feat(plugin): let a Rust-implemented plugin cross into the worker

PluginManager::getPluginCapability hands the plugin itself to the
capability constructor. Only a PHP-implemented plugin had an entity the
child could receive, so a Rust-implemented one bailed out; it now crosses
as a handle to an R-table entity behind Shirabe\RustPluginStub, or its
Capable flavour, since `$plugin instanceof Capable` is what decides
whether Composer asks a plugin for capabilities at all.

This is what the two capability tests of PluginInstallerTest were waiting
on: the mocked Capable plugin is Rust-side, and one of them asserts the
identity of the plugin read back out of $capability->args.

2 files changed, 106 insertions, 0 deletions

diff --git a/crates/shirabe-php-rpc/php/runtime/Shirabe/RustCapablePluginStub.php b/crates/shirabe-php-rpc/php/runtime/Shirabe/RustCapablePluginStub.php
new file mode 100644
index 00000000..7a7c7eef
--- /dev/null
+++ b/crates/shirabe-php-rpc/php/runtime/Shirabe/RustCapablePluginStub.php
@@ -0,0 +1,17 @@
+<?php
+
+// The Capable flavour of RustPluginStub: `$plugin instanceof Capable` decides whether Composer
+// asks a plugin for capabilities, so the stub class is picked to match what the Rust-side
+// plugin implements.
+
+namespace Shirabe;
+
+use Composer\Plugin\Capable;
+
+class RustCapablePluginStub extends RustPluginStub implements Capable
+{
+    public function getCapabilities()
+    {
+        return \ShirabeRpcRuntime::callRust($this->__rhandle, 'getCapabilities', []);
+    }
+}
diff --git a/crates/shirabe-php-rpc/php/runtime/Shirabe/RustPluginStub.php b/crates/shirabe-php-rpc/php/runtime/Shirabe/RustPluginStub.php
new file mode 100644
index 00000000..a60c889a
--- /dev/null
+++ b/crates/shirabe-php-rpc/php/runtime/Shirabe/RustPluginStub.php
@@ -0,0 +1,89 @@
+<?php
+
+// Proxy stub for a plugin whose implementation lives on the Rust side. It has no counterpart
+// class in Composer: a plugin is normally PHP code running in this process, and only a
+// Rust-implemented one needs a stand-in here (a capability constructor receives the plugin
+// itself as $ctorArgs['plugin']).
+
+namespace Shirabe;
+
+use Composer\Composer;
+use Composer\IO\IOInterface;
+use Composer\Plugin\PluginInterface;
+
+class RustPluginStub implements PluginInterface, \ShirabeRustStub
+{
+    /** @var int */
+    protected $__rhandle;
+    /** @var int */
+    protected $__epoch;
+
+    /**
+     * Binds a stub the registry built for an existing entity. Proxy instantiation bypasses
+     * the constructor, which belongs to plugin code building a new entity instead.
+     */
+    public function __shirabeBind(int $rhandle, int $epoch): void
+    {
+        $this->__rhandle = $rhandle;
+        $this->__epoch = $epoch;
+    }
+
+    public function __destruct()
+    {
+        \ShirabeRustObjectRegistry::release($this->__rhandle);
+    }
+
+    public function __shirabeRustHandleDescriptor(): array
+    {
+        return [
+            '__rhandle' => $this->__rhandle,
+            '__class' => static::class,
+            '__epoch' => $this->__epoch,
+        ];
+    }
+
+    public function __clone()
+    {
+        // PHP has already shallow-copied this stub, so both copies would point at one
+        // entity and release it twice. The Rust side clones the entity instead, applying
+        // whatever __clone semantics the real class defines, and this copy rebinds to the
+        // fresh handle. Entities without clone semantics answer with an explicit error.
+        [$this->__rhandle, $this->__epoch] = \ShirabeRpcRuntime::callRust($this->__rhandle, '__shirabeClone', []);
+        \ShirabeRustObjectRegistry::adopt($this->__rhandle, $this);
+    }
+
+    public function __get($name)
+    {
+        return \ShirabeRpcRuntime::callRust($this->__rhandle, '__get', [$name]);
+    }
+
+    public function __set($name, $value): void
+    {
+        \ShirabeRpcRuntime::callRust($this->__rhandle, '__set', [$name, $value]);
+    }
+
+    public function __isset($name): bool
+    {
+        return \ShirabeRpcRuntime::callRust($this->__rhandle, '__isset', [$name]);
+    }
+
+    public function __unset($name): void
+    {
+        \ShirabeRpcRuntime::callRust($this->__rhandle, '__unset', [$name]);
+    }
+
+    public function activate(Composer $composer, IOInterface $io)
+    {
+        \ShirabeRpcRuntime::callRust($this->__rhandle, 'activate', [$composer, $io]);
+    }
+
+    public function deactivate(Composer $composer, IOInterface $io)
+    {
+        \ShirabeRpcRuntime::callRust($this->__rhandle, 'deactivate', [$composer, $io]);
+    }
+
+    public function uninstall(Composer $composer, IOInterface $io)
+    {
+        \ShirabeRpcRuntime::callRust($this->__rhandle, 'uninstall', [$composer, $io]);
+    }
+}