Bug 1789902 - Part 1: Support accessing XPCOM static components from Rust, r=xpcom-reviewers,barret

This will allow us to replace some of the uses of Services.py with the
non-deprecated static components getters.

Differential Revision: https://phabricator.services.mozilla.com/D156890

docs/writing-rust-code/basics.md

@@ -52,11 +52,12 @@ reflects `nsresult` codes into Rust.
 - [xpcom](https://searchfox.org/mozilla-central/source/xpcom/rust/xpcom/src)
   provides multiple building blocks for a component's implementation.
   - The `RefPtr` type is for managing reference-counted pointers.
-  - XPCOM service getters are generated by
-    [xpcom/build/Services.py](https://searchfox.org/mozilla-central/source/xpcom/build/Services.py)
+  - XPCOM component getters are generated by
+    [xpcom/components/gen_static_components.py](https://searchfox.org/mozilla-central/source/xpcom/components/gen_static_components.py),
     and can be called like this:
     ```
-    let pref_service = xpcom::services::get_PrefService();
+    use xpcom::{interfaces::nsIPrefService, RefPtr};
+    let pref_service: RefPtr<nsIPrefService> = xpcom::components::Preferences::service()?;
     ```
   - There is also a `get_service` function that works like `do_GetService` in
     C++, as an alternative.

xpcom/components/gen_static_components.py

@@ -521,6 +521,57 @@ static inline ::mozilla::xpcom::CreateInstanceHelper Create(nsresult* aRv = null
 
         return res
 
+    # Generates the rust code for the `xpcom::components::<name>` entry
+    # corresponding to this component. This may not be called for modules
+    # without an explicit `name` (in which cases, `self.anonymous` will be
+    # true).
+    def lower_getters_rust(self):
+        assert not self.anonymous
+
+        substs = {
+            "name": self.name,
+            "id": "super::ModuleID::%s" % self.name,
+        }
+
+        res = (
+            """
+#[allow(non_snake_case)]
+pub mod %(name)s {
+    /// Get the singleton service instance for this component.
+    pub fn service<T: crate::XpCom>() -> Result<crate::RefPtr<T>, nserror::nsresult> {
+        let mut ga = crate::GetterAddrefs::<T>::new();
+        let rv = unsafe { super::Gecko_GetServiceByModuleID(%(id)s, &T::IID, ga.void_ptr()) };
+        if rv.failed() {
+            return Err(rv);
+        }
+        ga.refptr().ok_or(nserror::NS_ERROR_NO_INTERFACE)
+    }
+"""
+            % substs
+        )
+
+        if not self.singleton:
+            res += (
+                """
+    /// Create a new instance of this component.
+    pub fn create<T: crate::XpCom>() -> Result<crate::RefPtr<T>, nserror::nsresult> {
+        let mut ga = crate::GetterAddrefs::<T>::new();
+        let rv = unsafe { super::Gecko_CreateInstanceByModuleID(%(id)s, &T::IID, ga.void_ptr()) };
+        if rv.failed() {
+            return Err(rv);
+        }
+        ga.refptr().ok_or(nserror::NS_ERROR_NO_INTERFACE)
+    }
+"""
+                % substs
+            )
+
+        res += """\
+}
+"""
+
+        return res
+
 
 # Returns a quoted string literal representing the given raw string, with
 # certain special characters replaced so that it can be used in a C++-style
@@ -678,6 +729,17 @@ def gen_getters(entries):
     return "".join(entry.lower_getters() for entry in entries if not entry.anonymous)
 
 
+# Generates the rust getter code for each named component entry in the
+# `xpcom::components::` module.
+def gen_getters_rust(entries):
+    entries = list(entries)
+    entries.sort(key=lambda e: e.name)
+
+    return "".join(
+        entry.lower_getters_rust() for entry in entries if not entry.anonymous
+    )
+
+
 def gen_includes(substs, all_headers):
     headers = set()
     absolute_headers = set()
@@ -843,6 +905,8 @@ def gen_substs(manifests):
 
     substs["component_getters"] = gen_getters(cid_phf.entries)
 
+    substs["component_getters_rust"] = gen_getters_rust(cid_phf.entries)
+
     substs["module_cid_table"] = cid_phf.cxx_codegen(
         name="ModuleByCID",
         entry_type="StaticModule",
@@ -964,6 +1028,20 @@ static constexpr size_t kModuleInitCount = %(init_count)d;
 }  // namespace mozilla
 
 #endif
+"""
+            % substs
+        )
+
+    with open_output("components.rs") as fh:
+        fh.write(
+            """\
+/// Unique IDs for each statically-registered module.
+#[repr(u16)]
+pub enum ModuleID {
+%(module_ids)s
+}
+
+%(component_getters_rust)s
 """
             % substs
         )

xpcom/components/moz.build

@@ -43,6 +43,7 @@ if CONFIG["COMPILE_ENVIRONMENT"]:
         "StaticComponentData.h",
         "StaticComponents.cpp",
         "services.json",
+        "components.rs",
         script="gen_static_components.py",
         inputs=["!manifest-lists.json", "StaticComponents.cpp.in"],
     )

xpcom/components/nsComponentManager.cpp

@@ -1557,4 +1557,23 @@ const nsIServiceManager* Gecko_GetServiceManager() {
 const nsIComponentRegistrar* Gecko_GetComponentRegistrar() {
   return nsComponentManagerImpl::gComponentManager;
 }
+
+// FFI-compatible version of `GetServiceHelper::operator()`.
+nsresult Gecko_GetServiceByModuleID(ModuleID aId, const nsIID* aIID,
+                                    void** aResult) {
+  return nsComponentManagerImpl::gComponentManager->GetService(aId, *aIID,
+                                                               aResult);
+}
+
+// FFI-compatible version of `CreateInstanceHelper::operator()`.
+nsresult Gecko_CreateInstanceByModuleID(ModuleID aId, const nsIID* aIID,
+                                        void** aResult) {
+  const auto& entry = gStaticModules[size_t(aId)];
+  if (!entry.Active()) {
+    return NS_ERROR_FACTORY_NOT_REGISTERED;
+  }
+
+  nsresult rv = entry.CreateInstance(*aIID, aResult);
+  return rv;
+}
 }

xpcom/rust/xpcom/src/components.rs

+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! This module contains convenient accessors for static XPCOM components.
+//!
+//! The contents of this file are generated from
+//! `xpcom/components/gen_static_components.py`.
+
+extern "C" {
+    fn Gecko_GetServiceByModuleID(
+        id: ModuleID,
+        iid: &crate::nsIID,
+        result: *mut *mut libc::c_void,
+    ) -> nserror::nsresult;
+    fn Gecko_CreateInstanceByModuleID(
+        id: ModuleID,
+        iid: &crate::nsIID,
+        result: *mut *mut libc::c_void,
+    ) -> nserror::nsresult;
+}
+
+include!(mozbuild::objdir_path!("xpcom/components/components.rs"));

xpcom/rust/xpcom/src/lib.rs

@@ -38,6 +38,9 @@ pub mod interfaces;
 // XPCOM service getters.
 pub mod services;
 
+// XPCOM component getters.
+pub mod components;
+
 // Implementation details of the xpcom_macros crate.
 #[doc(hidden)]
 pub mod reexports;