test with new build-dir layout

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
         rust:
           - nightly
           # Check a ~3 months old nightly as "oldest supported version"
-          - nightly-2025-05-01
+          - nightly-2026-01-01
         # We want to run all of the above on Linux, macOS, windows-msvc, windows-gnu.
         # The semantics of combining `include` with other things in GHA are very strange
         # so this seems like the best way of doing that.
@@ -51,6 +51,18 @@ jobs:
       - name: Run tests
         run: cargo test --locked --target ${{ matrix.target }}
 
+  build-dir-new-layout:
+    name: Test Suite (build-dir-new-layout)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: nightly
+          components: rust-src
+      - name: Run tests
+        run: CARGO_UNSTABLE_BUILD_DIR_NEW_LAYOUT=true cargo test --locked
+
   check:
     name: Checks
     runs-on: ubuntu-latest

src/lib.rs

@@ -531,17 +531,17 @@ impl<'a> SysrootBuilder<'a> {
         fs::create_dir(&staging_lib_dir).context("failed to create staging/lib dir")?;
         let out_dir = build_target_dir
             .join(&target_name)
-            .join(DEFAULT_SYSROOT_PROFILE)
-            .join("deps");
-        for entry in fs::read_dir(&out_dir).context("failed to read cargo out dir")? {
-            let entry = entry.context("failed to read cargo out dir entry")?;
-            assert!(
-                entry.file_type().unwrap().is_file(),
-                "cargo out dir must not contain directories"
-            );
-            let entry = entry.path();
-            fs::copy(&entry, staging_lib_dir.join(entry.file_name().unwrap()))
-                .context("failed to copy cargo out file")?;
+            .join(DEFAULT_SYSROOT_PROFILE);
+        if out_dir.join("deps").exists() {
+            // Old build dir layout: $out/deps
+            copy_files(&out_dir.join("deps"), &staging_lib_dir)
+                .context("failed to copy cargo out dir (old layout)")?;
+        } else {
+            // New build dir layout: $out/build/*/*/out.
+            for_each_dir(&out_dir.join("build"), |dir| {
+                for_each_dir(dir, |dir| copy_files(&dir.join("out"), &staging_lib_dir))
+            })
+            .context("failed to copy cargo out dir (new layout)")?;
         }
 
         // Write the hash file (into the staging dir).
@@ -564,6 +564,31 @@ impl<'a> SysrootBuilder<'a> {
     }
 }
 
+/// Coopy all files in `from` to `to`.
+fn copy_files(from: &Path, to: &Path) -> Result<()> {
+    for entry in fs::read_dir(from)? {
+        let entry = entry?;
+        assert!(
+            entry.file_type()?.is_file(),
+            "cargo out dir must not contain directories"
+        );
+        fs::copy(&entry.path(), to.join(entry.file_name()))?;
+    }
+    Ok(())
+}
+
+/// Invoke the closure for each directory inside `path`.
+fn for_each_dir(path: &Path, f: impl Fn(&Path) -> Result<()>) -> Result<()> {
+    for entry in fs::read_dir(path)? {
+        let entry = entry?;
+        if !entry.file_type()?.is_dir() {
+            continue;
+        }
+        f(&entry.path())?;
+    }
+    Ok(())
+}
+
 /// Collect the patches from the sysroot's workspace `Cargo.toml`.
 fn extract_patches(src_dir: &Path) -> Table {
     // Assume no patch is needed if the workspace Cargo.toml doesn't exist

tests/tests.rs

@@ -1,3 +1,5 @@
+#![allow(clippy::useless_format)]
+
 use std::fs;
 use std::process::{self, Command};
 
@@ -17,9 +19,10 @@ fn run(cmd: &mut Command) {
 
 fn build_sysroot(b: SysrootBuilder) {
     let src_dir = rustc_sysroot_src(Command::new("rustc")).unwrap();
-    b.cargo(Command::new("cargo"))
-        .build_from_source(&src_dir)
-        .unwrap();
+    let mut cargo = Command::new("cargo");
+    // Cargo complains about unknown `-Z` flags but not about unknown env vars. :)
+    cargo.env("CARGO_UNSTABLE_JSON_TARGET_SPEC", "true");
+    b.cargo(cargo).build_from_source(&src_dir).unwrap();
 }
 
 fn test_sysroot_build(target: &str, mode: BuildMode, rustc_version: &VersionMeta) {
@@ -91,28 +94,11 @@ fn no_std() {
 
 #[test]
 fn json_target() {
-    // The syntax for `target-pointer-width` changed from `"64"`` to `64`. Figure out which one
-    // this rustc needs...
-    let sample_json = Command::new("rustc")
-        .args([
-            "-Zunstable-options",
-            "--print=target-spec-json",
-            "--target=x86_64-unknown-none",
-        ])
-        .output()
-        .unwrap()
-        .stdout;
-    let sample_json = String::from_utf8(sample_json).unwrap();
-    let ptr_width = if sample_json.contains(r#""target-pointer-width": 64"#) {
-        "64"
-    } else {
-        r#""64""#
-    };
     let target = format!(
         r#"{{
         "llvm-target": "x86_64-unknown-none",
         "target-endian": "little",
-        "target-pointer-width": {ptr_width},
+        "target-pointer-width": 64,
         "target-c-int-width": 32,
         "data-layout": "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128",
         "arch": "x86_64",