pyoxidizer: target appropriate Apple SDK when compiling custom config.c

Before this commit, our invocation of the cc crate would likely pick up
the default Apple SDK. This would work most of the time. However, during
scenarios like cross-compiling, it may not work. For example, if the
default SDK is a 10.15 SDK and we are compiling for aarch64, which is
only supported by the 11.0 SDK. In this case, you'd get a compiler
error about the supported target not being supported. Even if things
did work, building of the final binary would trigger full Apple SDK
checks and this would reveal an error.

This commit teaches the config.c compiling to use the same logic as
the Rust project / final binary building code for finding and validating
the Apple SDK. It should enable errors to be detected sooner. It
should also hopefully prevent hard-to-debug compiler errors from
occurring, instead presenting an actionable error about the Apple
SDK.

pyoxidizer/docs/pyoxidizer_history.rst

@@ -59,6 +59,17 @@ Bug Fixes
   properly update the ``PATH`` environment variable if that installation option
   is active. This affects PyOxidizer's own MSI installers.
 
+Other Relevant Changes
+^^^^^^^^^^^^^^^^^^^^^^
+
+* When building for Apple platforms, we now check for a compatible Apple SDK earlier
+  during binary building (when compiling a custom ``config.c`` for a custom
+  ``libpython``). This should surface missing dependencies sooner in the build
+  and potentially replace cryptic compiler error messages with an actionable one
+  about the Apple SDK. Related to this, we now target a specific Apple SDK when
+  compiling the aforementioned source file to ensure that the same, validated SDK
+  is consistently used.
+
 .. _version_0_15_0:
 
 0.15.0

pyoxidizer/src/project_building.rs

@@ -277,7 +277,7 @@ pub fn build_executable_with_rust_project<'a>(
 
     // Derive and write the artifacts needed to build a binary embedding Python.
     let embedded_data = exe
-        .to_embedded_python_context(logger, opt_level)
+        .to_embedded_python_context(logger, env, opt_level)
         .context("obtaining embedded python context")?;
     embedded_data
         .write_files(&artifacts_path)

pyoxidizer/src/py_packaging/binary.rs

@@ -8,6 +8,7 @@ Defining and manipulating binaries embedding Python.
 
 use {
     super::{config::PyembedPythonInterpreterConfig, distribution::AppleSdkInfo},
+    crate::environment::Environment,
     anyhow::{anyhow, Context, Result},
     python_packaging::{
         policy::PythonPackagingPolicy,
@@ -401,6 +402,7 @@ pub trait PythonBinaryBuilder {
     fn to_embedded_python_context(
         &self,
         logger: &slog::Logger,
+        env: &Environment,
         opt_level: &str,
     ) -> Result<EmbeddedPythonContext>;
 }

pyoxidizer/src/py_packaging/libpython.rs

@@ -7,7 +7,8 @@ Building a native binary containing Python.
 */
 
 use {
-    anyhow::{anyhow, Result},
+    crate::{environment::Environment, py_packaging::distribution::AppleSdkInfo},
+    anyhow::{anyhow, Context, Result},
     python_packaging::libpython::LibPythonBuildContext,
     slog::warn,
     std::{
@@ -56,13 +57,16 @@ pub struct LibpythonInfo {
 /// Create a static libpython from a Python distribution.
 ///
 /// Returns a vector of cargo: lines that can be printed in build scripts.
+#[allow(clippy::too_many_arguments)]
 pub fn link_libpython(
     logger: &slog::Logger,
+    env: &Environment,
     context: &LibPythonBuildContext,
     out_dir: &Path,
     host_triple: &str,
     target_triple: &str,
     opt_level: &str,
+    apple_sdk_info: Option<&AppleSdkInfo>,
 ) -> Result<LibpythonInfo> {
     let mut cargo_metadata: Vec<String> = Vec::new();
 
@@ -112,6 +116,23 @@ pub fn link_libpython(
         }
     }
 
+    // The cc crate will pick up the default Apple SDK by default. There could be a mismatch
+    // between it and what we want. For example, if we're building for aarch64 but the default
+    // SDK is a 10.15 SDK that doesn't support ARM. We attempt to mitigate this by resolving
+    // a compatible Apple SDK and pointing the compiler invocation at it via compiler flags.
+    if target_triple.contains("-apple-") {
+        let sdk_info = apple_sdk_info.ok_or_else(|| {
+            anyhow!("Apple SDK info should be defined when targeting Apple platforms")
+        })?;
+
+        let sdk = env
+            .resolve_apple_sdk(logger, sdk_info)
+            .context("resolving Apple SDK to use")?;
+
+        build.flag("-isysroot");
+        build.flag(&format!("{}", sdk.path.display()));
+    }
+
     build
         .out_dir(out_dir)
         .host(host_triple)

pyoxidizer/src/py_packaging/standalone_builder.rs

@@ -18,6 +18,7 @@ use {
         },
         standalone_distribution::StandaloneDistribution,
     },
+    crate::environment::Environment,
     anyhow::{anyhow, Context, Result},
     once_cell::sync::Lazy,
     python_packaging::{
@@ -308,6 +309,7 @@ impl StandalonePythonExecutableBuilder {
     fn resolve_python_linking_info(
         &self,
         logger: &slog::Logger,
+        env: &Environment,
         opt_level: &str,
     ) -> Result<PythonLinkingInfo> {
         let libpythonxy_filename;
@@ -336,11 +338,13 @@ impl StandalonePythonExecutableBuilder {
 
                 let library_info = link_libpython(
                     logger,
+                    env,
                     &LibPythonBuildContext::merge(&link_contexts),
                     &temp_dir_path,
                     &self.host_triple,
                     &self.target_triple,
                     opt_level,
+                    self.apple_sdk_info(),
                 )?;
 
                 libpythonxy_filename =
@@ -878,6 +882,7 @@ impl PythonBinaryBuilder for StandalonePythonExecutableBuilder {
     fn to_embedded_python_context(
         &self,
         logger: &slog::Logger,
+        env: &Environment,
         opt_level: &str,
     ) -> Result<EmbeddedPythonContext> {
         let mut file_seen = false;
@@ -985,7 +990,7 @@ impl PythonBinaryBuilder for StandalonePythonExecutableBuilder {
             }
         }
 
-        let linking_info = self.resolve_python_linking_info(logger, opt_level)?;
+        let linking_info = self.resolve_python_linking_info(logger, env, opt_level)?;
 
         if self.link_mode == LibpythonLinkMode::Dynamic {
             if let Some(p) = &self.target_distribution.libpython_shared_library {
@@ -1307,7 +1312,7 @@ pub mod tests {
         let logger = get_logger()?;
         let options = StandalonePythonExecutableBuilderOptions::default();
         let exe = options.new_builder()?;
-        let embedded = exe.to_embedded_python_context(&logger, "0")?;
+        let embedded = exe.to_embedded_python_context(&logger, &get_env()?, "0")?;
 
         let temp_dir = tempfile::Builder::new()
             .prefix("pyoxidizer-test")
@@ -1329,7 +1334,7 @@ pub mod tests {
         exe.resources_load_mode =
             PackedResourcesLoadMode::BinaryRelativePathMemoryMapped("resources".into());
 
-        let embedded = exe.to_embedded_python_context(&logger, "0")?;
+        let embedded = exe.to_embedded_python_context(&logger, &get_env()?, "0")?;
 
         assert_eq!(
             &embedded.config.packed_resources,

pyoxidizer/src/starlark/python_embedded_resources.rs

@@ -67,9 +67,11 @@ impl PythonEmbeddedResourcesValue {
             output_path.display()
         );
 
-        let embedded = self
-            .exe
-            .to_embedded_python_context(context.logger(), &context.build_opt_level)?;
+        let embedded = self.exe.to_embedded_python_context(
+            context.logger(),
+            context.env(),
+            &context.build_opt_level,
+        )?;
 
         std::fs::create_dir_all(&output_path)
             .with_context(|| format!("creating output directory: {}", output_path.display()))?;