Add cli option for tracing-filter (#35370)

Using environment variables is not really an option on ohos/android,
so add a CLI option to configure tracing.
Making it a `pref`, so that we can persist the filter
might also be desirable.

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

ports/servoshell/desktop/cli.rs

@@ -11,7 +11,6 @@ use crate::prefs::{parse_command_line_arguments, ArgumentParsingResult};
 
 pub fn main() {
     crate::crash_handler::install();
-    crate::init_tracing();
     crate::init_crypto();
     crate::resources::init();
 
@@ -27,6 +26,8 @@ pub fn main() {
         },
     };
 
+    crate::init_tracing(servoshell_preferences.tracing_filter.as_deref());
+
     let clean_shutdown = servoshell_preferences.clean_shutdown;
     let event_loop = EventsLoop::new(servoshell_preferences.headless, opts.output_file.is_some())
         .expect("Failed to create events loop");

ports/servoshell/egl/android/simpleservo.rs

@@ -52,7 +52,6 @@ pub fn init(
     waker: Box<dyn EventLoopWaker>,
     callbacks: Box<dyn HostTrait>,
 ) -> Result<(), &'static str> {
-    crate::init_tracing();
     crate::init_crypto();
     resources::set(Box::new(ResourceReaderInstance::new()));
 
@@ -69,6 +68,8 @@ pub fn init(
         },
     };
 
+    crate::init_tracing(servoshell_preferences.tracing_filter.as_deref());
+
     // Initialize surfman
     let connection = Connection::new().or(Err("Failed to create connection"))?;
     let adapter = connection

ports/servoshell/egl/ohos/simpleservo.rs

@@ -36,7 +36,6 @@ pub fn init(
     callbacks: Box<dyn HostTrait>,
 ) -> Result<Rc<RunningAppState>, &'static str> {
     info!("Entered simpleservo init function");
-    crate::init_tracing();
     crate::init_crypto();
     let resource_dir = PathBuf::from(&options.resource_dir).join("servo");
     resources::set(Box::new(ResourceReaderInstance::new(resource_dir)));
@@ -61,6 +60,8 @@ pub fn init(
         },
     };
 
+    crate::init_tracing(servoshell_preferences.tracing_filter.as_deref());
+
     // Initialize surfman
     let connection = Connection::new().or(Err("Failed to create connection"))?;
     let adapter = connection

ports/servoshell/lib.rs

@@ -44,7 +44,13 @@ pub fn init_crypto() {
         .expect("Error initializing crypto provider");
 }
 
-pub fn init_tracing() {
+pub fn init_tracing(filter_directives: Option<&str>) {
+    #[cfg(not(feature = "tracing"))]
+    {
+        if filter_directives.is_some() {
+            log::debug!("The tracing feature was not selected - ignoring trace filter directives");
+        }
+    }
     #[cfg(feature = "tracing")]
     {
         use tracing_subscriber::layer::SubscriberExt;
@@ -69,10 +75,16 @@ pub fn init_tracing() {
 
         // Filter events and spans by the directives in SERVO_TRACING, using EnvFilter as a global filter.
         // <https://docs.rs/tracing-subscriber/0.3.18/tracing_subscriber/layer/index.html#global-filtering>
-        let filter = tracing_subscriber::EnvFilter::builder()
-            .with_default_directive(tracing::level_filters::LevelFilter::OFF.into())
-            .with_env_var("SERVO_TRACING")
-            .from_env_lossy();
+        let filter_builder = tracing_subscriber::EnvFilter::builder()
+            .with_default_directive(tracing::level_filters::LevelFilter::OFF.into());
+        let filter = if let Some(filters) = &filter_directives {
+            filter_builder.parse_lossy(filters)
+        } else {
+            filter_builder
+                .with_env_var("SERVO_TRACING")
+                .from_env_lossy()
+        };
+
         let subscriber = subscriber.with(filter);
 
         // Same as SubscriberInitExt::init, but avoids initialising the tracing-log compat layer,

ports/servoshell/prefs.rs

@@ -37,6 +37,11 @@ pub(crate) struct ServoShellPreferences {
     /// Whether or not to run servoshell in headless mode. While running in headless
     /// mode, image output is supported.
     pub headless: bool,
+    /// Filter directives for our tracing implementation.
+    ///
+    /// Overrides directives specified via `SERVO_TRACING` if set.
+    /// See: <https://docs.rs/tracing-subscriber/0.3.19/tracing_subscriber/filter/struct.EnvFilter.html#directives>
+    pub tracing_filter: Option<String>,
 }
 
 impl Default for ServoShellPreferences {
@@ -50,6 +55,7 @@ impl Default for ServoShellPreferences {
             no_native_titlebar: true,
             searchpage: "https://duckduckgo.com/html/?q=%s".into(),
             headless: false,
+            tracing_filter: None,
         }
     }
 }
@@ -311,6 +317,13 @@ pub(crate) fn parse_command_line_arguments(args: Vec<String>) -> ArgumentParsing
         "Set custom user agent string (or ios / android / desktop for platform default)",
         "NCSA Mosaic/1.0 (X11;SunOS 4.1.4 sun4m)",
     );
+    opts.optmulti(
+        "",
+        "tracing-filter",
+        "Define a custom filter for traces. Overrides `SERVO_TRACING` if set.",
+        "FILTER",
+    );
+
     opts.optmulti(
         "",
         "pref",
@@ -353,6 +366,13 @@ pub(crate) fn parse_command_line_arguments(args: Vec<String>) -> ArgumentParsing
     if let Some(content_process) = opt_match.opt_str("content-process") {
         return ArgumentParsingResult::ContentProcess(content_process);
     }
+    // Env-Filter directives are comma seperated.
+    let filters = opt_match.opt_strs("tracing-filter").join(",");
+    let tracing_filter = if filters.is_empty() {
+        None
+    } else {
+        Some(filters)
+    };
 
     let mut debug_options = DebugOptions::default();
     for debug_string in opt_match.opt_strs("Z") {
@@ -544,6 +564,7 @@ pub(crate) fn parse_command_line_arguments(args: Vec<String>) -> ArgumentParsing
         device_pixel_ratio_override,
         clean_shutdown: opt_match.opt_present("clean-shutdown"),
         headless: opt_match.opt_present("z"),
+        tracing_filter,
         ..Default::default()
     };