Remove nll-dump-cause flag and always track causes

Author: spastorino

src/librustc/session/config.rs

@@ -1312,8 +1312,6 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "choose which RELRO level to use"),
     nll: bool = (false, parse_bool, [UNTRACKED],
                  "run the non-lexical lifetimes MIR pass"),
-    nll_dump_cause: bool = (false, parse_bool, [UNTRACKED],
-                 "dump cause information when reporting errors from NLL"),
     trans_time_graph: bool = (false, parse_bool, [UNTRACKED],
         "generate a graphical HTML report of time spent in trans and LLVM"),
     thinlto: Option<bool> = (None, parse_opt_bool, [TRACKED],

src/librustc/session/mod.rs

@@ -476,13 +476,6 @@ impl Session {
         *(self.features.borrow_mut()) = Some(features);
     }
 
-    /// If true, we should gather causal information during NLL
-    /// checking. This will eventually be the normal thing, but right
-    /// now it is too unoptimized.
-    pub fn nll_dump_cause(&self) -> bool {
-        self.opts.debugging_opts.nll_dump_cause
-    }
-
     /// Calculates the flavor of LTO to use for this compilation.
     pub fn lto(&self) -> config::Lto {
         // If our target has codegen requirements ignore the command line

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

@@ -72,8 +72,6 @@ pub struct RegionInferenceContext<'tcx> {
     universal_regions: UniversalRegions<'tcx>,
 }
 
-struct TrackCauses(bool);
-
 struct RegionDefinition<'tcx> {
     /// Why we created this variable. Mostly these will be
     /// `RegionVariableOrigin::NLL`, but some variables get created
@@ -250,15 +248,12 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             .map(|origin| RegionDefinition::new(origin))
             .collect();
 
-        let nll_dump_cause = ty::tls::with(|tcx| tcx.sess.nll_dump_cause());
-
         let mut result = Self {
             definitions,
             elements: elements.clone(),
             liveness_constraints: RegionValues::new(
                 elements,
                 num_region_variables,
-                TrackCauses(nll_dump_cause),
             ),
             inferred_values: None,
             constraints: Vec::new(),

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

@@ -17,7 +17,7 @@ use rustc::mir::{BasicBlock, Location, Mir};
 use rustc::ty::RegionVid;
 use syntax::codemap::Span;
 
-use super::{Cause, CauseExt, TrackCauses};
+use super::{Cause, CauseExt};
 
 /// Maps between the various kinds of elements of a region value to
 /// the internal indices that w use.
@@ -202,7 +202,6 @@ impl RegionValues {
     pub(super) fn new(
         elements: &Rc<RegionValueElements>,
         num_region_variables: usize,
-        track_causes: TrackCauses,
     ) -> Self {
         assert!(
             elements.num_universal_regions <= num_region_variables,
@@ -215,11 +214,7 @@ impl RegionValues {
                 RegionVid::new(num_region_variables),
                 RegionElementIndex::new(elements.num_elements()),
             ),
-            causes: if track_causes.0 {
-                Some(CauseMap::default())
-            } else {
-                None
-            },
+            causes: Some(CauseMap::default()),
         }
     }
 

src/test/ui/issue-45157.stderr

@@ -6,6 +6,9 @@ LL |         let mref = &mut u.s.a;
 ...
 LL |         let nref = &u.z.c;
    |                    ^^^^^^ immutable borrow occurs here
+LL |         //~^ ERROR cannot borrow `u.z.c` as immutable because it is also borrowed as mutable [E0502]
+LL |         println!("{} {}", mref, nref)
+   |                           ---- borrow later used here
 
 error[E0502]: cannot borrow `u.s.a` as mutable because it is also borrowed as immutable
   --> $DIR/issue-45157.rs:39:27
@@ -14,7 +17,9 @@ LL |         let nref = &u.z.c;
    |                    ------ immutable borrow occurs here
 LL |         //~^ ERROR cannot borrow `u.z.c` as immutable because it is also borrowed as mutable [E0502]
 LL |         println!("{} {}", mref, nref)
-   |                           ^^^^ mutable borrow occurs here
+   |                           ^^^^  ---- borrow later used here
+   |                           |
+   |                           mutable borrow occurs here
 
 error: aborting due to 2 previous errors
 

src/test/ui/nll/borrowed-local-error.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Znll-dump-cause
-
 #![feature(nll)]
 
 fn gimme(x: &(u32,)) -> &u32 {

src/test/ui/nll/borrowed-local-error.stderr

@@ -1,5 +1,5 @@
 error[E0597]: `v` does not live long enough
-  --> $DIR/borrowed-local-error.rs:22:9
+  --> $DIR/borrowed-local-error.rs:20:9
    |
 LL |       let x = gimme({
    |  _____________-

src/test/ui/nll/borrowed-match-issue-45045.stderr

@@ -10,6 +10,8 @@ LL | |         //~^ cannot use `e` because it was mutably borrowed [E0503]
 LL | |         Xyz::B => println!("b"),
 LL | |     };
    | |_____^ use of borrowed `e`
+LL |       *g = Xyz::B;
+   |       ----------- borrow later used here
 
 error[E0503]: cannot use `e` because it was mutably borrowed
   --> $DIR/borrowed-match-issue-45045.rs:25:9
@@ -19,6 +21,9 @@ LL |     let f = &mut e;
 ...
 LL |         Xyz::A => println!("a"),
    |         ^^^^^^ use of borrowed `e`
+...
+LL |     *g = Xyz::B;
+   |     ----------- borrow later used here
 
 error: aborting due to 2 previous errors
 

src/test/ui/nll/borrowed-referent-issue-38899.stderr

@@ -6,6 +6,9 @@ LL |     let x = &mut block;
 LL |     println!("{}", x.current);
 LL |     let p: &'a u8 = &*block.current;
    |                     ^^^^^^^^^^^^^^^ immutable borrow occurs here
+LL |     //~^ ERROR cannot borrow `*block.current` as immutable because it is also borrowed as mutable
+LL |     drop(x);
+   |          - borrow later used here
 
 error: aborting due to previous error
 

src/test/ui/nll/borrowed-temporary-error.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Znll-dump-cause
-
 #![feature(nll)]
 
 fn gimme(x: &(u32,)) -> &u32 {