Example of using a Rust crate in a binary

readme.md

This creates a crate called lib_test in toolkit/mozapps/update/rust and links it into the updater.

Because we're only currently allowing one Rust static library per C++ program (see bug 1310063) it may be best to introduce a level of indirection in case we want to include any other Rust in the updater, e.g. an updater_rust crate that just reexports everything. toolkit/library/rust uses this setup.

The lib_test.h file for inclusion in C++ came out of cbindgen, it seems like we manually run that rather than autogenerating as part of the build, you can find some instructions in another such file at source/gfx/webrender_bindings/webrender_ffi_generated.h

Though... we added cbindgen to the build environment, so we may be able to use it to generate a header as in bug 1478813. But if the interface changes rarely it may not be worth the trouble.

A helpful reference is https://firefox-source-docs.mozilla.org/build/buildsystem/rust.html

rust-lib-test.diff

diff --git a/Cargo.lock b/Cargo.lock
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1146,16 +1146,20 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "lazycell"
 version = "0.6.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
+name = "lib_test"
+version = "0.1.0"
+
+[[package]]
 name = "libc"
 version = "0.2.43"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "libloading"
 version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/Cargo.toml b/Cargo.toml
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,16 +7,17 @@
 members = [
   "js/src",
   "js/rust",
   "js/src/frontend/binsource", # Code generator.
   "testing/geckodriver",
   "toolkit/crashreporter/rust",
   "toolkit/library/gtest/rust",
   "toolkit/library/rust/",
+  "toolkit/mozapps/update/rust",
 ]
 
 # Excluded crates may be built as dependencies, but won't be considered members
 # of the workspace and their dev-dependencies won't be included.
 exclude = [
   # Exclude third-party code vendored into mozilla-central.
   "gfx/webrender",
   "gfx/webrender_api",
diff --git a/toolkit/mozapps/update/moz.build b/toolkit/mozapps/update/moz.build
--- a/toolkit/mozapps/update/moz.build
+++ b/toolkit/mozapps/update/moz.build
@@ -2,16 +2,17 @@
 # vim: set filetype=python:
 # 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/.
 
 XPIDL_MODULE = 'update'
 
 DIRS += [
+    'rust',
     'updater',
 ]
 
 XPIDL_SOURCES += [
     'nsIUpdateService.idl',
 ]
 
 TEST_DIRS += ['tests']
diff --git a/toolkit/mozapps/update/rust/Cargo.toml b/toolkit/mozapps/update/rust/Cargo.toml
new file mode 100644
--- /dev/null
+++ b/toolkit/mozapps/update/rust/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "lib_test"
+version = "0.1.0"
+
+[dependencies]
+
+[lib]
+path = "lib.rs"
+crate-type = ["staticlib"]
diff --git a/toolkit/mozapps/update/rust/lib.rs b/toolkit/mozapps/update/rust/lib.rs
new file mode 100644
--- /dev/null
+++ b/toolkit/mozapps/update/rust/lib.rs
@@ -0,0 +1,4 @@
+#[no_mangle]
+pub extern "C" fn exported_fn() -> u8 {
+  42
+}
diff --git a/toolkit/mozapps/update/rust/lib_test.h b/toolkit/mozapps/update/rust/lib_test.h
new file mode 100644
--- /dev/null
+++ b/toolkit/mozapps/update/rust/lib_test.h
@@ -0,0 +1,8 @@
+#include <cstdint>
+#include <cstdlib>
+
+extern "C" {
+
+uint8_t exported_fn();
+
+} // extern "C"
diff --git a/toolkit/mozapps/update/rust/moz.build b/toolkit/mozapps/update/rust/moz.build
new file mode 100644
--- /dev/null
+++ b/toolkit/mozapps/update/rust/moz.build
@@ -0,0 +1,5 @@
+# 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/.
+
+RustLibrary('lib_test')
diff --git a/toolkit/mozapps/update/updater/updater-common.build b/toolkit/mozapps/update/updater/updater-common.build
--- a/toolkit/mozapps/update/updater/updater-common.build
+++ b/toolkit/mozapps/update/updater/updater-common.build
@@ -44,16 +44,17 @@ if CONFIG['OS_ARCH'] == 'WINNT':
 elif CONFIG['OS_ARCH'] == 'Linux' and CONFIG['MOZ_VERIFY_MAR_SIGNATURE']:
     USE_LIBS += [
         'nss',
         'signmar',
     ]
     OS_LIBS += CONFIG['NSPR_LIBS']
 
 USE_LIBS += [
+    'lib_test',
     'mar',
     'updatecommon',
     'xz-embedded',
 ]
 
 if 'gtk' in CONFIG['MOZ_WIDGET_TOOLKIT']:
     have_progressui = 1
     srcs += [
@@ -87,16 +88,17 @@ SOURCES += sorted(srcs)
 
 DEFINES['NS_NO_XPCOM'] = True
 DisableStlWrapping()
 for var in ('MAR_CHANNEL_ID', 'MOZ_APP_VERSION'):
     DEFINES[var] = '"%s"' % CONFIG[var]
 
 LOCAL_INCLUDES += [
     '/toolkit/mozapps/update/common',
+    '/toolkit/mozapps/update/rust',
     '/xpcom/base', # for nsVersionComparator.cpp
 ]
 
 DELAYLOAD_DLLS += [
     'crypt32.dll',
     'comctl32.dll',
     'userenv.dll',
     'wsock32.dll',
diff --git a/toolkit/mozapps/update/updater/updater.cpp b/toolkit/mozapps/update/updater/updater.cpp
--- a/toolkit/mozapps/update/updater/updater.cpp
+++ b/toolkit/mozapps/update/updater/updater.cpp
@@ -29,16 +29,17 @@
  *  -----------
  *  method   = "remove" | "rmdir"
  */
 #include "bspatch.h"
 #include "progressui.h"
 #include "archivereader.h"
 #include "readstrings.h"
 #include "errors.h"
+#include "lib_test.h"
 
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <stdarg.h>
 
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -2645,16 +2646,20 @@ int LaunchCallbackAndPostProcessApps(int
 
 int NS_main(int argc, NS_tchar **argv)
 {
   // The callback is the remaining arguments starting at callbackIndex.
   // The argument specified by callbackIndex is the callback executable and the
   // argument prior to callbackIndex is the working directory.
   const int callbackIndex = 6;
 
+  if (exported_fn() != 42) {
+    return 1;
+  }
+
 #ifdef XP_MACOSX
   // We want to control file permissions explicitly, or else we could end up
   // corrupting installs for other users on the system. Accordingly, set the
   // umask to 0 for all file creations below and reset it on exit. See Bug 1337007
   UmaskContext umaskContext(0);
 
   bool isElevated =
     strstr(argv[0], "/Library/PrivilegedHelperTools/org.mozilla.updater") != 0;