Use composer classmap where available to remove need for reflection of vendor classes

src/Psalm/Checker/ProjectChecker.php

@@ -242,6 +242,11 @@ class ProjectChecker
      */
     public $register_global_functions = false;
 
+    /**
+     * @var ?array<string, string>
+     */
+    private $composer_classmap;
+
     const TYPE_CONSOLE = 'console';
     const TYPE_JSON = 'json';
     const TYPE_EMACS = 'emacs';
@@ -1408,7 +1413,6 @@ class ProjectChecker
      * @param  string $fq_class_name
      *
      * @return bool
-     * @psalm-suppress MixedMethodCall due to Reflection class weirdness
      */
     public function fileExistsForClassLike($fq_class_name)
     {
@@ -1422,6 +1426,24 @@ class ProjectChecker
             throw new \InvalidArgumentException('Why are you asking about a builtin class?');
         }
 
+        if (!$this->config) {
+            throw new \UnexpectedValueException('Config should be set here');
+        }
+
+        if ($this->composer_classmap === null) {
+            $this->composer_classmap = $this->config->getComposerClassMap();
+        }
+
+        if (isset($this->composer_classmap[$fq_class_name_lc])) {
+            if (file_exists($this->composer_classmap[$fq_class_name_lc])) {
+                $this->existing_classlikes_lc[$fq_class_name_lc] = true;
+                $this->existing_classlikes[$fq_class_name] = true;
+                $this->classlike_files[$fq_class_name_lc] = $this->composer_classmap[$fq_class_name_lc];
+
+                return true;
+            }
+        }
+
         $old_level = error_reporting();
 
         if (!$this->debug_output) {
@@ -1440,6 +1462,7 @@ class ProjectChecker
 
         error_reporting($old_level);
 
+        /** @psalm-suppress MixedMethodCall due to Reflection class weirdness */
         $file_path = (string)$reflected_class->getFileName();
 
         // if the file was autoloaded but exists in evaled code only, return false

src/Psalm/Config.php

@@ -713,4 +713,45 @@ class Config
             }
         }
     }
+
+    /**
+     * @return array<string, string>
+     */
+    public function getComposerClassMap()
+    {
+        $vendor_dir = $this->base_dir . 'vendor'; // this should ideally not be hardcoded
+
+        $autoload_files_classmap =
+            $vendor_dir . DIRECTORY_SEPARATOR . 'composer' . DIRECTORY_SEPARATOR . 'autoload_classmap.php';
+
+        if (!file_exists($autoload_files_classmap)) {
+            return [];
+        }
+
+        /**
+         * @psalm-suppress MixedAssignment
+         * @psalm-suppress UnresolvableInclude
+         */
+        $class_map = include_once $autoload_files_classmap;
+
+        if (is_array($class_map)) {
+            $composer_classmap = array_change_key_case($class_map);
+
+            $composer_classmap = array_filter(
+                $composer_classmap,
+                /**
+                 * @param string $file_path
+                 *
+                 * @return bool
+                 */
+                function ($file_path) use ($vendor_dir) {
+                    return strpos($file_path, $vendor_dir) === 0;
+                }
+            );
+        } else {
+            $composer_classmap = [];
+        }
+
+        return $composer_classmap;
+    }
 }