add hideAllErrorsExceptPassedFiles config option

for files only (not directories, since that wouldn't make practical sense)

src/Psalm/Config.php

@@ -295,6 +295,11 @@ class Config
      */
     public $hide_external_errors = false;
 
+    /**
+     * @var bool
+     */
+    public $hide_all_errors_except_passed_files = false;
+
     /** @var bool */
     public $allow_includes = true;
 
@@ -926,6 +931,7 @@ private static function fromXmlAndPaths(
             'useDocblockPropertyTypes' => 'use_docblock_property_types',
             'throwExceptionOnError' => 'throw_exception',
             'hideExternalErrors' => 'hide_external_errors',
+            'hideAllErrorsExceptPassedFiles' => 'hide_all_errors_except_passed_files',
             'resolveFromConfigFile' => 'resolve_from_config_file',
             'allowFileIncludes' => 'allow_includes',
             'strictBinaryOperands' => 'strict_binary_operands',
@@ -1567,6 +1573,13 @@ public function reportIssueInFile(string $issue_type, string $file_path): bool
 
         $project_analyzer = ProjectAnalyzer::getInstance();
 
+        // if the option is set and at least one file is passed via CLI
+        if ($this->hide_all_errors_except_passed_files
+            && $project_analyzer->check_paths_files
+            && !in_array($file_path, $project_analyzer->check_paths_files, true)) {
+            return false;
+        }
+
         $codebase = $project_analyzer->getCodebase();
 
         if (!$this->hide_external_errors) {

src/Psalm/Internal/Analyzer/ProjectAnalyzer.php

@@ -204,6 +204,11 @@ class ProjectAnalyzer
      */
     public $provide_completion = false;
 
+    /**
+     * @var list<string>
+     */
+    public $check_paths_files = [];
+
     /**
      * @var array<string,string>
      */
@@ -1178,6 +1183,7 @@ public function checkPaths(array $paths_to_check): void
             if (is_dir($path)) {
                 $this->checkDirWithConfig($path, $this->config, true);
             } elseif (is_file($path)) {
+                $this->check_paths_files[] = $path;
                 $this->codebase->addFilesToAnalyze([$path => $path]);
                 $this->config->hide_external_errors = $this->config->isInProjectDirs($path);
             }