Use the span of the user type for AscribeUserType

Also change the order of the fake read for let and the AscribeUserType,
so that we use the better span and message from the fake read in errors.

src/librustc/mir/mod.rs

@@ -710,7 +710,7 @@ pub struct LocalDecl<'tcx> {
     /// e.g. via `let x: T`, then we carry that type here. The MIR
     /// borrow checker needs this information since it can affect
     /// region inference.
-    pub user_ty: Option<CanonicalTy<'tcx>>,
+    pub user_ty: Option<(CanonicalTy<'tcx>, Span)>,
 
     /// Name of the local, used in debuginfo and pretty-printing.
     ///

src/librustc/mir/visit.rs

@@ -735,7 +735,7 @@ macro_rules! make_mir_visitor {
                     local,
                     source_info: *source_info,
                 });
-                if let Some(user_ty) = user_ty {
+                if let Some((user_ty, _)) = user_ty {
                     self.visit_user_ty(user_ty);
                 }
                 self.visit_source_info(source_info);

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

@@ -310,12 +310,12 @@ impl<'a, 'b, 'gcx, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'gcx, 'tcx> {
         self.super_local_decl(local, local_decl);
         self.sanitize_type(local_decl, local_decl.ty);
 
-        if let Some(user_ty) = local_decl.user_ty {
+        if let Some((user_ty, span)) = local_decl.user_ty {
             if let Err(terr) = self.cx.relate_type_and_user_type(
                 local_decl.ty,
                 ty::Variance::Invariant,
                 user_ty,
-                Locations::All(local_decl.source_info.span),
+                Locations::All(span),
                 ConstraintCategory::TypeAnnotation,
             ) {
                 span_mirbug!(

src/librustc_mir/build/matches/mod.rs

@@ -292,30 +292,32 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                     ..
                 },
                 user_ty: ascription_user_ty,
+                user_ty_span,
             } => {
                 let place =
                     self.storage_live_binding(block, var, irrefutable_pat.span, OutsideGuard);
                 unpack!(block = self.into(&place, block, initializer));
 
-                let source_info = self.source_info(irrefutable_pat.span);
+                // Inject a fake read, see comments on `FakeReadCause::ForLet`.
+                let pattern_source_info = self.source_info(irrefutable_pat.span);
                 self.cfg.push(
                     block,
                     Statement {
-                        source_info,
-                        kind: StatementKind::AscribeUserType(
-                            place.clone(),
-                            ty::Variance::Invariant,
-                            ascription_user_ty,
-                        ),
+                        source_info: pattern_source_info,
+                        kind: StatementKind::FakeRead(FakeReadCause::ForLet, place.clone()),
                     },
                 );
 
-                // Inject a fake read, see comments on `FakeReadCause::ForLet`.
+                let ty_source_info = self.source_info(user_ty_span);
                 self.cfg.push(
                     block,
                     Statement {
-                        source_info,
-                        kind: StatementKind::FakeRead(FakeReadCause::ForLet, place.clone()),
+                        source_info: ty_source_info,
+                        kind: StatementKind::AscribeUserType(
+                            place.clone(),
+                            ty::Variance::Invariant,
+                            ascription_user_ty,
+                        ),
                     },
                 );
 
@@ -489,7 +491,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
     pub fn visit_bindings(
         &mut self,
         pattern: &Pattern<'tcx>,
-        mut pattern_user_ty: Option<CanonicalTy<'tcx>>,
+        mut pattern_user_ty: Option<(CanonicalTy<'tcx>, Span)>,
         f: &mut impl FnMut(
             &mut Self,
             Mutability,
@@ -498,7 +500,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             NodeId,
             Span,
             Ty<'tcx>,
-            Option<CanonicalTy<'tcx>>,
+            Option<(CanonicalTy<'tcx>, Span)>,
         ),
     ) {
         match *pattern.kind {
@@ -549,16 +551,15 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 // FIXME(#47184): extract or handle `pattern_user_ty` somehow
                 self.visit_bindings(subpattern, None, f);
             }
-            PatternKind::AscribeUserType { ref subpattern, user_ty } => {
+            PatternKind::AscribeUserType { ref subpattern, user_ty, user_ty_span } => {
                 // This corresponds to something like
                 //
                 // ```
-                // let (p1: T1): T2 = ...;
+                // let A::<'a>(_): A<'static> = ...;
                 // ```
                 //
-                // Not presently possible, though maybe someday.
-                assert!(pattern_user_ty.is_none());
-                self.visit_bindings(subpattern, Some(user_ty), f)
+                // FIXME(#47184): handle `pattern_user_ty` somehow
+                self.visit_bindings(subpattern, Some((user_ty, user_ty_span)), f)
             }
             PatternKind::Leaf { ref subpatterns }
             | PatternKind::Variant {
@@ -1469,7 +1470,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
         num_patterns: usize,
         var_id: NodeId,
         var_ty: Ty<'tcx>,
-        user_var_ty: Option<CanonicalTy<'tcx>>,
+        user_var_ty: Option<(CanonicalTy<'tcx>, Span)>,
         has_guard: ArmHasGuard,
         opt_match_place: Option<(Option<Place<'tcx>>, Span)>,
         pat_span: Span,

src/librustc_mir/build/matches/simplify.rs

@@ -63,9 +63,9 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                                  candidate: &mut Candidate<'pat, 'tcx>)
                                  -> Result<(), MatchPair<'pat, 'tcx>> {
         match *match_pair.pattern.kind {
-            PatternKind::AscribeUserType { ref subpattern, user_ty } => {
+            PatternKind::AscribeUserType { ref subpattern, user_ty, user_ty_span } => {
                 candidate.ascriptions.push(Ascription {
-                    span: match_pair.pattern.span,
+                    span: user_ty_span,
                     user_ty,
                     source: match_pair.place.clone(),
                 });

src/librustc_mir/hair/cx/block.rs

@@ -92,6 +92,7 @@ fn mirror_stmts<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
                                     span: pattern.span,
                                     kind: Box::new(PatternKind::AscribeUserType {
                                         user_ty: *user_ty,
+                                        user_ty_span: ty.span,
                                         subpattern: pattern
                                     })
                                 };

src/librustc_mir/hair/pattern/mod.rs

@@ -71,6 +71,7 @@ pub enum PatternKind<'tcx> {
     AscribeUserType {
         user_ty: CanonicalTy<'tcx>,
         subpattern: Pattern<'tcx>,
+        user_ty_span: Span,
     },
 
     /// x, ref x, x @ P, etc
@@ -692,6 +693,7 @@ impl<'a, 'tcx> PatternContext<'a, 'tcx> {
             kind = PatternKind::AscribeUserType {
                 subpattern,
                 user_ty,
+                user_ty_span: span,
             };
         }
 
@@ -1015,9 +1017,11 @@ impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
             PatternKind::AscribeUserType {
                 ref subpattern,
                 user_ty,
+                user_ty_span,
             } => PatternKind::AscribeUserType {
                 subpattern: subpattern.fold_with(folder),
                 user_ty: user_ty.fold_with(folder),
+                user_ty_span,
             },
             PatternKind::Binding {
                 mutability,

src/test/mir-opt/basic_assignment.rs

@@ -55,8 +55,8 @@ fn main() {
 //        StorageDead(_3);
 //        StorageLive(_4);
 //        _4 = std::option::Option<std::boxed::Box<u32>>::None;
-//        AscribeUserType(_4, o, Canonical { variables: [], value: std::option::Option<std::boxed::Box<u32>> });
 //        FakeRead(ForLet, _4);
+//        AscribeUserType(_4, o, Canonical { variables: [], value: std::option::Option<std::boxed::Box<u32>> });
 //        StorageLive(_5);
 //        StorageLive(_6);
 //        _6 = move _4;

src/test/ui/nll/relate_tys/hr-fn-aaa-as-aba.stderr

@@ -5,10 +5,10 @@ LL |     let a: for<'a, 'b> fn(&'a u32, &'b u32) -> &'a u32 = make_it();
    |                                                          ^^^^^^^^^
 
 error: higher-ranked subtype error
-  --> $DIR/hr-fn-aaa-as-aba.rs:32:9
+  --> $DIR/hr-fn-aaa-as-aba.rs:32:12
    |
 LL |     let _: for<'a, 'b> fn(&'a u32, &'b u32) -> &'a u32 = make_it();
-   |         ^
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 2 previous errors
 

src/test/ui/nll/user-annotations/patterns.stderr

@@ -131,12 +131,12 @@ LL |     y //~ ERROR
    |     ^ returning this value requires that `'a` must outlive `'static`
 
 error: unsatisfied lifetime constraints
-  --> $DIR/patterns.rs:117:9
+  --> $DIR/patterns.rs:117:18
    |
 LL | fn a_to_static_then_static<'a>(x: &'a u32) -> &'static u32 {
    |                            -- lifetime `'a` defined here
 LL |     let (y, _z): (&'static u32, u32) = (x, 44); //~ ERROR
-   |         ^^^^^^^ type annotation requires that `'a` must outlive `'static`
+   |                  ^^^^^^^^^^^^^^^^^^^ type annotation requires that `'a` must outlive `'static`
 
 error: aborting due to 14 previous errors
 

src/test/ui/regions/region-object-lifetime-in-coercion.nll.stderr

@@ -1,10 +1,10 @@
 error[E0621]: explicit lifetime required in the type of `v`
-  --> $DIR/region-object-lifetime-in-coercion.rs:18:9
+  --> $DIR/region-object-lifetime-in-coercion.rs:18:12
    |
 LL | fn a(v: &[u8]) -> Box<Foo + 'static> {
    |         ----- help: add explicit lifetime `'static` to the type of `v`: `&'static [u8]`
 LL |     let x: Box<Foo + 'static> = Box::new(v);
-   |         ^ lifetime `'static` required
+   |            ^^^^^^^^^^^^^^^^^^ lifetime `'static` required
 
 error[E0621]: explicit lifetime required in the type of `v`
   --> $DIR/region-object-lifetime-in-coercion.rs:24:5

src/test/ui/regions/regions-addr-of-self.nll.stderr

@@ -1,10 +1,10 @@
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-addr-of-self.rs:17:13
+  --> $DIR/regions-addr-of-self.rs:17:16
    |
 LL |     pub fn chase_cat(&mut self) {
    |                      - let's call the lifetime of this reference `'1`
 LL |         let p: &'static mut usize = &mut self.cats_chased; //~ ERROR cannot infer
-   |             ^ type annotation requires that `'1` must outlive `'static`
+   |                ^^^^^^^^^^^^^^^^^^ type annotation requires that `'1` must outlive `'static`
 
 error: aborting due to previous error
 

src/test/ui/regions/regions-addr-of-upvar-self.nll.stderr

@@ -1,33 +1,33 @@
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-addr-of-upvar-self.rs:20:17
+  --> $DIR/regions-addr-of-upvar-self.rs:20:20
    |
 LL |         let _f = || {
    |                  -- lifetime `'1` represents this closure's body
 LL |             let p: &'static mut usize = &mut self.food; //~ ERROR cannot infer
-   |                 ^ type annotation requires that `'1` must outlive `'static`
+   |                    ^^^^^^^^^^^^^^^^^^ type annotation requires that `'1` must outlive `'static`
    |
    = note: closure implements `FnMut`, so references to captured variables can't escape the closure
 
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-addr-of-upvar-self.rs:20:17
+  --> $DIR/regions-addr-of-upvar-self.rs:20:20
    |
 LL |     pub fn chase_cat(&mut self) {
    |                      --------- lifetime `'2` appears in the type of `self`
 LL |         let _f = || {
    |                  -- lifetime `'1` represents this closure's body
 LL |             let p: &'static mut usize = &mut self.food; //~ ERROR cannot infer
-   |                 ^ type annotation requires that `'1` must outlive `'2`
+   |                    ^^^^^^^^^^^^^^^^^^ type annotation requires that `'1` must outlive `'2`
    |
    = note: closure implements `FnMut`, so references to captured variables can't escape the closure
 
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-addr-of-upvar-self.rs:20:17
+  --> $DIR/regions-addr-of-upvar-self.rs:20:20
    |
 LL |     pub fn chase_cat(&mut self) {
    |                      - let's call the lifetime of this reference `'1`
 LL |         let _f = || {
 LL |             let p: &'static mut usize = &mut self.food; //~ ERROR cannot infer
-   |                 ^ type annotation requires that `'1` must outlive `'static`
+   |                    ^^^^^^^^^^^^^^^^^^ type annotation requires that `'1` must outlive `'static`
 
 error[E0597]: `self` does not live long enough
   --> $DIR/regions-addr-of-upvar-self.rs:20:46

src/test/ui/regions/regions-infer-contravariance-due-to-decl.nll.stderr

@@ -1,13 +1,13 @@
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-infer-contravariance-due-to-decl.rs:35:9
+  --> $DIR/regions-infer-contravariance-due-to-decl.rs:35:12
    |
 LL | fn use_<'short,'long>(c: Contravariant<'short>,
    |         ------ ----- lifetime `'long` defined here
    |         |
    |         lifetime `'short` defined here
 ...
 LL |     let _: Contravariant<'long> = c; //~ ERROR E0623
-   |         ^ type annotation requires that `'short` must outlive `'long`
+   |            ^^^^^^^^^^^^^^^^^^^^ type annotation requires that `'short` must outlive `'long`
 
 error: aborting due to previous error
 

src/test/ui/regions/regions-infer-covariance-due-to-decl.nll.stderr

@@ -1,13 +1,13 @@
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-infer-covariance-due-to-decl.rs:32:9
+  --> $DIR/regions-infer-covariance-due-to-decl.rs:32:12
    |
 LL | fn use_<'short,'long>(c: Covariant<'long>,
    |         ------ ----- lifetime `'long` defined here
    |         |
    |         lifetime `'short` defined here
 ...
 LL |     let _: Covariant<'short> = c; //~ ERROR E0623
-   |         ^ type annotation requires that `'short` must outlive `'long`
+   |            ^^^^^^^^^^^^^^^^^ type annotation requires that `'short` must outlive `'long`
 
 error: aborting due to previous error
 

src/test/ui/regions/regions-variance-contravariant-use-covariant-in-second-position.nll.stderr

@@ -1,13 +1,13 @@
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-variance-contravariant-use-covariant-in-second-position.rs:35:9
+  --> $DIR/regions-variance-contravariant-use-covariant-in-second-position.rs:35:12
    |
 LL | fn use_<'short,'long>(c: S<'long, 'short>,
    |         ------ ----- lifetime `'long` defined here
    |         |
    |         lifetime `'short` defined here
 ...
 LL |     let _: S<'long, 'long> = c; //~ ERROR E0623
-   |         ^ type annotation requires that `'short` must outlive `'long`
+   |            ^^^^^^^^^^^^^^^ type annotation requires that `'short` must outlive `'long`
 
 error: aborting due to previous error
 

src/test/ui/regions/regions-variance-contravariant-use-covariant.nll.stderr

@@ -1,13 +1,13 @@
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-variance-contravariant-use-covariant.rs:33:9
+  --> $DIR/regions-variance-contravariant-use-covariant.rs:33:12
    |
 LL | fn use_<'short,'long>(c: Contravariant<'short>,
    |         ------ ----- lifetime `'long` defined here
    |         |
    |         lifetime `'short` defined here
 ...
 LL |     let _: Contravariant<'long> = c; //~ ERROR E0623
-   |         ^ type annotation requires that `'short` must outlive `'long`
+   |            ^^^^^^^^^^^^^^^^^^^^ type annotation requires that `'short` must outlive `'long`
 
 error: aborting due to previous error
 

src/test/ui/regions/regions-variance-covariant-use-contravariant.nll.stderr

@@ -1,13 +1,13 @@
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-variance-covariant-use-contravariant.rs:33:9
+  --> $DIR/regions-variance-covariant-use-contravariant.rs:33:12
    |
 LL | fn use_<'short,'long>(c: Covariant<'long>,
    |         ------ ----- lifetime `'long` defined here
    |         |
    |         lifetime `'short` defined here
 ...
 LL |     let _: Covariant<'short> = c; //~ ERROR E0623
-   |         ^ type annotation requires that `'short` must outlive `'long`
+   |            ^^^^^^^^^^^^^^^^^ type annotation requires that `'short` must outlive `'long`
 
 error: aborting due to previous error
 

src/test/ui/regions/regions-variance-invariant-use-contravariant.nll.stderr

@@ -1,13 +1,13 @@
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-variance-invariant-use-contravariant.rs:30:9
+  --> $DIR/regions-variance-invariant-use-contravariant.rs:30:12
    |
 LL | fn use_<'short,'long>(c: Invariant<'long>,
    |         ------ ----- lifetime `'long` defined here
    |         |
    |         lifetime `'short` defined here
 ...
 LL |     let _: Invariant<'short> = c; //~ ERROR E0623
-   |         ^ type annotation requires that `'short` must outlive `'long`
+   |            ^^^^^^^^^^^^^^^^^ type annotation requires that `'short` must outlive `'long`
 
 error: aborting due to previous error
 

src/test/ui/regions/regions-variance-invariant-use-covariant.nll.stderr

@@ -1,11 +1,11 @@
 error: unsatisfied lifetime constraints
-  --> $DIR/regions-variance-invariant-use-covariant.rs:27:9
+  --> $DIR/regions-variance-invariant-use-covariant.rs:27:12
    |
 LL | fn use_<'b>(c: Invariant<'b>) {
    |         -- lifetime `'b` defined here
 ...
 LL |     let _: Invariant<'static> = c; //~ ERROR mismatched types
-   |         ^ type annotation requires that `'b` must outlive `'static`
+   |            ^^^^^^^^^^^^^^^^^^ type annotation requires that `'b` must outlive `'static`
 
 error: aborting due to previous error
 

src/test/ui/try-block/try-block-bad-lifetime.stderr

@@ -2,7 +2,7 @@ error[E0597]: `my_string` does not live long enough
   --> $DIR/try-block-bad-lifetime.rs:25:33
    |
 LL |         let result: Result<(), &str> = try {
-   |             ------ borrow later used here
+   |             ------ borrow later stored here
 LL |             let my_string = String::from("");
 LL |             let my_str: & str = & my_string;
    |                                 ^^^^^^^^^^^ borrowed value does not live long enough