Auto merge of #52648 - davidtwco:issue-52533, r=nikomatsakis

[nll] improve the "fully elaborated type" case in region errors

Fixes #52533.

r? @nikomatsakis

30 files changed, 328 insertions, 149 deletions

diff --git a/src/librustc/infer/error_reporting/need_type_info.rs b/src/librustc/infer/error_reporting/need_type_info.rs
index dbcb63addb8..693219ec4b0 100644
--- a/src/librustc/infer/error_reporting/need_type_info.rs
+++ b/src/librustc/infer/error_reporting/need_type_info.rs
@@ -74,7 +74,7 @@ impl<'a, 'gcx, 'tcx> Visitor<'gcx> for FindLocalByTypeVisitor<'a, 'gcx, 'tcx> {
 
 
 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
-    fn extract_type_name(&self, ty: &'a Ty<'tcx>) -> String {
+    pub fn extract_type_name(&self, ty: &'a Ty<'tcx>) -> String {
         if let ty::TyInfer(ty::TyVar(ty_vid)) = (*ty).sty {
             let ty_vars = self.type_variables.borrow();
             if let TypeVariableOrigin::TypeParameterDefinition(_, name) =
diff --git a/src/librustc/util/ppaux.rs b/src/librustc/util/ppaux.rs
index c67453d2b20..15b5edaa3d5 100644
--- a/src/librustc/util/ppaux.rs
+++ b/src/librustc/util/ppaux.rs
@@ -19,7 +19,7 @@ use ty::{TyError, TyStr, TyArray, TySlice, TyFloat, TyFnDef, TyFnPtr};
 use ty::{TyParam, TyRawPtr, TyRef, TyNever, TyTuple};
 use ty::{TyClosure, TyGenerator, TyGeneratorWitness, TyForeign, TyProjection, TyAnon};
 use ty::{TyDynamic, TyInt, TyUint, TyInfer};
-use ty::{self, Ty, TyCtxt, TypeFoldable, GenericParamCount, GenericParamDefKind};
+use ty::{self, RegionVid, Ty, TyCtxt, TypeFoldable, GenericParamCount, GenericParamDefKind};
 use util::nodemap::FxHashSet;
 
 use std::cell::Cell;
@@ -32,6 +32,12 @@ use syntax::ast::CRATE_NODE_ID;
 use syntax::symbol::{Symbol, InternedString};
 use hir;
 
+thread_local! {
+    /// Mechanism for highlighting of specific regions for display in NLL region inference errors.
+    /// Contains region to highlight and counter for number to use when highlighting.
+    static HIGHLIGHT_REGION: Cell<Option<(RegionVid, usize)>> = Cell::new(None)
+}
+
 macro_rules! gen_display_debug_body {
     ( $with:path ) => {
         fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -562,6 +568,19 @@ pub fn parameterized<F: fmt::Write>(f: &mut F,
     PrintContext::new().parameterized(f, substs, did, projections)
 }
 
+fn get_highlight_region() -> Option<(RegionVid, usize)> {
+    HIGHLIGHT_REGION.with(|hr| hr.get())
+}
+
+pub fn with_highlight_region<R>(r: RegionVid, counter: usize, op: impl FnOnce() -> R) -> R {
+    HIGHLIGHT_REGION.with(|hr| {
+        assert_eq!(hr.get(), None);
+        hr.set(Some((r, counter)));
+        let r = op();
+        hr.set(None);
+        r
+    })
+}
 
 impl<'a, T: Print> Print for &'a T {
     fn print<F: fmt::Write>(&self, f: &mut F, cx: &mut PrintContext) -> fmt::Result {
@@ -733,7 +752,7 @@ define_print! {
 define_print! {
     () ty::RegionKind, (self, f, cx) {
         display {
-            if cx.is_verbose {
+            if cx.is_verbose || get_highlight_region().is_some() {
                 return self.print_debug(f, cx);
             }
 
@@ -905,6 +924,15 @@ impl fmt::Debug for ty::FloatVid {
 
 impl fmt::Debug for ty::RegionVid {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if let Some((region, counter)) = get_highlight_region() {
+            debug!("RegionVid.fmt: region={:?} self={:?} counter={:?}", region, self, counter);
+            return if *self == region {
+                write!(f, "'{:?}", counter)
+            } else {
+                write!(f, "'_")
+            }
+        }
+
         write!(f, "'_#{}r", self.index())
     }
 }
@@ -1022,9 +1050,11 @@ define_print! {
                 TyRef(r, ty, mutbl) => {
                     write!(f, "&")?;
                     let s = r.print_to_string(cx);
-                    write!(f, "{}", s)?;
-                    if !s.is_empty() {
-                        write!(f, " ")?;
+                    if s != "'_" {
+                        write!(f, "{}", s)?;
+                        if !s.is_empty() {
+                            write!(f, " ")?;
+                        }
                     }
                     ty::TypeAndMut { ty, mutbl }.print(f, cx)
                 }
diff --git a/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs b/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs
index 1b540ef74be..c2c5c6771b0 100644
--- a/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs
+++ b/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs
@@ -31,9 +31,7 @@ mod var_name;
 enum ConstraintCategory {
     Cast,
     Assignment,
-    AssignmentToUpvar,
     Return,
-    CallArgumentToUpvar,
     CallArgument,
     Other,
     Boring,
@@ -41,16 +39,13 @@ enum ConstraintCategory {
 
 impl fmt::Display for ConstraintCategory {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // Must end with a space. Allows for empty names to be provided.
         match self {
-            ConstraintCategory::Assignment | ConstraintCategory::AssignmentToUpvar => {
-                write!(f, "assignment")
-            }
-            ConstraintCategory::Return => write!(f, "return"),
-            ConstraintCategory::Cast => write!(f, "cast"),
-            ConstraintCategory::CallArgument | ConstraintCategory::CallArgumentToUpvar => {
-                write!(f, "argument")
-            }
-            _ => write!(f, "free region"),
+            ConstraintCategory::Assignment => write!(f, "assignment "),
+            ConstraintCategory::Return => write!(f, "return "),
+            ConstraintCategory::Cast => write!(f, "cast "),
+            ConstraintCategory::CallArgument => write!(f, "argument "),
+            _ => write!(f, ""),
         }
     }
 }
@@ -224,10 +219,10 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             "constraint_is_interesting: locations={:?} constraint={:?}",
             constraint.locations, constraint
         );
-        if let Locations::Interesting(_) = constraint.locations {
-            true
-        } else {
-            false
+
+        match constraint.locations {
+            Locations::Interesting(_) | Locations::All => true,
+            _ => false,
         }
     }
 
@@ -320,45 +315,26 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             }
         }
 
-        let category = match (
-            category,
+        let (fr_is_local, outlived_fr_is_local): (bool, bool) = (
             self.universal_regions.is_local_free_region(fr),
             self.universal_regions.is_local_free_region(outlived_fr),
-        ) {
-            (ConstraintCategory::Assignment, true, false) => ConstraintCategory::AssignmentToUpvar,
-            (ConstraintCategory::CallArgument, true, false) => {
-                ConstraintCategory::CallArgumentToUpvar
-            }
-            (category, _, _) => category,
+        );
+        debug!("report_error: fr_is_local={:?} outlived_fr_is_local={:?} category={:?}",
+               fr_is_local, outlived_fr_is_local, category);
+
+        match (category, fr_is_local, outlived_fr_is_local) {
+            (ConstraintCategory::Assignment, true, false) |
+            (ConstraintCategory::CallArgument, true, false) =>
+                self.report_escaping_data_error(mir, infcx, mir_def_id, fr, outlived_fr,
+                                                category, span, errors_buffer),
+            _ =>
+                self.report_general_error(mir, infcx, mir_def_id, fr, fr_is_local,
+                                          outlived_fr, outlived_fr_is_local,
+                                          category, span, errors_buffer),
         };
-
-        debug!("report_error: category={:?}", category);
-        match category {
-            ConstraintCategory::AssignmentToUpvar | ConstraintCategory::CallArgumentToUpvar => self
-                .report_closure_error(
-                    mir,
-                    infcx,
-                    mir_def_id,
-                    fr,
-                    outlived_fr,
-                    category,
-                    span,
-                    errors_buffer,
-                ),
-            _ => self.report_general_error(
-                mir,
-                infcx,
-                mir_def_id,
-                fr,
-                outlived_fr,
-                category,
-                span,
-                errors_buffer,
-            ),
-        }
     }
 
-    fn report_closure_error(
+    fn report_escaping_data_error(
         &self,
         mir: &Mir<'tcx>,
         infcx: &InferCtxt<'_, '_, 'tcx>,
@@ -373,29 +349,23 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         let outlived_fr_name_and_span =
             self.get_var_name_and_span_for_region(infcx.tcx, mir, outlived_fr);
 
+        let escapes_from = if infcx.tcx.is_closure(mir_def_id) { "closure" } else { "function" };
+
         if fr_name_and_span.is_none() && outlived_fr_name_and_span.is_none() {
-            return self.report_general_error(
-                mir,
-                infcx,
-                mir_def_id,
-                fr,
-                outlived_fr,
-                category,
-                span,
-                errors_buffer,
-            );
+            return self.report_general_error(mir, infcx, mir_def_id,
+                                             fr, true, outlived_fr, false,
+                                             category, span, errors_buffer);
         }
 
-        let mut diag = infcx
-            .tcx
-            .sess
-            .struct_span_err(span, &format!("borrowed data escapes outside of closure"));
+        let mut diag = infcx.tcx.sess.struct_span_err(
+            span, &format!("borrowed data escapes outside of {}", escapes_from),
+        );
 
         if let Some((outlived_fr_name, outlived_fr_span)) = outlived_fr_name_and_span {
             if let Some(name) = outlived_fr_name {
                 diag.span_label(
                     outlived_fr_span,
-                    format!("`{}` is declared here, outside of the closure body", name),
+                    format!("`{}` is declared here, outside of the {} body", name, escapes_from),
                 );
             }
         }
@@ -404,13 +374,12 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             if let Some(name) = fr_name {
                 diag.span_label(
                     fr_span,
-                    format!(
-                        "`{}` is a reference that is only valid in the closure body",
-                        name
-                    ),
+                    format!("`{}` is a reference that is only valid in the {} body",
+                            name, escapes_from),
                 );
 
-                diag.span_label(span, format!("`{}` escapes the closure body here", name));
+                diag.span_label(span, format!("`{}` escapes the {} body here",
+                                               name, escapes_from));
             }
         }
 
@@ -423,7 +392,9 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         infcx: &InferCtxt<'_, '_, 'tcx>,
         mir_def_id: DefId,
         fr: RegionVid,
+        fr_is_local: bool,
         outlived_fr: RegionVid,
+        outlived_fr_is_local: bool,
         category: ConstraintCategory,
         span: Span,
         errors_buffer: &mut Vec<Diagnostic>,
@@ -434,17 +405,28 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         );
 
         let counter = &mut 1;
-        let fr_name = self.give_region_a_name(infcx.tcx, mir, mir_def_id, fr, counter, &mut diag);
-        let outlived_fr_name =
-            self.give_region_a_name(infcx.tcx, mir, mir_def_id, outlived_fr, counter, &mut diag);
-
-        diag.span_label(
-            span,
-            format!(
-                "{} requires that `{}` must outlive `{}`",
-                category, fr_name, outlived_fr_name,
-            ),
-        );
+        let fr_name = self.give_region_a_name(
+            infcx, mir, mir_def_id, fr, counter, &mut diag);
+        let outlived_fr_name = self.give_region_a_name(
+            infcx, mir, mir_def_id, outlived_fr, counter, &mut diag);
+
+        let mir_def_name = if infcx.tcx.is_closure(mir_def_id) { "closure" } else { "function" };
+
+        match (category, outlived_fr_is_local, fr_is_local) {
+            (ConstraintCategory::Return, true, _) => {
+                diag.span_label(span, format!(
+                    "{} was supposed to return data with lifetime `{}` but it is returning \
+                    data with lifetime `{}`",
+                    mir_def_name, fr_name, outlived_fr_name,
+                ));
+            },
+            _ => {
+                diag.span_label(span, format!(
+                    "{}requires that `{}` must outlive `{}`",
+                    category, fr_name, outlived_fr_name,
+                ));
+            },
+        }
 
         diag.buffer(errors_buffer);
     }
diff --git a/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs b/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs
index c0eca026331..8505d8e1ef3 100644
--- a/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs
+++ b/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs
@@ -12,9 +12,11 @@ use borrow_check::nll::region_infer::RegionInferenceContext;
 use borrow_check::nll::ToRegionVid;
 use rustc::hir;
 use rustc::hir::def_id::DefId;
+use rustc::infer::InferCtxt;
 use rustc::mir::Mir;
 use rustc::ty::subst::{Substs, UnpackedKind};
 use rustc::ty::{self, RegionVid, Ty, TyCtxt};
+use rustc::util::ppaux::with_highlight_region;
 use rustc_errors::DiagnosticBuilder;
 use syntax::ast::Name;
 use syntax::symbol::keywords;
@@ -48,7 +50,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// and then return the name `'1` for us to use.
     crate fn give_region_a_name(
         &self,
-        tcx: TyCtxt<'_, '_, 'tcx>,
+        infcx: &InferCtxt<'_, '_, 'tcx>,
         mir: &Mir<'tcx>,
         mir_def_id: DefId,
         fr: RegionVid,
@@ -59,17 +61,18 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
         assert!(self.universal_regions.is_universal_region(fr));
 
-        self.give_name_from_error_region(tcx, mir_def_id, fr, counter, diag)
+        self.give_name_from_error_region(infcx.tcx, mir_def_id, fr, counter, diag)
             .or_else(|| {
                 self.give_name_if_anonymous_region_appears_in_arguments(
-                    tcx, mir, mir_def_id, fr, counter, diag)
+                    infcx, mir, mir_def_id, fr, counter, diag)
             })
             .or_else(|| {
                 self.give_name_if_anonymous_region_appears_in_upvars(
-                    tcx, mir, fr, counter, diag)
+                    infcx.tcx, mir, fr, counter, diag)
             })
             .or_else(|| {
-                self.give_name_if_anonymous_region_appears_in_output(tcx, mir, fr, counter, diag)
+                self.give_name_if_anonymous_region_appears_in_output(
+                    infcx.tcx, mir, fr, counter, diag)
             })
             .unwrap_or_else(|| span_bug!(mir.span, "can't make a name for free region {:?}", fr))
     }
@@ -130,7 +133,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// ```
     fn give_name_if_anonymous_region_appears_in_arguments(
         &self,
-        tcx: TyCtxt<'_, '_, 'tcx>,
+        infcx: &InferCtxt<'_, '_, 'tcx>,
         mir: &Mir<'tcx>,
         mir_def_id: DefId,
         fr: RegionVid,
@@ -138,12 +141,13 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         diag: &mut DiagnosticBuilder<'_>,
     ) -> Option<InternedString> {
         let implicit_inputs = self.universal_regions.defining_ty.implicit_inputs();
-        let argument_index = self.get_argument_index_for_region(tcx, fr)?;
+        let argument_index = self.get_argument_index_for_region(infcx.tcx, fr)?;
 
         let arg_ty =
             self.universal_regions.unnormalized_input_tys[implicit_inputs + argument_index];
         if let Some(region_name) = self.give_name_if_we_can_match_hir_ty_from_argument(
-            tcx,
+            infcx,
+            mir,
             mir_def_id,
             fr,
             arg_ty,
@@ -169,7 +173,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
     fn give_name_if_we_can_match_hir_ty_from_argument(
         &self,
-        tcx: TyCtxt<'_, '_, 'tcx>,
+        infcx: &InferCtxt<'_, '_, 'tcx>,
+        mir: &Mir<'tcx>,
         mir_def_id: DefId,
         needle_fr: RegionVid,
         argument_ty: Ty<'tcx>,
@@ -177,17 +182,24 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         counter: &mut usize,
         diag: &mut DiagnosticBuilder<'_>,
     ) -> Option<InternedString> {
-        let mir_node_id = tcx.hir.as_local_node_id(mir_def_id)?;
-        let fn_decl = tcx.hir.fn_decl(mir_node_id)?;
+        let mir_node_id = infcx.tcx.hir.as_local_node_id(mir_def_id)?;
+        let fn_decl = infcx.tcx.hir.fn_decl(mir_node_id)?;
         let argument_hir_ty: &hir::Ty = &fn_decl.inputs[argument_index];
         match argument_hir_ty.node {
             // This indicates a variable with no type annotation, like
             // `|x|`... in that case, we can't highlight the type but
             // must highlight the variable.
-            hir::TyKind::Infer => None,
+            hir::TyKind::Infer => self.give_name_if_we_cannot_match_hir_ty(
+                infcx,
+                mir,
+                needle_fr,
+                argument_ty,
+                counter,
+                diag,
+            ),
 
             _ => self.give_name_if_we_can_match_hir_ty(
-                tcx,
+                infcx.tcx,
                 needle_fr,
                 argument_ty,
                 argument_hir_ty,
@@ -197,6 +209,49 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         }
     }
 
+    /// Attempts to highlight the specific part of a type in an argument
+    /// that has no type annotation.
+    /// For example, we might produce an annotation like this:
+    ///
+    /// ```
+    ///  |     foo(|a, b| b)
+    ///  |          -  -
+    ///  |          |  |
+    ///  |          |  has type `&'1 u32`
+    ///  |          has type `&'2 u32`
+    /// ```
+    fn give_name_if_we_cannot_match_hir_ty(
+        &self,
+        infcx: &InferCtxt<'_, '_, 'tcx>,
+        mir: &Mir<'tcx>,
+        needle_fr: RegionVid,
+        argument_ty: Ty<'tcx>,
+        counter: &mut usize,
+        diag: &mut DiagnosticBuilder<'_>,
+    ) -> Option<InternedString> {
+        let type_name = with_highlight_region(needle_fr, *counter, || {
+            infcx.extract_type_name(&argument_ty)
+        });
+
+        debug!("give_name_if_we_cannot_match_hir_ty: type_name={:?} needle_fr={:?}",
+               type_name, needle_fr);
+        let assigned_region_name = if type_name.find(&format!("'{}", counter)).is_some() {
+            // Only add a label if we can confirm that a region was labelled.
+            let argument_index = self.get_argument_index_for_region(infcx.tcx, needle_fr)?;
+            let (_, span) = self.get_argument_name_and_span_for_region(mir, argument_index);
+            diag.span_label(span, format!("has type `{}`", type_name));
+
+            // This counter value will already have been used, so this function will increment it
+            // so the next value will be used next and return the region name that would have been
+            // used.
+            Some(self.synthesize_region_name(counter))
+        } else {
+            None
+        };
+
+        assigned_region_name
+    }
+
     /// Attempts to highlight the specific part of a type annotation
     /// that contains the anonymous reference we want to give a name
     /// to. For example, we might produce an annotation like this:
diff --git a/src/test/ui/error-codes/E0621-does-not-trigger-for-closures.nll.stderr b/src/test/ui/error-codes/E0621-does-not-trigger-for-closures.nll.stderr
index 9c7e3db67a6..0ac295c54bc 100644
--- a/src/test/ui/error-codes/E0621-does-not-trigger-for-closures.nll.stderr
+++ b/src/test/ui/error-codes/E0621-does-not-trigger-for-closures.nll.stderr
@@ -10,8 +10,8 @@ error: unsatisfied lifetime constraints
 LL |     invoke(&x, |a, b| if a > b { a } else { b }); //~ ERROR E0495
    |                ----------^^^^^-----------------
    |                |   |     |
-   |                |   |     free region requires that `'1` must outlive `'2`
-   |                |   lifetime `'1` appears in this argument
+   |                |   |     requires that `'1` must outlive `'2`
+   |                |   has type `&'1 i32`
    |                lifetime `'2` appears in return type
 
 error: aborting due to previous error
diff --git a/src/test/ui/impl-trait/static-return-lifetime-infered.nll.stderr b/src/test/ui/impl-trait/static-return-lifetime-infered.nll.stderr
index c6f8d2e519c..bbc63e6feca 100644
--- a/src/test/ui/impl-trait/static-return-lifetime-infered.nll.stderr
+++ b/src/test/ui/impl-trait/static-return-lifetime-infered.nll.stderr
@@ -10,21 +10,19 @@ warning: not reporting region error due to nll
 LL |         self.x.iter().map(|a| a.0)
    |                ^^^^
 
-error: borrowed data escapes outside of closure
+error: unsatisfied lifetime constraints
   --> $DIR/static-return-lifetime-infered.rs:17:9
    |
 LL |     fn iter_values_anon(&self) -> impl Iterator<Item=u32> {
-   |                         ----- `self` is a reference that is only valid in the closure body
+   |                         - let's call the lifetime of this reference `'1`
 LL |         self.x.iter().map(|a| a.0)
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^ `self` escapes the closure body here
+   |         ^^^^^^^^^^^^^ requires that `'1` must outlive `'static`
 
-error: borrowed data escapes outside of closure
+error: unsatisfied lifetime constraints
   --> $DIR/static-return-lifetime-infered.rs:21:9
    |
-LL |     fn iter_values<'a>(&'a self) -> impl Iterator<Item=u32> {
-   |                        -------- `self` is a reference that is only valid in the closure body
 LL |         self.x.iter().map(|a| a.0)
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^ `self` escapes the closure body here
+   |         ^^^^^^^^^^^^^ requires that `'a` must outlive `'static`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/in-band-lifetimes/impl/dyn-trait.nll.stderr b/src/test/ui/in-band-lifetimes/impl/dyn-trait.nll.stderr
index e26b1956d5e..f5d98e04ad8 100644
--- a/src/test/ui/in-band-lifetimes/impl/dyn-trait.nll.stderr
+++ b/src/test/ui/in-band-lifetimes/impl/dyn-trait.nll.stderr
@@ -4,13 +4,13 @@ warning: not reporting region error due to nll
 LL |     static_val(x); //~ ERROR cannot infer
    |                ^
 
-error: borrowed data escapes outside of closure
+error: borrowed data escapes outside of function
   --> $DIR/dyn-trait.rs:32:5
    |
 LL | fn with_dyn_debug_static<'a>(x: Box<dyn Debug + 'a>) {
-   |                              - `x` is a reference that is only valid in the closure body
+   |                              - `x` is a reference that is only valid in the function body
 LL |     static_val(x); //~ ERROR cannot infer
-   |     ^^^^^^^^^^^^^ `x` escapes the closure body here
+   |     ^^^^^^^^^^^^^ `x` escapes the function body here
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issue-10291.nll.stderr b/src/test/ui/issue-10291.nll.stderr
index 1358fe010b4..6de00ffd48c 100644
--- a/src/test/ui/issue-10291.nll.stderr
+++ b/src/test/ui/issue-10291.nll.stderr
@@ -8,7 +8,7 @@ error: unsatisfied lifetime constraints
   --> $DIR/issue-10291.rs:12:5
    |
 LL |     drop::<Box<for<'z> FnMut(&'z isize) -> &'z isize>>(Box::new(|z| {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ free region requires that `'x` must outlive `'static`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ requires that `'x` must outlive `'static`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issue-16683.nll.stderr b/src/test/ui/issue-16683.nll.stderr
index f9dda27da09..890bb426441 100644
--- a/src/test/ui/issue-16683.nll.stderr
+++ b/src/test/ui/issue-16683.nll.stderr
@@ -10,13 +10,13 @@ warning: not reporting region error due to nll
 LL |         self.a(); //~ ERROR cannot infer
    |              ^
 
-error: borrowed data escapes outside of closure
+error: borrowed data escapes outside of function
   --> $DIR/issue-16683.rs:14:9
    |
 LL |     fn b(&self) {
-   |          ----- `self` is a reference that is only valid in the closure body
+   |          ----- `self` is a reference that is only valid in the function body
 LL |         self.a(); //~ ERROR cannot infer
-   |         ^^^^^^^^ `self` escapes the closure body here
+   |         ^^^^^^^^ `self` escapes the function body here
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issue-17758.nll.stderr b/src/test/ui/issue-17758.nll.stderr
index 5775135aefc..c51a72f885d 100644
--- a/src/test/ui/issue-17758.nll.stderr
+++ b/src/test/ui/issue-17758.nll.stderr
@@ -10,13 +10,13 @@ warning: not reporting region error due to nll
 LL |         self.foo();
    |              ^^^
 
-error: borrowed data escapes outside of closure
+error: borrowed data escapes outside of function
   --> $DIR/issue-17758.rs:17:9
    |
 LL |     fn bar(&self) {
-   |            ----- `self` is a reference that is only valid in the closure body
+   |            ----- `self` is a reference that is only valid in the function body
 LL |         self.foo();
-   |         ^^^^^^^^^^ `self` escapes the closure body here
+   |         ^^^^^^^^^^ `self` escapes the function body here
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issue-40510-1.nll.stderr b/src/test/ui/issue-40510-1.nll.stderr
index 73a8d58290d..312ec6e742e 100644
--- a/src/test/ui/issue-40510-1.nll.stderr
+++ b/src/test/ui/issue-40510-1.nll.stderr
@@ -6,7 +6,7 @@ LL |        || {
    |  |_____|
    | ||
 LL | ||         &mut x
-   | ||         ^^^^^^ free region requires that `'1` must outlive `'2`
+   | ||         ^^^^^^ return requires that `'1` must outlive `'2`
 LL | ||     };
    | ||     -
    | ||_____|
diff --git a/src/test/ui/issue-40510-3.nll.stderr b/src/test/ui/issue-40510-3.nll.stderr
index 4133c69f031..eb44850e639 100644
--- a/src/test/ui/issue-40510-3.nll.stderr
+++ b/src/test/ui/issue-40510-3.nll.stderr
@@ -9,7 +9,7 @@ LL |  ||         || {
    |  ||_________^
 LL | |||             x.push(())
 LL | |||         }
-   | |||_________^ free region requires that `'1` must outlive `'2`
+   | |||_________^ requires that `'1` must outlive `'2`
 LL |  ||     };
    |  ||     -
    |  ||_____|
diff --git a/src/test/ui/issue-52213.nll.stderr b/src/test/ui/issue-52213.nll.stderr
index c288cf9ed82..7dd513d1b71 100644
--- a/src/test/ui/issue-52213.nll.stderr
+++ b/src/test/ui/issue-52213.nll.stderr
@@ -8,7 +8,7 @@ error: unsatisfied lifetime constraints
   --> $DIR/issue-52213.rs:13:11
    |
 LL |         ((u,),) => u,
-   |           ^ free region requires that `'a` must outlive `'b`
+   |           ^ requires that `'a` must outlive `'b`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issue-52533-1.nll.stderr b/src/test/ui/issue-52533-1.nll.stderr
new file mode 100644
index 00000000000..87fda1dd99c
--- /dev/null
+++ b/src/test/ui/issue-52533-1.nll.stderr
@@ -0,0 +1,17 @@
+warning: not reporting region error due to nll
+  --> $DIR/issue-52533-1.rs:19:18
+   |
+LL |     gimme(|x, y| y)
+   |                  ^
+
+error: unsatisfied lifetime constraints
+  --> $DIR/issue-52533-1.rs:19:18
+   |
+LL |     gimme(|x, y| y)
+   |            -  -  ^ closure was supposed to return data with lifetime `'1` but it is returning data with lifetime `'2`
+   |            |  |
+   |            |  has type `&Foo<'_, '1, u32>`
+   |            has type `&Foo<'_, '2, u32>`
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/issue-52533-1.rs b/src/test/ui/issue-52533-1.rs
new file mode 100644
index 00000000000..22af5a86702
--- /dev/null
+++ b/src/test/ui/issue-52533-1.rs
@@ -0,0 +1,21 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![allow(warnings)]
+
+struct Foo<'a, 'b, T: 'a + 'b> { x: &'a T, y: &'b T }
+
+fn gimme(_: impl for<'a, 'b, 'c> FnOnce(&'a Foo<'a, 'b, u32>,
+                                        &'a Foo<'a, 'c, u32>) -> &'a Foo<'a, 'b, u32>) { }
+
+fn main() {
+    gimme(|x, y| y)
+    //~^ ERROR mismatched types [E0308]
+}
diff --git a/src/test/ui/issue-52533-1.stderr b/src/test/ui/issue-52533-1.stderr
new file mode 100644
index 00000000000..38deb7d66de
--- /dev/null
+++ b/src/test/ui/issue-52533-1.stderr
@@ -0,0 +1,22 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-52533-1.rs:19:18
+   |
+LL |     gimme(|x, y| y)
+   |                  ^ lifetime mismatch
+   |
+   = note: expected type `&Foo<'_, '_, u32>`
+              found type `&Foo<'_, '_, u32>`
+note: the anonymous lifetime #4 defined on the body at 19:11...
+  --> $DIR/issue-52533-1.rs:19:11
+   |
+LL |     gimme(|x, y| y)
+   |           ^^^^^^^^
+note: ...does not necessarily outlive the anonymous lifetime #3 defined on the body at 19:11
+  --> $DIR/issue-52533-1.rs:19:11
+   |
+LL |     gimme(|x, y| y)
+   |           ^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/issue-52533.nll.stderr b/src/test/ui/issue-52533.nll.stderr
new file mode 100644
index 00000000000..a13b06e3204
--- /dev/null
+++ b/src/test/ui/issue-52533.nll.stderr
@@ -0,0 +1,17 @@
+warning: not reporting region error due to nll
+  --> $DIR/issue-52533.rs:15:16
+   |
+LL |     foo(|a, b| b)
+   |                ^
+
+error: unsatisfied lifetime constraints
+  --> $DIR/issue-52533.rs:15:16
+   |
+LL |     foo(|a, b| b)
+   |          -  -  ^ closure was supposed to return data with lifetime `'1` but it is returning data with lifetime `'2`
+   |          |  |
+   |          |  has type `&'1 u32`
+   |          has type `&'2 u32`
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/issue-52533.rs b/src/test/ui/issue-52533.rs
new file mode 100644
index 00000000000..08f2805cefd
--- /dev/null
+++ b/src/test/ui/issue-52533.rs
@@ -0,0 +1,17 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn foo(_: impl for<'a> FnOnce(&'a u32, &u32) -> &'a u32) {
+}
+
+fn main() {
+    foo(|a, b| b)
+    //~^ ERROR lifetime of reference outlives lifetime of borrowed content...
+}
diff --git a/src/test/ui/issue-52533.stderr b/src/test/ui/issue-52533.stderr
new file mode 100644
index 00000000000..76a2470a2e0
--- /dev/null
+++ b/src/test/ui/issue-52533.stderr
@@ -0,0 +1,20 @@
+error[E0312]: lifetime of reference outlives lifetime of borrowed content...
+  --> $DIR/issue-52533.rs:15:16
+   |
+LL |     foo(|a, b| b)
+   |                ^
+   |
+note: ...the reference is valid for the anonymous lifetime #2 defined on the body at 15:9...
+  --> $DIR/issue-52533.rs:15:9
+   |
+LL |     foo(|a, b| b)
+   |         ^^^^^^^^
+note: ...but the borrowed content is only valid for the anonymous lifetime #3 defined on the body at 15:9
+  --> $DIR/issue-52533.rs:15:9
+   |
+LL |     foo(|a, b| b)
+   |         ^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0312`.
diff --git a/src/test/ui/nll/closure-requirements/escape-argument-callee.stderr b/src/test/ui/nll/closure-requirements/escape-argument-callee.stderr
index d6f54218360..ccf116e640d 100644
--- a/src/test/ui/nll/closure-requirements/escape-argument-callee.stderr
+++ b/src/test/ui/nll/closure-requirements/escape-argument-callee.stderr
@@ -8,10 +8,10 @@ error: unsatisfied lifetime constraints
   --> $DIR/escape-argument-callee.rs:36:45
    |
 LL |         let mut closure = expect_sig(|p, y| *p = y);
-   |                                       -  -  ^^^^^^ free region requires that `'1` must outlive `'2`
+   |                                       -  -  ^^^^^^ requires that `'1` must outlive `'2`
    |                                       |  |
-   |                                       |  lifetime `'1` appears in this argument
-   |                                       lifetime `'2` appears in this argument
+   |                                       |  has type `&'1 i32`
+   |                                       has type `&mut &'2 i32`
 
 note: No external requirements
   --> $DIR/escape-argument-callee.rs:36:38
diff --git a/src/test/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.stderr b/src/test/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.stderr
index a7a50a3a029..b4508824901 100644
--- a/src/test/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.stderr
@@ -8,9 +8,9 @@ error: unsatisfied lifetime constraints
   --> $DIR/propagate-approximated-fail-no-postdom.rs:57:13
    |
 LL |         |_outlives1, _outlives2, _outlives3, x, y| {
-   |          ----------              ---------- lifetime `'2` appears in this argument
+   |          ----------              ---------- has type `std::cell::Cell<&'2 &u32>`
    |          |
-   |          lifetime `'1` appears in this argument
+   |          has type `std::cell::Cell<&&'1 u32>`
 ...
 LL |             demand_y(x, y, p) //~ ERROR
    |             ^^^^^^^^^^^^^^^^^ argument requires that `'1` must outlive `'2`
diff --git a/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.stderr b/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.stderr
index 3177cd7c28f..33e4240736f 100644
--- a/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.stderr
@@ -23,18 +23,18 @@ LL | |     });
    = note: number of external vids: 2
    = note: where '_#1r: '_#0r
 
-error: borrowed data escapes outside of closure
+error: borrowed data escapes outside of function
   --> $DIR/propagate-approximated-shorter-to-static-no-bound.rs:45:5
    |
 LL |   fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
-   |                     ------ `cell_a` is a reference that is only valid in the closure body
+   |                     ------ `cell_a` is a reference that is only valid in the function body
 LL | /     establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
 LL | |         //~^ ERROR
 LL | |
 LL | |         // Only works if 'x: 'y:
 LL | |         demand_y(x, y, x.get()) //~ WARNING not reporting region error due to nll
 LL | |     });
-   | |______^ `cell_a` escapes the closure body here
+   | |______^ `cell_a` escapes the function body here
 
 note: No external requirements
   --> $DIR/propagate-approximated-shorter-to-static-no-bound.rs:44:1
diff --git a/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.stderr b/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.stderr
index 089c88abcdd..5f98a0fd36d 100644
--- a/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.stderr
@@ -23,18 +23,18 @@ LL | |     });
    = note: number of external vids: 3
    = note: where '_#1r: '_#0r
 
-error: borrowed data escapes outside of closure
+error: borrowed data escapes outside of function
   --> $DIR/propagate-approximated-shorter-to-static-wrong-bound.rs:48:5
    |
 LL |   fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
-   |                     ------ `cell_a` is a reference that is only valid in the closure body
+   |                     ------ `cell_a` is a reference that is only valid in the function body
 LL | /     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
 LL | |         //~^ ERROR
 LL | |         // Only works if 'x: 'y:
 LL | |         demand_y(x, y, x.get())
 LL | |         //~^ WARNING not reporting region error due to nll
 LL | |     });
-   | |______^ `cell_a` escapes the closure body here
+   | |______^ `cell_a` escapes the function body here
 
 note: No external requirements
   --> $DIR/propagate-approximated-shorter-to-static-wrong-bound.rs:47:1
diff --git a/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr b/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr
index fb98c506c7d..40ebda4419b 100644
--- a/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr
@@ -8,9 +8,9 @@ error: unsatisfied lifetime constraints
   --> $DIR/propagate-fail-to-approximate-longer-no-bounds.rs:47:9
    |
 LL |     establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
-   |                                                ---------  - lifetime `'1` appears in this argument
+   |                                                ---------  - has type `&std::cell::Cell<&'1 u32>`
    |                                                |
-   |                                                lifetime `'2` appears in this argument
+   |                                                has type `&std::cell::Cell<&'2 &u32>`
 LL |         // Only works if 'x: 'y:
 LL |         demand_y(x, y, x.get())
    |         ^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'1` must outlive `'2`
diff --git a/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.stderr b/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.stderr
index 73d39a8502b..37ea6103976 100644
--- a/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.stderr
@@ -8,9 +8,9 @@ error: unsatisfied lifetime constraints
   --> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:51:9
    |
 LL |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
-   |                                                ----------  ---------- lifetime `'2` appears in this argument
+   |                                                ----------  ---------- has type `&std::cell::Cell<&'2 &u32>`
    |                                                |
-   |                                                lifetime `'1` appears in this argument
+   |                                                has type `&std::cell::Cell<&'1 &u32>`
 LL |         // Only works if 'x: 'y:
 LL |         demand_y(x, y, x.get())
    |         ^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'1` must outlive `'2`
diff --git a/src/test/ui/nll/closure-requirements/region-lbr-named-does-not-outlive-static.stderr b/src/test/ui/nll/closure-requirements/region-lbr-named-does-not-outlive-static.stderr
index d012dca2527..b0562711627 100644
--- a/src/test/ui/nll/closure-requirements/region-lbr-named-does-not-outlive-static.stderr
+++ b/src/test/ui/nll/closure-requirements/region-lbr-named-does-not-outlive-static.stderr
@@ -8,7 +8,7 @@ error: unsatisfied lifetime constraints
   --> $DIR/region-lbr-named-does-not-outlive-static.rs:19:5
    |
 LL |     &*x
-   |     ^^^ free region requires that `'a` must outlive `'static`
+   |     ^^^ requires that `'a` must outlive `'static`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/nll/closure-requirements/return-wrong-bound-region.stderr b/src/test/ui/nll/closure-requirements/return-wrong-bound-region.stderr
index 5724cdbd8c9..d6d1645ceea 100644
--- a/src/test/ui/nll/closure-requirements/return-wrong-bound-region.stderr
+++ b/src/test/ui/nll/closure-requirements/return-wrong-bound-region.stderr
@@ -8,10 +8,10 @@ error: unsatisfied lifetime constraints
   --> $DIR/return-wrong-bound-region.rs:21:23
    |
 LL |     expect_sig(|a, b| b); // ought to return `a`
-   |                 -  -  ^ free region requires that `'1` must outlive `'2`
+   |                 -  -  ^ closure was supposed to return data with lifetime `'1` but it is returning data with lifetime `'2`
    |                 |  |
-   |                 |  lifetime `'1` appears in this argument
-   |                 lifetime `'2` appears in this argument
+   |                 |  has type `&'1 i32`
+   |                 has type `&'2 i32`
 
 note: No external requirements
   --> $DIR/return-wrong-bound-region.rs:21:16
diff --git a/src/test/ui/nll/issue-50716.stderr b/src/test/ui/nll/issue-50716.stderr
index 8acf2ef51ec..f12ab9b4f96 100644
--- a/src/test/ui/nll/issue-50716.stderr
+++ b/src/test/ui/nll/issue-50716.stderr
@@ -1,11 +1,11 @@
-error: borrowed data escapes outside of closure
+error: borrowed data escapes outside of function
   --> $DIR/issue-50716.rs:25:14
    |
 LL | fn foo<'a, T: 'static>(s: Box<<&'a T as A>::X>)
-   |                        - `s` is a reference that is only valid in the closure body
+   |                        - `s` is a reference that is only valid in the function body
 ...
 LL |     let _x = *s; //~ ERROR
-   |              ^^ `s` escapes the closure body here
+   |              ^^ `s` escapes the function body here
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/nll/mir_check_cast_reify.stderr b/src/test/ui/nll/mir_check_cast_reify.stderr
index 13f90e1f159..d8f186a2232 100644
--- a/src/test/ui/nll/mir_check_cast_reify.stderr
+++ b/src/test/ui/nll/mir_check_cast_reify.stderr
@@ -4,14 +4,14 @@ warning: not reporting region error due to nll
 LL |     let f: fn(_) -> _ = foo;
    |                         ^^^
 
-error: borrowed data escapes outside of closure
+error: borrowed data escapes outside of function
   --> $DIR/mir_check_cast_reify.rs:48:5
    |
 LL | fn bar<'a>(x: &'a u32) -> &'static u32 {
-   |            - `x` is a reference that is only valid in the closure body
+   |            - `x` is a reference that is only valid in the function body
 ...
 LL |     f(x)
-   |     ^^^^ `x` escapes the closure body here
+   |     ^^^^ `x` escapes the function body here
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/nll/mir_check_cast_unsafe_fn.stderr b/src/test/ui/nll/mir_check_cast_unsafe_fn.stderr
index b08c6f32e6b..98c03e37814 100644
--- a/src/test/ui/nll/mir_check_cast_unsafe_fn.stderr
+++ b/src/test/ui/nll/mir_check_cast_unsafe_fn.stderr
@@ -4,14 +4,14 @@ warning: not reporting region error due to nll
 LL |     let g: unsafe fn(_) -> _ = f;
    |                                ^
 
-error: borrowed data escapes outside of closure
+error: borrowed data escapes outside of function
   --> $DIR/mir_check_cast_unsafe_fn.rs:20:14
    |
 LL | fn bar<'a>(input: &'a u32, f: fn(&'a u32) -> &'a u32) -> &'static u32 {
-   |            ----- `input` is a reference that is only valid in the closure body
+   |            ----- `input` is a reference that is only valid in the function body
 ...
 LL |     unsafe { g(input) }
-   |              ^^^^^^^^ `input` escapes the closure body here
+   |              ^^^^^^^^ `input` escapes the function body here
 
 error: aborting due to previous error