Fallback to the unmodified path in bindir_relative

src/bootstrap/builder.rs

@@ -1232,8 +1232,7 @@ impl<'a> Builder<'a> {
         }
 
         // Try to use a sysroot-relative bindir, in case it was configured absolutely.
-        let bindir = self.config.bindir_relative().unwrap_or(&self.config.bindir);
-        cargo.env("RUSTC_INSTALL_BINDIR", bindir);
+        cargo.env("RUSTC_INSTALL_BINDIR", self.config.bindir_relative());
 
         self.ci_env.force_coloring_in_ci(&mut cargo);
 

src/bootstrap/config.rs

@@ -647,15 +647,18 @@ impl Config {
         config
     }
 
-    /// Try to find the relative path of `bindir`.
-    pub fn bindir_relative(&self) -> Option<&Path> {
+    /// Try to find the relative path of `bindir`, otherwise return it in full.
+    pub fn bindir_relative(&self) -> &Path {
         let bindir = &self.bindir;
-        if bindir.is_relative() {
-            Some(bindir)
-        } else {
+        if bindir.is_absolute() {
             // Try to make it relative to the prefix.
-            bindir.strip_prefix(self.prefix.as_ref()?).ok()
+            if let Some(prefix) = &self.prefix {
+                if let Ok(stripped) = bindir.strip_prefix(prefix) {
+                    return stripped;
+                }
+            }
         }
+        bindir
     }
 
     /// Try to find the relative path of `libdir`.