Fix cargo test with extension-module feature.

CHANGELOG.md

@@ -57,6 +57,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Fix `cargo test` with `extension-module` feature. (Requires `cargo +nightly` for now.) #[2135](https://github.com/PyO3/pyo3/pull/2135)
 - Fix undefined symbol for `PyObject_HasAttr` on PyPy. [#2025](https://github.com/PyO3/pyo3/pull/2025)
 - Fix memory leak in `PyErr::into_value`. [#2026](https://github.com/PyO3/pyo3/pull/2026)
 - Fix clippy warning `needless-option-as-deref` in code generated by `#[pyfunction]` and `#[pymethods]`. [#2040](https://github.com/PyO3/pyo3/pull/2040)

guide/src/faq.md

@@ -15,17 +15,17 @@ PyO3 provides a struct [`GILOnceCell`] which works equivalently to `OnceCell` bu
 
 [`GILOnceCell`]: {{#PYO3_DOCS_URL}}/pyo3/once_cell/struct.GILOnceCell.html
 
-## I can't run `cargo test`: I'm having linker issues like "Symbol not found" or "Undefined reference to _PyExc_SystemError"!
+## I can't run `cargo test` or `cargo run`: I'm having linker issues like "Symbol not found" or "Undefined reference to _PyExc_SystemError"!
 
-Currently, [#340](https://github.com/PyO3/pyo3/issues/340) causes `cargo test` to fail with linking errors when the `extension-module` feature is activated. For now you can work around this by making the `extension-module` feature optional and running the tests with `cargo test --no-default-features`:
+On unix operating systems the `extension-module` feature is required to disable linking against libpython to meet criteria of how Python extension modules should be built.
 
-```toml
-[dependencies.pyo3]
-{{#PYO3_CRATE_VERSION}}
+PyO3 is able to re-enable linking for binaries and tests in the project, but it requires a nightly cargo. To use this feature, you must use nightly cargo, e.g.:
 
-[features]
-extension-module = ["pyo3/extension-module"]
-default = ["extension-module"]
+```
+# For cargo test
+cargo +nightly test
+# For cargo run
+cargo +nightly run
 ```
 
 ## I can't run `cargo test`: my crate cannot be found for tests in `tests/` directory!

pyo3-build-config/src/lib.rs

@@ -55,6 +55,14 @@ fn _add_extension_module_link_args(target_os: &str, mut writer: impl std::io::Wr
         writeln!(writer, "cargo:rustc-cdylib-link-arg=-undefined").unwrap();
         writeln!(writer, "cargo:rustc-cdylib-link-arg=dynamic_lookup").unwrap();
     }
+    if target_os != "windows" && target_os != "android" {
+        let interpreter_config = get();
+        let lib_name = interpreter_config.lib_name.as_ref().unwrap();
+        println!("cargo:rustc-link-arg-bins=-l{}", lib_name);
+        println!("cargo:rustc-link-arg-tests=-l{}", lib_name);
+        println!("cargo:rustc-link-arg-benches=-l{}", lib_name);
+        println!("cargo:rustc-link-arg-examples=-l{}", lib_name);
+    }
 }
 
 /// Loads the configuration determined from the build environment.