Switch from error! and println! to warn!, and set the default log level to warn on debug builds.

components/style/properties/gecko.mako.rs

@@ -610,15 +610,11 @@ impl ${style_struct.gecko_struct_name} {
     % for longhand in stub_longhands:
     #[allow(non_snake_case)]
     pub fn set_${longhand.ident}(&mut self, _: longhands::${longhand.ident}::computed_value::T) {
-        if cfg!(debug_assertions) {
+        warn!("stylo: Unimplemented property setter: ${longhand.name}");
-            println!("stylo: Unimplemented property setter: ${longhand.name}");
-        }
     }
     #[allow(non_snake_case)]
     pub fn copy_${longhand.ident}_from(&mut self, _: &Self) {
-        if cfg!(debug_assertions) {
+        warn!("stylo: Unimplemented property setter: ${longhand.name}");
-            println!("stylo: Unimplemented property setter: ${longhand.name}");
-        }
     }
     % if longhand.need_clone:
     #[allow(non_snake_case)]
@@ -2628,7 +2624,7 @@ clip-path
         clip_path.mType = StyleShapeSourceType::None;
 
         match v {
-            ShapeSource::Url(..) => println!("stylo: clip-path: url() not yet implemented"),
+            ShapeSource::Url(..) => warn!("stylo: clip-path: url() not yet implemented"),
             ShapeSource::None => {} // don't change the type
             ShapeSource::Box(reference) => {
                 clip_path.mReferenceBox = reference.into();

components/style/properties/helpers.mako.rs

@@ -119,7 +119,7 @@
                         % if allow_empty:
                             try!(dest.write_str("none"));
                         % else:
-                            error!("Found empty value for property ${name}");
+                            warn!("Found empty value for property ${name}");
                         % endif
                     }
                     for i in iter {
@@ -146,7 +146,7 @@
                         % if allow_empty:
                             try!(dest.write_str("none"));
                         % else:
-                            error!("Found empty value for property ${name}");
+                            warn!("Found empty value for property ${name}");
                         % endif
                     }
                     for i in iter {

components/style/restyle_hints.rs

@@ -103,7 +103,7 @@ impl From<nsRestyleHint> for RestyleHint {
         // FIXME(bholley): Finish aligning the binary representations here and
         // then .expect() the result of the checked version.
         if Self::from_bits(raw_bits).is_none() {
-            error!("stylo: dropping unsupported restyle hint bits");
+            warn!("stylo: dropping unsupported restyle hint bits");
         }
 
         Self::from_bits_truncate(raw_bits)

components/style/rule_tree/mod.rs

@@ -471,7 +471,7 @@ impl RuleNode {
             }
             None => {
                 if indent != 0 {
-                    error!("How has this happened?");
+                    warn!("How has this happened?");
                 }
                 let _ = write!(writer, "(root)");
             }

components/style/values/specified/url.rs

@@ -101,7 +101,7 @@ impl SpecifiedUrl {
                 // FIXME(heycam) should ensure we always have a principal, etc.,
                 // when parsing style attributes and re-parsing due to CSS
                 // Variables.
-                println!("stylo: skipping declaration without ParserContextExtraData");
+                warn!("stylo: skipping declaration without ParserContextExtraData");
                 return Err(())
             },
         };

ports/geckolib/glue.rs

@@ -6,12 +6,13 @@ use app_units::Au;
 use atomic_refcell::AtomicRefMut;
 use cssparser::Parser;
 use cssparser::ToCss as ParserToCss;
-use env_logger;
+use env_logger::LogBuilder;
 use euclid::Size2D;
 use parking_lot::RwLock;
 use selectors::Element;
 use servo_url::ServoUrl;
 use std::borrow::Cow;
+use std::env;
 use std::fmt::Write;
 use std::mem;
 use std::ptr;
@@ -91,10 +92,13 @@ use stylesheet_loader::StylesheetLoader;
 
 #[no_mangle]
 pub extern "C" fn Servo_Initialize() -> () {
-    // Enable standard Rust logging.
+    // Initialize logging.
-    //
+    let mut builder = LogBuilder::new();
-    // See https://doc.rust-lang.org/log/env_logger/index.html for instructions.
+    let default_level = if cfg!(debug_assertions) { "warn" } else { "error" };
-    env_logger::init().unwrap();
+    match env::var("RUST_LOG") {
+      Ok(v) => builder.parse(&v).init().unwrap(),
+      _ => builder.parse(default_level).init().unwrap(),
+    };
 
     // Pretend that we're a Servo Layout thread, to make some assertions happy.
     thread_state::initialize(thread_state::LAYOUT);
@@ -318,8 +322,8 @@ pub extern "C" fn Servo_AnimationValues_Populate(anim: RawGeckoAnimationValueLis
 
     // we should have gone through both iterators
     if iter.next().is_some() || geckoiter.next().is_some() {
-        error!("stylo: Mismatched sizes of Gecko and Servo \
+        warn!("stylo: Mismatched sizes of Gecko and Servo \
-                array during animation value construction");
+               array during animation value construction");
     }
 }
 
@@ -671,7 +675,7 @@ pub extern "C" fn Servo_ResolvePseudoStyle(element: RawGeckoElementBorrowed,
 
     // FIXME(bholley): Assert against this.
     if data.get_styles().is_none() {
-        error!("Calling Servo_ResolvePseudoStyle on unstyled element");
+        warn!("Calling Servo_ResolvePseudoStyle on unstyled element");
         return if is_probe {
             Strong::null()
         } else {
@@ -962,7 +966,7 @@ pub extern "C" fn Servo_DeclarationBlock_AddPresValue(declarations: RawServoDecl
     let long = match prop {
         Ok(PropertyId::Longhand(long)) => long,
         _ => {
-            error!("stylo: unknown presentation property with id {:?}", property);
+            warn!("stylo: unknown presentation property with id {:?}", property);
             return
         }
     };
@@ -977,7 +981,7 @@ pub extern "C" fn Servo_DeclarationBlock_AddPresValue(declarations: RawServoDecl
                     )
                 ))
             } else {
-                error!("stylo: got unexpected non-integer value for font-size presentation attribute");
+                warn!("stylo: got unexpected non-integer value for font-size presentation attribute");
                 return
             }
         }
@@ -990,12 +994,12 @@ pub extern "C" fn Servo_DeclarationBlock_AddPresValue(declarations: RawServoDecl
                     }
                 ))
             } else {
-                error!("stylo: got unexpected non-integer value for color presentation attribute");
+                warn!("stylo: got unexpected non-integer value for color presentation attribute");
                 return
             }
         }
         _ => {
-            error!("stylo: cannot handle longhand {:?} from presentation attribute", long);
+            warn!("stylo: cannot handle longhand {:?} from presentation attribute", long);
             return
         }
     };
@@ -1116,7 +1120,7 @@ pub extern "C" fn Servo_TakeChangeHint(element: RawGeckoElementBorrowed) -> nsCh
         data.clear_restyle();
         d
     } else {
-        error!("Trying to get change hint from unstyled element");
+        warn!("Trying to get change hint from unstyled element");
         GeckoRestyleDamage::empty()
     };
 
@@ -1134,7 +1138,7 @@ pub extern "C" fn Servo_ResolveStyle(element: RawGeckoElementBorrowed,
     let data = unsafe { element.ensure_data() }.borrow_mut();
 
     if !data.has_current_styles() {
-        error!("Resolving style on unstyled element with lazy computation forbidden.");
+        warn!("Resolving style on unstyled element with lazy computation forbidden.");
         let per_doc_data = PerDocumentStyleData::from_ffi(raw_data).borrow();
         return per_doc_data.default_computed_values().clone().into_strong();
     }