Replace extension-module feature with PYO3_MAKE_EXTENSION_MODULE

Author: davidhewitt

CHANGELOG.md

@@ -12,10 +12,12 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Correct FFI definitions `Py_SetProgramName` and `Py_SetPythonHome` to take `*const` argument instead of `*mut`. [#1021](https://github.com/PyO3/pyo3/pull/1021)
 - Rename `PyString::to_string` to `to_str`, change return type `Cow<str>` to `&str`. [#1023](https://github.com/PyO3/pyo3/pull/1023)
 - Correct FFI definition `_PyLong_AsByteArray` `*mut c_uchar` argument instead of `*const c_uchar`. [#1029](https://github.com/PyO3/pyo3/pull/1029)
+- Replace `extension-module` feature with `PYO3_MAKE_EXTENSION_MODULE` environment variable. See the migration guide for help with upgrading. [#1040](https://github.com/PyO3/pyo3/pull/1040)
 
 ### Removed
 - Remove `PyString::as_bytes`. [#1023](https://github.com/PyO3/pyo3/pull/1023)
 - Remove `Python::register_any`. [#1023](https://github.com/PyO3/pyo3/pull/1023)
+- Remove `extension-module` feature. [#1040](https://github.com/PyO3/pyo3/pull/1040)
 
 ### Fixed
 - Conversion from types with an `__index__` method to Rust BigInts. [#1027](https://github.com/PyO3/pyo3/pull/1027)

Cargo.toml

@@ -44,11 +44,6 @@ nightly = []
 # this is no longer needed internally, but setuptools-rust assumes this feature
 python3 = []
 
-# Use this feature when building an extension module.
-# It tells the linker to keep the python symbols unresolved,
-# so that the module can also be used with statically linked python interpreters.
-extension-module = []
-
 # The stable cpython abi as defined in PEP 384. Currently broken with
 # many compilation errors. Pull Requests working towards fixing that
 # are welcome.

README.md

@@ -48,7 +48,6 @@ crate-type = ["cdylib"]
 
 [dependencies.pyo3]
 version = "0.11.1"
-features = ["extension-module"]
 ```
 
 **`src/lib.rs`**

build.rs

@@ -485,7 +485,7 @@ fn configure(interpreter_config: &InterpreterConfig) -> Result<String> {
 
     check_target_architecture(interpreter_config)?;
 
-    let is_extension_module = env::var_os("CARGO_FEATURE_EXTENSION_MODULE").is_some();
+    let is_extension_module = env::var_os("PYO3_MAKE_EXTENSION_MODULE").is_some();
     if !is_extension_module || cfg!(target_os = "windows") {
         println!("{}", get_rustc_link_lib(&interpreter_config)?);
         if let Some(libdir) = &interpreter_config.libdir {

examples/rustapi_module/Cargo.toml

@@ -9,7 +9,6 @@ edition = "2018"
 
 [dependencies.pyo3]
 path = "../../"
-features = ["extension-module"]
 
 [lib]
 name = "rustapi_module"

examples/word-count/Cargo.toml

@@ -6,7 +6,7 @@ edition = "2018"
 
 [dependencies]
 rayon = "1.0.2"
-pyo3 = { path = "../..", features = ["extension-module"] }
+pyo3 = { path = "../.." }
 
 [lib]
 name = "word_count"

guide/src/building_and_distribution.md

@@ -8,35 +8,15 @@ PyO3 uses a build script to determine the Python version and set the correct lin
 
 Different linker arguments must be set for libraries/extension modules and binaries, which includes both standalone binaries and tests. (More specifically, binaries must be told where to find libpython and libraries must not link to libpython for [manylinux](https://www.python.org/dev/peps/pep-0513/) compliance).
 
-Since PyO3's build script can't know whether you're building a binary or a library, you have to activate the `extension-module` feature to get the build options for a library, or it'll default to binary.
-
-If you have e.g. a library crate and a profiling crate alongside, you need to use optional features. E.g. you put the following in the library crate:
-
-```toml
-[dependencies]
-pyo3 = "0.6"
-
-[lib]
-name = "hyperjson"
-crate-type = ["rlib", "cdylib"]
-
-[features]
-default = ["pyo3/extension-module"]
-```
-
-And this in the profiling crate:
-
-```toml
-[dependencies]
-my_main_crate = { path = "..", default-features = false }
-pyo3 = "0.6"
-```
+Since PyO3's build script can't know whether you're building a binary or a library, it defaults to building for binaries. To build a library, you should set the `PYO3_MAKE_EXTENSION_MODULE` environment variable to a nonempty value.
 
 On Linux/macOS you might have to change `LD_LIBRARY_PATH` to include libpython, while on windows you might need to set `LIB` to include `pythonxy.lib` (where x and y are major and minor version), which is normally either in the `libs` or `Lib` folder of a Python installation.
 
 ## Distribution
 
-There are two ways to distribute your module as a Python package: The old, [setuptools-rust](https://github.com/PyO3/setuptools-rust), and the new, [maturin](https://github.com/pyo3/maturin). setuptools-rust needs several configuration files (`setup.py`, `MANIFEST.in`, `build-wheels.sh`, etc.). maturin doesn't need any configuration files, however it does not support some functionality of setuptools such as package data ([pyo3/maturin#258](https://github.com/PyO3/maturin/issues/258)) and requires a rigid project structure, while setuptools-rust allows (and sometimes requires) configuration with python code.
+There are two ways to distribute your module as a Python package:
+- [`maturin`](https://github.com/pyo3/maturin) is the typical way to build and package PyO3 extension modules. It is deliberately opinionated about project structure, which allows it to need minimal configuration.
+- [`setuptools-rust`](https://github.com/PyO3/setuptools-rust), in contrast, needs several configuration files (`setup.py`, `MANIFEST.in`, `build-wheels.sh`, etc.). This complexity comes at added flexibility, allowing configuration using python code.
 
 ## Cross Compiling
 

guide/src/faq.md

@@ -17,13 +17,4 @@ PyO3 provides a struct [`GILOnceCell`] which works equivalently to `OnceCell` bu
 
 ## I can't run `cargo test`: I'm having linker issues like "Symbol not found" or "Undefined reference to _PyExc_SystemError"!
 
-Currently, [#341](https://github.com/PyO3/pyo3/issues/341) 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`:
-
-```toml
-[dependencies.pyo3]
-version = "*"
-
-[features]
-extension-module = ["pyo3/extension-module"]
-default = ["extension-module"]
-```
+If `PYO3_MAKE_EXTENSION_MODULE` environment variable is non-empty, PyO3 will not link against libpython. This will lead to errors like the above at link time.

src/lib.rs

@@ -37,7 +37,9 @@
 //!
 //! ## Using Rust from Python
 //!
-//! PyO3 can be used to generate a native Python module.
+//! PyO3 can be used to generate a native Python module. For a zero-configuration
+//! package to aid with compiling and packaging the module, see
+//! [`maturin`](https://github.com/PyO3/maturin).
 //!
 //! **`Cargo.toml`**
 //!
@@ -53,7 +55,6 @@
 //!
 //! [dependencies.pyo3]
 //! version = "0.11.1"
-//! features = ["extension-module"]
 //! ```
 //!
 //! **`src/lib.rs`**