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 #48879

Author: bors

src/bootstrap/test.rs

@@ -538,6 +538,7 @@ impl Step for RustdocUi {
             target: self.target,
             mode: "ui",
             suite: "rustdoc-ui",
+            compare_mode: None,
         })
     }
 }
@@ -590,19 +591,44 @@ macro_rules! default_test {
     }
 }
 
+macro_rules! default_test_with_compare_mode {
+    ($name:ident { path: $path:expr, mode: $mode:expr, suite: $suite:expr,
+                   compare_mode: $compare_mode:expr }) => {
+        test_with_compare_mode!($name { path: $path, mode: $mode, suite: $suite, default: true,
+                                        host: false, compare_mode: $compare_mode });
+    }
+}
+
 macro_rules! host_test {
     ($name:ident { path: $path:expr, mode: $mode:expr, suite: $suite:expr }) => {
         test!($name { path: $path, mode: $mode, suite: $suite, default: true, host: true });
     }
 }
 
 macro_rules! test {
+    ($name:ident { path: $path:expr, mode: $mode:expr, suite: $suite:expr, default: $default:expr,
+                   host: $host:expr }) => {
+        test_definitions!($name { path: $path, mode: $mode, suite: $suite, default: $default,
+                                  host: $host, compare_mode: None });
+    }
+}
+
+macro_rules! test_with_compare_mode {
+    ($name:ident { path: $path:expr, mode: $mode:expr, suite: $suite:expr, default: $default:expr,
+                   host: $host:expr, compare_mode: $compare_mode:expr }) => {
+        test_definitions!($name { path: $path, mode: $mode, suite: $suite, default: $default,
+                                  host: $host, compare_mode: Some($compare_mode) });
+    }
+}
+
+macro_rules! test_definitions {
     ($name:ident {
         path: $path:expr,
         mode: $mode:expr,
         suite: $suite:expr,
         default: $default:expr,
-        host: $host:expr
+        host: $host:expr,
+        compare_mode: $compare_mode:expr
     }) => {
         #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
         pub struct $name {
@@ -634,16 +660,18 @@ macro_rules! test {
                     target: self.target,
                     mode: $mode,
                     suite: $suite,
+                    compare_mode: $compare_mode,
                 })
             }
         }
     }
 }
 
-default_test!(Ui {
+default_test_with_compare_mode!(Ui {
     path: "src/test/ui",
     mode: "ui",
-    suite: "ui"
+    suite: "ui",
+    compare_mode: "nll"
 });
 
 default_test!(RunPass {
@@ -804,6 +832,7 @@ struct Compiletest {
     target: Interned<String>,
     mode: &'static str,
     suite: &'static str,
+    compare_mode: Option<&'static str>,
 }
 
 impl Step for Compiletest {
@@ -823,6 +852,7 @@ impl Step for Compiletest {
         let target = self.target;
         let mode = self.mode;
         let suite = self.suite;
+        let compare_mode = self.compare_mode;
 
         // Skip codegen tests if they aren't enabled in configuration.
         if !builder.config.codegen_tests && suite == "codegen" {
@@ -1044,6 +1074,15 @@ impl Step for Compiletest {
                  suite, mode, &compiler.host, target));
         let _time = util::timeit(&builder);
         try_run(builder, &mut cmd);
+
+        if let Some(compare_mode) = compare_mode {
+            cmd.arg("--compare-mode").arg(compare_mode);
+            let _folder = builder.fold_output(|| format!("test_{}_{}", suite, compare_mode));
+            builder.info(&format!("Check compiletest suite={} mode={} compare_mode={} ({} -> {})",
+                                  suite, mode, compare_mode, &compiler.host, target));
+            let _time = util::timeit(&builder);
+            try_run(builder, &mut cmd);
+        }
     }
 }
 

src/librustc/session/config.rs

@@ -1259,6 +1259,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         useful for profiling / PGO."),
     relro_level: Option<RelroLevel> = (None, parse_relro_level, [TRACKED],
         "choose which RELRO level to use"),
+    nll_subminimal_causes: bool = (false, parse_bool, [UNTRACKED],
+        "when tracking region error causes, accept subminimal results for faster execution."),
     disable_nll_user_type_assert: bool = (false, parse_bool, [UNTRACKED],
         "disable user provided type assertion in NLL"),
     trans_time_graph: bool = (false, parse_bool, [UNTRACKED],

src/librustc_mir/borrow_check/nll/region_infer/values.rs

@@ -14,7 +14,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::indexed_vec::Idx;
 use rustc_data_structures::indexed_vec::IndexVec;
 use rustc::mir::{BasicBlock, Location, Mir};
-use rustc::ty::RegionVid;
+use rustc::ty::{self, RegionVid};
 use syntax::codemap::Span;
 
 use super::{Cause, CauseExt, TrackCauses};
@@ -263,7 +263,17 @@ impl RegionValues {
             if let Some(causes) = &mut self.causes {
                 let cause = make_cause(causes);
                 let old_cause = causes.get_mut(&(r, i)).unwrap();
-                if cause < **old_cause {
+                // #49998: compare using root cause alone to avoid
+                // useless traffic from similar outlives chains.
+
+                let overwrite = if ty::tls::with(|tcx| {
+                    tcx.sess.opts.debugging_opts.nll_subminimal_causes
+                }) {
+                    cause.root_cause() < old_cause.root_cause()
+                } else {
+                    cause < **old_cause
+                };
+                if overwrite {
                     *old_cause = Rc::new(cause);
                     return true;
                 }

src/test/ui/borrowck/borrowck-closures-two-mut.nll.stderr

@@ -1,4 +1,4 @@
-warning: not reporting region error due to -Znll
+warning: not reporting region error due to nll
   --> $DIR/issue-45983.rs:17:27
    |
 LL |     give_any(|y| x = Some(y));
@@ -16,7 +16,7 @@ error[E0594]: cannot assign to immutable item `x`
 LL |     give_any(|y| x = Some(y));
    |                  ^^^^^^^^^^^ cannot mutate
    |
-   = note: Value not mutable causing this error: `x`
+   = note: the value which is causing this path not to be mutable is...: `x`
 
 error[E0596]: cannot borrow immutable item `x` as mutable
   --> $DIR/issue-45983.rs:17:14

src/test/ui/borrowck/issue-45983.nll.stderr

@@ -1,4 +1,4 @@
-warning: not reporting region error due to -Znll
+warning: not reporting region error due to nll
   --> $DIR/issue-7573.rs:27:31
    |
 LL |     let mut lines_to_use: Vec<&CrateId> = Vec::new();

src/test/ui/borrowck/issue-7573.nll.stderr

@@ -1,4 +1,4 @@
-warning: not reporting region error due to -Znll
+warning: not reporting region error due to nll
   --> $DIR/regions-escape-bound-fn-2.rs:18:27
    |
 LL |     with_int(|y| x = Some(y));

src/test/ui/borrowck/regions-escape-bound-fn-2.nll.stderr

@@ -1,4 +1,4 @@
-warning: not reporting region error due to -Znll
+warning: not reporting region error due to nll
   --> $DIR/regions-escape-bound-fn.rs:18:22
    |
 LL |     with_int(|y| x = Some(y));

src/test/ui/borrowck/regions-escape-bound-fn.nll.stderr

@@ -1,4 +1,4 @@
-warning: not reporting region error due to -Znll
+warning: not reporting region error due to nll
   --> $DIR/regions-escape-unboxed-closure.rs:16:27
    |
 LL |     with_int(&mut |y| x = Some(y));

src/test/ui/borrowck/regions-escape-unboxed-closure.nll.stderr

@@ -1,22 +1,22 @@
-warning: not reporting region error due to -Znll
+warning: not reporting region error due to nll
   --> $DIR/expect-region-supply-region.rs:28:13
    |
 LL |         f = Some(x); //~ ERROR borrowed data cannot be stored outside of its closure
    |             ^^^^^^^
 
-warning: not reporting region error due to -Znll
+warning: not reporting region error due to nll
   --> $DIR/expect-region-supply-region.rs:38:13
    |
 LL |         f = Some(x); //~ ERROR borrowed data cannot be stored outside of its closure
    |             ^^^^^^^
 
-warning: not reporting region error due to -Znll
+warning: not reporting region error due to nll
   --> $DIR/expect-region-supply-region.rs:47:33
    |
 LL |     closure_expecting_bound(|x: &'x u32| {
    |                                 ^^^^^^^
 
-warning: not reporting region error due to -Znll
+warning: not reporting region error due to nll
   --> $DIR/expect-region-supply-region.rs:52:13
    |
 LL |         f = Some(x);