Auto merge of #49900 - pnkfelix:compare-mode-nll-followup-3, r=nikomatsakis

Add src/test/ui regression testing for NLL

This PR changes `x.py test` so that when you are running the `ui` test suite, it will also always run `compiletest` in the new `--compare-mode=nll`, which just double-checks that when running under the experimental NLL mode, the output matches the `<source-name>.nll.stderr` file, if present.

In order to reduce the chance of a developer revolt in response to this change, this PR also includes some changes to make the `--compare-mode=nll` more user-friendly:

 1. It now generates nll-specific .stamp files, and uses them (so that repeated runs can reuse previously cached results).
 2. Each line of terminal output distinguishes whether we are running under `--compare-mode=nll` by printing with the prefix `[ui (nll)]` instead of just the prefix `[ui]`.

Subtask of rust-lang/rust#48879

3 files changed, 22 insertions, 7 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..37f7af0abe8 100644
--- a/src/tools/compiletest/src/main.rs
+++ b/src/tools/compiletest/src/main.rs
@@ -626,7 +626,7 @@ pub fn make_test(config: &Config, testpaths: &TestPaths) -> test::TestDescAndFn
 
     // Debugging emscripten code doesn't make sense today
     let ignore = early_props.ignore
-        || (!up_to_date(config, testpaths, &early_props) && config.compare_mode.is_none())
+        || !up_to_date(config, testpaths, &early_props)
         || (config.mode == DebugInfoGdb || config.mode == DebugInfoLldb)
             && config.target.contains("emscripten");
 
@@ -642,10 +642,15 @@ pub fn make_test(config: &Config, testpaths: &TestPaths) -> test::TestDescAndFn
 }
 
 fn stamp(config: &Config, testpaths: &TestPaths) -> PathBuf {
+    let mode_suffix = match config.compare_mode {
+        Some(ref mode) => format!("-{}", mode.to_str()),
+        None => format!(""),
+    };
     let stamp_name = format!(
-        "{}-{}.stamp",
+        "{}-{}{}.stamp",
         testpaths.file.file_name().unwrap().to_str().unwrap(),
-        config.stage_id
+        config.stage_id,
+        mode_suffix
     );
     config
         .build_base
@@ -728,7 +733,11 @@ 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 {
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index e79aefb7236..c16dbd0272a 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -2811,7 +2811,7 @@ impl<'test> TestCx<'test> {
         normalized
     }
 
-    fn load_expected_output(&self, kind: &str) -> String {
+    fn expected_output_path(&self, kind: &str) -> PathBuf {
         let mut path = expected_output_path(&self.testpaths,
                                             self.revision,
                                             &self.config.compare_mode,
@@ -2822,6 +2822,11 @@ impl<'test> TestCx<'test> {
             path = expected_output_path(&self.testpaths, self.revision, &None, kind);
         }
 
+        path
+    }
+
+    fn load_expected_output(&self, kind: &str) -> String {
+        let path = self.expected_output_path(kind);
         if path.exists() {
             match self.load_expected_output_from_path(&path) {
                 Ok(x) => x,
@@ -2875,7 +2880,8 @@ impl<'test> TestCx<'test> {
             }
         }
 
-        let output_file = self.output_base_name().with_extension(kind);
+        let expected_output_path = self.expected_output_path(kind);
+        let output_file = self.output_base_name().with_file_name(&expected_output_path);
         match File::create(&output_file).and_then(|mut f| f.write_all(actual.as_bytes())) {
             Ok(()) => {}
             Err(e) => self.fatal(&format!(