Fix dSYM uplifting when symlink is broken

src/cargo/core/compiler/mod.rs

@@ -486,7 +486,12 @@ fn hardlink_or_copy(src: &Path, dst: &Path) -> CargoResult<()> {
     if is_same_file(src, dst).unwrap_or(false) {
         return Ok(());
     }
-    if dst.exists() {
+
+    // NB: we can't use dst.exists(), as if dst is a broken symlink,
+    // dst.exists() will return false. This is problematic, as we still need to
+    // unlink dst in this case. symlink_metadata(dst).is_ok() will tell us
+    // whether dst exists *without* following symlinks, which is what we want.
+    if fs::symlink_metadata(dst).is_ok() {
         paths::remove_file(&dst)?;
     }
 

tests/testsuite/build.rs

@@ -4167,6 +4167,34 @@ fn uplift_dsym_of_bin_on_mac() {
     assert!(!p.target_debug_dir().join("d.dSYM").exists());
 }
 
+#[cargo_test]
+#[cfg(any(target_os = "macos", target_os = "ios"))]
+fn uplift_dsym_of_bin_on_mac_when_broken_link_exists() {
+    let p = project()
+        .file("src/main.rs", "fn main() { panic!(); }")
+        .build();
+    let dsym = p.target_debug_dir().join("foo.dSYM");
+
+    p.cargo("build").run();
+    assert!(dsym.is_dir());
+
+    // Simulate the situation where the underlying dSYM bundle goes missing
+    // but the uplifted symlink to it remains. This would previously cause
+    // builds to permanently fail until the bad symlink was manually removed.
+    dsym.rm_rf();
+    p.symlink(
+        p.target_debug_dir()
+            .join("deps")
+            .join("foo-baaaaaadbaaaaaad.dSYM"),
+        &dsym,
+    );
+    assert!(dsym.is_symlink());
+    assert!(!dsym.exists());
+
+    p.cargo("build").run();
+    assert!(dsym.is_dir());
+}
+
 #[cargo_test]
 #[cfg(all(target_os = "windows", target_env = "msvc"))]
 fn uplift_pdb_of_bin_on_windows() {