Add export-config feature to pyo3-build-config

CHANGELOG.md

@@ -8,6 +8,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Allow to allow dependent crates to access values from `pyo3-build-config` via cargo link env vars. [#2092](https://github.com/PyO3/pyo3/pull/2092)
+
 ### Fixed
 
 - Considered `PYTHONFRAMEWORK` when cross compiling in order that on macos cross compiling against a [Framework bundle](https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPFrameworks/Concepts/FrameworkAnatomy.html) is considered shared. [#2233](https://github.com/PyO3/pyo3/pull/2233)

Cargo.toml

@@ -87,7 +87,18 @@ nightly = []
 
 # Activates all additional features
 # This is mostly intended for testing purposes - activating *all* of these isn't particularly useful.
-full = ["macros", "pyproto", "multiple-pymethods", "num-bigint", "num-complex", "hashbrown", "serde", "indexmap", "eyre", "anyhow"]
+full = [
+    "macros",
+    "pyproto",
+    "multiple-pymethods",
+    "num-bigint",
+    "num-complex",
+    "hashbrown",
+    "serde",
+    "indexmap",
+    "eyre",
+    "anyhow",
+]
 
 [[bench]]
 name = "bench_call"

pyo3-build-config/src/impl_.rs

@@ -8,6 +8,7 @@ use std::{
     io::{BufRead, BufReader, Read, Write},
     path::{Path, PathBuf},
     process::{Command, Stdio},
+    str,
     str::FromStr,
 };
 
@@ -153,7 +154,7 @@ impl InterpreterConfig {
         }
 
         for flag in &self.build_flags.0 {
-            println!("cargo:rustc-cfg=py_sys_config=\"{}\"", flag)
+            println!("cargo:rustc-cfg=py_sys_config=\"{}\"", flag);
         }
     }
 
@@ -339,6 +340,15 @@ print("mingw", get_platform().startswith("mingw"))
         InterpreterConfig::from_reader(reader)
     }
 
+    #[doc(hidden)]
+    pub fn from_cargo_link_env() -> Result<Self> {
+        // un-escape any newlines in the exported config
+        let buf = cargo_env_var("DEP_PYTHON_PYO3_CONFIG")
+            .unwrap()
+            .replace("\\n", "\n");
+        InterpreterConfig::from_reader(buf.as_bytes())
+    }
+
     #[doc(hidden)]
     pub fn from_reader(reader: impl Read) -> Result<Self> {
         let reader = BufReader::new(reader);
@@ -419,6 +429,19 @@ print("mingw", get_platform().startswith("mingw"))
         })
     }
 
+    #[doc(hidden)]
+    pub fn to_cargo_link_env(&self) -> Result<()> {
+        let mut buf = Vec::new();
+        self.to_writer(&mut buf)?;
+        // escape newlines in env var
+        if let Ok(config) = str::from_utf8(&buf) {
+            println!("cargo:PYO3_CONFIG={}", config.replace('\n', "\\n"));
+        } else {
+            bail!("unable to emit interpreter config to link env for downstream use");
+        }
+        Ok(())
+    }
+
     #[doc(hidden)]
     pub fn to_writer(&self, mut writer: impl Write) -> Result<()> {
         macro_rules! write_line {
@@ -461,6 +484,30 @@ print("mingw", get_platform().startswith("mingw"))
         }
         Ok(())
     }
+
+    /// Run a python script using the executable of this InterpreterConfig with additional
+    /// environment variables (e.g. PYTHONPATH) set.
+    pub fn run_python_script_with_envs<I, K, V>(&self, script: &str, envs: I) -> Result<String>
+    where
+        I: IntoIterator<Item = (K, V)>,
+        K: AsRef<OsStr>,
+        V: AsRef<OsStr>,
+    {
+        run_python_script_with_envs(
+            Path::new(self.executable.as_ref().expect("no interpreter executable")),
+            script,
+            envs,
+        )
+    }
+
+    /// Run a python script using the executable of this InterpreterConfig.
+    pub fn run_python_script(&self, script: &str) -> Result<String> {
+        run_python_script_with_envs(
+            Path::new(self.executable.as_ref().expect("no interpreter executable")),
+            script,
+            std::iter::empty::<(&str, &str)>(),
+        )
+    }
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
@@ -545,6 +592,11 @@ fn is_abi3() -> bool {
     cargo_env_var("CARGO_FEATURE_ABI3").is_some()
 }
 
+#[allow(unused)]
+pub fn link_env_var_set() -> bool {
+    cargo_env_var("DEP_PYTHON_PYO3_CONFIG").is_some()
+}
+
 #[derive(Debug, PartialEq)]
 struct TargetInfo {
     /// The `arch` component of the compilation target triple.
@@ -1183,8 +1235,20 @@ fn default_lib_name_unix(
 
 /// Run a python script using the specified interpreter binary.
 fn run_python_script(interpreter: &Path, script: &str) -> Result<String> {
+    run_python_script_with_envs(interpreter, script, std::iter::empty::<(&str, &str)>())
+}
+
+/// Run a python script using the specified interpreter binary with additional environment
+/// variables (e.g. PYTHONPATH) set.
+fn run_python_script_with_envs<I, K, V>(interpreter: &Path, script: &str, envs: I) -> Result<String>
+where
+    I: IntoIterator<Item = (K, V)>,
+    K: AsRef<OsStr>,
+    V: AsRef<OsStr>,
+{
     let out = Command::new(interpreter)
         .env("PYTHONIOENCODING", "utf-8")
+        .envs(envs)
         .stdin(Stdio::piped())
         .stdout(Stdio::piped())
         .stderr(Stdio::inherit())
@@ -1848,4 +1912,29 @@ mod tests {
                 .is_none()
         );
     }
+
+    #[test]
+    fn test_run_python_script() {
+        // as above, this should be okay in CI where Python is presumed installed
+        let interpreter = make_interpreter_config()
+            .expect("could not get InterpreterConfig from installed interpreter");
+        let out = interpreter
+            .run_python_script("print(2 + 2)")
+            .expect("failed to run Python script");
+        assert_eq!(out.trim_end(), "4");
+    }
+
+    #[test]
+    fn test_run_python_script_with_envs() {
+        // as above, this should be okay in CI where Python is presumed installed
+        let interpreter = make_interpreter_config()
+            .expect("could not get InterpreterConfig from installed interpreter");
+        let out = interpreter
+            .run_python_script_with_envs(
+                "import os; print(os.getenv('PYO3_TEST'))",
+                vec![("PYO3_TEST", "42")],
+            )
+            .expect("failed to run Python script");
+        assert_eq!(out.trim_end(), "42");
+    }
 }

pyo3-build-config/src/lib.rs

@@ -61,7 +61,6 @@ fn _add_extension_module_link_args(target_os: &str, mut writer: impl std::io::Wr
 /// Loads the configuration determined from the build environment.
 ///
 /// Because this will never change in a given compilation run, this is cached in a `once_cell`.
-#[doc(hidden)]
 #[cfg(feature = "resolve-config")]
 pub fn get() -> &'static InterpreterConfig {
     static CONFIG: OnceCell<InterpreterConfig> = OnceCell::new();
@@ -72,6 +71,8 @@ pub fn get() -> &'static InterpreterConfig {
             Ok(abi3_config())
         } else if impl_::cross_compile_env_vars().any() {
             InterpreterConfig::from_path(DEFAULT_CROSS_COMPILE_CONFIG_PATH)
+        } else if impl_::link_env_var_set() {
+            InterpreterConfig::from_cargo_link_env()
         } else {
             InterpreterConfig::from_reader(Cursor::new(HOST_CONFIG))
         }

pyo3-ffi/build.rs

@@ -69,6 +69,9 @@ fn emit_link_config(interpreter_config: &InterpreterConfig) -> Result<()> {
         }
     }
 
+    // serialize the whole interpreter config in DEP_PYTHON_PYO3_CONFIG
+    interpreter_config.to_cargo_link_env()?;
+
     Ok(())
 }