pyo3-build-config: Add python3-dll-a crate support

Automatically generate `python3.dll` import libraries for Windows
compile targets in the build script.

Adds a new PyO3 crate feature `generate-abi3-import-lib` enabling
automatic import library generation.

Closes PyO3#2231

Cargo.toml

@@ -78,6 +78,9 @@ 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", "pyo3-build-config/abi3-py310", "pyo3-ffi/abi3-py310"]
 
+# Automatically generates `python3.dll` import libraries for Windows targets.
+generate-abi3-import-lib = ["pyo3-build-config/python3-dll-a"]
+
 # Changes `Python::with_gil` and `Python::acquire_gil` to automatically initialize the
 # Python interpreter if needed.
 auto-initialize = []

pyo3-build-config/Cargo.toml

@@ -12,9 +12,11 @@ edition = "2018"
 
 [dependencies]
 once_cell = "1"
+python3-dll-a = { version = "0.2", optional = true }
 target-lexicon = "0.12"
 
 [build-dependencies]
+python3-dll-a = { version = "0.2", optional = true }
 target-lexicon = "0.12"
 
 [features]

pyo3-build-config/src/abi3_import_lib.rs

@@ -0,0 +1,48 @@
+//! Optional `python3.dll` import library generator for Windows
+
+use std::env;
+use std::path::PathBuf;
+
+use python3_dll_a::generate_implib_for_target;
+
+use crate::errors::{Context, Result};
+
+use super::{Architecture, OperatingSystem, Triple};
+
+/// Generates the `python3.dll` import library for Windows targets.
+///
+/// Places the generated import library into the build script output directory
+/// and returns the full library directory path.
+///
+/// Does nothing if the target OS is not Windows.
+pub(super) fn generate_abi3_import_lib(target: &Triple) -> Result<Option<String>> {
+    if target.operating_system != OperatingSystem::Windows {
+        return Ok(None);
+    }
+
+    let out_dir = env::var_os("OUT_DIR")
+        .expect("generate_abi3_import_lib() must be called from a build script");
+
+    // Put the newly created import library into the build script output directory.
+    let mut out_lib_dir = PathBuf::from(out_dir);
+    out_lib_dir.push("lib");
+
+    // Convert `Architecture` enum to rustc `target_arch` option format.
+    let arch = match target.architecture {
+        // i686, i586, etc.
+        Architecture::X86_32(_) => "x86".to_string(),
+        other => other.to_string(),
+    };
+
+    let env = target.environment.to_string();
+
+    generate_implib_for_target(&out_lib_dir, &arch, &env)
+        .context("failed to generate python3.dll import library")?;
+
+    let out_lib_dir_string = out_lib_dir
+        .to_str()
+        .ok_or("build directory is not a valid UTF-8 string")?
+        .to_owned();
+
+    Ok(Some(out_lib_dir_string))
+}

pyo3-build-config/src/impl_.rs

@@ -1,3 +1,11 @@
+//! Main implementation module included in both the `pyo3-build-config` library crate
+//! and its build script.
+
+// Optional python3.dll import library generator for Windows
+#[cfg(feature = "python3-dll-a")]
+#[path = "abi3_import_lib.rs"]
+mod abi3_import_lib;
+
 use std::{
     collections::{HashMap, HashSet},
     convert::AsRef,
@@ -1352,6 +1360,7 @@ fn cross_compile_from_sysconfigdata(
 /// Windows, macOS and Linux.
 ///
 /// Must be called from a PyO3 crate build script.
+#[allow(unused_mut)]
 fn default_cross_compile(cross_compile_config: &CrossCompileConfig) -> Result<InterpreterConfig> {
     let version = cross_compile_config
         .version
@@ -1381,7 +1390,13 @@ fn default_cross_compile(cross_compile_config: &CrossCompileConfig) -> Result<In
         None
     };
 
-    let lib_dir = cross_compile_config.lib_dir_string();
+    let mut lib_dir = cross_compile_config.lib_dir_string();
+
+    // Auto generate python3.dll import libraries for Windows targets.
+    #[cfg(feature = "python3-dll-a")]
+    if abi3 && lib_dir.is_none() {
+        lib_dir = self::abi3_import_lib::generate_abi3_import_lib(&cross_compile_config.target)?;
+    }
 
     Ok(InterpreterConfig {
         implementation,
@@ -1641,7 +1656,7 @@ pub fn make_cross_compile_config() -> Result<Option<InterpreterConfig>> {
 
 /// 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)]
+#[allow(dead_code, unused_mut)]
 pub fn make_interpreter_config() -> Result<InterpreterConfig> {
     let abi3_version = get_abi3_version();
 
@@ -1651,7 +1666,15 @@ pub fn make_interpreter_config() -> Result<InterpreterConfig> {
         Ok(interpreter_config)
     } else if let Some(version) = abi3_version {
         let host = Triple::host();
-        Ok(default_abi3_config(&host, version))
+        let mut interpreter_config = default_abi3_config(&host, version);
+
+        // Auto generate python3.dll import libraries for Windows targets.
+        #[cfg(feature = "python3-dll-a")]
+        {
+            interpreter_config.lib_dir = self::abi3_import_lib::generate_abi3_import_lib(&host)?;
+        }
+
+        Ok(interpreter_config)
     } else {
         bail!("An abi3-py3* feature must be specified when compiling without a Python interpreter.")
     }