support using the in-tree compiler_builtins

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
         rust:
           - nightly
           # Check a ~3 months old nightly as "oldest supported version"
-          - nightly-2025-01-01
+          - nightly-2025-05-01
         # 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.

src/lib.rs

@@ -301,18 +301,21 @@ impl<'a> SysrootBuilder<'a> {
     fn gen_manifest(&self, src_dir: &Path) -> String {
         let have_sysroot_crate = src_dir.join("sysroot").exists();
         let crates = match &self.config {
+            // As long as the sysroot has a ptch for compiler_builtins, we need to include it in the
+            // NoStd variant explicitly.
             SysrootConfig::NoStd => format!(
                 r#"
                 [dependencies.core]
                 path = {src_dir_core:?}
                 [dependencies.alloc]
                 path = {src_dir_alloc:?}
                 [dependencies.compiler_builtins]
+                path = {src_dir_builtins:?}
                 features = ["rustc-dep-of-std", "mem"]
-                version = "*"
                 "#,
                 src_dir_core = src_dir.join("core"),
                 src_dir_alloc = src_dir.join("alloc"),
+                src_dir_builtins = src_dir.join("compiler-builtins").join("compiler-builtins"),
             ),
             SysrootConfig::WithStd { std_features } if have_sysroot_crate => format!(
                 r#"
@@ -524,7 +527,7 @@ impl<'a> SysrootBuilder<'a> {
             TempDir::new_in(&self.sysroot_dir).context("failed to create staging dir")?;
         // Copy the output to `$staging/lib`.
         let staging_lib_dir = staging_dir.path().join("lib");
-        fs::create_dir(&staging_lib_dir).context("faiked to create staging/lib dir")?;
+        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)

tests/tests.rs

@@ -95,7 +95,7 @@ fn json_target() {
         "llvm-target": "x86_64-unknown-none",
         "target-endian": "little",
         "target-pointer-width": "64",
-        "target-c-int-width": "32",
+        "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",
         "os": "none",