stop inlining config into pyo3-build-config; generate directly in pyo3-ffi

Cargo.toml

@@ -22,6 +22,9 @@ exclude = [
     "/tests/ui",
 ]
 edition = "2021"
+# this allows PyO3 to forward build-config from `pyo3-ffi` to avoid downstream crates
+# needing to depend on `pyo3-ffi` directly to use `pyo3-build-config` functionality.
+links = "pyo3-python"
 rust-version.workspace = true
 
 [dependencies]
@@ -82,7 +85,7 @@ uuid = { version = "1.10.0", features = ["v4"] }
 parking_lot = { version = "0.12.3", features = ["arc_lock"] }
 
 [build-dependencies]
-pyo3-build-config = { path = "pyo3-build-config", version = "=0.28.3", features = ["resolve-config"] }
+pyo3-build-config = { path = "pyo3-build-config", version = "=0.28.3" }
 
 [features]
 default = ["macros"]
@@ -106,16 +109,16 @@ multiple-pymethods = ["inventory", "pyo3-macros/multiple-pymethods"]
 extension-module = ["pyo3-ffi/extension-module"]
 
 # Use the Python limited API. See https://www.python.org/dev/peps/pep-0384/ for more.
-abi3 = ["pyo3-build-config/abi3", "pyo3-ffi/abi3"]
+abi3 = ["pyo3-ffi/abi3"]
 
 # With abi3, we can manually set the minimum Python version.
-abi3-py38 = ["abi3-py39", "pyo3-build-config/abi3-py38", "pyo3-ffi/abi3-py38"]
-abi3-py39 = ["abi3-py310", "pyo3-build-config/abi3-py39", "pyo3-ffi/abi3-py39"]
-abi3-py310 = ["abi3-py311", "pyo3-build-config/abi3-py310", "pyo3-ffi/abi3-py310"]
-abi3-py311 = ["abi3-py312", "pyo3-build-config/abi3-py311", "pyo3-ffi/abi3-py311"]
-abi3-py312 = ["abi3-py313", "pyo3-build-config/abi3-py312", "pyo3-ffi/abi3-py312"]
-abi3-py313 = ["abi3-py314", "pyo3-build-config/abi3-py313", "pyo3-ffi/abi3-py313"]
-abi3-py314 = ["abi3", "pyo3-build-config/abi3-py314", "pyo3-ffi/abi3-py314"]
+abi3-py38 = ["abi3-py39", "pyo3-ffi/abi3-py38"]
+abi3-py39 = ["abi3-py310", "pyo3-ffi/abi3-py39"]
+abi3-py310 = ["abi3-py311", "pyo3-ffi/abi3-py310"]
+abi3-py311 = ["abi3-py312", "pyo3-ffi/abi3-py311"]
+abi3-py312 = ["abi3-py313", "pyo3-ffi/abi3-py312"]
+abi3-py313 = ["abi3-py314", "pyo3-ffi/abi3-py313"]
+abi3-py314 = ["abi3", "pyo3-ffi/abi3-py314"]
 
 # deprecated: no longer needed, raw-dylib is used instead
 generate-import-lib = ["pyo3-ffi/generate-import-lib"]

build.rs

@@ -43,6 +43,10 @@ fn configure_pyo3() -> Result<()> {
 
     print_feature_cfgs();
 
+    // Forwards interpreter config under the links = "pyo3-python" configuration,
+    // which allows consumers of `pyo3-build-config` APIs to depend on pyo3 instead of pyo3-ffi.
+    interpreter_config.to_cargo_dep_env()?;
+
     // Make `cargo test` etc work on macOS with Xcode bundled Python
     add_python_framework_link_args();
 

guide/src/building-and-distribution/multiple-python-versions.md

@@ -36,11 +36,11 @@ To see a full reference of all the `#[cfg]` flags provided, see the [`pyo3-build
 
 You can use the `#[cfg]` flags in just two steps:
 
-1. Add `pyo3-build-config` with the [`resolve-config`](../features.md#resolve-config) feature enabled to your crate's build dependencies in `Cargo.toml`:
+1. Add `pyo3-build-config` to your crate's build dependencies in `Cargo.toml`:
 
    ```toml
    [build-dependencies]
-   pyo3-build-config = { {{#PYO3_CRATE_VERSION}}, features = ["resolve-config"] }
+   pyo3-build-config = {{#PYO3_CRATE_VERSION}}
    ```
 
 2. Add a [`build.rs`](https://doc.rust-lang.org/cargo/reference/build-scripts.html) file to your crate with the following contents:

guide/src/features.md

@@ -105,12 +105,6 @@ See [the `#[pyclass]` implementation details](class.md#implementation-details) f
 The `nightly` feature needs the nightly Rust compiler.
 This allows PyO3 to use the `auto_traits` and `negative_impls` features to fix the `Python::detach` function.
 
-### `resolve-config`
-
-The `resolve-config` feature of the `pyo3-build-config` crate controls whether that crate's build script automatically resolves a Python interpreter / build configuration.
-This feature is primarily useful when building PyO3 itself.
-By default this feature is not enabled, meaning you can freely use `pyo3-build-config` as a standalone library to read or write PyO3 build configuration files or resolve metadata about a Python interpreter.
-
 ## Optional Dependencies
 
 These features enable conversions between Python types and types from other Rust crates, enabling easy access to the rest of the Rust ecosystem.

newsfragments/5862.changed.md

@@ -0,0 +1 @@
+Deprecate `pyo3-build-config/resolve-config` feature.

pyo3-benches/Cargo.toml

@@ -20,7 +20,7 @@ rust_decimal = { version = "1.0.0", default-features = false }
 hashbrown = "0.16"
 
 [features]
-abi3 = ["pyo3-build-config/abi3"]
+abi3 = ["pyo3/abi3"]
 
 [[bench]]
 name = "bench_any"

pyo3-build-config/Cargo.toml

@@ -20,25 +20,11 @@ target-lexicon = "0.13.3"
 [features]
 default = []
 
-# Attempt to resolve a Python interpreter config for building in the build
-# script. If this feature isn't enabled, the build script no-ops.
+# deprecated
 resolve-config = []
 
 # deprecated
 extension-module = []
 
 # deprecated: no longer needed, raw-dylib is used instead
 generate-import-lib = []
-
-# These features are enabled by pyo3 when building Stable ABI extension modules.
-abi3 = []
-abi3-py38 = ["abi3-py39"]
-abi3-py39 = ["abi3-py310"]
-abi3-py310 = ["abi3-py311"]
-abi3-py311 = ["abi3-py312"]
-abi3-py312 = ["abi3-py313"]
-abi3-py313 = ["abi3-py314"]
-abi3-py314 = ["abi3"]
-
-[package.metadata.docs.rs]
-features = ["resolve-config"]

pyo3-build-config/src/impl_.rs

@@ -1,6 +1,3 @@
-//! Main implementation module included in both the `pyo3-build-config` library crate
-//! and its build script.
-
 #[cfg(test)]
 use std::cell::RefCell;
 use std::{
@@ -61,9 +58,7 @@ pub fn cargo_env_var(var: &str) -> Option<String> {
 /// Gets an external environment variable, and registers the build script to rerun if
 /// the variable changes.
 pub fn env_var(var: &str) -> Option<OsString> {
-    if cfg!(feature = "resolve-config") {
-        println!("cargo:rerun-if-env-changed={var}");
-    }
+    println!("cargo:rerun-if-env-changed={var}");
     #[cfg(test)]
     {
         READ_ENV_VARS.with(|env_vars| {
@@ -490,7 +485,8 @@ print("gil_disabled", get_config_var("Py_GIL_DISABLED"))
 
     #[doc(hidden)]
     pub fn from_cargo_dep_env() -> Option<Result<Self>> {
-        cargo_env_var("DEP_PYTHON_PYO3_CONFIG")
+        cargo_env_var("DEP_PYTHON_PYO3_CONFIG") // from `pyo3-ffi`
+            .or_else(|| cargo_env_var("DEP_PYO3_PYTHON_PYO3_CONFIG")) // forwared by `pyo3`
             .map(|buf| InterpreterConfig::from_reader(&*unescape(&buf)))
     }
 
@@ -583,7 +579,6 @@ print("gil_disabled", get_config_var("Py_GIL_DISABLED"))
     /// This requires knowledge of the final target, so cannot be done when the config file is
     /// inlined into `pyo3-build-config` at build time and instead needs to be done when
     /// resolving the build config for linking.
-    #[cfg(any(test, feature = "resolve-config"))]
     pub(crate) fn apply_default_lib_name_to_config_file(&mut self, target: &Triple) {
         if self.lib_name.is_none() {
             self.lib_name = Some(default_lib_name_for_target(
@@ -1909,9 +1904,7 @@ pub fn make_cross_compile_config() -> Result<Option<InterpreterConfig>> {
     Ok(interpreter_config)
 }
 
-/// Generates an interpreter config which will be hard-coded into the pyo3-build-config crate.
-/// Only used by `pyo3-build-config` build script.
-#[allow(dead_code, unused_mut)]
+/// Generates an interpreter config suitable for the build host.
 pub fn make_interpreter_config() -> Result<InterpreterConfig> {
     let host = Triple::host();
     let abi3_version = get_abi3_version();
@@ -2874,17 +2867,17 @@ mod tests {
     }
 
     #[test]
-    #[cfg(all(
-        target_os = "linux",
-        target_arch = "x86_64",
-        feature = "resolve-config"
-    ))]
+    #[cfg(all(target_os = "linux", target_arch = "x86_64",))]
     fn parse_sysconfigdata() {
         // A best effort attempt to get test coverage for the sysconfigdata parsing.
         // Might not complete successfully depending on host installation; that's ok as long as
         // CI demonstrates this path is covered!
 
-        let interpreter_config = crate::get();
+        let Ok(interpreter_config) = make_interpreter_config() else {
+            // Couldn't get an interpreter config, won't be able to test a matching sysconfigdata,
+            // never mind. (This is intended for coverage, don't mind if it fails if it doesn't run.)
+            return;
+        };
 
         let lib_dir = match &interpreter_config.lib_dir {
             Some(lib_dir) => Path::new(lib_dir),
@@ -2910,7 +2903,16 @@ mod tests {
             _ => return,
         };
         let sysconfigdata = super::parse_sysconfigdata(sysconfigdata_path).unwrap();
-        let parsed_config = InterpreterConfig::from_sysconfigdata(&sysconfigdata).unwrap();
+        let mut parsed_config = InterpreterConfig::from_sysconfigdata(&sysconfigdata).unwrap();
+
+        // Workaround case where empty `PYTHONFRAMEWORKPREFIX` is returned as empty string instead of None,
+        // which causes the assert_eq! below to fail.
+        //
+        // TODO: probably should deprecate using this variable at all, seemingly only used in `add_python_framework_link_args`
+        // which is probably a strictly worse version of `add_libpython_rpath_link_args`.
+        if parsed_config.python_framework_prefix.as_deref() == Some("") {
+            parsed_config.python_framework_prefix = None;
+        }
 
         assert_eq!(
             parsed_config,