Change output of `compiletest` to include the compare-mode when present.

E.g. when running with `--compare-mode=nll`, then each test line will
look like e.g.:

```
test [ui (nll)] ui/issue-10969.rs ... ok
```

2 files changed, 6 insertions, 2 deletions

diff --git a/src/tools/compiletest/src/common.rs b/src/tools/compiletest/src/common.rs
index 41fc67a66f4..365b47447f2 100644
--- a/src/tools/compiletest/src/common.rs
+++ b/src/tools/compiletest/src/common.rs
@@ -101,7 +101,7 @@ pub enum CompareMode {
 }
 
 impl CompareMode {
-    fn to_str(&self) -> &'static str {
+    pub(crate) fn to_str(&self) -> &'static str {
         match *self {
             CompareMode::Nll => "nll"
         }
diff --git a/src/tools/compiletest/src/main.rs b/src/tools/compiletest/src/main.rs
index ae4f4aa4046..f61ab7bae45 100644
--- a/src/tools/compiletest/src/main.rs
+++ b/src/tools/compiletest/src/main.rs
@@ -728,7 +728,11 @@ pub fn make_test_name(config: &Config, testpaths: &TestPaths) -> test::TestName
     let path = PathBuf::from(config.src_base.file_name().unwrap())
         .join(&testpaths.relative_dir)
         .join(&testpaths.file.file_name().unwrap());
-    test::DynTestName(format!("[{}] {}", config.mode, path.display()))
+    let mode_suffix = match config.compare_mode {
+        Some(ref mode) => format!(" ({})", mode.to_str()),
+        None => format!(""),
+    };
+    test::DynTestName(format!("[{}{}] {}", config.mode, mode_suffix, path.display()))
 }
 
 pub fn make_test_closure(config: &Config, testpaths: &TestPaths) -> test::TestFn {