build-std: remove sysroot probe

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

@@ -29,6 +29,8 @@ pub struct TargetInfo {
     crate_types: RefCell<HashMap<String, Option<(String, String)>>>,
     /// `cfg` information extracted from `rustc --print=cfg`.
     cfg: Vec<Cfg>,
+    /// Path to the sysroot.
+    pub sysroot: PathBuf,
     /// Path to the "lib" or "bin" directory that rustc uses for its dynamic
     /// libraries.
     pub sysroot_host_libdir: PathBuf,
@@ -134,13 +136,13 @@ impl TargetInfo {
                 output_err_info(&process, &output, &error)
             ),
         };
-        let mut sysroot_host_libdir = PathBuf::from(line);
-        if cfg!(windows) {
-            sysroot_host_libdir.push("bin");
+        let sysroot = PathBuf::from(line);
+        let sysroot_host_libdir = if cfg!(windows) {
+            sysroot.join("bin")
         } else {
-            sysroot_host_libdir.push("lib");
-        }
-        let mut sysroot_target_libdir = PathBuf::from(line);
+            sysroot.join("lib")
+        };
+        let mut sysroot_target_libdir = sysroot.clone();
         sysroot_target_libdir.push("lib");
         sysroot_target_libdir.push("rustlib");
         sysroot_target_libdir.push(match &kind {
@@ -162,6 +164,7 @@ impl TargetInfo {
         Ok(TargetInfo {
             crate_type_process,
             crate_types: RefCell::new(map),
+            sysroot,
             sysroot_host_libdir,
             sysroot_target_libdir,
             // recalculate `rustflags` from above now that we have `cfg`

src/cargo/core/compiler/standard_lib.rs

@@ -36,7 +36,7 @@ pub fn resolve_std<'cfg>(
     requested_target: CompileKind,
     crates: &[String],
 ) -> CargoResult<(PackageSet<'cfg>, Resolve, ResolvedFeatures)> {
-    let src_path = detect_sysroot_src_path(ws)?;
+    let src_path = detect_sysroot_src_path(target_data)?;
     let to_patch = [
         "rustc-std-workspace-core",
         "rustc-std-workspace-alloc",
@@ -163,21 +163,19 @@ pub fn generate_std_roots<'a>(
         .collect::<CargoResult<Vec<_>>>()
 }
 
-fn detect_sysroot_src_path(ws: &Workspace<'_>) -> CargoResult<PathBuf> {
+fn detect_sysroot_src_path(target_data: &RustcTargetData) -> CargoResult<PathBuf> {
     if let Some(s) = env::var_os("__CARGO_TESTS_ONLY_SRC_ROOT") {
         return Ok(s.into());
     }
 
     // NOTE: This is temporary until we figure out how to acquire the source.
-    // If we decide to keep the sysroot probe, then BuildConfig will need to
-    // be restructured so that the TargetInfo is created earlier and passed
-    // in, so we don't have this extra call to rustc.
-    let rustc = ws.config().load_global_rustc(Some(ws))?;
-    let output = rustc.process().arg("--print=sysroot").exec_with_output()?;
-    let s = String::from_utf8(output.stdout)
-        .map_err(|e| anyhow::format_err!("rustc didn't return utf8 output: {:?}", e))?;
-    let sysroot = PathBuf::from(s.trim());
-    let src_path = sysroot.join("lib").join("rustlib").join("src").join("rust");
+    let src_path = target_data
+        .info(CompileKind::Host)
+        .sysroot
+        .join("lib")
+        .join("rustlib")
+        .join("src")
+        .join("rust");
     let lock = src_path.join("Cargo.lock");
     if !lock.exists() {
         anyhow::bail!(