convert from an UnlessNll flag to a SuppressRegionErrors flag

Hopefully this will help clarify the behavior in the various borrowck
modes

src/librustc/infer/error_reporting/mod.rs

@@ -55,7 +55,7 @@
 //! ported to this system, and which relies on string concatenation at the
 //! time of error detection.
 
-use infer::{self, UnlessNll};
+use infer::{self, SuppressRegionErrors};
 use super::{InferCtxt, RegionVariableOrigin, SubregionOrigin, TypeTrace, ValuePairs};
 use super::region_constraints::GenericKind;
 use super::lexical_region_resolve::RegionResolutionError;
@@ -68,7 +68,6 @@ use middle::region;
 use traits::{ObligationCause, ObligationCauseCode};
 use ty::{self, subst::Subst, Region, Ty, TyCtxt, TypeFoldable, TyKind};
 use ty::error::TypeError;
-use session::config::BorrowckMode;
 use syntax::ast::DUMMY_NODE_ID;
 use syntax_pos::{Pos, Span};
 use errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
@@ -298,20 +297,12 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         &self,
         region_scope_tree: &region::ScopeTree,
         errors: &Vec<RegionResolutionError<'tcx>>,
-        unless_nll: UnlessNll,
+        suppress: SuppressRegionErrors,
     ) {
-        debug!("report_region_errors(): {} errors to start", errors.len());
+        debug!("report_region_errors(): {} errors to start, suppress = {:?}", errors.len(), suppress);
 
-        // If the errors will later be reported by NLL, choose wether to display them or not based
-        // on the borrowck mode
-        if unless_nll.0 {
-            match self.tcx.borrowck_mode() {
-                // If we're on AST or Migrate mode, report AST region errors
-                BorrowckMode::Ast | BorrowckMode::Migrate => {},
-                // If we're on MIR or Compare mode, don't report AST region errors as they should
-                // be reported by NLL
-                BorrowckMode::Compare | BorrowckMode::Mir => return,
-            }
+        if suppress.suppressed() {
+            return;
         }
 
         // try to pre-process the errors, which will group some of them

src/librustc/infer/mod.rs

@@ -24,6 +24,7 @@ use middle::free_region::RegionRelations;
 use middle::lang_items;
 use middle::region;
 use rustc_data_structures::unify as ut;
+use session::config::BorrowckMode;
 use std::cell::{Cell, Ref, RefCell, RefMut};
 use std::collections::BTreeMap;
 use std::fmt;
@@ -80,15 +81,37 @@ pub type Bound<T> = Option<T>;
 pub type UnitResult<'tcx> = RelateResult<'tcx, ()>; // "unify result"
 pub type FixupResult<T> = Result<T, FixupError>; // "fixup result"
 
-/// A flag that is given when running region resolution: if true, it
-/// indicates that we should not report the region errors to the user
-/// if NLL is enabled, since NLL will also detect them (and do a
-/// better job of it).
-///
-/// Currently, NLL only runs on HIR bodies, so you should use `false`
-/// unless you are region-checking a `hir::Body` (basically, a fn or
-/// expression).
-pub struct UnlessNll(pub bool);
+/// A flag that is used to suppress region errors. This is normally
+/// false, but sometimes -- when we are doing region checks that the
+/// NLL borrow checker will also do -- it might be set to true.
+#[derive(Copy, Clone, Default, Debug)]
+pub struct SuppressRegionErrors {
+    suppressed: bool
+}
+
+impl SuppressRegionErrors {
+    pub fn suppressed(self) -> bool {
+        self.suppressed
+    }
+
+    /// Indicates that the MIR borrowck will repeat these region
+    /// checks, so we should ignore errors if NLL is (unconditionally)
+    /// enabled.
+    pub fn when_nll_is_enabled(tcx: TyCtxt<'_, '_, '_>) -> Self {
+        match tcx.borrowck_mode() {
+            // If we're on AST or Migrate mode, report AST region errors
+            BorrowckMode::Ast | BorrowckMode::Migrate => SuppressRegionErrors {
+                suppressed: false
+            },
+
+            // If we're on MIR or Compare mode, don't report AST region errors as they should
+            // be reported by NLL
+            BorrowckMode::Compare | BorrowckMode::Mir => SuppressRegionErrors {
+                suppressed: true
+            },
+        }
+    }
+}
 
 pub struct InferCtxt<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
     pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
@@ -1049,7 +1072,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         region_context: DefId,
         region_map: &region::ScopeTree,
         outlives_env: &OutlivesEnvironment<'tcx>,
-        unless_nll: UnlessNll,
+        suppress: SuppressRegionErrors,
     ) {
         assert!(
             self.is_tainted_by_errors() || self.region_obligations.borrow().is_empty(),
@@ -1081,7 +1104,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             // this infcx was in use.  This is totally hokey but
             // otherwise we have a hard time separating legit region
             // errors from silly ones.
-            self.report_region_errors(region_map, &errors, unless_nll);
+            self.report_region_errors(region_map, &errors, suppress);
         }
     }
 

src/librustc/traits/mod.rs

@@ -20,7 +20,7 @@ pub use self::ObligationCauseCode::*;
 use chalk_engine;
 use hir;
 use hir::def_id::DefId;
-use infer::UnlessNll;
+use infer::SuppressRegionErrors;
 use infer::outlives::env::OutlivesEnvironment;
 use middle::region;
 use mir::interpret::ConstEvalErr;
@@ -720,7 +720,7 @@ pub fn normalize_param_env_or_error<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             region_context,
             &region_scope_tree,
             &outlives_env,
-            UnlessNll(false),
+            SuppressRegionErrors::default(),
         );
 
         let predicates = match infcx.fully_resolve(&predicates) {

src/librustc_typeck/check/dropck.rs

@@ -11,7 +11,7 @@
 use check::regionck::RegionCtxt;
 
 use hir::def_id::DefId;
-use rustc::infer::{self, InferOk, UnlessNll};
+use rustc::infer::{self, InferOk, SuppressRegionErrors};
 use rustc::infer::outlives::env::OutlivesEnvironment;
 use rustc::middle::region;
 use rustc::ty::subst::{Subst, Substs, UnpackedKind};
@@ -128,7 +128,7 @@ fn ensure_drop_params_and_item_params_correspond<'a, 'tcx>(
         // conservative. -nmatsakis
         let outlives_env = OutlivesEnvironment::new(ty::ParamEnv::empty());
 
-        infcx.resolve_regions_and_report_errors(drop_impl_did, &region_scope_tree, &outlives_env, UnlessNll(false));
+        infcx.resolve_regions_and_report_errors(drop_impl_did, &region_scope_tree, &outlives_env, SuppressRegionErrors::default());
         Ok(())
     })
 }

src/librustc_typeck/check/regionck.rs

@@ -88,8 +88,8 @@ use middle::mem_categorization as mc;
 use middle::mem_categorization::Categorization;
 use middle::region;
 use rustc::hir::def_id::DefId;
-use rustc::infer::{self, RegionObligation, UnlessNll};
 use rustc::infer::outlives::env::OutlivesEnvironment;
+use rustc::infer::{self, RegionObligation, SuppressRegionErrors};
 use rustc::ty::adjustment;
 use rustc::ty::subst::Substs;
 use rustc::ty::{self, Ty};
@@ -140,7 +140,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             rcx.visit_body(body);
             rcx.visit_region_obligations(id);
         }
-        rcx.resolve_regions_and_report_errors(UnlessNll(true));
+        rcx.resolve_regions_and_report_errors(SuppressRegionErrors::when_nll_is_enabled(self.tcx));
 
         assert!(self.tables.borrow().free_region_map.is_empty());
         self.tables.borrow_mut().free_region_map = rcx.outlives_environment.into_free_region_map();
@@ -162,7 +162,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             .add_implied_bounds(self, wf_tys, item_id, span);
         rcx.outlives_environment.save_implied_bounds(item_id);
         rcx.visit_region_obligations(item_id);
-        rcx.resolve_regions_and_report_errors(UnlessNll(false));
+        rcx.resolve_regions_and_report_errors(SuppressRegionErrors::default());
     }
 
     /// Region check a function body. Not invoked on closures, but
@@ -190,7 +190,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             rcx.visit_fn_body(fn_id, body, self.tcx.hir.span(fn_id));
         }
 
-        rcx.resolve_regions_and_report_errors(UnlessNll(true));
+        rcx.resolve_regions_and_report_errors(SuppressRegionErrors::when_nll_is_enabled(self.tcx));
 
         // In this mode, we also copy the free-region-map into the
         // tables of the enclosing fcx. In the other regionck modes
@@ -355,7 +355,8 @@ impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
             body_id.node_id,
             span,
         );
-        self.outlives_environment.save_implied_bounds(body_id.node_id);
+        self.outlives_environment
+            .save_implied_bounds(body_id.node_id);
         self.link_fn_args(
             region::Scope {
                 id: body.value.hir_id.local_id,
@@ -392,7 +393,7 @@ impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
         self.select_all_obligations_or_error();
     }
 
-    fn resolve_regions_and_report_errors(&self, unless_nll: UnlessNll) {
+    fn resolve_regions_and_report_errors(&self, suppress: SuppressRegionErrors) {
         self.infcx.process_registered_region_obligations(
             self.outlives_environment.region_bound_pairs_map(),
             self.implicit_region_bound,
@@ -403,7 +404,7 @@ impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
             self.subject_def_id,
             &self.region_scope_tree,
             &self.outlives_environment,
-            unless_nll,
+            suppress,
         );
     }
 

src/librustc_typeck/coherence/builtin.rs

@@ -11,7 +11,7 @@
 //! Check properties that are required by built-in traits and set
 //! up data structures required by type-checking/codegen.
 
-use rustc::infer::UnlessNll;
+use rustc::infer::SuppressRegionErrors;
 use rustc::infer::outlives::env::OutlivesEnvironment;
 use rustc::middle::region;
 use rustc::middle::lang_items::UnsizeTraitLangItem;
@@ -397,7 +397,7 @@ pub fn coerce_unsized_info<'a, 'gcx>(gcx: TyCtxt<'a, 'gcx, 'gcx>,
             impl_did,
             &region_scope_tree,
             &outlives_env,
-            UnlessNll(false),
+            SuppressRegionErrors::default(),
         );
 
         CoerceUnsizedInfo {