Auto merge of #6856 - glandium:DYLD_FALLBACK_LIBRARY_PATH, r=alexcrichton

Cleanups wrt DYLD_FALLBACK_LIBRARY_PATH handling

Author: bors

src/cargo/core/compiler/compilation.rs

@@ -178,16 +178,17 @@ impl<'cfg> Compilation<'cfg> {
             search_path
         };
 
-        search_path.extend(util::dylib_path().into_iter());
-        if cfg!(target_os = "macos") {
+        let dylib_path = util::dylib_path();
+        let dylib_path_is_empty = dylib_path.is_empty();
+        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. Since Cargo is explicitly setting the value, make sure the
-            // defaults still work.
-            if let Ok(home) = env::var("HOME") {
+            // set or set to an empty string. Since Cargo is explicitly setting
+            // the value, make sure the defaults still work.
+            if let Some(home) = env::var_os("HOME") {
                 search_path.push(PathBuf::from(home).join("lib"));
             }
             search_path.push(PathBuf::from("/usr/local/lib"));
-            search_path.push(PathBuf::from("/lib"));
             search_path.push(PathBuf::from("/usr/lib"));
         }
         let search_path = join_paths(&search_path, util::dylib_path_envvar())?;

tests/testsuite/run.rs

@@ -1223,6 +1223,13 @@ fn run_link_system_path_macos() {
     )
     .unwrap();
     p.root().rm_rf();
-    p2.cargo("run").run();
-    p2.cargo("test").run();
+    const VAR: &str = "DYLD_FALLBACK_LIBRARY_PATH";
+    // Reset DYLD_FALLBACK_LIBRARY_PATH so that we don't inherit anything that
+    // was set by the cargo that invoked the test.
+    p2.cargo("run").env_remove(VAR).run();
+    p2.cargo("test").env_remove(VAR).run();
+    // Ensure this still works when DYLD_FALLBACK_LIBRARY_PATH has
+    // a value set.
+    p2.cargo("run").env(VAR, &libdir).run();
+    p2.cargo("test").env(VAR, &libdir).run();
 }