Add new tests for extern and foreign fns and name mangling.

Author: rpjohnst

src/test/compile-fail/generic-no-mangle.rs

@@ -0,0 +1,18 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// ignore-test this should fail to compile (#15844)
+
+#[no_mangle]
+fn foo<T>() {} //~ ERROR generic functions must be mangled
+
+#[no_mangle]
+extern fn foo<T>() {} //~ ERROR generic functions must be mangled
+

src/test/run-make/extern-fn-mangle/Makefile

@@ -0,0 +1,7 @@
+-include ../tools.mk
+
+all:
+	$(CC) -std=c99 test.c -c -o $(TMPDIR)/test.o
+	$(AR) rcs $(TMPDIR)/libtest.a $(TMPDIR)/test.o
+	$(RUSTC) test.rs -L $(TMPDIR)
+	$(call RUN,test) || exit 1

src/test/run-make/extern-fn-mangle/test.c

@@ -0,0 +1,8 @@
+#include <stdint.h>
+
+uint32_t foo();
+uint32_t bar();
+
+uint32_t add() {
+	return foo() + bar();
+}

src/test/run-make/extern-fn-mangle/test.rs

@@ -0,0 +1,25 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[no_mangle]
+pub extern "C" fn foo() -> i32 { 3 }
+
+#[no_mangle]
+pub extern "C" fn bar() -> i32 { 5 }
+
+#[link(name = "test", kind = "static")]
+extern {
+    fn add() -> i32;
+}
+
+fn main() {
+    let back = unsafe { add() };
+    assert_eq!(8, back);
+}