Add abi3-py* features

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Added
 - Add support for building for CPython limited API. This required a few minor changes to runtime behaviour of of pyo3 `#[pyclass]` types. See the migration guide for full details. [#1152](https://github.com/PyO3/pyo3/pull/1152)
+  - Add feature flags `abi3-py*`  to set the minimum Python version when using the limited API. [#1263]((https://github.com/PyO3/pyo3/pull/1263))
 - Add argument names to `TypeError` messages generated by pymethod wrappers. [#1212](https://github.com/PyO3/pyo3/pull/1212)
 - Add `PyEval_SetProfile` and `PyEval_SetTrace` to FFI. [#1255](https://github.com/PyO3/pyo3/pull/1255)
 - Add context.h functions (`PyContext_New`, etc) to FFI. [#1259](https://github.com/PyO3/pyo3/pull/1259)

Cargo.toml

@@ -35,9 +35,13 @@ rustversion = "1.0"
 [features]
 default = ["macros"]
 macros = ["ctor", "indoc", "inventory", "paste", "pyo3cls", "unindent"]
-# Use the Python limited API. See https://www.python.org/dev/peps/pep-0384/ for
-# more.
+# Use the Python limited API. See https://www.python.org/dev/peps/pep-0384/ for more.
 abi3 = []
+# With abi3, we can manually set the minimum Python version.
+abi3-py36 = ["abi3-py37"]
+abi3-py37 = ["abi3-py38"]
+abi3-py38 = ["abi3-py39"]
+abi3-py39 = ["abi3"]
 
 # Optimizes PyObject to Vec conversion and so on.
 nightly = []

build.rs

@@ -9,7 +9,10 @@ use std::{
     str::FromStr,
 };
 
-const PY3_MIN_MINOR: u8 = 5;
+/// Minimum required Python version.
+const PY3_MIN_MINOR: u8 = 6;
+/// Maximum Python version that can be used as minimum required Python version with abi3.
+const ABI3_MAX_MINOR: u8 = 9;
 const CFG_KEY: &str = "py_sys_config";
 
 type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;
@@ -770,12 +773,25 @@ fn configure(interpreter_config: &InterpreterConfig) -> Result<String> {
         bail!("Python 2 is not supported");
     }
 
-    if env::var_os("CARGO_FEATURE_ABI3").is_some() {
+    let minor = if env::var_os("CARGO_FEATURE_ABI3").is_some() {
         println!("cargo:rustc-cfg=Py_LIMITED_API");
-    }
+        // Check any `abi3-py3*` feature is set. If not, use the interpreter version.
+        let abi3_minor = (PY3_MIN_MINOR..=ABI3_MAX_MINOR)
+            .find(|i| env::var_os(format!("CARGO_FEATURE_ABI3_PY3{}", i)).is_some());
+        match (abi3_minor, interpreter_config.version.minor) {
+            (Some(abi3_minor), Some(interpreter_minor)) if abi3_minor > interpreter_minor => bail!(
+                "You cannot set a mininimum Python version {} higher than the interpreter version {}",
+                abi3_minor,
+                interpreter_minor
+            ),
+            _ => abi3_minor.or(interpreter_config.version.minor),
+        }
+    } else {
+        interpreter_config.version.minor
+    };
 
-    if let Some(minor) = interpreter_config.version.minor {
-        for i in 6..=minor {
+    if let Some(minor) = minor {
+        for i in PY3_MIN_MINOR..=minor {
             println!("cargo:rustc-cfg=Py_3_{}", i);
             flags += format!("CFG_Py_3_{},", i).as_ref();
         }
@@ -820,7 +836,26 @@ fn check_target_architecture(interpreter_config: &InterpreterConfig) -> Result<(
     Ok(())
 }
 
+fn abi3_without_interpreter() -> Result<()> {
+    println!("cargo:rustc-cfg=Py_LIMITED_API");
+    let mut flags = "FLAG_WITH_THREAD=1".to_string();
+    for minor in PY3_MIN_MINOR..=ABI3_MAX_MINOR {
+        println!("cargo:rustc-cfg=Py_3_{}", minor);
+        flags += &format!(",CFG_Py_3_{}", minor);
+    }
+    println!("cargo:rustc-cfg=py_sys_config=\"WITH_THREAD\"");
+    println!("cargo:python_flags={}", flags);
+    Ok(())
+}
+
 fn main() -> Result<()> {
+    // If PYO3_NO_PYTHON is set with abi3, we can build PyO3 without calling Python (UNIX only).
+    // We only check for the abi3-py3{ABI3_MAX_MINOR} because lower versions depend on it.
+    if env::var_os("PYO3_NO_PYTHON").is_some()
+        && env::var_os(format!("CARGO_FEATURE_ABI3_PY3{}", ABI3_MAX_MINOR)).is_some()
+    {
+        return abi3_without_interpreter();
+    }
     // 1. Setup cfg variables so we can do conditional compilation in this library based on the
     // python interpeter's compilation flags. This is necessary for e.g. matching the right unicode
     // and threading interfaces.  First check if we're cross compiling, if so, we cannot run the

guide/src/building_and_distribution.md

@@ -58,6 +58,16 @@ pyo3 = { version = "...", features = ["abi3"]}
 
 3. Ensure that the `.whl` is correctly marked as `abi3`. For projects using `setuptools`, this is accomplished by passing `--py-limited-api=cp3x` (where `x` is the minimum Python version supported by the wheel, e.g. `--py-limited-api=cp35` for Python 3.5) to `setup.py bdist_wheel`.
 
+### Minimum Python version for `abi3`
+
+Because a single `abi3` wheel can be used with many different Python versions, PyO3 has feature flags `abi3-py36`, `abi3-py37`, `abi-py38` etc. to set the minimum required Python version for your `abi3` wheel.
+For example, if you set the `abi3-py36` feature, your extension wheel can be used on all Python 3 versions from Python 3.6 and up. `maturin` and `setuptools-rust` will give the wheel a name like `my-extension-1.0-cp36-abi3-manylinux2020_x86_64.whl`.
+If you set more that one of these api version feature flags the highest version always wins. For example, with both `abi3-py36` and `abi3-py38` set, PyO3 would build a wheel which supports Python 3.8 and up.
+PyO3 is only able to link your extension module to api3 version up to and including your host Python version. E.g., if you set `abi3-py38` and try to compile the crate with a host of Python 3.6, the build will fail.
+
+As an advanced feature, you can build PyO3 wheel without calling Python interpreter with
+the environment variable `PYO3_NO_PYTHON` set, but this only works on *NIX.
+
 ## Cross Compiling
 
 Cross compiling PyO3 modules is relatively straightforward and requires a few pieces of software:
@@ -107,4 +117,3 @@ For an example of how to build python extensions using Bazel, see https://github
 
 [maturin]: https://github.com/PyO3/maturin
 [setuptools-rust]: https://github.com/PyO3/setuptools-rust
-