rust-cpython: prepare for writing tests that require libpython

rust-cpython: prepare for writing tests that require libpython

What I wanted is to disable the "cpython/extension-module<ver>" feature
while building tests executable, but that seems not doable. Instead,
this patch adds new features dedicated for tests.

The make rule is extracted so that we can easily run cargo tests.

Added a minimal test of ref-sharing as an example. More tests will follow.

--- a/Makefile	Sat Oct 05 10:21:34 2019 -0400
+++ b/Makefile	Mon Oct 14 16:15:19 2019 +0900
@@ -113,7 +113,7 @@
 tests:
         # Run Rust tests if cargo is installed
 	if command -v $(CARGO) >/dev/null 2>&1; then \
-		cd $(HGROOT)/rust/hg-cpython && $(CARGO) test --quiet --all; \
+		$(MAKE) rust-tests; \
 	fi
 	cd tests && $(PYTHON) run-tests.py $(TESTFLAGS)
 
@@ -127,6 +127,13 @@
         $(MAKE) -f $(HGROOT)/contrib/Makefile.python PYTHONVER=$* PREFIX=$(HGPYTHONS)/$* python )
 	cd tests && $(HGPYTHONS)/$*/bin/python run-tests.py $(TESTFLAGS)
 
+rust-tests: py_feature = $(shell $(PYTHON) -c \
+ 'import sys; print(["python27-bin", "python3-bin"][sys.version_info[0] >= 3])')
+rust-tests:
+	cd $(HGROOT)/rust/hg-cpython \
+		&& $(CARGO) test --quiet --all \
+			--no-default-features --features "$(py_feature)"
+
 check-code:
 	hg manifest | xargs python contrib/check-code.py
 
@@ -248,6 +255,7 @@
 
 .PHONY: help all local build doc cleanbutpackages clean install install-bin \
 	install-doc install-home install-home-bin install-home-doc \
-	dist dist-notests check tests check-code format-c update-pot \
+	dist dist-notests check tests rust-tests check-code format-c \
+	update-pot \
 	$(packaging_targets) \
 	osx

--- a/rust/hg-cpython/Cargo.toml	Sat Oct 05 10:21:34 2019 -0400
+++ b/rust/hg-cpython/Cargo.toml	Mon Oct 14 16:15:19 2019 +0900
@@ -11,9 +11,14 @@
 [features]
 default = ["python27"]
 
+# Features to build an extension module:
 python27 = ["cpython/python27-sys", "cpython/extension-module-2-7"]
+python3 = ["cpython/python3-sys", "cpython/extension-module"]
 
-python3 = ["cpython/python3-sys", "cpython/extension-module"]
+# Enable one of these features to build a test executable linked to libpython:
+# e.g. cargo test --no-default-features --features python27-bin
+python27-bin = ["cpython/python27-sys"]
+python3-bin = ["cpython/python3-sys"]
 
 [dependencies]
 hg-core = { path = "../hg-core" }

--- a/rust/hg-cpython/src/lib.rs	Sat Oct 05 10:21:34 2019 -0400
+++ b/rust/hg-cpython/src/lib.rs	Mon Oct 14 16:15:19 2019 +0900
@@ -72,3 +72,10 @@
     )?;
     Ok(())
 });
+
+#[cfg(not(any(feature = "python27-bin", feature = "python3-bin")))]
+#[test]
+#[ignore]
+fn libpython_must_be_linked_to_run_tests() {
+    // stub function to tell that some tests wouldn't run
+}

--- a/rust/hg-cpython/src/ref_sharing.rs	Sat Oct 05 10:21:34 2019 -0400
+++ b/rust/hg-cpython/src/ref_sharing.rs	Mon Oct 14 16:15:19 2019 +0900
@@ -490,3 +490,34 @@
         }
     };
 }
+
+#[cfg(test)]
+#[cfg(any(feature = "python27-bin", feature = "python3-bin"))]
+mod test {
+    use super::*;
+    use cpython::{GILGuard, Python};
+
+    py_class!(class Owner |py| {
+        data string: PySharedRefCell<String>;
+    });
+    py_shared_ref!(Owner, String, string, string_shared);
+
+    fn prepare_env() -> (GILGuard, Owner) {
+        let gil = Python::acquire_gil();
+        let py = gil.python();
+        let owner =
+            Owner::create_instance(py, PySharedRefCell::new("new".to_owned()))
+                .unwrap();
+        (gil, owner)
+    }
+
+    #[test]
+    fn test_borrow_mut_while_leaked() {
+        let (gil, owner) = prepare_env();
+        let py = gil.python();
+        assert!(owner.string_shared(py).borrow_mut().is_ok());
+        let _leaked = owner.string_shared(py).leak_immutable().unwrap();
+        // TODO: will be allowed
+        assert!(owner.string_shared(py).borrow_mut().is_err());
+    }
+}