Add default subscriber to Masonry (#252)

This subscriber uses EnvFilter to change its value depending on the
RUST_LOG env variable, so log levels can be changed without recompiling
the app.

Cargo.lock

@@ -1303,6 +1303,7 @@ dependencies = [
  "smallvec",
  "tempfile",
  "tracing",
+ "tracing-subscriber",
  "unicode-segmentation",
  "vello",
  "wgpu",
@@ -1430,6 +1431,16 @@ dependencies = [
  "jni-sys",
 ]
 
+[[package]]
+name = "nu-ansi-term"
+version = "0.46.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "77a8165726e8236064dbb45459242600304b42a5ea24ee2948e18e023bf7ba84"
+dependencies = [
+ "overload",
+ "winapi",
+]
+
 [[package]]
 name = "num-traits"
 version = "0.2.18"
@@ -1569,6 +1580,12 @@ dependencies = [
  "libredox",
 ]
 
+[[package]]
+name = "overload"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b15813163c1d831bf4a13c3610c05c0d03b39feb07f7e09fa234dac9b15aaf39"
+
 [[package]]
 name = "owned_ttf_parser"
 version = "0.20.0"
@@ -2348,6 +2365,18 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c06d3da6113f116aaee68e4d601191614c9053067f9ab7f6edbcb161237daa54"
 dependencies = [
  "once_cell",
+ "valuable",
+]
+
+[[package]]
+name = "tracing-log"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ee855f1f400bd0e5c02d150ae5de3840039a3f54b025156404e34c23c03f47c3"
+dependencies = [
+ "log",
+ "once_cell",
+ "tracing-core",
 ]
 
 [[package]]
@@ -2356,9 +2385,12 @@ version = "0.3.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ad0f048c97dbd9faa9b7df56362b8ebcaa52adb06b498c050d2f4e32f90a7a8b"
 dependencies = [
+ "nu-ansi-term",
  "sharded-slab",
+ "smallvec",
  "thread_local",
  "tracing-core",
+ "tracing-log",
 ]
 
 [[package]]
@@ -2402,6 +2434,12 @@ version = "0.2.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f962df74c8c05a667b5ee8bcf162993134c104e96440b663c8daa176dc772d8c"
 
+[[package]]
+name = "valuable"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "830b7e5d4d90034032940e4ace0d9a9a057e7a45cd94e6c007832e39edb82f6d"
+
 [[package]]
 name = "vello"
 version = "0.1.0"

crates/masonry/Cargo.toml

@@ -36,6 +36,7 @@ pollster = "0.3.0"
 unicode-segmentation = "1.11.0"
 # TODO: Is this still the most up-to-date crate for this?
 xi-unicode = "0.3.0"
+tracing-subscriber = "0.3.18"
 
 [dev-dependencies]
 float-cmp = { version = "0.8.0", features = ["std"], default-features = false }

crates/masonry/examples/calc.rs

@@ -358,5 +358,5 @@ pub fn main() {
         in_num: false,
     };
 
-    masonry::event_loop_runner::run(build_calc(), window, event_loop, calc_state);
+    masonry::event_loop_runner::run(build_calc(), window, event_loop, calc_state).unwrap();
 }

crates/masonry/examples/custom_widget.rs

@@ -143,7 +143,7 @@ pub fn main() {
         .create_window(Window::default_attributes().with_title("Fancy colots"))
         .unwrap();
 
-    masonry::event_loop_runner::run(CustomWidget(my_string), window, event_loop, Driver);
+    masonry::event_loop_runner::run(CustomWidget(my_string), window, event_loop, Driver).unwrap();
 }
 
 fn make_image_data(width: usize, height: usize) -> Vec<u8> {

crates/masonry/examples/hello_masonry.rs

@@ -45,7 +45,7 @@ pub fn main() {
         )
         .unwrap();
 
-    masonry::event_loop_runner::run(build_root_widget(), window, event_loop, Driver);
+    masonry::event_loop_runner::run(build_root_widget(), window, event_loop, Driver).unwrap();
 }
 
 fn build_root_widget() -> impl Widget {

crates/masonry/examples/simple_image.rs

@@ -41,5 +41,5 @@ pub fn main() {
         )
         .unwrap();
 
-    masonry::event_loop_runner::run(image, window, event_loop, Driver);
+    masonry::event_loop_runner::run(image, window, event_loop, Driver).unwrap();
 }

crates/masonry/src/event_loop_runner.rs

@@ -4,6 +4,7 @@
 use std::num::NonZeroUsize;
 use std::sync::Arc;
 
+use tracing::subscriber::SetGlobalDefaultError;
 use tracing::warn;
 use vello::kurbo::Affine;
 use vello::util::{RenderContext, RenderSurface};
@@ -11,6 +12,7 @@ use vello::{peniko::Color, AaSupport, RenderParams, Renderer, RendererOptions, S
 use wgpu::PresentMode;
 use winit::application::ApplicationHandler;
 use winit::dpi::LogicalPosition;
+use winit::error::EventLoopError;
 use winit::event::WindowEvent as WinitWindowEvent;
 use winit::event_loop::{ActiveEventLoop, EventLoop};
 use winit::window::{Window, WindowId};
@@ -35,7 +37,7 @@ pub fn run(
     window: Window,
     event_loop: EventLoop<()>,
     app_driver: impl AppDriver + 'static,
-) {
+) -> Result<(), EventLoopError> {
     let window = Arc::new(window);
     let mut render_cx = RenderContext::new().unwrap();
     let size = window.inner_size();
@@ -57,13 +59,20 @@ pub fn run(
         app_driver: Box::new(app_driver),
     };
 
-    let _ = event_loop.run_app(&mut main_state);
+    // If there is no default tracing subscriber, we set our own. If one has
+    // already been set, we get an error which we swallow.
+    // By now, we're about to take control of the event loop. The user is unlikely
+    // to try to set their own subscriber once the event loop has started.
+    let _ = try_init_tracing();
+
+    event_loop.run_app(&mut main_state)
 }
 
 impl ApplicationHandler for MainState<'_> {
     fn resumed(&mut self, _event_loop: &ActiveEventLoop) {
         // FIXME: initialize window in this handler because initializing it before running the event loop is deprecated
     }
+
     fn window_event(&mut self, event_loop: &ActiveEventLoop, _: WindowId, event: WinitWindowEvent) {
         match event {
             WinitWindowEvent::RedrawRequested => {
@@ -249,3 +258,45 @@ impl MainState<'_> {
         device.poll(wgpu::Maintain::Wait);
     }
 }
+
+pub(crate) fn try_init_tracing() -> Result<(), SetGlobalDefaultError> {
+    #[cfg(not(target_arch = "wasm32"))]
+    {
+        use tracing_subscriber::filter::LevelFilter;
+        use tracing_subscriber::prelude::*;
+        let filter_layer = if cfg!(debug_assertions) {
+            LevelFilter::DEBUG
+        } else {
+            LevelFilter::INFO
+        };
+        let fmt_layer = tracing_subscriber::fmt::layer()
+            // Display target (eg "my_crate::some_mod::submod") with logs
+            .with_target(true);
+
+        let registry = tracing_subscriber::registry()
+            .with(filter_layer)
+            .with(fmt_layer);
+        tracing::dispatcher::set_global_default(registry.into())
+    }
+
+    // Note - tracing-wasm might not work in headless Node.js. Probably doesn't matter anyway,
+    // because this is a GUI framework, so wasm targets will virtually always be browsers.
+    #[cfg(target_arch = "wasm32")]
+    {
+        // Ignored if the panic hook is already set
+        console_error_panic_hook::set_once();
+
+        let max_level = if cfg!(debug_assertions) {
+            tracing::Level::DEBUG
+        } else {
+            tracing::Level::INFO
+        };
+        let config = tracing_wasm::WASMLayerConfigBuilder::new()
+            .set_max_level(max_level)
+            .build();
+
+        tracing::subscriber::set_global_default(
+            Registry::default().with(tracing_wasm::WASMLayer::new(config)),
+        )
+    }
+}

crates/masonry/src/testing/harness.rs

@@ -20,6 +20,7 @@ use super::screenshots::get_image_diff;
 use super::snapshot_utils::get_cargo_workspace;
 use crate::action::Action;
 use crate::event::{PointerEvent, PointerState, TextEvent, WindowEvent};
+use crate::event_loop_runner::try_init_tracing;
 use crate::render_root::{RenderRoot, RenderRootSignal, WindowSizePolicy};
 use crate::widget::{WidgetMut, WidgetRef};
 use crate::{Color, Handled, Point, Size, Vec2, Widget, WidgetId};
@@ -173,6 +174,13 @@ impl TestHarness {
         let mouse_state = PointerState::empty();
         let window_size = PhysicalSize::new(window_size.width as _, window_size.height as _);
 
+        // If there is no default tracing subscriber, we set our own. If one has
+        // already been set, we get an error which we swallow.
+        // Having a default subscriber is helpful for tests; swallowing errors means
+        // we don't panic if the user has already set one, or a test creates multiple
+        // harnesses.
+        let _ = try_init_tracing();
+
         let mut harness = TestHarness {
             render_root: RenderRoot::new(root_widget, WindowSizePolicy::User, 1.0),
             mouse_state,

crates/xilem_masonry/src/lib.rs

@@ -196,8 +196,7 @@ where
         Logic: 'static,
         View: 'static,
     {
-        event_loop_runner::run(self.root_widget, window, event_loop, self.driver);
-        Ok(())
+        event_loop_runner::run(self.root_widget, window, event_loop, self.driver)
     }
 }
 pub trait MasonryView<State, Action = ()>: Send + 'static {