crown: Pass --cfg crown to rustc from crown (#35073)

* crown: Pass `--cfg crown` to rustc from crown

also includes minor fix in crown for wrapper running based on clippy code

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

* fix doc

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

* Update python/servo/command_base.py

Co-authored-by: Martin Robinson <mrobinson@igalia.com>
Signed-off-by: Samson <16504129+sagudev@users.noreply.github.com>

---------

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>
Signed-off-by: Samson <16504129+sagudev@users.noreply.github.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

python/servo/command_base.py

@@ -807,14 +807,12 @@ class CommandBase(object):
                           f'already set to `{current_rustc}` in the parent environment.\n'
                           'These options conflict, please specify only one of them.')
                     sys.exit(1)
-            features += ["crown"]
             env['CARGO_BUILD_RUSTC'] = 'crown'
-            # Changing `RUSTC` or `CARGO_BUILD_RUSTC` does not cause `cargo check` to
-            # recheck files with the new compiler. `cargo build` is not affected and
-            # triggers a rebuild as expected. To also make `check` work as expected,
-            # we add a dummy `cfg` to RUSTFLAGS when using crown, so as to have different
-            # RUSTFLAGS when using `crown`, to reliably trigger re-checking.
-            env['RUSTFLAGS'] = env.get('RUSTFLAGS', "") + " --cfg=crown"
+            # Modyfing `RUSTC` or `CARGO_BUILD_RUSTC` to use a linter does not cause
+            # `cargo check` to rebuild. To work around this bug use a `crown` feature
+            # to invalidate caches and force a rebuild / relint.
+            # See https://github.com/servo/servo/issues/35072#issuecomment-2600749483
+            features += ["crown"]
 
         if "-p" not in cargo_args:  # We're building specific package, that may not have features
             features += list(self.features)

support/crown/src/main.rs

@@ -22,6 +22,7 @@ extern crate rustc_span;
 extern crate rustc_trait_selection;
 extern crate rustc_type_ir;
 
+use std::path::Path;
 use std::process::ExitCode;
 
 use rustc_driver::Callbacks;
@@ -64,7 +65,16 @@ fn main() -> ExitCode {
     let handler =
         rustc_session::EarlyDiagCtxt::new(rustc_session::config::ErrorOutputType::default());
     rustc_driver::init_logger(&handler, rustc_log::LoggerConfig::from_env("CROWN_LOG"));
-    let args: Vec<_> = std::env::args().collect();
+    let mut args: Vec<_> = std::env::args().collect();
+
+    // Setting RUSTC_WRAPPER causes Cargo to pass 'rustc' as the first argument.
+    // We're invoking the compiler programmatically, so we ignore this
+    if args.get(1).map(Path::new).and_then(Path::file_stem) == Some("rustc".as_ref()) {
+        args.remove(1);
+    }
+
+    // Pass cfg(crown) to rustc
+    args.extend(["--cfg".to_owned(), "crown".to_owned()]);
 
     match rustc_driver::RunCompiler::new(&args, &mut MyCallbacks).run() {
         Ok(_) => ExitCode::SUCCESS,

support/crown/tests/run-pass/cfg_crown.rs

@@ -0,0 +1,10 @@
+/* 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/. */
+//@rustc-env:RUSTC_BOOTSTRAP=1
+
+#![allow(dead_code)]
+
+const _: () = assert!(cfg!(crown), "cfg(crown) not set!");
+
+fn main() {}