fix(build-std): behavior revert of 125e873

This is kinda a revert of 125e873
in terms of the behavior.

After this, now `std_resolve` is always resolved by the same set of
packages that Cargo will use to generate the unit graph, (technically
the same set of crates + `sysroot`), by sharing the same set of primary
packages via `std_crates` functions.

Author: weihanglo

src/cargo/core/compiler/standard_lib.rs

@@ -44,10 +44,14 @@ fn std_crates<'a>(crates: &'a [String], default: &'static str, units: &[Unit]) -
 }
 
 /// Resolve the standard library dependencies.
+///
+/// * `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],
 ) -> CargoResult<(PackageSet<'gctx>, Resolve, ResolvedFeatures)> {
     if build_config.build_plan {
         ws.gctx()
@@ -65,10 +69,21 @@ 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);
-    // `sysroot` + the default feature set below should give us a good default
-    // Resolve, which includes `libtest` as well.
-    let specs = Packages::Packages(vec!["sysroot".into()]);
-    let specs = specs.to_package_id_specs(&std_ws)?;
+    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" }, &[]);
+        // `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());
+        specs.to_package_id_specs(&std_ws)?
+    };
     let features = match &gctx.cli_unstable().build_std_features {
         Some(list) => list.clone(),
         None => vec![

src/cargo/ops/cargo_compile/mod.rs

@@ -289,9 +289,14 @@ pub fn create_bcx<'a, 'gctx>(
         resolved_features,
     } = resolve;
 
-    let std_resolve_features = if gctx.cli_unstable().build_std.is_some() {
-        let (std_package_set, std_resolve, std_features) =
-            standard_lib::resolve_std(ws, &mut target_data, &build_config)?;
+    let std_resolve_features = if let Some(crates) = &gctx.cli_unstable().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,
+        )?;
         pkg_set.add_set(std_package_set);
         Some((std_resolve, std_features))
     } else {

src/cargo/ops/cargo_fetch.rs

@@ -64,8 +64,14 @@ pub fn fetch<'a>(
     }
 
     // If -Zbuild-std was passed, download dependencies for the standard library.
-    if gctx.cli_unstable().build_std.is_some() {
-        let (std_package_set, _, _) = standard_lib::resolve_std(ws, &mut data, &build_config)?;
+    if let Some(crates) = &gctx.cli_unstable().build_std {
+        let (std_package_set, _, _) = standard_lib::resolve_std(
+            ws,
+            &mut data,
+            &build_config,
+            crates,
+            &build_config.requested_kinds,
+        )?;
         packages.add_set(std_package_set);
     }
 

tests/build-std/main.rs

@@ -438,10 +438,5 @@ fn test_panic_abort() {
         .build_std_arg("std,panic_abort")
         .env("RUSTFLAGS", "-C panic=abort")
         .arg("-Zbuild-std-features=panic_immediate_abort")
-        .with_status(101)
-        .with_stderr_data(str![[r#"
-[ERROR] package ID specification `panic_unwind` did not match any packages
-
-"#]])
         .run();
 }