Make the crown disabled warning clearer and less scary (servo#37535)

Instead of printing a Rust compilation warning, simply print a message
before every build (when using `mach`) that shows the build
configuration and whether or not `crown` is enabled.

Fixes servo#32597.

Signed-off-by: Martin Robinson <[email protected]>

Author: mrobinson

components/script/lib.rs

@@ -5,12 +5,8 @@
 #![cfg_attr(crown, feature(register_tool))]
 #![deny(unsafe_code)]
 #![doc = "The script crate contains all matters DOM."]
-// Register the linter `crown`, which is the Servo-specific linter for the script
-// crate. Issue a warning if `crown` is not being used to compile, but not when
-// building rustdoc or running clippy.
+// Register the linter `crown`, which is the Servo-specific linter for the script crate.
 #![cfg_attr(crown, register_tool(crown))]
-#![cfg_attr(any(doc, clippy), allow(unknown_lints))]
-#![deny(crown_is_not_used)]
 
 // These are used a lot so let's keep them for now
 #[macro_use]

components/script_bindings/lib.rs

@@ -3,12 +3,8 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 #![cfg_attr(crown, feature(register_tool))]
-// Register the linter `crown`, which is the Servo-specific linter for the script
-// crate. Issue a warning if `crown` is not being used to compile, but not when
-// building rustdoc or running clippy.
+// Register the linter `crown`, which is the Servo-specific linter for the script crate.
 #![cfg_attr(crown, register_tool(crown))]
-#![cfg_attr(any(doc, clippy), allow(unknown_lints))]
-#![deny(crown_is_not_used)]
 
 #[macro_use]
 extern crate js;

python/servo/build_commands.py

@@ -146,8 +146,9 @@ def build(
         # Gather Cargo build timings (https://doc.rust-lang.org/cargo/reference/timings.html).
         opts = ["--timings"] + opts
 
+        crown_enabled = "enabled" if kwargs.get("use_crown", False) else "disabled (no JS garbage collection linting)"
+        print(f"Building `{build_type.directory_name()}` build with crown {crown_enabled}.")
         if very_verbose:
-            print(["Calling", "cargo", "build"] + opts)
             for key in env:
                 print((key, env[key]))
 

support/crown/src/crown_is_not_used.rs

@@ -35,8 +35,6 @@ mod unrooted_must_root;
 #[cfg(feature = "trace_in_no_trace_lint")]
 mod trace_in_no_trace;
 
-mod crown_is_not_used;
-
 struct MyCallbacks;
 
 impl Callbacks for MyCallbacks {
@@ -51,7 +49,6 @@ impl Callbacks for MyCallbacks {
                 return;
             }
 
-            crown_is_not_used::register(lint_store);
             #[cfg(feature = "unrooted_must_root_lint")]
             unrooted_must_root::register(lint_store);
             #[cfg(feature = "trace_in_no_trace_lint")]