make abi3 feature apply to config imported from PYO3_BUILD_CONFIG

pyo3-build-config/build.rs

@@ -12,7 +12,7 @@ mod errors;
 use std::{env, path::Path};
 
 use errors::{Context, Result};
-use impl_::{env_var, make_interpreter_config, InterpreterConfig};
+use impl_::{make_interpreter_config, InterpreterConfig};
 
 fn configure(interpreter_config: Option<InterpreterConfig>, name: &str) -> Result<bool> {
     let target = Path::new(&env::var_os("OUT_DIR").unwrap()).join(name);
@@ -29,28 +29,12 @@ fn configure(interpreter_config: Option<InterpreterConfig>, name: &str) -> Resul
     }
 }
 
-/// If PYO3_CONFIG_FILE is set, copy it into the crate.
-fn config_file() -> Result<Option<InterpreterConfig>> {
-    if let Some(path) = env_var("PYO3_CONFIG_FILE") {
-        let path = Path::new(&path);
-        println!("cargo:rerun-if-changed={}", path.display());
-        // Absolute path is necessary because this build script is run with a cwd different to the
-        // original `cargo build` instruction.
-        ensure!(
-            path.is_absolute(),
-            "PYO3_CONFIG_FILE must be an absolute path"
-        );
-
-        let interpreter_config = InterpreterConfig::from_path(path)
-            .context("failed to parse contents of PYO3_CONFIG_FILE")?;
-        Ok(Some(interpreter_config))
-    } else {
-        Ok(None)
-    }
-}
-
 fn generate_build_configs() -> Result<()> {
-    let configured = configure(config_file()?, "pyo3-build-config-file.txt")?;
+    // If PYO3_CONFIG_FILE is set, copy it into the crate.
+    let configured = configure(
+        InterpreterConfig::from_pyo3_config_file_env().transpose()?,
+        "pyo3-build-config-file.txt",
+    )?;
 
     if configured {
         // Don't bother trying to find an interpreter on the host system

pyo3-build-config/src/impl_.rs

@@ -402,6 +402,34 @@ print("ext_suffix", get_config_var("EXT_SUFFIX"))
         })
     }
 
+    /// Import an externally-provided config file.
+    ///
+    /// The `abi3` features, if set, may apply an `abi3` constraint to the Python version.
+    pub(super) fn from_pyo3_config_file_env() -> Option<Result<Self>> {
+        cargo_env_var("PYO3_CONFIG_FILE").map(|path| {
+            let path = Path::new(&path);
+            println!("cargo:rerun-if-changed={}", path.display());
+            // Absolute path is necessary because this build script is run with a cwd different to the
+            // original `cargo build` instruction.
+            ensure!(
+                path.is_absolute(),
+                "PYO3_CONFIG_FILE must be an absolute path"
+            );
+
+            let mut config = InterpreterConfig::from_path(path)
+                .context("failed to parse contents of PYO3_CONFIG_FILE")?;
+            // If the abi3 feature is enabled, the minimum Python version is constrained by the abi3
+            // feature.
+            //
+            // TODO: abi3 is a property of the build mode, not the interpreter. Should this be
+            // removed from `InterpreterConfig`?
+            config.abi3 |= is_abi3();
+            config.fixup_for_abi3_version(get_abi3_version())?;
+
+            Ok(config)
+        })
+    }
+
     #[doc(hidden)]
     pub fn from_path(path: impl AsRef<Path>) -> Result<Self> {
         let path = path.as_ref();