Fix linker problem with importing modules in ct_python on unix.

Author: m-ou-se

macros/Cargo.toml

@@ -17,3 +17,6 @@ proc_macro = true
 proc-macro2 = { version = "1.0", features = ["span-locations"] }
 quote = "1.0"
 pyo3 = { version = "0.10.0", default-features = false }
+
+[target.'cfg(unix)'.dependencies]
+libc = "0.2.71"

macros/src/run.rs

@@ -3,7 +3,31 @@ use proc_macro2::{Span, TokenStream};
 use pyo3::{ffi, AsPyPointer, PyObject, PyResult, Python};
 use std::str::FromStr;
 
+#[cfg(unix)]
+fn ensure_libpython_symbols_loaded(py: Python) -> PyResult<()>{
+	// On Unix, Rustc loads proc-macro crates with RTLD_LOCAL, which (at least
+	// on Linux) means all their dependencies (in our case: libpython) don't
+	// get their symbols made available globally either. This means that
+	// loading modules (e.g. `import math`) will fail, as those modules refer
+	// back to symbols of libpython.
+	//
+	// This function tries to (re)load the right version of libpython, but this
+	// time with RTLD_GLOBAL enabled.
+
+	let sysconfig = py.import("sysconfig")?;
+	let libdir: String = sysconfig.call1("get_config_var", ("LIBDIR",))?.extract()?;
+	let so_name: String = sysconfig.call1("get_config_var", ("INSTSONAME",))?.extract()?;
+	let path = std::ffi::CString::new(format!("{}/{}", libdir, so_name)).unwrap();
+	unsafe {
+		libc::dlopen(path.as_ptr(), libc::RTLD_NOW | libc::RTLD_GLOBAL);
+	}
+	Ok(())
+}
+
 fn run_and_capture(py: Python, code: PyObject) -> PyResult<String> {
+	#[cfg(unix)]
+	let _ = ensure_libpython_symbols_loaded(py);
+
 	let globals = py.import("__main__")?.dict().copy()?;
 
 	let sys = py.import("sys")?;