From e888c1306fefd708503f00fe5f9ff759a7f6b0dd Mon Sep 17 00:00:00 2001
From: Lin Yihai <linyihai@huawei.com>
Date: Wed, 28 Aug 2024 15:43:34 +0800
Subject: [PATCH 1/2] test: Add test for issue-14194

---
 tests/testsuite/build.rs | 60 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/tests/testsuite/build.rs b/tests/testsuite/build.rs
index bb13046e50f..3cc4aa8b8c5 100644
--- a/tests/testsuite/build.rs
+++ b/tests/testsuite/build.rs
@@ -2154,6 +2154,66 @@ fn crate_library_path_env_var() {
     setenv_for_removing_empty_component(p.cargo("run")).run();
 }
 
+// See https://github.com/rust-lang/cargo/issues/14194
+#[cargo_test]
+fn issue_14194_deduplicate_library_path_env_var() {
+    let p = project()
+        .file(
+            "src/main.rs",
+            &format!(
+                r#"
+                    use std::process::Command;
+                    fn main() {{
+                        let level: i32 = std::env::args().nth(1).unwrap().parse().unwrap();
+                        let txt = "var.txt";
+                        let lib_path = std::env::var("{}").unwrap();
+
+                        // Make sure we really have something in dylib search path.
+                        let count = std::env::split_paths(&lib_path).count();
+                        assert!(count > 0);
+
+                        if level >= 3 {{
+                            std::fs::write(txt, &lib_path).unwrap();
+                        }} else {{
+                            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);
+                        }}
+
+                        if level == 0 {{
+                            return;
+                        }}
+                        
+                        let _  = Command::new(std::env!("CARGO"))
+                        .arg("run")
+                        .arg("--")
+                        .arg((level - 1).to_string())
+                        .status()
+                        .unwrap();
+                    }}
+                "#,
+                dylib_path_envvar(),
+            ),
+        )
+        .build();
+
+    setenv_for_removing_empty_component(p.cargo("run -- 3"))
+        .with_stderr_data(str![[r#"
+[COMPILING] foo v0.0.1 ([ROOT]/foo)
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+[RUNNING] `target/debug/foo[EXE] 3`
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+[RUNNING] `target/debug/foo[EXE] 2`
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+[RUNNING] `target/debug/foo[EXE] 1`
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+[RUNNING] `target/debug/foo[EXE] 0`
+
+"#]])
+        .run();
+}
+
 // Regression test for #4277
 #[cargo_test]
 fn build_with_fake_libc_not_loading() {

From 54dbc2bf66381314a546b366faa913294af0b6d5 Mon Sep 17 00:00:00 2001
From: Lin Yihai <linyihai@huawei.com>
Date: Wed, 28 Aug 2024 16:04:01 +0800
Subject: [PATCH 2/2] fix: Avoid inserting `search_path` again.

---
 src/cargo/core/compiler/compilation.rs | 6 +++++-
 tests/testsuite/build.rs               | 2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/cargo/core/compiler/compilation.rs b/src/cargo/core/compiler/compilation.rs
index 8ec625d77a4..5ecf77d4c6a 100644
--- a/src/cargo/core/compiler/compilation.rs
+++ b/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
diff --git a/tests/testsuite/build.rs b/tests/testsuite/build.rs
index 3cc4aa8b8c5..b7c87615437 100644
--- a/tests/testsuite/build.rs
+++ b/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 {{