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.

Author: matthewjasper

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