allow build-std to be configured per-target in .cargo/config.toml

.github/workflows/main.yml

@@ -256,6 +256,7 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - run: rustup update nightly && rustup default nightly
+    - run: rustup target add aarch64-unknown-none
     - run: rustup component add rust-src
     - run: cargo build
     - run: cargo test -p cargo --test build-std

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

@@ -1096,6 +1096,24 @@ impl<'gctx> RustcTargetData<'gctx> {
         }
     }
 
+    /// Returns an iterator that contains all possible non-host targets for this session,
+    /// including those set by artifact dependencies or per-pkg-targets.
+    ///
+    /// Should be called only after workspace resolution to ensure that all targets have
+    /// been collected.
+    pub fn all_kinds(&self) -> impl Iterator<Item = CompileKind> + '_ {
+        self.target_config.keys().copied().map(CompileKind::Target)
+    }
+
+    /// Returns whether `build_std` was enabled in any of the targets we have queried.
+    pub fn build_std(&self) -> bool {
+        self.host_config.build_std.is_some()
+            || self
+                .target_config
+                .values()
+                .any(|config| config.build_std.is_some())
+    }
+
     pub fn get_unsupported_std_targets(&self) -> Vec<&str> {
         let mut unsupported = Vec::new();
         for (target, target_info) in &self.target_info {

src/cargo/core/compiler/standard_lib.rs

@@ -10,48 +10,78 @@ use crate::core::{PackageId, PackageSet, Resolve, Workspace};
 use crate::ops::{self, Packages};
 use crate::util::errors::CargoResult;
 
+use std::borrow::Borrow;
 use std::collections::{HashMap, HashSet};
+use std::hash::Hash;
 use std::path::PathBuf;
 
 use super::BuildConfig;
 
-fn std_crates<'a>(crates: &'a [String], default: &'static str, units: &[Unit]) -> HashSet<&'a str> {
-    let mut crates = HashSet::from_iter(crates.iter().map(|s| s.as_str()));
+fn add_default_std_crates<T: Borrow<str> + From<&'static str> + Eq + Hash>(
+    crates: &mut HashSet<T>,
+    default: &'static str,
+    include_libtest: bool,
+) {
     // This is a temporary hack until there is a more principled way to
     // declare dependencies in Cargo.toml.
     if crates.is_empty() {
-        crates.insert(default);
+        crates.insert(default.into());
     }
     if crates.contains("std") {
-        crates.insert("core");
-        crates.insert("alloc");
-        crates.insert("proc_macro");
-        crates.insert("panic_unwind");
-        crates.insert("compiler_builtins");
-        // Only build libtest if it looks like it is needed (libtest depends on libstd)
-        // If we know what units we're building, we can filter for libtest depending on the jobs.
-        if units
-            .iter()
-            .any(|unit| unit.mode.is_rustc_test() && unit.target.harness())
-        {
-            crates.insert("test");
+        crates.insert("core".into());
+        crates.insert("alloc".into());
+        crates.insert("proc_macro".into());
+        crates.insert("panic_unwind".into());
+        crates.insert("compiler_builtins".into());
+        if include_libtest {
+            crates.insert("test".into());
         }
     } else if crates.contains("core") {
-        crates.insert("compiler_builtins");
+        crates.insert("compiler_builtins".into());
     }
+}
+
+fn std_crates(
+    target_data: &RustcTargetData<'_>,
+    cli_crates: Option<&[String]>,
+    include_libtest: bool,
+) -> HashMap<CompileKind, HashSet<String>> {
+    let mut map = HashMap::new();
+    for kind in target_data.all_kinds().chain([CompileKind::Host]) {
+        let requested_crates = if let Some(crates) = &target_data.target_config(kind).build_std {
+            crates.val.as_slice()
+        } else if let Some(cli_crates) = cli_crates {
+            cli_crates
+        } else {
+            continue;
+        };
 
-    crates
+        let mut actual_crates = requested_crates
+            .iter()
+            .map(Clone::clone)
+            .collect::<HashSet<_>>();
+        add_default_std_crates(
+            &mut actual_crates,
+            if target_data.info(kind).maybe_support_std() {
+                "std"
+            } else {
+                "core"
+            },
+            include_libtest,
+        );
+        map.insert(kind, actual_crates);
+    }
+    map
 }
 
 /// Resolve the standard library dependencies.
 ///
-/// * `crates` is the arg value from `-Zbuild-std`.
+/// * `cli_crates` is the arg value from `-Zbuild-std`.
 pub fn resolve_std<'gctx>(
     ws: &Workspace<'gctx>,
     target_data: &mut RustcTargetData<'gctx>,
     build_config: &BuildConfig,
-    crates: &[String],
-    kinds: &[CompileKind],
+    cli_crates: Option<&[String]>,
 ) -> CargoResult<(PackageSet<'gctx>, Resolve, ResolvedFeatures)> {
     if build_config.build_plan {
         ws.gctx()
@@ -69,31 +99,32 @@ pub fn resolve_std<'gctx>(
     // `[dev-dependencies]`. No need for us to generate a `Resolve` which has
     // those included because we'll never use them anyway.
     std_ws.set_require_optional_deps(false);
+    let mut build_std_features = HashSet::new();
     let specs = {
-        // If there is anything looks like needing std, resolve with it.
-        // If not, we assume only `core` maye be needed, as `core the most fundamental crate.
-        //
-        // This may need a UI overhaul if `build-std` wants to fully support multi-targets.
-        let maybe_std = kinds
-            .iter()
-            .any(|kind| target_data.info(*kind).maybe_support_std());
-        let mut crates = std_crates(crates, if maybe_std { "std" } else { "core" }, &[]);
+        let mut set = HashSet::new();
+        for (compile_kind, new_set) in std_crates(target_data, cli_crates, false) {
+            set.extend(new_set);
+            if let Some(features) = &target_data.target_config(compile_kind).build_std_features {
+                build_std_features.extend(features.val.as_slice().iter().map(String::clone));
+            } else if let Some(features) = &gctx.cli_unstable().build_std_features {
+                build_std_features.extend(features.iter().map(String::clone));
+            } else {
+                build_std_features
+                    .extend(["panic-unwind", "backtrace", "default"].map(String::from));
+            }
+        }
         // `sysroot` is not in the default set because it is optional, but it needs
-        // to be part of the resolve in case we do need it or `libtest`.
-        crates.insert("sysroot");
-        let specs = Packages::Packages(crates.into_iter().map(Into::into).collect());
+        // to be part of the resolve in case we do need it for `libtest`.
+        set.insert("sysroot".into());
+        let specs = Packages::Packages(set.into_iter().collect());
         specs.to_package_id_specs(&std_ws)?
     };
-    let features = match &gctx.cli_unstable().build_std_features {
-        Some(list) => list.clone(),
-        None => vec![
-            "panic-unwind".to_string(),
-            "backtrace".to_string(),
-            "default".to_string(),
-        ],
-    };
+
+    let build_std_features = build_std_features.into_iter().collect::<Vec<_>>();
     let cli_features = CliFeatures::from_command_line(
-        &features, /*all_features*/ false, /*uses_default_features*/ false,
+        &build_std_features,
+        /*all_features*/ false,
+        /*uses_default_features*/ false,
     )?;
     let dry_run = false;
     let resolve = ops::resolve_ws_with_opts(
@@ -118,76 +149,62 @@ pub fn resolve_std<'gctx>(
 /// * `crates` is the arg value from `-Zbuild-std`.
 /// * `units` is the root units of the build.
 pub fn generate_std_roots(
-    crates: &[String],
+    cli_crates: Option<&[String]>,
     units: &[Unit],
     std_resolve: &Resolve,
     std_features: &ResolvedFeatures,
-    kinds: &[CompileKind],
     package_set: &PackageSet<'_>,
     interner: &UnitInterner,
     profiles: &Profiles,
     target_data: &RustcTargetData<'_>,
 ) -> CargoResult<HashMap<CompileKind, Vec<Unit>>> {
     // Generate a map of Units for each kind requested.
-    let mut ret = HashMap::new();
-    let (maybe_std, maybe_core): (Vec<&CompileKind>, Vec<_>) = kinds
+    let mut ret: HashMap<CompileKind, Vec<Unit>> = HashMap::new();
+    // Only build libtest if it looks like it is needed (libtest depends on libstd)
+    // If we know what units we're building, we can filter for libtest depending on the jobs.
+    let include_libtest = units
         .iter()
-        .partition(|kind| target_data.info(**kind).maybe_support_std());
-    for (default_crate, kinds) in [("core", maybe_core), ("std", maybe_std)] {
-        if kinds.is_empty() {
-            continue;
-        }
-        generate_roots(
-            &mut ret,
-            default_crate,
-            crates,
-            units,
-            std_resolve,
-            std_features,
-            &kinds,
-            package_set,
-            interner,
-            profiles,
-            target_data,
-        )?;
-    }
+        .any(|unit| unit.mode.is_rustc_test() && unit.target.harness());
+    let crates = std_crates(target_data, cli_crates, include_libtest);
 
-    Ok(ret)
-}
+    let all_crates = crates
+        .values()
+        .flat_map(|set| set)
+        .map(|s| s.as_str())
+        .collect::<HashSet<_>>();
+    // collect as `Vec` for stable order
+    let all_crates = all_crates.into_iter().collect::<Vec<_>>();
+    let std_ids = all_crates
+        .iter()
+        .map(|crate_name| {
+            std_resolve
+                .query(crate_name)
+                .map(|pkg_id| (pkg_id, *crate_name))
+        })
+        .collect::<CargoResult<HashMap<PackageId, &str>>>()?;
+    let std_pkgs = package_set.get_many(std_ids.keys().copied())?;
 
-fn generate_roots(
-    ret: &mut HashMap<CompileKind, Vec<Unit>>,
-    default: &'static str,
-    crates: &[String],
-    units: &[Unit],
-    std_resolve: &Resolve,
-    std_features: &ResolvedFeatures,
-    kinds: &[&CompileKind],
-    package_set: &PackageSet<'_>,
-    interner: &UnitInterner,
-    profiles: &Profiles,
-    target_data: &RustcTargetData<'_>,
-) -> CargoResult<()> {
-    let std_ids = std_crates(crates, default, units)
+    // a map of the requested std crate and its actual package.
+    let std_pkgs = std_pkgs
         .iter()
-        .map(|crate_name| std_resolve.query(crate_name))
-        .collect::<CargoResult<Vec<PackageId>>>()?;
-    let std_pkgs = package_set.get_many(std_ids)?;
+        .map(|pkg| (*std_ids.get(&pkg.package_id()).unwrap(), *pkg))
+        .collect::<HashMap<_, _>>();
 
-    for pkg in std_pkgs {
-        let lib = pkg
-            .targets()
-            .iter()
-            .find(|t| t.is_lib())
-            .expect("std has a lib");
-        // I don't think we need to bother with Check here, the difference
-        // in time is minimal, and the difference in caching is
-        // significant.
-        let mode = CompileMode::Build;
-        let features = std_features.activated_features(pkg.package_id(), FeaturesFor::NormalOrDev);
-        for kind in kinds {
-            let kind = **kind;
-            let list = ret.entry(kind).or_insert_with(Vec::new);
+    for (&kind, crates) in &crates {
+        let list = ret.entry(kind).or_default();
+        for krate in crates {
+            let pkg = std_pkgs.get(krate.as_str()).unwrap();
+            let lib = pkg
+                .targets()
+                .iter()
+                .find(|t| t.is_lib())
+                .expect("std has a lib");
+            // I don't think we need to bother with Check here, the difference
+            // in time is minimal, and the difference in caching is
+            // significant.
+            let mode = CompileMode::Build;
+            let features =
+                std_features.activated_features(pkg.package_id(), FeaturesFor::NormalOrDev);
             let unit_for = UnitFor::new_normal(kind);
             let profile = profiles.get_profile(
                 pkg.package_id(),
@@ -213,7 +230,8 @@ fn generate_roots(
             ));
         }
     }
-    Ok(())
+
+    Ok(ret)
 }
 
 fn detect_sysroot_src_path(target_data: &RustcTargetData<'_>) -> CargoResult<PathBuf> {

src/cargo/core/compiler/unit_dependencies.rs

@@ -177,16 +177,19 @@ fn attach_std_deps(
     let mut found = false;
     for (unit, deps) in state.unit_dependencies.iter_mut() {
         if !unit.kind.is_host() && !unit.mode.is_run_custom_build() {
-            deps.extend(std_roots[&unit.kind].iter().map(|unit| UnitDep {
-                unit: unit.clone(),
-                unit_for: UnitFor::new_normal(unit.kind),
-                extern_crate_name: unit.pkg.name(),
-                dep_name: None,
-                // TODO: Does this `public` make sense?
-                public: true,
-                noprelude: true,
-            }));
-            found = true;
+            // only attach roots for which the user has requested `build-std` for.
+            if let Some(roots) = std_roots.get(&unit.kind) {
+                deps.extend(roots.iter().map(|unit| UnitDep {
+                    unit: unit.clone(),
+                    unit_for: UnitFor::new_normal(unit.kind),
+                    extern_crate_name: unit.pkg.name(),
+                    dep_name: None,
+                    // TODO: Does this `public` make sense?
+                    public: true,
+                    noprelude: true,
+                }));
+                found = true;
+            }
         }
     }
     // And also include the dependencies of the standard library itself. Don't

src/cargo/ops/cargo_compile/mod.rs

@@ -287,13 +287,13 @@ pub fn create_bcx<'a, 'gctx>(
         resolved_features,
     } = resolve;
 
-    let std_resolve_features = if let Some(crates) = &gctx.cli_unstable().build_std {
+    let build_std = gctx.cli_unstable().build_std.is_some() || target_data.build_std();
+    let std_resolve_features = if build_std {
         let (std_package_set, std_resolve, std_features) = standard_lib::resolve_std(
             ws,
             &mut target_data,
             &build_config,
-            crates,
-            &build_config.requested_kinds,
+            gctx.cli_unstable().build_std.as_deref(),
         )?;
         pkg_set.add_set(std_package_set);
         Some((std_resolve, std_features))
@@ -354,14 +354,6 @@ pub fn create_bcx<'a, 'gctx>(
     // assuming `--target $HOST` was specified. See
     // `rebuild_unit_graph_shared` for more on why this is done.
     let explicit_host_kind = CompileKind::Target(CompileTarget::new(&target_data.rustc.host)?);
-    let explicit_host_kinds: Vec<_> = build_config
-        .requested_kinds
-        .iter()
-        .map(|kind| match kind {
-            CompileKind::Host => explicit_host_kind,
-            CompileKind::Target(t) => CompileKind::Target(*t),
-        })
-        .collect();
 
     // Passing `build_config.requested_kinds` instead of
     // `explicit_host_kinds` here so that `generate_root_units` can do
@@ -398,14 +390,13 @@ pub fn create_bcx<'a, 'gctx>(
         Vec::new()
     };
 
-    let std_roots = if let Some(crates) = gctx.cli_unstable().build_std.as_ref() {
+    let std_roots = if build_std {
         let (std_resolve, std_features) = std_resolve_features.as_ref().unwrap();
         standard_lib::generate_std_roots(
-            &crates,
+            gctx.cli_unstable().build_std.as_deref(),
             &units,
             std_resolve,
             std_features,
-            &explicit_host_kinds,
             &pkg_set,
             interner,
             &profiles,