1 files changed, 76 insertions, 0 deletions
diff --git a/scripts/linters/src/Linters/NoExceptionDowncast.php b/scripts/linters/src/Linters/NoExceptionDowncast.php
new file mode 100644
index 00000000..8d60712b
--- /dev/null
+++ b/scripts/linters/src/Linters/NoExceptionDowncast.php
@@ -0,0 +1,76 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Shirabe\Lint\Linters;
+
+use Shirabe\Lint\Linter;
+use Shirabe\Lint\Support\FileFinder;
+use Shirabe\Lint\Support\Paths;
+
+/**
+ * A ported exception travels as an `AnyThrowable`, never as itself, so `downcast_ref::<X>()`
+ * against an exception type compiles and always answers `None`. It would also answer only for the
+ * exact class, where PHP's `catch` answers for every subclass too.
+ */
+final class NoExceptionDowncast implements Linter
+{
+    private const DOWNCAST_RE = '/\bdowncast(?:_ref|_mut)?::<\s*(?:[A-Za-z_][A-Za-z0-9_]*\s*::\s*)*([A-Za-z_][A-Za-z0-9_]*)\s*>/';
+
+    private const EXCEPTION_DEFINITION_RE = '/\b(?:impl_php_exception|define_php_exception)!\(\s*(?:@accessors\s+)?\$?([A-Za-z_][A-Za-z0-9_]*)/';
+
+    public function name(): string
+    {
+        return 'no_exception_downcast';
+    }
+
+    public function failureIntro(): string
+    {
+        return "Found `downcast` against a ported PHP exception type.\n"
+            . 'An exception is carried by an `AnyThrowable`, so this never matches; '
+            . 'use `Catch::catch` / `Catch::catch_mut`, which match subclasses too:';
+    }
+
+    public function check(string $rootDir, array $excludes): array
+    {
+        $exceptionTypes = $this->exceptionTypes($rootDir);
+        $errors = [];
+
+        foreach (FileFinder::rustFiles($rootDir) as $path) {
+            $relative = Paths::relativeTo($rootDir, $path);
+            if (in_array($relative, $excludes, true)) {
+                continue;
+            }
+
+            foreach (file($path) as $idx => $line) {
+                if (!preg_match(self::DOWNCAST_RE, $line, $m)) {
+                    continue;
+                }
+                if (!isset($exceptionTypes[$m[1]])) {
+                    continue;
+                }
+
+                $errors[] = "{$relative}:" . ($idx + 1) . ": downcast to `{$m[1]}`";
+            }
+        }
+
+        return $errors;
+    }
+
+    /** @return array<string, true> the type name of every ported exception */
+    private function exceptionTypes(string $rootDir): array
+    {
+        $types = [];
+
+        foreach (FileFinder::rustFiles($rootDir) as $path) {
+            preg_match_all(self::EXCEPTION_DEFINITION_RE, file_get_contents($path), $matches);
+            foreach ($matches[1] as $name) {
+                if ($name !== 'ty') {
+                    $types[$name] = true;
+                }
+            }
+        }
+
+        return $types;
+    }
+}