fix: Avoid inserting search_path again.

Author: linyihai

src/cargo/core/compiler/compilation.rs

@@ -323,7 +323,11 @@ impl<'gctx> Compilation<'gctx> {
 
         let dylib_path = paths::dylib_path();
         let dylib_path_is_empty = dylib_path.is_empty();
-        search_path.extend(dylib_path.into_iter());
+        if dylib_path.starts_with(&search_path) {
+            search_path = dylib_path;
+        } else {
+            search_path.extend(dylib_path.into_iter());
+        }
         if cfg!(target_os = "macos") && dylib_path_is_empty {
             // These are the defaults when DYLD_FALLBACK_LIBRARY_PATH isn't
             // set or set to an empty string. Since Cargo is explicitly setting

tests/testsuite/build.rs

@@ -2178,7 +2178,7 @@ fn issue_14194_deduplicate_library_path_env_var() {
                             let prev_lib_path = std::fs::read_to_string(txt).unwrap();
                             // Ensure no duplicate insertion to dylib search paths
                             // when calling `cargo run` recursively.
-                            assert_ne!(lib_path, prev_lib_path);
+                            assert_eq!(lib_path, prev_lib_path);
                         }}
 
                         if level == 0 {{