Devtools device description: improve how Servo is advertised in Firefox's about:debugging (fixes #27528) (#32227)

* Devtools device description: fix the case of the 'platformversion' property

* Devtools device description: expose the properties Firefox expects for the display name and version of the server

When connecting to Servo from Firefox (about:debugging), it will display "Servo (71.0)" instead of "{$name} (${version})".

* Devtools device description: update versions to match those in the UA string

* Devtools device description: expose a property (appbuildid) Firefox expects to compare versions for compatibility (_compareVersionCompatibility function)

* Devtools device description: advertise a current platform version to remove the incompatibility warning in Firefox's about:debugging

* Devtools preference actor: fix retrieving the actual preference by its key

* Devtools preference actor: translate Firefox preference names onto the corresponding Servo preference names

* Devtools device description: downgrade the platform version to prevent a confusing warning in about:debugging if the build ID is newer than that of Firefox (likely)

* Devtools device description: add comments

* Devtools device description: use CARGO_PKG_VERSION for the user-visible version number

components/devtools/Cargo.toml

@@ -10,6 +10,9 @@ publish = false
 name = "devtools"
 path = "lib.rs"
 
+[build-dependencies]
+chrono = "0.4"
+
 [dependencies]
 chrono = "0.4"
 crossbeam-channel = { workspace = true }

components/devtools/actors/device.rs

@@ -17,12 +17,24 @@ struct GetDescriptionReply {
     value: SystemInfo,
 }
 
+// This is only a minimal subset of the properties exposed/expected by Firefox
+// (see https://searchfox.org/mozilla-central/source/devtools/shared/system.js#45)
 #[derive(Serialize)]
 struct SystemInfo {
     apptype: String,
-    platformVersion: String,
+    // Display version
+    version: String,
+    // Build ID (timestamp with format YYYYMMDDhhmmss), used for compatibility checks
+    // (see https://searchfox.org/mozilla-central/source/devtools/client/shared/remote-debugging/version-checker.js#82)
+    appbuildid: String,
+    // Firefox major.minor version number, use for compatibility checks
+    platformversion: String,
+    // Display name
+    brandName: String,
 }
 
+include!(concat!(env!("OUT_DIR"), "/build_id.rs"));
+
 pub struct DeviceActor {
     pub name: String,
 }
@@ -45,7 +57,10 @@ impl Actor for DeviceActor {
                     from: self.name(),
                     value: SystemInfo {
                         apptype: "servo".to_string(),
-                        platformVersion: "71.0".to_string(),
+                        version: env!("CARGO_PKG_VERSION").to_string(),
+                        appbuildid: BUILD_ID.to_string(),
+                        platformversion: "124.0".to_string(),
+                        brandName: "Servo".to_string(),
                     },
                 };
                 let _ = stream.write_json_packet(&msg);

components/devtools/actors/preference.rs

@@ -2,6 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
+use std::collections::HashMap;
 use std::net::TcpStream;
 
 use serde::Serialize;
@@ -32,11 +33,23 @@ impl Actor for PreferenceActor {
         &self,
         _registry: &ActorRegistry,
         msg_type: &str,
-        _msg: &Map<String, Value>,
+        msg: &Map<String, Value>,
         stream: &mut TcpStream,
         _id: StreamId,
     ) -> Result<ActorMessageStatus, ()> {
-        let pref_value = pref_map().get(msg_type);
+        let mut key = msg.get("value").unwrap().as_str().unwrap();
+
+        // Mapping to translate a Firefox preference name onto the corresponding Servo preference name
+        let pref_name_mapping: HashMap<&str, &str> =
+            [("dom.serviceWorkers.enabled", "dom.serviceworker.enabled")]
+                .iter()
+                .copied()
+                .collect();
+        if pref_name_mapping.contains_key(key) {
+            key = pref_name_mapping.get(key).unwrap();
+        }
+
+        let pref_value = pref_map().get(key);
         Ok(handle_preference_value(
             pref_value,
             self.name(),

components/devtools/build.rs

@@ -0,0 +1,20 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use std::path::Path;
+use std::{env, fs};
+
+use chrono::Local;
+
+fn main() {
+    let path = Path::new(&env::var_os("OUT_DIR").unwrap()).join("build_id.rs");
+    fs::write(
+        path,
+        format!(
+            "const BUILD_ID: &str = \"{}\";",
+            Local::now().format("%Y%m%d%H%M%S")
+        ),
+    )
+    .unwrap();
+}