pyembed: adjust lifetime return value from acquire_gil()

See the inline comments for more.

Closes #345.

docs/history.rst

@@ -69,6 +69,9 @@ Bug Fixes
   to be equivalent to the parent package to partially emulate CPython's
   behavior. See :ref:`oxidized_importer_dunder_init_module_names` for more.
   (#317)
+* The lifetime of ``pyembed::MainPythonInterpreter.acquire_gil()``'s return
+  value has been adjusted so the Rust compiler will refuse to compile code
+  that could crash due to attempting to use a finalized interpreter. (#345)
 
 New Features
 ^^^^^^^^^^^^

pyembed/src/interpreter.rs

@@ -422,7 +422,12 @@ impl<'python, 'interpreter, 'resources> MainPythonInterpreter<'python, 'interpre
     }
 
     /// Ensure the Python GIL is acquired, returning a handle on the interpreter.
-    pub fn acquire_gil(&mut self) -> Result<Python<'python>, &'static str> {
+    ///
+    /// The returned value has a lifetime of the `MainPythonInterpreter`
+    /// instance. This is because `MainPythonInterpreter.drop()` finalizes
+    /// the interpreter. The borrow checker should refuse to compile code
+    /// where the returned `Python` outlives `self`.
+    pub fn acquire_gil(&mut self) -> Result<Python<'_>, &'static str> {
         match self.interpreter_state {
             InterpreterState::NotStarted => {
                 return Err("interpreter not initialized");

pyembed/src/test/main_python_interpreter.rs

@@ -9,15 +9,12 @@ use {
 
 rusty_fork_test! {
     #[test]
-    #[should_panic]
     fn test_instantiate_interpreter() {
-        let py = {
-            let mut config = OxidizedPythonInterpreterConfig::default();
-            config.interpreter_config.parse_argv = Some(false);
-            config.set_missing_path_configuration = false;
-            let mut interp = MainPythonInterpreter::new(config).unwrap();
-            interp.acquire_gil().unwrap()
-        };
+        let mut config = OxidizedPythonInterpreterConfig::default();
+        config.interpreter_config.parse_argv = Some(false);
+        config.set_missing_path_configuration = false;
+        let mut interp = MainPythonInterpreter::new(config).unwrap();
+        let py = interp.acquire_gil().unwrap();
         py.import("sys").unwrap();
     }
 }