Pass rustflags to artifacts built with implicit targets when using target-applies-to-host

src/cargo/core/compiler/build_context/mod.rs

@@ -134,19 +134,6 @@ impl<'a, 'gctx> BuildContext<'a, 'gctx> {
         self.build_config.jobs
     }
 
-    /// Extra compiler flags to pass to `rustc` for a given unit.
-    ///
-    /// Although it depends on the caller, in the current Cargo implementation,
-    /// these flags take precedence over those from [`BuildContext::extra_args_for`].
-    ///
-    /// As of now, these flags come from environment variables and configurations.
-    /// See [`TargetInfo.rustflags`] for more on how Cargo collects them.
-    ///
-    /// [`TargetInfo.rustflags`]: TargetInfo::rustflags
-    pub fn rustflags_args(&self, unit: &Unit) -> &[String] {
-        &self.target_data.info(unit.kind).rustflags
-    }
-
     /// Extra compiler flags to pass to `rustdoc` for a given unit.
     ///
     /// Although it depends on the caller, in the current Cargo implementation,

src/cargo/core/compiler/build_context/target_info.rs

@@ -23,6 +23,7 @@ use std::cell::RefCell;
 use std::collections::hash_map::{Entry, HashMap};
 use std::path::{Path, PathBuf};
 use std::str::{self, FromStr};
+use std::sync::Arc;
 
 /// Information about the platform target gleaned from querying rustc.
 ///
@@ -52,7 +53,7 @@ pub struct TargetInfo {
     /// target libraries.
     pub sysroot_target_libdir: PathBuf,
     /// Extra flags to pass to `rustc`, see [`extra_args`].
-    pub rustflags: Vec<String>,
+    pub rustflags: Arc<[String]>,
     /// Extra flags to pass to `rustdoc`, see [`extra_args`].
     pub rustdocflags: Vec<String>,
     /// Whether or not rustc (stably) supports the `--check-cfg` flag.
@@ -312,7 +313,7 @@ impl TargetInfo {
                 crate_types: RefCell::new(map),
                 sysroot,
                 sysroot_target_libdir,
-                rustflags,
+                rustflags: rustflags.into(),
                 rustdocflags: extra_args(
                     gctx,
                     requested_kinds,
@@ -867,7 +868,10 @@ pub struct RustcTargetData<'gctx> {
 
     /// Build information for the "host", which is information about when
     /// `rustc` is invoked without a `--target` flag. This is used for
-    /// procedural macros, build scripts, etc.
+    /// selecting a linker, and applying link overrides.
+    ///
+    /// The configuration read into this depends on whether or not
+    /// `target-applies-to-host=true`.
     host_config: TargetConfig,
     /// Information about the host platform.
     host_info: TargetInfo,
@@ -889,7 +893,10 @@ impl<'gctx> RustcTargetData<'gctx> {
         let mut target_config = HashMap::new();
         let mut target_info = HashMap::new();
         let target_applies_to_host = gctx.target_applies_to_host()?;
+        let host_target = CompileTarget::new(&rustc.host)?;
         let host_info = TargetInfo::new(gctx, requested_kinds, &rustc, CompileKind::Host)?;
+
+        // This config is used for link overrides and choosing a linker.
         let host_config = if target_applies_to_host {
             gctx.target_cfg_triple(&rustc.host)?
         } else {
@@ -902,9 +909,21 @@ impl<'gctx> RustcTargetData<'gctx> {
         // needs access to the target config data, create a copy so that it
         // can be found. See `rebuild_unit_graph_shared` for why this is done.
         if requested_kinds.iter().any(CompileKind::is_host) {
-            let ct = CompileTarget::new(&rustc.host)?;
-            target_info.insert(ct, host_info.clone());
-            target_config.insert(ct, gctx.target_cfg_triple(&rustc.host)?);
+            target_config.insert(host_target, gctx.target_cfg_triple(&rustc.host)?);
+
+            // If target_applies_to_host is true, the host_info is the target info,
+            // otherwise we need to build target info for the target.
+            if target_applies_to_host {
+                target_info.insert(host_target, host_info.clone());
+            } else {
+                let host_target_info = TargetInfo::new(
+                    gctx,
+                    requested_kinds,
+                    &rustc,
+                    CompileKind::Target(host_target),
+                )?;
+                target_info.insert(host_target, host_target_info);
+            }
         };
 
         let mut res = RustcTargetData {

src/cargo/core/compiler/custom_build.rs

@@ -352,10 +352,7 @@ fn build_work(build_runner: &mut BuildRunner<'_, '_>, unit: &Unit) -> CargoResul
             cmd.env("RUSTC_WORKSPACE_WRAPPER", wrapper);
         }
     }
-    cmd.env(
-        "CARGO_ENCODED_RUSTFLAGS",
-        bcx.rustflags_args(unit).join("\x1f"),
-    );
+    cmd.env("CARGO_ENCODED_RUSTFLAGS", unit.rustflags.join("\x1f"));
     cmd.env_remove("RUSTFLAGS");
 
     if build_runner.bcx.ws.gctx().extra_verbose() {

src/cargo/core/compiler/fingerprint/mod.rs

@@ -1417,7 +1417,7 @@ fn calculate_normal(
     let extra_flags = if unit.mode.is_doc() || unit.mode.is_doc_scrape() {
         build_runner.bcx.rustdocflags_args(unit)
     } else {
-        build_runner.bcx.rustflags_args(unit)
+        &unit.rustflags
     }
     .to_vec();
 
@@ -1512,7 +1512,7 @@ fn calculate_run_custom_build(
 An I/O error happened. Please make sure you can access the file.
 
 By default, if your project contains a build script, cargo scans all files in
-it to determine whether a rebuild is needed. If you don't expect to access the 
+it to determine whether a rebuild is needed. If you don't expect to access the
 file, specify `rerun-if-changed` in your build script.
 See https://doc.rust-lang.org/cargo/reference/build-scripts.html#rerun-if-changed for more information.";
             pkg_fingerprint(build_runner.bcx, &unit.pkg).map_err(|err| {
@@ -1542,7 +1542,7 @@ See https://doc.rust-lang.org/cargo/reference/build-scripts.html#rerun-if-change
             .collect::<CargoResult<Vec<_>>>()?
     };
 
-    let rustflags = build_runner.bcx.rustflags_args(unit).to_vec();
+    let rustflags = unit.rustflags.to_vec();
 
     Ok(Fingerprint {
         local: Mutex::new(local),

src/cargo/core/compiler/mod.rs

@@ -683,7 +683,7 @@ 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);
-    base.args(build_runner.bcx.rustflags_args(unit));
+    base.args(&unit.rustflags);
     if build_runner.bcx.gctx.cli_unstable().binary_dep_depinfo {
         base.arg("-Z").arg("binary-dep-depinfo");
     }

src/cargo/core/compiler/standard_lib.rs

@@ -178,6 +178,7 @@ pub fn generate_std_roots(
     package_set: &PackageSet<'_>,
     interner: &UnitInterner,
     profiles: &Profiles,
+    target_data: &RustcTargetData<'_>,
 ) -> CargoResult<HashMap<CompileKind, Vec<Unit>>> {
     // Generate the root Units for the standard library.
     let std_ids = crates
@@ -216,6 +217,7 @@ pub fn generate_std_roots(
                 *kind,
                 mode,
                 features.clone(),
+                target_data.info(*kind).rustflags.clone(),
                 /*is_std*/ true,
                 /*dep_hash*/ 0,
                 IsArtifact::No,

src/cargo/core/compiler/unit.rs

@@ -14,6 +14,7 @@ use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::ops::Deref;
 use std::rc::Rc;
+use std::sync::Arc;
 
 /// All information needed to define a unit.
 ///
@@ -59,6 +60,17 @@ pub struct UnitInner {
     /// The `cfg` features to enable for this unit.
     /// This must be sorted.
     pub features: Vec<InternedString>,
+    /// Extra compiler flags to pass to `rustc` for a given unit.
+    ///
+    /// Although it depends on the caller, in the current Cargo implementation,
+    /// these flags take precedence over those from [`BuildContext::extra_args_for`].
+    ///
+    /// As of now, these flags come from environment variables and configurations.
+    /// See [`TargetInfo.rustflags`] for more on how Cargo collects them.
+    ///
+    /// [`BuildContext::extra_args_for`]: crate::core::compiler::build_context::BuildContext::extra_args_for
+    /// [`TargetInfo.rustflags`]: crate::core::compiler::build_context::TargetInfo::rustflags
+    pub rustflags: Arc<[String]>,
     // if `true`, the dependency is an artifact dependency, requiring special handling when
     // calculating output directories, linkage and environment variables provided to builds.
     pub artifact: IsArtifact,
@@ -151,6 +163,7 @@ impl fmt::Debug for Unit {
             .field("kind", &self.kind)
             .field("mode", &self.mode)
             .field("features", &self.features)
+            .field("rustflags", &self.rustflags)
             .field("artifact", &self.artifact.is_true())
             .field(
                 "artifact_target_for_features",
@@ -198,6 +211,7 @@ impl UnitInterner {
         kind: CompileKind,
         mode: CompileMode,
         features: Vec<InternedString>,
+        rustflags: Arc<[String]>,
         is_std: bool,
         dep_hash: u64,
         artifact: IsArtifact,
@@ -231,6 +245,7 @@ impl UnitInterner {
             kind,
             mode,
             features,
+            rustflags,
             is_std,
             dep_hash,
             artifact,

src/cargo/core/compiler/unit_dependencies.rs

@@ -859,6 +859,7 @@ fn new_unit_dep_with_profile(
         kind,
         mode,
         features,
+        state.target_data.info(kind).rustflags.clone(),
         state.is_std,
         /*dep_hash*/ 0,
         artifact.map_or(IsArtifact::No, |_| IsArtifact::Yes),

src/cargo/ops/cargo_compile/mod.rs

@@ -360,6 +360,7 @@ pub fn create_bcx<'a, 'gctx>(
     let generator = UnitGenerator {
         ws,
         packages: &to_builds,
+        target_data: &target_data,
         filter,
         requested_kinds: &build_config.requested_kinds,
         explicit_host_kind,
@@ -399,6 +400,7 @@ pub fn create_bcx<'a, 'gctx>(
             &pkg_set,
             interner,
             &profiles,
+            &target_data,
         )?
     } else {
         Default::default()
@@ -694,6 +696,7 @@ fn traverse_and_share(
             to_host.unwrap(),
             unit.mode,
             unit.features.clone(),
+            unit.rustflags.clone(),
             unit.is_std,
             unit.dep_hash,
             unit.artifact,
@@ -719,6 +722,7 @@ fn traverse_and_share(
         canonical_kind,
         unit.mode,
         unit.features.clone(),
+        unit.rustflags.clone(),
         unit.is_std,
         new_dep_hash,
         unit.artifact,
@@ -880,6 +884,7 @@ fn override_rustc_crate_types(
             unit.kind,
             unit.mode,
             unit.features.clone(),
+            unit.rustflags.clone(),
             unit.is_std,
             unit.dep_hash,
             unit.artifact,

src/cargo/ops/cargo_compile/unit_generator.rs

@@ -4,8 +4,8 @@ use std::fmt::Write;
 
 use crate::core::compiler::rustdoc::RustdocScrapeExamples;
 use crate::core::compiler::unit_dependencies::IsArtifact;
-use crate::core::compiler::UnitInterner;
 use crate::core::compiler::{CompileKind, CompileMode, Unit};
+use crate::core::compiler::{RustcTargetData, UnitInterner};
 use crate::core::dependency::DepKind;
 use crate::core::profiles::{Profiles, UnitFor};
 use crate::core::resolver::features::{self, FeaturesFor};
@@ -47,6 +47,7 @@ struct Proposal<'a> {
 pub(super) struct UnitGenerator<'a, 'gctx> {
     pub ws: &'a Workspace<'gctx>,
     pub packages: &'a [&'a Package],
+    pub target_data: &'a RustcTargetData<'gctx>,
     pub filter: &'a CompileFilter,
     pub requested_kinds: &'a [CompileKind],
     pub explicit_host_kind: CompileKind,
@@ -162,13 +163,15 @@ impl<'a> UnitGenerator<'a, '_> {
                     unit_for,
                     kind,
                 );
+                let kind = kind.for_target(target);
                 self.interner.intern(
                     pkg,
                     target,
                     profile,
-                    kind.for_target(target),
+                    kind,
                     target_mode,
                     features.clone(),
+                    self.target_data.info(kind).rustflags.clone(),
                     /*is_std*/ false,
                     /*dep_hash*/ 0,
                     IsArtifact::No,

tests/testsuite/rustflags.rs

@@ -1599,14 +1599,18 @@ fn target_applies_to_host_rustflags_works() {
         )
         .build();
 
-    // Use RUSTFLAGS to pass an argument that would generate an error
-    // but it is ignored.
+    // Use RUSTFLAGS to pass an argument that will generate an error.
     p.cargo("check")
         .masquerade_as_nightly_cargo(&["target-applies-to-host"])
         .arg("-Ztarget-applies-to-host")
         .env("CARGO_TARGET_APPLIES_TO_HOST", "false")
         .env("RUSTFLAGS", r#"--cfg feature="flag""#)
-        .with_status(0)
+        .with_status(101)
+        .with_stderr_data(
+            "[CHECKING] foo v0.0.1 ([ROOT]/foo)
+[ERROR] flag passed
+...",
+        )
         .run();
 }