add integration tests, unwind across FFI boundary

 ### Changes

    This commit introduces some new fixtures to the `run-make-fulldeps`
    test suite.

        * c-unwind-abi-hello-world: A simple "happy path" fixture. This
          involves calling from Rust, into C, and back into a Rust
          `C-unwind` function.

        * c-unwind-abi-catch-panic: Exercise unwinding a panic. This
          reuses much of the same code, but instead catches a panic and
          downcasts it into an integer.

        * c-unwind-abi-catch-lib-panic: This is similar to the previous
         `*catch-panic` test, however in this case the Rust code that
         panics resides in a separate crate.

Author: katelyn a. martin

src/test/run-make-fulldeps/c-unwind-abi-catch-lib-panic/Makefile

@@ -0,0 +1,18 @@
+-include ../tools.mk
+
+all:
+	# Compile `panic.rs` and `add.c` into object files.
+	#
+	# Note that we invoke `rustc` directly, so we may emit an object rather
+	# than an archive. We'll do that later.
+	$(BARE_RUSTC) $(RUSTFLAGS)  \
+		--out-dir $(TMPDIR) \
+		--emit=obj panic.rs
+	$(call COMPILE_OBJ,$(TMPDIR)/add.o,add.c)
+
+	# Now, create an archive using these two objects.
+	$(AR) crus $(TMPDIR)/libadd.a $(TMPDIR)/add.o $(TMPDIR)/panic.o
+
+	# Compile `main.rs`, which will link into our library, and run it.
+	$(RUSTC) main.rs
+	$(call RUN,main)

src/test/run-make-fulldeps/c-unwind-abi-catch-lib-panic/add.c

@@ -0,0 +1,12 @@
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+
+// An external function, defined in Rust.
+extern void panic_if_greater_than_10(unsigned x);
+
+unsigned add_small_numbers(unsigned a, unsigned b) {
+    unsigned c = a + b;
+    panic_if_greater_than_10(c);
+    return c;
+}

src/test/run-make-fulldeps/c-unwind-abi-catch-lib-panic/main.rs

@@ -0,0 +1,30 @@
+//! A test for calling `C-unwind` functions across foreign function boundaries.
+//!
+//! This test triggers a panic in a Rust library that our foreign function invokes. This shows
+//! that we can unwind through the C code in that library, and catch the underlying panic.
+#![feature(c_unwind)]
+
+use std::panic::{catch_unwind, AssertUnwindSafe};
+
+fn main() {
+    // Call `add_small_numbers`, passing arguments that will trigger a panic, and catch it.
+    let caught_unwind = catch_unwind(AssertUnwindSafe(|| {
+        let (a, b) = (10, 1);
+        let _c = unsafe { add_small_numbers(a, b) };
+        unreachable!("should have unwound instead of returned");
+    }));
+
+    // Assert that we did indeed panic, then unwrap and downcast the panic into the sum.
+    assert!(caught_unwind.is_err());
+    let panic_obj = caught_unwind.unwrap_err();
+    let panic_u32 = *panic_obj.downcast_ref::<u32>().unwrap();
+    assert_eq!(panic_u32, 11);
+}
+
+#[link(name = "add")]
+extern "C-unwind" {
+    /// An external function, defined in C.
+    ///
+    /// Returns the sum of two numbers, or panics if the sum is greater than 10.
+    fn add_small_numbers(a: u32, b: u32) -> u32;
+}

src/test/run-make-fulldeps/c-unwind-abi-catch-lib-panic/panic.rs

@@ -0,0 +1,12 @@
+#![crate_type = "staticlib"]
+#![feature(c_unwind)]
+
+/// This function will panic if `x` is greater than 10.
+///
+/// This function is called by `add_small_numbers`.
+#[no_mangle]
+pub extern "C-unwind" fn panic_if_greater_than_10(x: u32) {
+    if x > 10 {
+        panic!(x); // That is too big!
+    }
+}

src/test/run-make-fulldeps/c-unwind-abi-catch-panic/Makefile

@@ -0,0 +1,5 @@
+-include ../tools.mk
+
+all: $(call NATIVE_STATICLIB,add)
+	$(RUSTC) main.rs
+	$(call RUN,main) || exit 1

src/test/run-make-fulldeps/c-unwind-abi-catch-panic/add.c

@@ -0,0 +1,12 @@
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+
+// An external function, defined in Rust.
+extern void panic_if_greater_than_10(unsigned x);
+
+unsigned add_small_numbers(unsigned a, unsigned b) {
+    unsigned c = a + b;
+    panic_if_greater_than_10(c);
+    return c;
+}

src/test/run-make-fulldeps/c-unwind-abi-catch-panic/main.rs

@@ -0,0 +1,39 @@
+//! A test for calling `C-unwind` functions across foreign function boundaries.
+//!
+//! This test triggers a panic when calling a foreign function that calls *back* into Rust.
+#![feature(c_unwind)]
+
+use std::panic::{catch_unwind, AssertUnwindSafe};
+
+fn main() {
+    // Call `add_small_numbers`, passing arguments that will trigger a panic, and catch it.
+    let caught_unwind = catch_unwind(AssertUnwindSafe(|| {
+        let (a, b) = (10, 1);
+        let _c = unsafe { add_small_numbers(a, b) };
+        unreachable!("should have unwound instead of returned");
+    }));
+
+    // Assert that we did indeed panic, then unwrap and downcast the panic into the sum.
+    assert!(caught_unwind.is_err());
+    let panic_obj = caught_unwind.unwrap_err();
+    let panic_u32 = *panic_obj.downcast_ref::<u32>().unwrap();
+    assert_eq!(panic_u32, 11);
+}
+
+#[link(name = "add", kind = "static")]
+extern "C-unwind" {
+    /// An external function, defined in C.
+    ///
+    /// Returns the sum of two numbers, or panics if the sum is greater than 10.
+    fn add_small_numbers(a: u32, b: u32) -> u32;
+}
+
+/// This function will panic if `x` is greater than 10.
+///
+/// This function is called by `add_small_numbers`.
+#[no_mangle]
+pub extern "C-unwind" fn panic_if_greater_than_10(x: u32) {
+    if x > 10 {
+        panic!(x); // That is too big!
+    }
+}

src/test/run-make-fulldeps/c-unwind-abi-hello-world/Makefile

@@ -0,0 +1,5 @@
+-include ../tools.mk
+
+all: $(call NATIVE_STATICLIB,add)
+	$(RUSTC) main.rs
+	$(call RUN,main) || exit 1

src/test/run-make-fulldeps/c-unwind-abi-hello-world/add.c

@@ -0,0 +1,12 @@
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+
+// An external function, defined in Rust.
+extern void panic_if_greater_than_10(unsigned x);
+
+unsigned add_small_numbers(unsigned a, unsigned b) {
+    unsigned c = a + b;
+    panic_if_greater_than_10(c);
+    return c;
+}

src/test/run-make-fulldeps/c-unwind-abi-hello-world/main.rs

@@ -0,0 +1,29 @@
+//! A test for calling `C-unwind` functions across foreign function boundaries.
+//!
+//! This test does *not* trigger a panic. The exercises the "happy path" when calling a foreign
+//! function that calls *back* into Rust.
+#![feature(c_unwind)]
+
+fn main() {
+    let (a, b) = (9, 1);
+    let c = unsafe { add_small_numbers(a, b) };
+    assert_eq!(c, 10);
+}
+
+#[link(name = "add", kind = "static")]
+extern {
+    /// An external function, defined in C.
+    ///
+    /// Returns the sum of two numbers, or panics if the sum is greater than 10.
+    fn add_small_numbers(a: u32, b: u32) -> u32;
+}
+
+/// This function will panic if `x` is greater than 10.
+///
+/// This function is called by `add_small_numbers`.
+#[no_mangle]
+pub extern "C-unwind" fn panic_if_greater_than_10(x: u32) {
+    if x > 10 {
+        panic!(x); // That is too big!
+    }
+}