8832..9b787cf0661 100644
--- a/tests/UnusedCodeTest.php
+++ b/tests/UnusedCodeTest.php
@@ -584,6 +584,28 @@ function inc(array $arr) : array {
                         return $arr;
                     }'
             ],
+            'pureFunctionUsesMethodBeforeReturning' => [
+                '<?php
+                    /** @psalm-external-mutation-free */
+                    class Counter {
+                        private int $count = 0;
+
+                        public function __construct(int $count) {
+                            $this->count = $count;
+                        }
+
+                        public function increment() : void {
+                            $this->count++;
+                        }
+                    }
+
+                    /** @psalm-pure */
+                    function makesACounter(int $i) : Counter {
+                        $c = new Counter($i);
+                        $c->increment();
+                        return $c;
+                    }',
+            ],
         ];
     }