Add test that overrides cfg_if with the one from crates.io

Author: gnzlbg

src/libcore/Cargo.toml

@@ -21,6 +21,7 @@ path = "../libcore/benches/lib.rs"
 
 [dev-dependencies]
 rand = "0.6"
+cfg_if = "1.0"
 
 [features]
 # Make panics and failed asserts immediately abort without formatting any message

src/libcore/tests/cfg_if_override.rs

@@ -1,3 +1,5 @@
+//! Test that overriding cfg_if with our own cfg_if macro does not break
+//! anything.
 #![feature(cfg_if)]
 
 macro_rules! cfg_if {

src/libcore/tests/cfg_if_stable_override.rs

@@ -0,0 +1,55 @@
+//! Test that using cfg_if from the cfg_if crate does not break anything.
+
+#[macro_use(cfg_if)]
+extern crate cfg_if;
+
+cfg_if! {
+    if #[cfg(test)] {
+        use core::option::Option as Option2;
+        fn works1() -> Option2<u32> { Some(1) }
+    } else {
+        fn works1() -> Option<u32> { None }
+    }
+}
+
+cfg_if! {
+    if #[cfg(foo)] {
+        fn works2() -> bool { false }
+    } else if #[cfg(test)] {
+        fn works2() -> bool { true }
+    } else {
+        fn works2() -> bool { false }
+    }
+}
+
+cfg_if! {
+    if #[cfg(foo)] {
+        fn works3() -> bool { false }
+    } else {
+        fn works3() -> bool { true }
+    }
+}
+
+cfg_if! {
+    if #[cfg(test)] {
+        use core::option::Option as Option3;
+        fn works4() -> Option3<u32> { Some(1) }
+    }
+}
+
+cfg_if! {
+    if #[cfg(foo)] {
+        fn works5() -> bool { false }
+    } else if #[cfg(test)] {
+        fn works5() -> bool { true }
+    }
+}
+
+#[test]
+fn it_works() {
+    assert!(works1().is_some());
+    assert!(works2());
+    assert!(works3());
+    assert!(works4().is_some());
+    assert!(works5());
+}