Rollup merge of #89734 - estebank:issue-72312, r=nikomatsakis

Point at capture points for non-`'static` reference crossing a `yield` point

```
error[E0759]: `self` has an anonymous lifetime `'_` but it needs to satisfy a `'static` lifetime requirement
  --> $DIR/issue-72312.rs:10:24
   |
LL |     pub async fn start(&self) {
   |                        ^^^^^ this data with an anonymous lifetime `'_`...
...
LL |         require_static(async move {
   |         -------------- ...is required to live as long as `'static` here...
LL |             &self;
   |             ----- ...and is captured here
   |
note: `'static` lifetime requirement introduced by this trait bound
  --> $DIR/issue-72312.rs:2:22
   |
LL | fn require_static<T: 'static>(val: T) -> T {
   |                      ^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0759`.
```

Fix #72312.

Author: matthiaskrgr

compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs

@@ -368,6 +368,7 @@ fn try_extract_error_from_fulfill_cx<'tcx>(
                 error_region,
                 cause.clone(),
                 placeholder_region,
+                vec![],
             ),
         ),
         (Some(error_region), _) => NiceRegionError::new(

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -384,6 +384,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         sub_r,
                         sup_origin,
                         sup_r,
+                        _,
                     ) => {
                         if sub_r.is_placeholder() {
                             self.report_placeholder_failure(sub_origin, sub_r, sup_r).emit();
@@ -464,7 +465,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         errors.sort_by_key(|u| match *u {
             RegionResolutionError::ConcreteFailure(ref sro, _, _) => sro.span(),
             RegionResolutionError::GenericBoundFailure(ref sro, _, _) => sro.span(),
-            RegionResolutionError::SubSupConflict(_, ref rvo, _, _, _, _) => rvo.span(),
+            RegionResolutionError::SubSupConflict(_, ref rvo, _, _, _, _, _) => rvo.span(),
             RegionResolutionError::UpperBoundUniverseConflict(_, ref rvo, _, _, _) => rvo.span(),
         });
         errors

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mod.rs

@@ -67,7 +67,7 @@ impl<'cx, 'tcx> NiceRegionError<'cx, 'tcx> {
     pub fn regions(&self) -> Option<(Span, ty::Region<'tcx>, ty::Region<'tcx>)> {
         match (&self.error, self.regions) {
             (Some(ConcreteFailure(origin, sub, sup)), None) => Some((origin.span(), sub, sup)),
-            (Some(SubSupConflict(_, _, origin, sub, _, sup)), None) => {
+            (Some(SubSupConflict(_, _, origin, sub, _, sup, _)), None) => {
                 Some((origin.span(), sub, sup))
             }
             (None, Some((span, sub, sup))) => Some((span, sub, sup)),

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/placeholder_error.rs

@@ -34,6 +34,7 @@ impl NiceRegionError<'me, 'tcx> {
                 sub_placeholder @ ty::RePlaceholder(_),
                 _,
                 sup_placeholder @ ty::RePlaceholder(_),
+                _,
             )) => self.try_report_trait_placeholder_mismatch(
                 Some(self.tcx().mk_region(ty::ReVar(*vid))),
                 cause,
@@ -49,6 +50,7 @@ impl NiceRegionError<'me, 'tcx> {
                 sub_placeholder @ ty::RePlaceholder(_),
                 _,
                 _,
+                _,
             )) => self.try_report_trait_placeholder_mismatch(
                 Some(self.tcx().mk_region(ty::ReVar(*vid))),
                 cause,
@@ -64,6 +66,7 @@ impl NiceRegionError<'me, 'tcx> {
                 _,
                 _,
                 sup_placeholder @ ty::RePlaceholder(_),
+                _,
             )) => self.try_report_trait_placeholder_mismatch(
                 Some(self.tcx().mk_region(ty::ReVar(*vid))),
                 cause,
@@ -79,6 +82,7 @@ impl NiceRegionError<'me, 'tcx> {
                 _,
                 SubregionOrigin::Subtype(box TypeTrace { cause, values }),
                 sup_placeholder @ ty::RePlaceholder(_),
+                _,
             )) => self.try_report_trait_placeholder_mismatch(
                 Some(self.tcx().mk_region(ty::ReVar(*vid))),
                 cause,

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs

@@ -10,7 +10,8 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::{walk_ty, ErasedMap, NestedVisitorMap, Visitor};
 use rustc_hir::{self as hir, GenericBound, Item, ItemKind, Lifetime, LifetimeName, Node, TyKind};
 use rustc_middle::ty::{
-    self, AssocItemContainer, RegionKind, Ty, TyCtxt, TypeFoldable, TypeVisitor,
+    self, AssocItemContainer, RegionKind, StaticLifetimeVisitor, Ty, TyCtxt, TypeFoldable,
+    TypeVisitor,
 };
 use rustc_span::symbol::Ident;
 use rustc_span::{MultiSpan, Span};
@@ -23,16 +24,17 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
     pub(super) fn try_report_static_impl_trait(&self) -> Option<ErrorReported> {
         debug!("try_report_static_impl_trait(error={:?})", self.error);
         let tcx = self.tcx();
-        let (var_origin, sub_origin, sub_r, sup_origin, sup_r) = match self.error.as_ref()? {
+        let (var_origin, sub_origin, sub_r, sup_origin, sup_r, spans) = match self.error.as_ref()? {
             RegionResolutionError::SubSupConflict(
                 _,
                 var_origin,
                 sub_origin,
                 sub_r,
                 sup_origin,
                 sup_r,
+                spans,
             ) if **sub_r == RegionKind::ReStatic => {
-                (var_origin, sub_origin, sub_r, sup_origin, sup_r)
+                (var_origin, sub_origin, sub_r, sup_origin, sup_r, spans)
             }
             RegionResolutionError::ConcreteFailure(
                 SubregionOrigin::Subtype(box TypeTrace { cause, .. }),
@@ -74,7 +76,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
                     err.span_label(
                         cause.span,
                         &format!(
-                            "...is captured and required to live as long as `'static` here \
+                            "...is used and required to live as long as `'static` here \
                              because of an implicit lifetime bound on the {}",
                             match ctxt.assoc_item.container {
                                 AssocItemContainer::TraitContainer(id) =>
@@ -123,56 +125,101 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             param_name,
             lifetime,
         );
-        err.span_label(param.param_ty_span, &format!("this data with {}...", lifetime));
-        debug!("try_report_static_impl_trait: param_info={:?}", param);
 
-        // We try to make the output have fewer overlapping spans if possible.
-        if (sp == sup_origin.span() || !return_sp.overlaps(sup_origin.span()))
-            && sup_origin.span() != return_sp
-        {
-            // FIXME: account for `async fn` like in `async-await/issues/issue-62097.rs`
-
-            // Customize the spans and labels depending on their relative order so
-            // that split sentences flow correctly.
-            if sup_origin.span().overlaps(return_sp) && sp == sup_origin.span() {
-                // Avoid the following:
-                //
-                // error: cannot infer an appropriate lifetime
-                //   --> $DIR/must_outlive_least_region_or_bound.rs:18:50
-                //    |
-                // LL | fn foo(x: &i32) -> Box<dyn Debug> { Box::new(x) }
-                //    |           ----                      ---------^-
+        let (mention_influencer, influencer_point) =
+            if sup_origin.span().overlaps(param.param_ty_span) {
+                // Account for `async fn` like in `async-await/issues/issue-62097.rs`.
+                // The desugaring of `async `fn`s causes `sup_origin` and `param` to point at the same
+                // place (but with different `ctxt`, hence `overlaps` instead of `==` above).
                 //
-                // and instead show:
+                // This avoids the following:
                 //
-                // error: cannot infer an appropriate lifetime
-                //   --> $DIR/must_outlive_least_region_or_bound.rs:18:50
-                //    |
-                // LL | fn foo(x: &i32) -> Box<dyn Debug> { Box::new(x) }
-                //    |           ----                               ^
-                err.span_label(
-                    sup_origin.span(),
-                    "...is captured here, requiring it to live as long as `'static`",
-                );
+                // LL |     pub async fn run_dummy_fn(&self) {
+                //    |                               ^^^^^
+                //    |                               |
+                //    |                               this data with an anonymous lifetime `'_`...
+                //    |                               ...is captured here...
+                (false, sup_origin.span())
             } else {
-                err.span_label(sup_origin.span(), "...is captured here...");
-                if return_sp < sup_origin.span() {
-                    err.span_note(
-                        return_sp,
-                        "...and is required to live as long as `'static` here",
+                (!sup_origin.span().overlaps(return_sp), param.param_ty_span)
+            };
+        err.span_label(influencer_point, &format!("this data with {}...", lifetime));
+
+        debug!("try_report_static_impl_trait: param_info={:?}", param);
+
+        let mut spans = spans.clone();
+
+        if mention_influencer {
+            spans.push(sup_origin.span());
+        }
+        // We dedup the spans *ignoring* expansion context.
+        spans.sort();
+        spans.dedup_by_key(|span| (span.lo(), span.hi()));
+
+        // We try to make the output have fewer overlapping spans if possible.
+        let require_msg = if spans.is_empty() {
+            "...is used and required to live as long as `'static` here"
+        } else {
+            "...and is required to live as long as `'static` here"
+        };
+        let require_span =
+            if sup_origin.span().overlaps(return_sp) { sup_origin.span() } else { return_sp };
+
+        for span in &spans {
+            err.span_label(*span, "...is used here...");
+        }
+
+        if spans.iter().any(|sp| sp.overlaps(return_sp) || *sp > return_sp) {
+            // If any of the "captured here" labels appears on the same line or after
+            // `require_span`, we put it on a note to ensure the text flows by appearing
+            // always at the end.
+            err.span_note(require_span, require_msg);
+        } else {
+            // We don't need a note, it's already at the end, it can be shown as a `span_label`.
+            err.span_label(require_span, require_msg);
+        }
+
+        if let SubregionOrigin::RelateParamBound(_, _, Some(bound)) = sub_origin {
+            err.span_note(*bound, "`'static` lifetime requirement introduced by this bound");
+        }
+        if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = sub_origin {
+            if let ObligationCauseCode::ReturnValue(hir_id)
+            | ObligationCauseCode::BlockTailExpression(hir_id) = &cause.code
+            {
+                let parent_id = tcx.hir().get_parent_item(*hir_id);
+                if let Some(fn_decl) = tcx.hir().fn_decl_by_hir_id(parent_id) {
+                    let mut span: MultiSpan = fn_decl.output.span().into();
+                    let mut add_label = true;
+                    if let hir::FnRetTy::Return(ty) = fn_decl.output {
+                        let mut v = StaticLifetimeVisitor(vec![], tcx.hir());
+                        v.visit_ty(ty);
+                        if !v.0.is_empty() {
+                            span = v.0.clone().into();
+                            for sp in v.0 {
+                                span.push_span_label(
+                                    sp,
+                                    "`'static` requirement introduced here".to_string(),
+                                );
+                            }
+                            add_label = false;
+                        }
+                    }
+                    if add_label {
+                        span.push_span_label(
+                            fn_decl.output.span(),
+                            "requirement introduced by this return type".to_string(),
+                        );
+                    }
+                    span.push_span_label(
+                        cause.span,
+                        "because of this returned expression".to_string(),
                     );
-                } else {
-                    err.span_label(
-                        return_sp,
-                        "...and is required to live as long as `'static` here",
+                    err.span_note(
+                        span,
+                        "`'static` lifetime requirement introduced by the return type",
                     );
                 }
             }
-        } else {
-            err.span_label(
-                return_sp,
-                "...is captured and required to live as long as `'static` here",
-            );
         }
 
         let fn_returns = tcx.return_type_impl_or_dyn_traits(anon_reg_sup.def_id);

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/trait_impl_difference.rs

@@ -28,6 +28,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             _sub,
             sup_origin,
             _sup,
+            _,
         ) = error.clone()
         {
             if let (&Subtype(ref sup_trace), &Subtype(ref sub_trace)) = (&sup_origin, &sub_origin) {

compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs

@@ -19,6 +19,7 @@ use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_middle::ty::{ReEarlyBound, ReEmpty, ReErased, ReFree, ReStatic};
 use rustc_middle::ty::{ReLateBound, RePlaceholder, ReVar};
 use rustc_middle::ty::{Region, RegionVid};
+use rustc_span::Span;
 use std::fmt;
 
 /// This function performs lexical region resolution given a complete
@@ -96,6 +97,7 @@ pub enum RegionResolutionError<'tcx> {
         Region<'tcx>,
         SubregionOrigin<'tcx>,
         Region<'tcx>,
+        Vec<Span>, // All the influences on a given value that didn't meet its constraints.
     ),
 
     /// Indicates a `'b: 'a` constraint where `'a` is in a universe that
@@ -567,7 +569,30 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                     // if this rule starts to create problems we'll
                     // have to revisit this portion of the code and
                     // think hard about it. =) -- nikomatsakis
-                    self.collect_error_for_expanding_node(graph, &mut dup_vec, node_vid, errors);
+
+                    // Obtain the spans for all the places that can
+                    // influence the constraints on this value for
+                    // richer diagnostics in `static_impl_trait`.
+                    let influences: Vec<Span> = self
+                        .data
+                        .constraints
+                        .iter()
+                        .filter_map(|(constraint, origin)| match (constraint, origin) {
+                            (
+                                Constraint::VarSubVar(_, sup),
+                                SubregionOrigin::DataBorrowed(_, sp),
+                            ) if sup == &node_vid => Some(*sp),
+                            _ => None,
+                        })
+                        .collect();
+
+                    self.collect_error_for_expanding_node(
+                        graph,
+                        &mut dup_vec,
+                        node_vid,
+                        errors,
+                        influences,
+                    );
                 }
             }
         }
@@ -621,6 +646,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         dup_vec: &mut IndexVec<RegionVid, Option<RegionVid>>,
         node_idx: RegionVid,
         errors: &mut Vec<RegionResolutionError<'tcx>>,
+        influences: Vec<Span>,
     ) {
         // Errors in expanding nodes result from a lower-bound that is
         // not contained by an upper-bound.
@@ -667,13 +693,15 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                          sup: {:?}",
                         origin, node_idx, lower_bound.region, upper_bound.region
                     );
+
                     errors.push(RegionResolutionError::SubSupConflict(
                         node_idx,
                         origin,
                         lower_bound.origin.clone(),
                         lower_bound.region,
                         upper_bound.origin.clone(),
                         upper_bound.region,
+                        influences,
                     ));
                     return;
                 }

compiler/rustc_middle/src/ty/context.rs

@@ -1481,40 +1481,8 @@ impl<'tcx> TyCtxt<'tcx> {
         scope_def_id: LocalDefId,
     ) -> Vec<&'tcx hir::Ty<'tcx>> {
         let hir_id = self.hir().local_def_id_to_hir_id(scope_def_id);
-        let hir_output = match self.hir().get(hir_id) {
-            Node::Item(hir::Item {
-                kind:
-                    ItemKind::Fn(
-                        hir::FnSig {
-                            decl: hir::FnDecl { output: hir::FnRetTy::Return(ty), .. },
-                            ..
-                        },
-                        ..,
-                    ),
-                ..
-            })
-            | Node::ImplItem(hir::ImplItem {
-                kind:
-                    hir::ImplItemKind::Fn(
-                        hir::FnSig {
-                            decl: hir::FnDecl { output: hir::FnRetTy::Return(ty), .. },
-                            ..
-                        },
-                        _,
-                    ),
-                ..
-            })
-            | Node::TraitItem(hir::TraitItem {
-                kind:
-                    hir::TraitItemKind::Fn(
-                        hir::FnSig {
-                            decl: hir::FnDecl { output: hir::FnRetTy::Return(ty), .. },
-                            ..
-                        },
-                        _,
-                    ),
-                ..
-            }) => ty,
+        let hir_output = match self.hir().fn_decl_by_hir_id(hir_id) {
+            Some(hir::FnDecl { output: hir::FnRetTy::Return(ty), .. }) => ty,
             _ => return vec![],
         };