Merge pull request #2253 from ravenexp/target-lexicon

pyo3-build-config: Replace `TargetInfo` with `target_lexicon::Triple`

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Add new public `pyo3-build-config` API using the types from `target_lexicon` crate. Deprecate `cross_compiling()`. [#2253](https://github.com/PyO3/pyo3/pull/2253)
 - Allow dependent crates to access config values from `pyo3-build-config` via cargo link dep env vars. [#2092](https://github.com/PyO3/pyo3/pull/2092)
 - Added methods on `InterpreterConfig` to run Python scripts using the configured executable. [#2092](https://github.com/PyO3/pyo3/pull/2092)
 - Added FFI definitions for `PyType_FromModuleAndSpec`, `PyType_GetModule`, `PyType_GetModuleState` and `PyModule_AddType`. [#2250](https://github.com/PyO3/pyo3/pull/2250)

pyo3-build-config/Cargo.toml

@@ -12,6 +12,10 @@ edition = "2018"
 
 [dependencies]
 once_cell = "1"
+target-lexicon = "0.12"
+
+[build-dependencies]
+target-lexicon = "0.12"
 
 [features]
 default = []

pyo3-build-config/src/impl_.rs

@@ -12,6 +12,10 @@ use std::{
     str::FromStr,
 };
 
+pub use target_lexicon::Triple;
+
+use target_lexicon::{Architecture, BinaryFormat, Environment, OperatingSystem, Vendor};
+
 use crate::{
     bail, ensure,
     errors::{Context, Error, Result},
@@ -40,6 +44,16 @@ pub fn env_var(var: &str) -> Option<OsString> {
     env::var_os(var)
 }
 
+/// Gets the compilation target triple from environment variables set by Cargo.
+///
+/// Must be called from a crate build script.
+pub fn target_triple_from_env() -> Triple {
+    env::var("TARGET")
+        .expect("target_triple_from_env() must be called from a build script")
+        .parse()
+        .expect("Unrecognized TARGET environment variable value")
+}
+
 /// Configuration needed by PyO3 to build for the correct Python implementation.
 ///
 /// Usually this is queried directly from the Python interpreter, or overridden using the
@@ -524,6 +538,29 @@ print("mingw", get_platform().startswith("mingw"))
             envs,
         )
     }
+
+    /// Lowers the configured version to the abi3 version, if set.
+    fn fixup_for_abi3_version(&mut self, abi3_version: Option<PythonVersion>) -> Result<()> {
+        // PyPy doesn't support abi3; don't adjust the version
+        if self.implementation.is_pypy() {
+            return Ok(());
+        }
+
+        if let Some(version) = abi3_version {
+            ensure!(
+                version <= self.version,
+                "cannot set a minimum Python version {} higher than the interpreter version {} \
+                (the minimum Python version is implied by the abi3-py3{} feature)",
+                version,
+                self.version,
+                version.minor,
+            );
+
+            self.version = version;
+        }
+
+        Ok(())
+    }
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
@@ -608,52 +645,37 @@ fn is_abi3() -> bool {
     cargo_env_var("CARGO_FEATURE_ABI3").is_some()
 }
 
-#[derive(Debug, PartialEq)]
-struct TargetInfo {
-    /// The `arch` component of the compilation target triple.
-    ///
-    /// e.g. x86_64, i386, arm, thumb, mips, etc.
-    arch: String,
-
-    /// The `vendor` component of the compilation target triple.
-    ///
-    /// e.g. apple, pc, unknown, etc.
-    vendor: String,
-
-    /// The `os` component of the compilation target triple.
-    ///
-    /// e.g. darwin, freebsd, linux, windows, etc.
-    os: String,
+/// Gets the minimum supported Python version from PyO3 `abi3-py*` features.
+///
+/// Must be called from a PyO3 crate build script.
+pub fn get_abi3_version() -> Option<PythonVersion> {
+    let minor_version = (MINIMUM_SUPPORTED_VERSION.minor..=ABI3_MAX_MINOR)
+        .find(|i| cargo_env_var(&format!("CARGO_FEATURE_ABI3_PY3{}", i)).is_some());
+    minor_version.map(|minor| PythonVersion { major: 3, minor })
 }
 
-impl TargetInfo {
-    fn from_cargo_env() -> Result<Self> {
-        Ok(Self {
-            arch: cargo_env_var("CARGO_CFG_TARGET_ARCH")
-                .ok_or("expected CARGO_CFG_TARGET_ARCH env var")?,
-            vendor: cargo_env_var("CARGO_CFG_TARGET_VENDOR")
-                .ok_or("expected CARGO_CFG_TARGET_VENDOR env var")?,
-            os: cargo_env_var("CARGO_CFG_TARGET_OS")
-                .ok_or("expected CARGO_CFG_TARGET_OS env var")?,
-        })
-    }
+/// Checks if the `extension-module` feature is enabled for the PyO3 crate.
+///
+/// Must be called from a PyO3 crate build script.
+pub fn is_extension_module() -> bool {
+    cargo_env_var("CARGO_FEATURE_EXTENSION_MODULE").is_some()
+}
 
-    fn to_target_triple(&self) -> String {
-        format!(
-            "{}-{}-{}",
-            if self.arch == "x86" {
-                "i686"
-            } else {
-                &self.arch
-            },
-            self.vendor,
-            if self.os == "macos" {
-                "darwin"
-            } else {
-                &self.os
-            }
-        )
-    }
+/// Checks if we need to link to `libpython` for the current build target.
+///
+/// Must be called from a crate PyO3 build script.
+pub fn is_linking_libpython() -> bool {
+    is_linking_libpython_for_target(&target_triple_from_env())
+}
+
+/// Checks if we need to link to `libpython` for the target.
+///
+/// Must be called from a crate PyO3 build script.
+fn is_linking_libpython_for_target(target: &Triple) -> bool {
+    target.operating_system == OperatingSystem::Windows
+        || target.environment == Environment::Android
+        || target.environment == Environment::Androideabi
+        || !is_extension_module()
 }
 
 /// Configuration needed by PyO3 to cross-compile for a target platform.
@@ -668,32 +690,63 @@ pub struct CrossCompileConfig {
     /// The version of the Python library to link against.
     version: Option<PythonVersion>,
 
-    /// The target information
-    target_info: TargetInfo,
+    /// The compile target triple (e.g. aarch64-unknown-linux-gnu)
+    target: Triple,
 }
 
 impl CrossCompileConfig {
-    fn from_env_vars(env_vars: CrossCompileEnvVars, target_info: TargetInfo) -> Result<Self> {
-        Ok(CrossCompileConfig {
-            lib_dir: env_vars
-                .pyo3_cross_lib_dir
-                .ok_or(
-                    "The PYO3_CROSS_LIB_DIR environment variable must be set when cross-compiling",
-                )?
-                .into(),
-            target_info,
-            version: env_vars
-                .pyo3_cross_python_version
-                .map(|os_string| {
-                    let utf8_str = os_string
-                        .to_str()
-                        .ok_or("PYO3_CROSS_PYTHON_VERSION is not valid utf-8.")?;
-                    utf8_str
-                        .parse()
-                        .context("failed to parse PYO3_CROSS_PYTHON_VERSION")
-                })
-                .transpose()?,
-        })
+    /// Creates a new cross compile config struct from PyO3 environment variables
+    /// and the build environment when cross compilation mode is detected.
+    ///
+    /// Returns `None` when not cross compiling.
+    fn try_from_env_vars_host_target(
+        env_vars: CrossCompileEnvVars,
+        host: &Triple,
+        target: &Triple,
+    ) -> Result<Option<Self>> {
+        if env_vars.any() || Self::is_cross_compiling_from_to(host, target) {
+            let lib_dir = env_vars.lib_dir_path()?;
+            let version = env_vars.parse_version()?;
+            let target = target.clone();
+
+            Ok(Some(CrossCompileConfig {
+                lib_dir,
+                target,
+                version,
+            }))
+        } else {
+            Ok(None)
+        }
+    }
+
+    /// Checks if compiling on `host` for `target` required "real" cross compilation.
+    ///
+    /// Returns `false` if the target Python interpreter can run on the host.
+    fn is_cross_compiling_from_to(host: &Triple, target: &Triple) -> bool {
+        // Not cross-compiling if arch-vendor-os is all the same
+        // e.g. x86_64-unknown-linux-musl on x86_64-unknown-linux-gnu host
+        //      x86_64-pc-windows-gnu on x86_64-pc-windows-msvc host
+        let mut compatible = host.architecture == target.architecture
+            && host.vendor == target.vendor
+            && host.operating_system == target.operating_system;
+
+        // Not cross-compiling to compile for 32-bit Python from windows 64-bit
+        compatible |= target.operating_system == OperatingSystem::Windows
+            && host.operating_system == OperatingSystem::Windows;
+
+        // Not cross-compiling to compile for x86-64 Python from macOS arm64 and vice versa
+        compatible |= target.operating_system == OperatingSystem::Darwin
+            && host.operating_system == OperatingSystem::Darwin;
+
+        !compatible
+    }
+
+    /// Converts `lib_dir` member field to an UTF-8 string.
+    ///
+    /// The conversion can not fail because `PYO3_CROSS_LIB_DIR` variable
+    /// is ensured contain a valid UTF-8 string.
+    fn lib_dir_string(&self) -> String {
+        self.lib_dir.to_str().unwrap().to_owned()
     }
 }
 
@@ -709,6 +762,44 @@ impl CrossCompileEnvVars {
             || self.pyo3_cross_lib_dir.is_some()
             || self.pyo3_cross_python_version.is_some()
     }
+
+    /// Parses `PYO3_CROSS_PYTHON_VERSION` environment variable value
+    /// into `PythonVersion`.
+    fn parse_version(&self) -> Result<Option<PythonVersion>> {
+        let version = self
+            .pyo3_cross_python_version
+            .as_ref()
+            .map(|os_string| {
+                let utf8_str = os_string
+                    .to_str()
+                    .ok_or("PYO3_CROSS_PYTHON_VERSION is not valid a UTF-8 string")?;
+                utf8_str
+                    .parse()
+                    .context("failed to parse PYO3_CROSS_PYTHON_VERSION")
+            })
+            .transpose()?;
+
+        Ok(version)
+    }
+
+    /// Converts the stored `PYO3_CROSS_LIB_DIR` variable value (if any)
+    /// into a `PathBuf` instance.
+    ///
+    /// Ensures that the path is a valid UTF-8 string.
+    fn lib_dir_path(&self) -> Result<PathBuf> {
+        let lib_dir = self.pyo3_cross_lib_dir.as_ref().map(PathBuf::from);
+
+        if let Some(dir) = lib_dir.as_ref() {
+            ensure!(
+                dir.to_str().is_some(),
+                "PYO3_CROSS_LIB_DIR variable value is not a valid UTF-8 string"
+            );
+            Ok(dir.clone())
+        } else {
+            // FIXME: Relax this restriction in the future.
+            bail!("The PYO3_CROSS_LIB_DIR environment variable must be set when cross-compiling")
+        }
+    }
 }
 
 pub(crate) fn cross_compile_env_vars() -> CrossCompileEnvVars {
@@ -733,39 +824,76 @@ pub(crate) fn cross_compile_env_vars() -> CrossCompileEnvVars {
 ///   `PYO3_CROSS_LIB_DIR`.
 ///
 /// See the [PyO3 User Guide](https://pyo3.rs/) for more info on cross-compiling.
+#[deprecated(
+    since = "0.17.0",
+    note = "please use cross_compiling_from_to() instead"
+)]
 pub fn cross_compiling(
     host: &str,
     target_arch: &str,
     target_vendor: &str,
     target_os: &str,
 ) -> Result<Option<CrossCompileConfig>> {
-    let env_vars = cross_compile_env_vars();
+    let host: Triple = host.parse().map_err(|_| "bad host triple")?;
 
-    let target_info = TargetInfo {
-        arch: target_arch.to_owned(),
-        vendor: target_vendor.to_owned(),
-        os: target_os.to_owned(),
+    let architecture: Architecture = target_arch.parse().map_err(|_| "bad target arch")?;
+    let vendor: Vendor = target_vendor.parse().map_err(|_| "bad target vendor")?;
+    let operating_system: OperatingSystem = target_os.parse().map_err(|_| "bad target os")?;
+
+    // FIXME: This is a very bad approximation that only works
+    // for the current `CrossCompileConfig` implementation.
+    let environment = match operating_system {
+        OperatingSystem::Windows => Environment::Msvc,
+        _ => Environment::Gnu,
     };
 
-    if !env_vars.any() && is_not_cross_compiling(host, &target_info) {
-        return Ok(None);
-    }
+    // FIXME: This field is currently unused.
+    let binary_format = BinaryFormat::Elf;
 
-    CrossCompileConfig::from_env_vars(env_vars, target_info).map(Some)
+    let target = Triple {
+        architecture,
+        vendor,
+        operating_system,
+        environment,
+        binary_format,
+    };
+
+    cross_compiling_from_to(&host, &target)
 }
 
-fn is_not_cross_compiling(host: &str, target_info: &TargetInfo) -> bool {
-    let target_triple = target_info.to_target_triple();
-    // Not cross-compiling if arch-vendor-os is all the same
-    // e.g. x86_64-unknown-linux-musl on x86_64-unknown-linux-gnu host
-    //      x86_64-pc-windows-gnu on x86_64-pc-windows-msvc host
-    host.starts_with(&target_triple)
-        // Not cross-compiling to compile for 32-bit Python from windows 64-bit
-        || (target_triple == "i686-pc-windows" && host.starts_with("x86_64-pc-windows"))
-        // Not cross-compiling to compile for x86-64 Python from macOS arm64
-        || (target_triple == "x86_64-apple-darwin" && host == "aarch64-apple-darwin")
-        // Not cross-compiling to compile for arm64 Python from macOS x86_64
-        || (target_triple == "aarch64-apple-darwin" && host == "x86_64-apple-darwin")
+/// Detect whether we are cross compiling and return an assembled CrossCompileConfig if so.
+///
+/// This function relies on PyO3 cross-compiling environment variables:
+///
+///   * `PYO3_CROSS`: If present, forces PyO3 to configure as a cross-compilation.
+///   * `PYO3_CROSS_LIB_DIR`: If present, must be set to the directory containing
+///   the target's libpython DSO and the associated `_sysconfigdata*.py` file for
+///   Unix-like targets, or the Python DLL import libraries for the Windows target.
+///   * `PYO3_CROSS_PYTHON_VERSION`: Major and minor version (e.g. 3.9) of the target Python
+///   installation. This variable is only needed if PyO3 cannnot determine the version to target
+///   from `abi3-py3*` features, or if there are multiple versions of Python present in
+///   `PYO3_CROSS_LIB_DIR`.
+///
+/// See the [PyO3 User Guide](https://pyo3.rs/) for more info on cross-compiling.
+pub fn cross_compiling_from_to(
+    host: &Triple,
+    target: &Triple,
+) -> Result<Option<CrossCompileConfig>> {
+    let env_vars = cross_compile_env_vars();
+    CrossCompileConfig::try_from_env_vars_host_target(env_vars, host, target)
+}
+
+/// Detect whether we are cross compiling from Cargo and `PYO3_CROSS_*` environment
+/// variables and return an assembled `CrossCompileConfig` if so.
+///
+/// This must be called from PyO3's build script, because it relies on environment
+/// variables such as `CARGO_CFG_TARGET_OS` which aren't available at any other time.
+pub fn cross_compiling_from_cargo_env() -> Result<Option<CrossCompileConfig>> {
+    let env_vars = cross_compile_env_vars();
+    let host = Triple::host();
+    let target = target_triple_from_env();
+
+    CrossCompileConfig::try_from_env_vars_host_target(env_vars, &host, &target)
 }
 
 #[allow(non_camel_case_types)]
@@ -1091,15 +1219,11 @@ fn search_lib_dir(path: impl AsRef<Path>, cross: &CrossCompileConfig) -> Vec<Pat
                     search_lib_dir(f.path(), cross)
                 } else if file_name.starts_with("lib.") {
                     // check if right target os
-                    if !file_name.contains(if cross.target_info.os == "android" {
-                        "linux"
-                    } else {
-                        &cross.target_info.os
-                    }) {
+                    if !file_name.contains(&cross.target.operating_system.to_string()) {
                         continue;
                     }
                     // Check if right arch
-                    if !file_name.contains(&cross.target_info.arch) {
+                    if !file_name.contains(&cross.target.architecture.to_string()) {
                         continue;
                     }
                     search_lib_dir(f.path(), cross)
@@ -1124,7 +1248,10 @@ fn search_lib_dir(path: impl AsRef<Path>, cross: &CrossCompileConfig) -> Vec<Pat
     if sysconfig_paths.len() > 1 {
         let temp = sysconfig_paths
             .iter()
-            .filter(|p| p.to_string_lossy().contains(&cross.target_info.arch))
+            .filter(|p| {
+                p.to_string_lossy()
+                    .contains(&cross.target.architecture.to_string())
+            })
             .cloned()
             .collect::<Vec<PathBuf>>();
         if !temp.is_empty() {
@@ -1150,11 +1277,19 @@ fn cross_compile_from_sysconfigdata(
 fn windows_hardcoded_cross_compile(
     cross_compile_config: CrossCompileConfig,
 ) -> Result<InterpreterConfig> {
-    let version = cross_compile_config.version.or_else(get_abi3_version)
-        .ok_or("PYO3_CROSS_PYTHON_VERSION or an abi3-py3* feature must be specified when cross-compiling for Windows.")?;
+    let version = cross_compile_config
+        .version
+        .or_else(get_abi3_version)
+        .ok_or(
+            "PYO3_CROSS_PYTHON_VERSION or an abi3-py3* feature must be specified \
+            when cross-compiling and PYO3_CROSS_LIB_DIR is not set.",
+        )?;
 
     let abi3 = is_abi3();
     let implementation = PythonImplementation::CPython;
+    let mingw = cross_compile_config.target.environment == Environment::Gnu;
+
+    let lib_dir = Some(cross_compile_config.lib_dir_string());
 
     Ok(InterpreterConfig {
         implementation,
@@ -1165,9 +1300,9 @@ fn windows_hardcoded_cross_compile(
             version,
             PythonImplementation::CPython,
             abi3,
-            false,
+            mingw,
         )),
-        lib_dir: cross_compile_config.lib_dir.to_str().map(String::from),
+        lib_dir,
         executable: None,
         pointer_width: None,
         build_flags: BuildFlags::default(),
@@ -1303,7 +1438,7 @@ fn conda_env_interpreter(conda_prefix: &OsStr, windows: bool) -> PathBuf {
 
 fn get_env_interpreter() -> Option<PathBuf> {
     match (env_var("VIRTUAL_ENV"), env_var("CONDA_PREFIX")) {
-        // Use cfg rather can CARGO_TARGET_OS because this affects where files are located on the
+        // Use cfg rather than CARGO_CFG_TARGET_OS because this affects where files are located on the
         // build host
         (Some(dir), None) => Some(venv_interpreter(&dir, cfg!(windows))),
         (None, Some(dir)) => Some(conda_env_interpreter(&dir, cfg!(windows))),
@@ -1347,62 +1482,16 @@ pub fn find_interpreter() -> Result<PathBuf> {
     }
 }
 
-pub fn get_abi3_version() -> Option<PythonVersion> {
-    let minor_version = (MINIMUM_SUPPORTED_VERSION.minor..=ABI3_MAX_MINOR)
-        .find(|i| cargo_env_var(&format!("CARGO_FEATURE_ABI3_PY3{}", i)).is_some());
-    minor_version.map(|minor| PythonVersion { major: 3, minor })
-}
-
-/// Lowers the configured version to the abi3 version, if set.
-fn fixup_config_for_abi3(
-    config: &mut InterpreterConfig,
-    abi3_version: Option<PythonVersion>,
-) -> Result<()> {
-    // PyPy doesn't support abi3; don't adjust the version
-    if config.implementation.is_pypy() {
-        return Ok(());
-    }
-
-    if let Some(version) = abi3_version {
-        ensure!(
-            version <= config.version,
-            "cannot set a minimum Python version {} higher than the interpreter version {} \
-             (the minimum Python version is implied by the abi3-py3{} feature)",
-            version,
-            config.version,
-            version.minor,
-        );
-
-        config.version = version;
-    }
-    Ok(())
-}
-
 /// Generates an interpreter config suitable for cross-compilation.
 ///
 /// This must be called from PyO3's build script, because it relies on environment variables such as
 /// CARGO_CFG_TARGET_OS which aren't available at any other time.
 pub fn make_cross_compile_config() -> Result<Option<InterpreterConfig>> {
-    let env_vars = cross_compile_env_vars();
-
-    let host = cargo_env_var("HOST").ok_or("expected HOST env var")?;
-    let target = cargo_env_var("TARGET").ok_or("expected TARGET env var")?;
-
-    let target_info = TargetInfo::from_cargo_env()?;
-
-    let interpreter_config = if env_vars.any() {
-        let cross_config = CrossCompileConfig::from_env_vars(env_vars, target_info)?;
+    let interpreter_config = if let Some(cross_config) = cross_compiling_from_cargo_env()? {
         let mut interpreter_config = load_cross_compile_config(cross_config)?;
-        fixup_config_for_abi3(&mut interpreter_config, get_abi3_version())?;
+        interpreter_config.fixup_for_abi3_version(get_abi3_version())?;
         Some(interpreter_config)
     } else {
-        ensure!(
-            host == target || is_not_cross_compiling(&host, &target_info),
-            "PyO3 detected compile host {host} and build target {target}, but none of PYO3_CROSS, PYO3_CROSS_LIB_DIR \
-             or PYO3_CROSS_PYTHON_VERSION environment variables are set.",
-            host=host,
-            target=target,
-        );
         None
     };
 
@@ -1414,13 +1503,14 @@ pub fn make_cross_compile_config() -> Result<Option<InterpreterConfig>> {
 #[allow(dead_code)]
 pub fn make_interpreter_config() -> Result<InterpreterConfig> {
     let mut interpreter_config = InterpreterConfig::from_interpreter(find_interpreter()?)?;
-    fixup_config_for_abi3(&mut interpreter_config, get_abi3_version())?;
+    interpreter_config.fixup_for_abi3_version(get_abi3_version())?;
     Ok(interpreter_config)
 }
 
 #[cfg(test)]
 mod tests {
     use std::{io::Cursor, iter::FromIterator};
+    use target_lexicon::triple;
 
     use super::*;
 
@@ -1670,11 +1760,7 @@ mod tests {
         let cross_config = CrossCompileConfig {
             lib_dir: "C:\\some\\path".into(),
             version: Some(PythonVersion { major: 3, minor: 7 }),
-            target_info: TargetInfo {
-                os: "os".into(),
-                arch: "arch".into(),
-                vendor: "vendor".into(),
-            },
+            target: triple!("i686-pc-windows-msvc"),
         };
 
         assert_eq!(
@@ -1695,6 +1781,32 @@ mod tests {
         );
     }
 
+    #[test]
+    fn mingw_hardcoded_cross_compile() {
+        let cross_config = CrossCompileConfig {
+            lib_dir: "/usr/lib/mingw".into(),
+            version: Some(PythonVersion { major: 3, minor: 8 }),
+            target: triple!("i686-pc-windows-gnu"),
+        };
+
+        assert_eq!(
+            super::windows_hardcoded_cross_compile(cross_config).unwrap(),
+            InterpreterConfig {
+                implementation: PythonImplementation::CPython,
+                version: PythonVersion { major: 3, minor: 8 },
+                shared: true,
+                abi3: false,
+                lib_name: Some("python3.8".into()),
+                lib_dir: Some("/usr/lib/mingw".into()),
+                executable: None,
+                pointer_width: None,
+                build_flags: BuildFlags::default(),
+                suppress_build_script_link_lines: false,
+                extra_build_script_lines: vec![],
+            }
+        );
+    }
+
     #[test]
     fn default_lib_name_windows() {
         use PythonImplementation::*;
@@ -1780,6 +1892,36 @@ mod tests {
         );
     }
 
+    #[test]
+    fn parse_cross_python_version() {
+        let env_vars = CrossCompileEnvVars {
+            pyo3_cross: None,
+            pyo3_cross_lib_dir: None,
+            pyo3_cross_python_version: Some("3.9".into()),
+        };
+
+        assert_eq!(
+            env_vars.parse_version().unwrap(),
+            Some(PythonVersion { major: 3, minor: 9 })
+        );
+
+        let env_vars = CrossCompileEnvVars {
+            pyo3_cross: None,
+            pyo3_cross_lib_dir: None,
+            pyo3_cross_python_version: None,
+        };
+
+        assert_eq!(env_vars.parse_version().unwrap(), None);
+
+        let env_vars = CrossCompileEnvVars {
+            pyo3_cross: None,
+            pyo3_cross_lib_dir: None,
+            pyo3_cross_python_version: Some("100".into()),
+        };
+
+        assert!(env_vars.parse_version().is_err());
+    }
+
     #[test]
     fn interpreter_version_reduced_to_abi3() {
         let mut config = InterpreterConfig {
@@ -1796,7 +1938,9 @@ mod tests {
             extra_build_script_lines: vec![],
         };
 
-        fixup_config_for_abi3(&mut config, Some(PythonVersion { major: 3, minor: 7 })).unwrap();
+        config
+            .fixup_for_abi3_version(Some(PythonVersion { major: 3, minor: 7 }))
+            .unwrap();
         assert_eq!(config.version, PythonVersion { major: 3, minor: 7 });
     }
 
@@ -1816,12 +1960,13 @@ mod tests {
             extra_build_script_lines: vec![],
         };
 
-        assert!(
-            fixup_config_for_abi3(&mut config, Some(PythonVersion { major: 3, minor: 8 }))
-                .unwrap_err()
-                .to_string()
-                .contains("cannot set a minimum Python version 3.8 higher than the interpreter version 3.7")
-        );
+        assert!(config
+            .fixup_for_abi3_version(Some(PythonVersion { major: 3, minor: 8 }))
+            .unwrap_err()
+            .to_string()
+            .contains(
+                "cannot set a minimum Python version 3.8 higher than the interpreter version 3.7"
+            ));
     }
 
     #[test]
@@ -1846,11 +1991,7 @@ mod tests {
         let cross = CrossCompileConfig {
             lib_dir: lib_dir.into(),
             version: Some(interpreter_config.version),
-            target_info: TargetInfo {
-                arch: "x86_64".into(),
-                vendor: "unknown".into(),
-                os: "linux".into(),
-            },
+            target: triple!("x86_64-unknown-linux-gnu"),
         };
 
         let sysconfigdata_path = match find_sysconfigdata(&cross) {
@@ -1906,6 +2047,7 @@ mod tests {
     }
 
     #[test]
+    #[allow(deprecated)]
     fn test_not_cross_compiling() {
         assert!(
             cross_compiling("aarch64-apple-darwin", "x86_64", "apple", "darwin")
@@ -1924,6 +2066,51 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_not_cross_compiling_from_to() {
+        assert!(cross_compiling_from_to(
+            &triple!("x86_64-unknown-linux-gnu"),
+            &triple!("x86_64-unknown-linux-gnu"),
+        )
+        .unwrap()
+        .is_none());
+
+        assert!(cross_compiling_from_to(
+            &triple!("x86_64-apple-darwin"),
+            &triple!("x86_64-apple-darwin")
+        )
+        .unwrap()
+        .is_none());
+
+        assert!(cross_compiling_from_to(
+            &triple!("aarch64-apple-darwin"),
+            &triple!("x86_64-apple-darwin")
+        )
+        .unwrap()
+        .is_none());
+
+        assert!(cross_compiling_from_to(
+            &triple!("x86_64-apple-darwin"),
+            &triple!("aarch64-apple-darwin")
+        )
+        .unwrap()
+        .is_none());
+
+        assert!(cross_compiling_from_to(
+            &triple!("x86_64-pc-windows-msvc"),
+            &triple!("i686-pc-windows-msvc")
+        )
+        .unwrap()
+        .is_none());
+
+        assert!(cross_compiling_from_to(
+            &triple!("x86_64-unknown-linux-gnu"),
+            &triple!("x86_64-unknown-linux-musl")
+        )
+        .unwrap()
+        .is_none());
+    }
+
     #[test]
     fn test_run_python_script() {
         // as above, this should be okay in CI where Python is presumed installed

pyo3-build-config/src/lib.rs

@@ -17,9 +17,11 @@ use std::{env, process::Command};
 #[cfg(feature = "resolve-config")]
 use once_cell::sync::OnceCell;
 
+#[allow(deprecated)]
 pub use impl_::{
-    cross_compiling, find_all_sysconfigdata, parse_sysconfigdata, BuildFlag, BuildFlags,
-    CrossCompileConfig, InterpreterConfig, PythonImplementation, PythonVersion,
+    cross_compiling, cross_compiling_from_to, find_all_sysconfigdata, parse_sysconfigdata,
+    BuildFlag, BuildFlags, CrossCompileConfig, InterpreterConfig, PythonImplementation,
+    PythonVersion, Triple,
 };
 
 /// Adds all the [`#[cfg]` flags](index.html) to the current compilation.
@@ -166,7 +168,8 @@ pub mod pyo3_build_script_impl {
         pub use crate::errors::*;
     }
     pub use crate::impl_::{
-        cargo_env_var, env_var, make_cross_compile_config, InterpreterConfig, PythonVersion,
+        cargo_env_var, env_var, is_linking_libpython, make_cross_compile_config, InterpreterConfig,
+        PythonVersion,
     };
 
     /// Gets the configuration for use from PyO3's build script.
@@ -180,7 +183,7 @@ pub mod pyo3_build_script_impl {
             InterpreterConfig::from_reader(Cursor::new(CONFIG_FILE))
         } else if !ABI3_CONFIG.is_empty() {
             Ok(abi3_config())
-        } else if let Some(interpreter_config) = impl_::make_cross_compile_config()? {
+        } else if let Some(interpreter_config) = make_cross_compile_config()? {
             // This is a cross compile and need to write the config file.
             let path = Path::new(DEFAULT_CROSS_COMPILE_CONFIG_PATH);
             let parent_dir = path.parent().ok_or_else(|| {

pyo3-ffi/build.rs

@@ -1,8 +1,8 @@
 use pyo3_build_config::{
     bail, ensure, print_feature_cfgs,
     pyo3_build_script_impl::{
-        cargo_env_var, env_var, errors::Result, resolve_interpreter_config, InterpreterConfig,
-        PythonVersion,
+        cargo_env_var, env_var, errors::Result, is_linking_libpython, resolve_interpreter_config,
+        InterpreterConfig, PythonVersion,
     },
 };
 
@@ -44,33 +44,27 @@ fn ensure_target_pointer_width(interpreter_config: &InterpreterConfig) -> Result
 
 fn emit_link_config(interpreter_config: &InterpreterConfig) -> Result<()> {
     let target_os = cargo_env_var("CARGO_CFG_TARGET_OS").unwrap();
-    let is_extension_module = cargo_env_var("CARGO_FEATURE_EXTENSION_MODULE").is_some();
-    if target_os == "windows" || target_os == "android" || !is_extension_module {
-        // windows and android - always link
-        // other systems - only link if not extension module
-        println!(
-            "cargo:rustc-link-lib={link_model}{alias}{lib_name}",
-            link_model = if interpreter_config.shared {
-                ""
-            } else {
-                "static="
-            },
-            alias = if target_os == "windows" {
-                "pythonXY:"
-            } else {
-                ""
-            },
-            lib_name = interpreter_config.lib_name.as_ref().ok_or(
-                "attempted to link to Python shared library but config does not contain lib_name"
-            )?,
-        );
-        if let Some(lib_dir) = &interpreter_config.lib_dir {
-            println!("cargo:rustc-link-search=native={}", lib_dir);
-        }
-    }
 
-    // serialize the whole interpreter config in DEP_PYTHON_PYO3_CONFIG
-    interpreter_config.to_cargo_dep_env()?;
+    println!(
+        "cargo:rustc-link-lib={link_model}{alias}{lib_name}",
+        link_model = if interpreter_config.shared {
+            ""
+        } else {
+            "static="
+        },
+        alias = if target_os == "windows" {
+            "pythonXY:"
+        } else {
+            ""
+        },
+        lib_name = interpreter_config.lib_name.as_ref().ok_or(
+            "attempted to link to Python shared library but config does not contain lib_name"
+        )?,
+    );
+
+    if let Some(lib_dir) = &interpreter_config.lib_dir {
+        println!("cargo:rustc-link-search=native={}", lib_dir);
+    }
 
     Ok(())
 }
@@ -92,7 +86,10 @@ fn configure_pyo3() -> Result<()> {
     ensure_python_version(&interpreter_config)?;
     ensure_target_pointer_width(&interpreter_config)?;
 
-    if !interpreter_config.suppress_build_script_link_lines {
+    // Serialize the whole interpreter config into DEP_PYTHON_PYO3_CONFIG env var.
+    interpreter_config.to_cargo_dep_env()?;
+
+    if is_linking_libpython() && !interpreter_config.suppress_build_script_link_lines {
         emit_link_config(&interpreter_config)?;
     }