do not pass cdylib link args to test

Author: usamoi

src/cargo/core/compiler/mod.rs

@@ -360,6 +360,7 @@ fn rustc(
                     pass_l_flag,
                     &target,
                     current_id,
+                    mode,
                 )?;
                 add_plugin_deps(&mut rustc, &script_outputs, &build_scripts, &root_output)?;
             }
@@ -494,6 +495,7 @@ fn rustc(
         pass_l_flag: bool,
         target: &Target,
         current_id: PackageId,
+        mode: CompileMode,
     ) -> CargoResult<()> {
         for key in build_scripts.to_link.iter() {
             let output = build_script_outputs.get(key.1).ok_or_else(|| {
@@ -521,7 +523,9 @@ fn rustc(
                 // now, continue allowing it for cdylib only.
                 // See https://github.com/rust-lang/cargo/issues/9562
                 if lt.applies_to(target) && (key.0 == current_id || *lt == LinkArgTarget::Cdylib) {
-                    rustc.arg("-C").arg(format!("link-arg={}", arg));
+                    if !mode.is_any_test() || target.is_test() || target.is_bench() {
+                        rustc.arg("-C").arg(format!("link-arg={}", arg));
+                    }
                 }
             }
         }

tests/testsuite/build_script_extra_link_arg.rs

@@ -403,3 +403,39 @@ fn build_script_extra_link_arg_examples() {
         )
         .run();
 }
+
+#[cargo_test]
+fn issue_12663() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.5.0"
+                authors = ["wycats@example.com"]
+                edition = "2015"
+
+                [lib]
+                crate-type = ["lib", "cdylib"]
+            "#,
+        )
+        .file(
+            "src/lib.rs",
+            r#"
+                #[test]
+                fn noop() {}
+            "#,
+        )
+        .file(
+            "build.rs",
+            r#"
+                fn main() {
+                    println!("cargo::rustc-cdylib-link-arg=-lhack");
+                }
+            "#,
+        )
+        .build();
+
+    p.cargo("test --lib").run();
+}