Rollup merge of #42219 - pwoolcoc:add-allow-fail-to-libtest, r=GuillaumeGomez

add `allow_fail` test attribute

This change allows the user to add an `#[allow_fail]` attribute to
tests that will cause the test to compile & run, but if the test fails
it will not cause the entire test run to fail. The test output will
show the failure, but in yellow instead of red, and also indicate that
it was an allowed failure.

Here is an example of the output: http://imgur.com/a/wt7ga

2 files changed, 19 insertions, 3 deletions

diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index d7d3a70f3c7..74bf19b841e 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -354,6 +354,9 @@ declare_features! (
 
     // rustc internal
     (active, abi_thiscall, "1.19.0", None),
+
+    // Allows a test to fail without failing the whole suite
+    (active, allow_fail, "1.19.0", Some(42219)),
 );
 
 declare_features! (
@@ -812,6 +815,11 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
                                              "used internally by rustc",
                                              cfg_fn!(rustc_attrs))),
 
+    ("allow_fail", Normal, Gated(Stability::Unstable,
+                                 "allow_fail",
+                                 "allow_fail attribute is currently unstable",
+                                 cfg_fn!(allow_fail))),
+
     // Crate level attributes
     ("crate_name", CrateLevel, Ungated),
     ("crate_type", CrateLevel, Ungated),
diff --git a/src/libsyntax/test.rs b/src/libsyntax/test.rs
index a0d1785c6ff..86f5f42eac7 100644
--- a/src/libsyntax/test.rs
+++ b/src/libsyntax/test.rs
@@ -52,7 +52,8 @@ struct Test {
     path: Vec<Ident> ,
     bench: bool,
     ignore: bool,
-    should_panic: ShouldPanic
+    should_panic: ShouldPanic,
+    allow_fail: bool,
 }
 
 struct TestCtxt<'a> {
@@ -133,7 +134,8 @@ impl<'a> fold::Folder for TestHarnessGenerator<'a> {
                         path: self.cx.path.clone(),
                         bench: is_bench_fn(&self.cx, &i),
                         ignore: is_ignored(&i),
-                        should_panic: should_panic(&i, &self.cx)
+                        should_panic: should_panic(&i, &self.cx),
+                        allow_fail: is_allowed_fail(&i),
                     };
                     self.cx.testfns.push(test);
                     self.tests.push(i.ident);
@@ -383,6 +385,10 @@ fn is_ignored(i: &ast::Item) -> bool {
     i.attrs.iter().any(|attr| attr.check_name("ignore"))
 }
 
+fn is_allowed_fail(i: &ast::Item) -> bool {
+    i.attrs.iter().any(|attr| attr.check_name("allow_fail"))
+}
+
 fn should_panic(i: &ast::Item, cx: &TestCtxt) -> ShouldPanic {
     match i.attrs.iter().find(|attr| attr.check_name("should_panic")) {
         Some(attr) => {
@@ -668,6 +674,7 @@ fn mk_test_desc_and_fn_rec(cx: &TestCtxt, test: &Test) -> P<ast::Expr> {
             }
         }
     };
+    let allow_fail_expr = ecx.expr_bool(span, test.allow_fail);
 
     // self::test::TestDesc { ... }
     let desc_expr = ecx.expr_struct(
@@ -675,7 +682,8 @@ fn mk_test_desc_and_fn_rec(cx: &TestCtxt, test: &Test) -> P<ast::Expr> {
         test_path("TestDesc"),
         vec![field("name", name_expr),
              field("ignore", ignore_expr),
-             field("should_panic", fail_expr)]);
+             field("should_panic", fail_expr),
+             field("allow_fail", allow_fail_expr)]);
 
 
     let mut visible_path = match cx.toplevel_reexport {