macos: automatically provide required linker arguments

CHANGELOG.md

@@ -26,6 +26,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - The `auto-initialize` feature is no longer enabled by default. [#1443](https://github.com/PyO3/pyo3/pull/1443)
 - Change `PyCFunction::new()` and `PyCFunction::new_with_keywords()` to take `&'static str` arguments rather than implicitly copying (and leaking) them. [#1450](https://github.com/PyO3/pyo3/pull/1450)
 - Deprecate `PyModule` methods `call`, `call0`, `call1` and `get`. [#1492](https://github.com/PyO3/pyo3/pull/1492)
+- Automatically provide `-undefined` and `dynamic_lookup` linker arguments on macOS with `extension-module` feature. [#1539](https://github.com/PyO3/pyo3/pull/1539)
 
 ### Removed
 - Remove deprecated exception names `BaseException` etc. [#1426](https://github.com/PyO3/pyo3/pull/1426)

README.md

@@ -80,22 +80,6 @@ fn string_sum(py: Python, m: &PyModule) -> PyResult<()> {
 }
 ```
 
-On Windows and Linux, you can build normally with `cargo build --release`. On macOS, you need to set additional linker arguments. One option is to compile with `cargo rustc --release -- -C link-arg=-undefined -C link-arg=dynamic_lookup`, the other is to create a `.cargo/config` with the following content:
-
-```toml
-[target.x86_64-apple-darwin]
-rustflags = [
-  "-C", "link-arg=-undefined",
-  "-C", "link-arg=dynamic_lookup",
-]
-
-[target.aarch64-apple-darwin]
-rustflags = [
-  "-C", "link-arg=-undefined",
-  "-C", "link-arg=dynamic_lookup",
-]
-```
-
 While developing, you can symlink (or copy) and rename the shared library from the target folder: On MacOS, rename `libstring_sum.dylib` to `string_sum.so`, on Windows `libstring_sum.dll` to `string_sum.pyd`, and on Linux `libstring_sum.so` to `string_sum.so`. Then open a Python shell in the same folder and you'll be able to `import string_sum`.
 
 To build, test and publish your crate as a Python module, you can use [maturin](https://github.com/PyO3/maturin) or [setuptools-rust](https://github.com/PyO3/setuptools-rust). You can find an example for setuptools-rust in [examples/word-count](https://github.com/PyO3/pyo3/tree/main/examples/word-count), while maturin should work on your crate without any configuration.

build.rs

@@ -729,19 +729,32 @@ fn configure(interpreter_config: &InterpreterConfig) -> Result<()> {
     }
 
     check_target_architecture(interpreter_config)?;
-    let target_os = env::var_os("CARGO_CFG_TARGET_OS").unwrap();
 
+    let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap();
     let is_extension_module = env::var_os("CARGO_FEATURE_EXTENSION_MODULE").is_some();
-    if !is_extension_module || target_os == "windows" || target_os == "android" {
+    match (is_extension_module, target_os.as_str()) {
-        println!("{}", get_rustc_link_lib(&interpreter_config));
+        (_, "windows") => {
-        if let Some(libdir) = &interpreter_config.libdir {
+            // always link on windows, even with extension module
-            println!("cargo:rustc-link-search=native={}", libdir);
+            println!("{}", get_rustc_link_lib(&interpreter_config));
-        } else if target_os == "windows" {
             println!(
                 "cargo:rustc-link-search=native={}\\libs",
                 interpreter_config.base_prefix
             );
         }
+        (true, "macos") => {
+            // with extension module on macos some extra linker arguments are needed
+            println!("cargo:rustc-cdylib-link-arg=-undefined");
+            println!("cargo:rustc-cdylib-link-arg=dynamic_lookup");
+        }
+        (false, _) | (_, "android") => {
+            // other systems, only link libs if not extension module
+            // android always link.
+            println!("{}", get_rustc_link_lib(&interpreter_config));
+            if let Some(libdir) = &interpreter_config.libdir {
+                println!("cargo:rustc-link-search=native={}", libdir);
+            }
+        }
+        _ => {}
     }
 
     if interpreter_config.shared {
@@ -885,10 +898,6 @@ fn main_impl() -> Result<()> {
         println!("cargo:rustc-cfg={}=\"{}\"", CFG_KEY, flag)
     }
 
-    if env::var_os("TARGET") == Some("x86_64-apple-darwin".into()) {
-        // TODO: Find out how we can set -undefined dynamic_lookup here (if this is possible)
-    }
-
     for var in &[
         "LIB",
         "LD_LIBRARY_PATH",

src/lib.rs

@@ -82,26 +82,6 @@
 //! }
 //! ```
 //!
-//! On Windows and linux, you can build normally with `cargo build
-//! --release`. On macOS, you need to set additional linker arguments. One
-//! option is to compile with `cargo rustc --release -- -C link-arg=-undefined
-//! -C link-arg=dynamic_lookup`, the other is to create a `.cargo/config` with
-//! the following content:
-//!
-//! ```toml
-//! [target.x86_64-apple-darwin]
-//! rustflags = [
-//!   "-C", "link-arg=-undefined",
-//!   "-C", "link-arg=dynamic_lookup",
-//! ]
-//!
-//! [target.aarch64-apple-darwin]
-//! rustflags = [
-//!   "-C", "link-arg=-undefined",
-//!   "-C", "link-arg=dynamic_lookup",
-//! ]
-//! ```
-//!
 //! While developing, you symlink (or copy) and rename the shared library from
 //! the target folder: On macOS, rename `libstring_sum.dylib` to
 //! `string_sum.so`, on Windows `libstring_sum.dll` to `string_sum.pyd` and on