add coverage for `emit_pyo3_cfgs`

build.rs

@@ -33,10 +33,12 @@ fn ensure_auto_initialize_ok(interpreter_config: &InterpreterConfig) -> Result<(
 fn configure_pyo3() -> Result<()> {
     let interpreter_config = pyo3_build_config::get();
 
-    interpreter_config.emit_pyo3_cfgs();
-
     ensure_auto_initialize_ok(interpreter_config)?;
 
+    for cfg in interpreter_config.build_script_outputs() {
+        println!("{}", cfg)
+    }
+
     // Emit cfgs like `thread_local_const_init`
     print_feature_cfgs();
 

pyo3-build-config/src/errors.rs

@@ -12,15 +12,21 @@ macro_rules! ensure {
     ($condition:expr, $($args: tt)+) => { if !($condition) { bail!($($args)+) } };
 }
 
-/// Show warning. If needed, please extend this macro to support arguments.
+/// Show warning.
 #[macro_export]
 #[doc(hidden)]
 macro_rules! warn {
-    ($msg: literal) => {
-        println!(concat!("cargo:warning=", $msg))
+    ($($args: tt)+) => {
+        println!("{}", $crate::format_warn!($($args)+))
     };
-    ($fmt: expr, $($args: tt)+) => {
-        println!("cargo:warning={}", format_args!($fmt, $($args)+))
+}
+
+/// Format warning into string.
+#[macro_export]
+#[doc(hidden)]
+macro_rules! format_warn {
+    ($($args: tt)+) => {
+        format!("cargo:warning={}", format_args!($($args)+))
     };
 }
 

pyo3-build-config/src/impl_.rs

@@ -27,7 +27,7 @@ use target_lexicon::{Environment, OperatingSystem};
 use crate::{
     bail, ensure,
     errors::{Context, Error, Result},
-    warn,
+    format_warn, warn,
 };
 
 /// Minimum Python version PyO3 supports.
@@ -154,31 +154,35 @@ pub struct InterpreterConfig {
 
 impl InterpreterConfig {
     #[doc(hidden)]
-    pub fn emit_pyo3_cfgs(&self) {
+    pub fn build_script_outputs(&self) -> Vec<String> {
         // This should have been checked during pyo3-build-config build time.
         assert!(self.version >= MINIMUM_SUPPORTED_VERSION);
 
+        let mut out = vec![];
+
         // pyo3-build-config was released when Python 3.6 was supported, so minimum flag to emit is
         // Py_3_6 (to avoid silently breaking users who depend on this cfg).
         for i in 6..=self.version.minor {
-            println!("cargo:rustc-cfg=Py_3_{}", i);
+            out.push(format!("cargo:rustc-cfg=Py_3_{}", i));
         }
 
         if self.implementation.is_pypy() {
-            println!("cargo:rustc-cfg=PyPy");
+            out.push("cargo:rustc-cfg=PyPy".to_owned());
             if self.abi3 {
-                warn!(
+                out.push(format_warn!(
                     "PyPy does not yet support abi3 so the build artifacts will be version-specific. \
                     See https://foss.heptapod.net/pypy/pypy/-/issues/3397 for more information."
-                );
+                ));
             }
         } else if self.abi3 {
-            println!("cargo:rustc-cfg=Py_LIMITED_API");
+            out.push("cargo:rustc-cfg=Py_LIMITED_API".to_owned());
         }
 
         for flag in &self.build_flags.0 {
-            println!("cargo:rustc-cfg=py_sys_config=\"{}\"", flag);
+            out.push(format!("cargo:rustc-cfg=py_sys_config=\"{}\"", flag));
         }
+
+        out
     }
 
     #[doc(hidden)]
@@ -1011,12 +1015,12 @@ impl BuildFlags {
         Self(
             BuildFlags::ALL
                 .iter()
-                .cloned()
                 .filter(|flag| {
                     config_map
                         .get_value(&flag.to_string())
                         .map_or(false, |value| value == "1")
                 })
+                .cloned()
                 .collect(),
         )
         .fixup()
@@ -2581,4 +2585,114 @@ mod tests {
             .expect("failed to run Python script");
         assert_eq!(out.trim_end(), "42");
     }
+
+    #[test]
+    fn test_build_script_outputs_base() {
+        let interpreter_config = InterpreterConfig {
+            implementation: PythonImplementation::CPython,
+            version: PythonVersion { major: 3, minor: 8 },
+            shared: true,
+            abi3: false,
+            lib_name: Some("python3".into()),
+            lib_dir: None,
+            executable: None,
+            pointer_width: None,
+            build_flags: BuildFlags::default(),
+            suppress_build_script_link_lines: false,
+            extra_build_script_lines: vec![],
+        };
+        assert_eq!(
+            interpreter_config.build_script_outputs(),
+            [
+                "cargo:rustc-cfg=Py_3_6".to_owned(),
+                "cargo:rustc-cfg=Py_3_7".to_owned(),
+                "cargo:rustc-cfg=Py_3_8".to_owned(),
+            ]
+        );
+
+        let interpreter_config = InterpreterConfig {
+            implementation: PythonImplementation::PyPy,
+            ..interpreter_config
+        };
+        assert_eq!(
+            interpreter_config.build_script_outputs(),
+            [
+                "cargo:rustc-cfg=Py_3_6".to_owned(),
+                "cargo:rustc-cfg=Py_3_7".to_owned(),
+                "cargo:rustc-cfg=Py_3_8".to_owned(),
+                "cargo:rustc-cfg=PyPy".to_owned(),
+            ]
+        );
+    }
+
+    #[test]
+    fn test_build_script_outputs_abi3() {
+        let interpreter_config = InterpreterConfig {
+            implementation: PythonImplementation::CPython,
+            version: PythonVersion { major: 3, minor: 7 },
+            shared: true,
+            abi3: true,
+            lib_name: Some("python3".into()),
+            lib_dir: None,
+            executable: None,
+            pointer_width: None,
+            build_flags: BuildFlags::default(),
+            suppress_build_script_link_lines: false,
+            extra_build_script_lines: vec![],
+        };
+
+        assert_eq!(
+            interpreter_config.build_script_outputs(),
+            [
+                "cargo:rustc-cfg=Py_3_6".to_owned(),
+                "cargo:rustc-cfg=Py_3_7".to_owned(),
+                "cargo:rustc-cfg=Py_LIMITED_API".to_owned(),
+            ]
+        );
+
+        let interpreter_config = InterpreterConfig {
+            implementation: PythonImplementation::PyPy,
+            ..interpreter_config
+        };
+        assert_eq!(
+            interpreter_config.build_script_outputs(),
+            [
+                "cargo:rustc-cfg=Py_3_6".to_owned(),
+                "cargo:rustc-cfg=Py_3_7".to_owned(),
+                "cargo:rustc-cfg=PyPy".to_owned(),
+                "cargo:warning=PyPy does not yet support abi3 so the build artifacts \
+            will be version-specific. See https://foss.heptapod.net/pypy/pypy/-/issues/3397 \
+            for more information."
+                    .to_owned(),
+            ]
+        );
+    }
+
+    #[test]
+    fn test_build_script_outputs_debug() {
+        let mut build_flags = BuildFlags::default();
+        build_flags.0.insert(BuildFlag::Py_DEBUG);
+        let interpreter_config = InterpreterConfig {
+            implementation: PythonImplementation::CPython,
+            version: PythonVersion { major: 3, minor: 7 },
+            shared: true,
+            abi3: false,
+            lib_name: Some("python3".into()),
+            lib_dir: None,
+            executable: None,
+            pointer_width: None,
+            build_flags,
+            suppress_build_script_link_lines: false,
+            extra_build_script_lines: vec![],
+        };
+
+        assert_eq!(
+            interpreter_config.build_script_outputs(),
+            [
+                "cargo:rustc-cfg=Py_3_6".to_owned(),
+                "cargo:rustc-cfg=Py_3_7".to_owned(),
+                "cargo:rustc-cfg=py_sys_config=\"Py_DEBUG\"".to_owned(),
+            ]
+        );
+    }
 }

pyo3-build-config/src/lib.rs

@@ -42,7 +42,9 @@ use target_lexicon::OperatingSystem;
 /// For examples of how to use these attributes, [see PyO3's guide](https://pyo3.rs/latest/building_and_distribution/multiple_python_versions.html).
 #[cfg(feature = "resolve-config")]
 pub fn use_pyo3_cfgs() {
-    get().emit_pyo3_cfgs();
+    for cargo_command in get().build_script_outputs() {
+        println!("{}", cargo_command)
+    }
 }
 
 /// Adds linker arguments suitable for PyO3's `extension-module` feature.

pyo3-ffi/build.rs

@@ -93,7 +93,9 @@ fn configure_pyo3() -> Result<()> {
         emit_link_config(&interpreter_config)?;
     }
 
-    interpreter_config.emit_pyo3_cfgs();
+    for cfg in interpreter_config.build_script_outputs() {
+        println!("{}", cfg)
+    }
 
     // Extra lines come last, to support last write wins.
     for line in &interpreter_config.extra_build_script_lines {
@@ -109,7 +111,7 @@ fn configure_pyo3() -> Result<()> {
 fn print_config_and_exit(config: &InterpreterConfig) {
     println!("\n-- PYO3_PRINT_CONFIG=1 is set, printing configuration and halting compile --");
     config
-        .to_writer(&mut std::io::stdout())
+        .to_writer(std::io::stdout())
         .expect("failed to print config to stdout");
     println!("\nnote: unset the PYO3_PRINT_CONFIG environment variable and retry to compile with the above config");
     std::process::exit(101);