fix(cargo-rustc): stabilize higher precedence trailing flags

This was always enabled on nightly since 1.83-nightly (2024-09).
We have no feedback since then, so assume it is a low-impact change.

This stabilization is targeted at 1.85 (2025-02-20)

Author: weihanglo

src/cargo/core/compiler/mod.rs

@@ -696,10 +696,8 @@ fn prepare_rustc(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> CargoResult
     base.inherit_jobserver(&build_runner.jobserver);
     build_deps_args(&mut base, build_runner, unit)?;
     add_cap_lints(build_runner.bcx, unit, &mut base);
-    if cargo_rustc_higher_args_precedence(build_runner) {
-        if let Some(args) = build_runner.bcx.extra_args_for(unit) {
-            base.args(args);
-        }
+    if let Some(args) = build_runner.bcx.extra_args_for(unit) {
+        base.args(args);
     }
     base.args(&unit.rustflags);
     if build_runner.bcx.gctx.cli_unstable().binary_dep_depinfo {
@@ -754,12 +752,6 @@ fn prepare_rustdoc(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> CargoResu
 
     rustdoc.args(unit.pkg.manifest().lint_rustflags());
 
-    if !cargo_rustc_higher_args_precedence(build_runner) {
-        if let Some(args) = build_runner.bcx.extra_args_for(unit) {
-            rustdoc.args(args);
-        }
-    }
-
     let metadata = build_runner.metadata_for_doc_units[unit];
     rustdoc
         .arg("-C")
@@ -800,10 +792,8 @@ fn prepare_rustdoc(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> CargoResu
 
     rustdoc::add_output_format(build_runner, unit, &mut rustdoc)?;
 
-    if cargo_rustc_higher_args_precedence(build_runner) {
-        if let Some(args) = build_runner.bcx.extra_args_for(unit) {
-            rustdoc.args(args);
-        }
+    if let Some(args) = build_runner.bcx.extra_args_for(unit) {
+        rustdoc.args(args);
     }
     rustdoc.args(&unit.rustdocflags);
 
@@ -1107,11 +1097,6 @@ fn build_base_args(
 
     cmd.args(unit.pkg.manifest().lint_rustflags());
     cmd.args(&profile_rustflags);
-    if !cargo_rustc_higher_args_precedence(build_runner) {
-        if let Some(args) = build_runner.bcx.extra_args_for(unit) {
-            cmd.args(args);
-        }
-    }
 
     // `-C overflow-checks` is implied by the setting of `-C debug-assertions`,
     // so we only need to provide `-C overflow-checks` if it differs from
@@ -2001,19 +1986,3 @@ fn scrape_output_path(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> CargoR
         .outputs(unit)
         .map(|outputs| outputs[0].path.clone())
 }
-
-/// Provides a way to change the precedence of `cargo rustc -- <flags>`.
-///
-/// This is intended to be a short-live function.
-///
-/// See <https://github.com/rust-lang/cargo/issues/14346>
-fn cargo_rustc_higher_args_precedence(build_runner: &BuildRunner<'_, '_>) -> bool {
-    build_runner.bcx.gctx.nightly_features_allowed
-        && build_runner
-            .bcx
-            .gctx
-            .get_env("__CARGO_RUSTC_ORIG_ARGS_PRIO")
-            .ok()
-            .as_deref()
-            != Some("1")
-}

tests/testsuite/rustc.rs

@@ -817,42 +817,11 @@ fn precedence() {
 
     p.cargo("rustc --release -v -- --cfg cargo_rustc -C strip=symbols")
         .env("RUSTFLAGS", "--cfg from_rustflags")
-        .masquerade_as_nightly_cargo(&["cargo-rustc-precedence"])
         .with_stderr_data(str![[r#"
 [COMPILING] foo v0.0.0 ([ROOT]/foo)
 [RUNNING] `rustc [..]-C strip=debuginfo [..]--cfg cargo_rustc -C strip=symbols --cfg from_rustflags`
 [FINISHED] `release` profile [optimized] target(s) in [ELAPSED]s
 
 "#]])
         .run();
-
-    // Ensure the short-live env var to work
-    p.cargo("clean").run();
-    p.cargo("rustc --release -v -- --cfg cargo_rustc -C strip=symbols")
-        .env("RUSTFLAGS", "--cfg from_rustflags")
-        .env("__CARGO_RUSTC_ORIG_ARGS_PRIO", "1")
-        .masquerade_as_nightly_cargo(&["cargo-rustc-precedence"])
-        .with_stderr_data(
-            str![[r#"
-[COMPILING] foo v0.0.0 ([ROOT]/foo)
-[RUNNING] `rustc [..]--cfg cargo_rustc -C strip=symbols [..]-C strip=debuginfo [..]--cfg from_rustflags`
-[FINISHED] `release` profile [optimized] target(s) in [ELAPSED]s
-
-"#]]
-        )
-        .run();
-
-    // Ensure non-nightly to work as before
-    p.cargo("clean").run();
-    p.cargo("rustc --release -v -- --cfg cargo_rustc -C strip=symbols")
-        .env("RUSTFLAGS", "--cfg from_rustflags")
-        .with_stderr_data(
-            str![[r#"
-[COMPILING] foo v0.0.0 ([ROOT]/foo)
-[RUNNING] `rustc [..]--cfg cargo_rustc -C strip=symbols [..]-C strip=debuginfo [..]--cfg from_rustflags`
-[FINISHED] `release` profile [optimized] target(s) in [ELAPSED]s
-
-"#]]
-        )
-        .run();
 }