stdbuf: fix build.rs to propagate custom profiles to libstdbuf nested build

The PROFILE env var only returns the base profile name ('release' or 'debug'),
not the actual profile. For example, when building with --profile=release-small,
PROFILE=release, so the old code would pass --release to the nested libstdbuf
build, causing it to be compiled with release settings instead of release-small
settings (opt-level=z, strip=true, etc.).

Fix this by extracting the actual profile name from OUT_DIR, which always
contains the real profile name in its path (.../target/{profile}/build/...).
This correctly handles all custom profiles like release-small, profiling, etc.

Fixes: #12434

Signed-off-by: Etienne Cordonnier <ecordonnier@snap.com>

Author: Ecordonnier

src/uu/stdbuf/build.rs

@@ -85,12 +85,21 @@ fn main() {
     cmd.current_dir(libstdbuf_src)
         .args(["build", "--target-dir", build_dir.to_str().unwrap()]);
 
-    // Get the current profile
-    let profile = env::var("PROFILE").unwrap_or_else(|_| "debug".to_string());
-
-    // Pass the release flag if we're in release mode
-    if profile == "release" || profile == "bench" {
-        cmd.arg("--release");
+    // Determine the actual profile from OUT_DIR since PROFILE env var only gives the base profile
+    // for inherited profiles (e.g., PROFILE=release for both release and release-small).
+    // OUT_DIR is always .../target/[triple/]{profile}/build/{pkg-hash}/out, so the profile
+    // is exactly 3 parent levels up — regardless of whether a target triple is in the path.
+    let profile = Path::new(&out_dir)
+        .parent() // .../build/{pkg-hash}
+        .and_then(|p| p.parent()) // .../build
+        .and_then(|p| p.parent()) // .../{profile}
+        .and_then(|p| p.file_name())
+        .and_then(|s| s.to_str())
+        .unwrap_or("debug");
+
+    // Pass the profile to the nested build (for release, release-small, profiling, bench, etc.)
+    if profile != "debug" {
+        cmd.arg("--profile").arg(profile);
     }
 
     // Pass the target architecture if we're cross-compiling
@@ -112,17 +121,17 @@ fn main() {
     // Check multiple possible locations for the built library
     let possible_paths = if !target.is_empty() && target != "unknown" {
         vec![
-            build_dir.join(&target).join(&profile).join(&lib_name),
+            build_dir.join(&target).join(profile).join(&lib_name),
             build_dir
                 .join(&target)
-                .join(&profile)
+                .join(profile)
                 .join("deps")
                 .join(&lib_name),
         ]
     } else {
         vec![
-            build_dir.join(&profile).join(&lib_name),
-            build_dir.join(&profile).join("deps").join(&lib_name),
+            build_dir.join(profile).join(&lib_name),
+            build_dir.join(profile).join("deps").join(&lib_name),
         ]
     };