From a032978a854504de6b3faab5fe98a36eb6435236 Mon Sep 17 00:00:00 2001
From: Matthew Brown <github@muglug.com>
Date: Sun, 8 Sep 2019 11:49:14 -0400
Subject: [PATCH] Use a better check for functional purity

---
 .../Expression/Call/FunctionCallAnalyzer.php  |  7 ++++--
 src/Psalm/Internal/Codebase/Functions.php     | 23 +++++++++++--------
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/src/Psalm/Internal/Analyzer/Statements/Expression/Call/FunctionCallAnalyzer.php b/src/Psalm/Internal/Analyzer/Statements/Expression/Call/FunctionCallAnalyzer.php
index dc2d5e12d..edb5aaa88 100644
--- a/src/Psalm/Internal/Analyzer/Statements/Expression/Call/FunctionCallAnalyzer.php
+++ b/src/Psalm/Internal/Analyzer/Statements/Expression/Call/FunctionCallAnalyzer.php
@@ -619,8 +619,10 @@ class FunctionCallAnalyzer extends \Psalm\Internal\Analyzer\Statements\Expressio
                 || $codebase->find_unused_variables
                 || !$config->remember_property_assignments_after_call)
         ) {
+            $must_use = false;
+
             $callmap_function_pure = $function_id && $in_call_map
-                ? $codebase->functions->isCallMapFunctionPure($codebase, $function_id, $stmt->args)
+                ? $codebase->functions->isCallMapFunctionPure($codebase, $function_id, $stmt->args, $must_use)
                 : null;
 
             if (($function_storage
@@ -643,7 +645,8 @@ class FunctionCallAnalyzer extends \Psalm\Internal\Analyzer\Statements\Expressio
                     $context->removeAllObjectVars();
                 }
             } elseif ($function_id
-                && (($function_storage && $function_storage->pure) || $callmap_function_pure === true)
+                && (($function_storage && $function_storage->pure)
+                    || ($callmap_function_pure === true && $must_use))
                 && $codebase->find_unused_variables
                 && !$context->inside_conditional
                 && !$context->inside_unset
diff --git a/src/Psalm/Internal/Codebase/Functions.php b/src/Psalm/Internal/Codebase/Functions.php
index 883f32869..e2c3564a9 100644
--- a/src/Psalm/Internal/Codebase/Functions.php
+++ b/src/Psalm/Internal/Codebase/Functions.php
@@ -264,8 +264,12 @@ class Functions
     /**
      * @param array<int, \PhpParser\Node\Arg> $args
      */
-    public function isCallMapFunctionPure(Codebase $codebase, string $function_id, array $args) : bool
-    {
+    public function isCallMapFunctionPure(
+        Codebase $codebase,
+        string $function_id,
+        array $args,
+        bool &$must_use
+    ) : bool {
         $impure_functions = [
             // file io
             'chdir', 'chgrp', 'chmod', 'chown', 'chroot', 'closedir', 'copy', 'file_put_contents',
@@ -309,7 +313,7 @@ class Functions
             'shell_exec', 'exec', 'system', 'passthru', 'pcntl_exec',
 
             // well-known functions
-            'libxml_use_internal_errors', 'array_map', 'curl_exec',
+            'libxml_use_internal_errors', 'curl_exec',
             'mt_srand', 'openssl_pkcs7_sign', 'mysqli_select_db', 'preg_replace_callback',
             'mt_rand', 'rand',
 
@@ -346,11 +350,6 @@ class Functions
             return false;
         }
 
-        // $matches is basically the (conditional) output of these functions
-        if ($function_id === 'preg_match' || $function_id === 'preg_match_all') {
-            return true;
-        }
-
         $function_callable = \Psalm\Internal\Codebase\CallMap::getCallableFromCallMapById(
             $codebase,
             $function_id,
@@ -361,10 +360,16 @@ class Functions
             return false;
         }
 
+        $must_use = true;
+
         foreach ($function_callable->params as $i => $param) {
-            if ($param->by_ref && isset($args[$i])) {
+            if ($param->type && $param->type->hasCallableType() && isset($args[$i])) {
                 return false;
             }
+
+            if ($param->by_ref && isset($args[$i])) {
+                $must_use = false;
+            }
         }
 
         return true;