Disable some nice region errors in NLL mode.

src/librustc/infer/error_reporting/nice_region_error/mod.rs

@@ -64,6 +64,12 @@ impl<'cx, 'gcx, 'tcx> NiceRegionError<'cx, 'gcx, 'tcx> {
         Self { tcx, error: None, regions: Some((span, sub, sup)), tables }
     }
 
+    pub fn try_report_from_nll(&self) -> Option<ErrorReported> {
+        // Due to the improved diagnostics returned by the MIR borrow checker, only a subset of
+        // the nice region errors are required when running under the MIR borrow checker.
+        self.try_report_named_anon_conflict()
+    }
+
     pub fn try_report(&self) -> Option<ErrorReported> {
         self.try_report_named_anon_conflict()
             .or_else(|| self.try_report_anon_anon_conflict())

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

@@ -310,7 +310,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         if let (Some(f), Some(o)) = (self.to_error_region(fr), self.to_error_region(outlived_fr)) {
             let tables = infcx.tcx.typeck_tables_of(mir_def_id);
             let nice = NiceRegionError::new_from_span(infcx.tcx, span, o, f, Some(tables));
-            if let Some(_error_reported) = nice.try_report() {
+            if let Some(_error_reported) = nice.try_report_from_nll() {
                 return;
             }
         }

src/test/compile-fail/nll/where_clauses_in_functions.rs

@@ -21,7 +21,7 @@ where
 
 fn bar<'a, 'b>(x: &'a u32, y: &'b u32) -> (&'a u32, &'b u32) {
     foo(x, y)
-    //~^ ERROR lifetime mismatch [E0623]
+    //~^ ERROR unsatisfied lifetime constraints
     //~| WARNING not reporting region error due to nll
 }
 

src/test/compile-fail/nll/where_clauses_in_structs.rs

@@ -21,7 +21,7 @@ struct Foo<'a: 'b, 'b> {
 
 fn bar<'a, 'b>(x: Cell<&'a u32>, y: Cell<&'b u32>) {
     Foo { x, y };
-    //~^ ERROR lifetime mismatch [E0623]
+    //~^ ERROR unsatisfied lifetime constraints
     //~| WARNING not reporting region error due to nll
 }
 

src/test/ui/in-band-lifetimes/mismatched.nll.stderr

@@ -18,15 +18,15 @@ LL | fn foo(x: &'a u32, y: &u32) -> &'a u32 { y } //~ ERROR explicit lifetime re
    |                    |
    |                    consider changing the type of `y` to `&'a u32`
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/mismatched.rs:16:46
    |
 LL | fn foo2(x: &'a u32, y: &'b u32) -> &'a u32 { y } //~ ERROR lifetime mismatch
-   |                        -------     -------   ^ ...but data from `y` is returned here
-   |                        |
-   |                        this parameter and the return type are declared with different lifetimes...
+   |             --          --                   ^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
+   |             |           |
+   |             |           lifetime `'b` defined here
+   |             lifetime `'a` defined here
 
 error: aborting due to 2 previous errors
 
-Some errors occurred: E0621, E0623.
-For more information about an error, try `rustc --explain E0621`.
+For more information about this error, try `rustc --explain E0621`.

src/test/ui/lifetime-errors/ex1-return-one-existing-name-if-else-using-impl.nll.stderr

@@ -4,17 +4,16 @@ warning: not reporting region error due to nll
 LL |         if x > y { x } else { y } //~ ERROR lifetime mismatch
    |                    ^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex1-return-one-existing-name-if-else-using-impl.rs:21:12
    |
 LL |     fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
-   |                   ----                 -------
-   |                   |
-   |                   this parameter and the return type are declared with different lifetimes...
+   |            --     - let's call the lifetime of this reference `'1`
+   |            |
+   |            lifetime `'a` defined here
 LL | 
 LL |         if x > y { x } else { y } //~ ERROR lifetime mismatch
-   |            ^^^^^ ...but data from `x` is returned here
+   |            ^^^^^ requires that `'1` must outlive `'a`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex1-return-one-existing-name-return-type-is-anon.nll.stderr

@@ -4,17 +4,16 @@ warning: not reporting region error due to nll
 LL |     x //~ ERROR lifetime mismatch
    |     ^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex1-return-one-existing-name-return-type-is-anon.rs:18:5
    |
 LL |   fn foo<'a>(&self, x: &'a i32) -> &i32 {
-   |                        -------     ----
-   |                        |
-   |                        this parameter and the return type are declared with different lifetimes...
+   |          --  - let's call the lifetime of this reference `'1`
+   |          |
+   |          lifetime `'a` defined here
 LL | 
 LL |     x //~ ERROR lifetime mismatch
-   |     ^ ...but data from `x` is returned here
+   |     ^ function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'1`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex1-return-one-existing-name-self-is-anon.nll.stderr

@@ -4,17 +4,16 @@ warning: not reporting region error due to nll
 LL |         if true { x } else { self } //~ ERROR lifetime mismatch
    |                              ^^^^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex1-return-one-existing-name-self-is-anon.rs:18:9
    |
 LL |     fn foo<'a>(&self, x: &'a Foo) -> &'a Foo {
-   |                -----                 -------
-   |                |
-   |                this parameter and the return type are declared with different lifetimes...
+   |            --  - let's call the lifetime of this reference `'1`
+   |            |
+   |            lifetime `'a` defined here
 LL | 
 LL |         if true { x } else { self } //~ ERROR lifetime mismatch
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ ...but data from `self` is returned here
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ requires that `'1` must outlive `'a`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex2b-push-no-existing-names.nll.stderr

@@ -4,14 +4,15 @@ warning: not reporting region error due to nll
 LL |     x.push(y); //~ ERROR lifetime mismatch
    |            ^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex2b-push-no-existing-names.rs:16:5
    |
 LL | fn foo(x: &mut Vec<Ref<i32>>, y: Ref<i32>) {
-   |                    --------      -------- these two types are declared with different lifetimes...
+   |                    --------      -------- lifetime `'1` appears in this type
+   |                    |
+   |                    lifetime `'2` appears in this type
 LL |     x.push(y); //~ ERROR lifetime mismatch
-   |     ^^^^^^^^^ ...but data from `y` flows into `x` here
+   |     ^^^^^^^^^ argument requires that `'1` must outlive `'2`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex2c-push-inference-variable.nll.stderr

@@ -4,15 +4,16 @@ warning: not reporting region error due to nll
 LL |     let z = Ref { data: y.data };
    |             ^^^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex2c-push-inference-variable.rs:17:5
    |
 LL | fn foo<'a, 'b, 'c>(x: &'a mut Vec<Ref<'b, i32>>, y: Ref<'c, i32>) {
-   |                                   ------------      ------------ these two types are declared with different lifetimes...
+   |            --  -- lifetime `'c` defined here
+   |            |
+   |            lifetime `'b` defined here
 LL |     let z = Ref { data: y.data };
 LL |     x.push(z); //~ ERROR lifetime mismatch
-   |     ^^^^^^^^^ ...but data from `y` flows into `x` here
+   |     ^^^^^^^^^ argument requires that `'c` must outlive `'b`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex2d-push-inference-variable-2.nll.stderr

@@ -4,15 +4,16 @@ warning: not reporting region error due to nll
 LL |     let b = Ref { data: y.data };
    |             ^^^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex2d-push-inference-variable-2.rs:18:5
    |
 LL | fn foo<'a, 'b, 'c>(x: &'a mut Vec<Ref<'b, i32>>, y: Ref<'c, i32>) {
-   |                                   ------------      ------------ these two types are declared with different lifetimes...
+   |            --  -- lifetime `'c` defined here
+   |            |
+   |            lifetime `'b` defined here
 ...
 LL |     a.push(b);
-   |     ^^^^^^^^^ ...but data from `y` flows into `x` here
+   |     ^^^^^^^^^ argument requires that `'c` must outlive `'b`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex2e-push-inference-variable-3.nll.stderr

@@ -4,15 +4,16 @@ warning: not reporting region error due to nll
 LL |     let b = Ref { data: y.data };
    |             ^^^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex2e-push-inference-variable-3.rs:18:5
    |
 LL | fn foo<'a, 'b, 'c>(x: &'a mut Vec<Ref<'b, i32>>, y: Ref<'c, i32>) {
-   |                                   ------------      ------------ these two types are declared with different lifetimes...
+   |            --  -- lifetime `'c` defined here
+   |            |
+   |            lifetime `'b` defined here
 ...
 LL |     Vec::push(a, b);
-   |     ^^^^^^^^^^^^^^^ ...but data from `y` flows into `x` here
+   |     ^^^^^^^^^^^^^^^ argument requires that `'c` must outlive `'b`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex3-both-anon-regions-2.nll.stderr

@@ -4,14 +4,15 @@ warning: not reporting region error due to nll
 LL |     *v = x; //~ ERROR lifetime mismatch
    |          ^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex3-both-anon-regions-2.rs:12:5
    |
 LL | fn foo(&mut (ref mut v, w): &mut (&u8, &u8), x: &u8) {
-   |                                   ---           --- these two types are declared with different lifetimes...
+   |                                   -             - let's call the lifetime of this reference `'1`
+   |                                   |
+   |                                   let's call the lifetime of this reference `'2`
 LL |     *v = x; //~ ERROR lifetime mismatch
-   |     ^^^^^^ ...but data from `x` flows here
+   |     ^^^^^^ requires that `'1` must outlive `'2`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex3-both-anon-regions-3.nll.stderr

@@ -10,22 +10,25 @@ warning: not reporting region error due to nll
 LL |     z.push((x,y)); //~ ERROR lifetime mismatch
    |               ^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex3-both-anon-regions-3.rs:12:5
    |
 LL | fn foo(z: &mut Vec<(&u8,&u8)>, (x, y): (&u8, &u8)) {
-   |                     ---                 --- these two types are declared with different lifetimes...
+   |                     -                   - let's call the lifetime of this reference `'1`
+   |                     |
+   |                     let's call the lifetime of this reference `'2`
 LL |     z.push((x,y)); //~ ERROR lifetime mismatch
-   |     ^^^^^^^^^^^^^ ...but data flows into `z` here
+   |     ^^^^^^^^^^^^^ argument requires that `'1` must outlive `'2`
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex3-both-anon-regions-3.rs:12:5
    |
 LL | fn foo(z: &mut Vec<(&u8,&u8)>, (x, y): (&u8, &u8)) {
-   |                         ---                  --- these two types are declared with different lifetimes...
+   |                         -                    - let's call the lifetime of this reference `'1`
+   |                         |
+   |                         let's call the lifetime of this reference `'2`
 LL |     z.push((x,y)); //~ ERROR lifetime mismatch
-   |     ^^^^^^^^^^^^^ ...but data flows into `z` here
+   |     ^^^^^^^^^^^^^ argument requires that `'1` must outlive `'2`
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex3-both-anon-regions-both-are-structs-2.nll.stderr

@@ -4,14 +4,15 @@ warning: not reporting region error due to nll
 LL |     x.b = y.b; //~ ERROR lifetime mismatch
    |           ^^^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex3-both-anon-regions-both-are-structs-2.rs:16:5
    |
 LL | fn foo(mut x: Ref, y: Ref) {
-   |               ---     --- these two types are declared with different lifetimes...
+   |               ---     --- lifetime `'1` appears in this type
+   |               |
+   |               lifetime `'2` appears in this type
 LL |     x.b = y.b; //~ ERROR lifetime mismatch
-   |     ^^^^^^^^^ ...but data from `y` flows into `x` here
+   |     ^^^^^^^^^ requires that `'1` must outlive `'2`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex3-both-anon-regions-both-are-structs-3.nll.stderr

@@ -4,16 +4,16 @@ warning: not reporting region error due to nll
 LL |     x.a = x.b; //~ ERROR lifetime mismatch
    |           ^^^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex3-both-anon-regions-both-are-structs-3.rs:16:5
    |
 LL | fn foo(mut x: Ref) {
    |               ---
    |               |
-   |               this type is declared with multiple lifetimes...
+   |               lifetime `'1` appears in this type
+   |               lifetime `'2` appears in this type
 LL |     x.a = x.b; //~ ERROR lifetime mismatch
-   |     ^^^^^^^^^ ...but data with one lifetime flows into the other here
+   |     ^^^^^^^^^ requires that `'1` must outlive `'2`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex3-both-anon-regions-both-are-structs-4.nll.stderr

@@ -4,16 +4,16 @@ warning: not reporting region error due to nll
 LL |     x.a = x.b; //~ ERROR lifetime mismatch
    |           ^^^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex3-both-anon-regions-both-are-structs-4.rs:16:5
    |
 LL | fn foo(mut x: Ref) {
    |               ---
    |               |
-   |               this type is declared with multiple lifetimes...
+   |               lifetime `'1` appears in this type
+   |               lifetime `'2` appears in this type
 LL |     x.a = x.b; //~ ERROR lifetime mismatch
-   |     ^^^^^^^^^ ...but data with one lifetime flows into the other here
+   |     ^^^^^^^^^ requires that `'1` must outlive `'2`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex3-both-anon-regions-both-are-structs-earlybound-regions.nll.stderr

@@ -4,15 +4,16 @@ warning: not reporting region error due to nll
 LL |     x.push(y); //~ ERROR lifetime mismatch
    |            ^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex3-both-anon-regions-both-are-structs-earlybound-regions.rs:18:5
    |
 LL | fn foo<'a, 'b>(mut x: Vec<Ref<'a>>, y: Ref<'b>)
-   |                           -------      ------- these two types are declared with different lifetimes...
+   |        --  -- lifetime `'b` defined here
+   |        |
+   |        lifetime `'a` defined here
 ...
 LL |     x.push(y); //~ ERROR lifetime mismatch
-   |     ^^^^^^^^^ ...but data from `y` flows into `x` here
+   |     ^^^^^^^^^ argument requires that `'b` must outlive `'a`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex3-both-anon-regions-both-are-structs-latebound-regions.nll.stderr

@@ -4,14 +4,15 @@ warning: not reporting region error due to nll
 LL |     x.push(y); //~ ERROR lifetime mismatch
    |            ^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex3-both-anon-regions-both-are-structs-latebound-regions.rs:15:5
    |
 LL | fn foo<'a, 'b>(mut x: Vec<Ref<'a>>, y: Ref<'b>) {
-   |                           -------      ------- these two types are declared with different lifetimes...
+   |        --  -- lifetime `'b` defined here
+   |        |
+   |        lifetime `'a` defined here
 LL |     x.push(y); //~ ERROR lifetime mismatch
-   |     ^^^^^^^^^ ...but data from `y` flows into `x` here
+   |     ^^^^^^^^^ argument requires that `'b` must outlive `'a`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.

src/test/ui/lifetime-errors/ex3-both-anon-regions-both-are-structs.nll.stderr

@@ -4,14 +4,15 @@ warning: not reporting region error due to nll
 LL |     x.push(y); //~ ERROR lifetime mismatch
    |            ^
 
-error[E0623]: lifetime mismatch
+error: unsatisfied lifetime constraints
   --> $DIR/ex3-both-anon-regions-both-are-structs.rs:15:5
    |
 LL | fn foo(mut x: Vec<Ref>, y: Ref) {
-   |                   ---      --- these two types are declared with different lifetimes...
+   |                   ---      --- lifetime `'1` appears in this type
+   |                   |
+   |                   lifetime `'2` appears in this type
 LL |     x.push(y); //~ ERROR lifetime mismatch
-   |     ^^^^^^^^^ ...but data from `y` flows into `x` here
+   |     ^^^^^^^^^ argument requires that `'1` must outlive `'2`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.