Modify find_expr from Span to better account for closures

Start pointing to where bindings where declared when they are captured in closures:

```
error[E0597]: `x` does not live long enough
  --> $DIR/suggest-return-closure.rs:23:9
   |
LL |     let x = String::new();
   |         - binding `x` declared here
...
LL |     |c| {
   |     --- value captured here
LL |         x.push(c);
   |         ^ borrowed value does not live long enough
...
LL | }
   | -- borrow later used here
   | |
   | `x` dropped here while still borrowed
```

Suggest cloning in more cases involving closures:

```
error[E0507]: cannot move out of `foo` in pattern guard
  --> $DIR/issue-27282-move-ref-mut-into-guard.rs:11:19
   |
LL |             if { (|| { let mut bar = foo; bar.take() })(); false } => {},
   |                   ^^                 --- move occurs because `foo` has type `&mut Option<&i32>`, which does not implement the `Copy` trait
   |                   |
   |                   `foo` is moved here
   |
   = note: variables bound in patterns cannot be moved from until after the end of the pattern guard
help: consider cloning the value if the performance cost is acceptable
   |
LL |             if { (|| { let mut bar = foo.clone(); bar.take() })(); false } => {},
   |                                         ++++++++
```

Author: estebank

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2017,7 +2017,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
     pub(crate) fn find_expr(&self, span: Span) -> Option<&hir::Expr<'_>> {
         let tcx = self.infcx.tcx;
         let body_id = tcx.hir_node(self.mir_hir_id()).body_id()?;
-        let mut expr_finder = FindExprBySpan::new(span);
+        let mut expr_finder = FindExprBySpan::new(span, tcx);
         expr_finder.visit_expr(tcx.hir().body(body_id).value);
         expr_finder.result
     }
@@ -2051,14 +2051,14 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             };
 
             let mut expr_finder =
-                FindExprBySpan::new(self.body.local_decls[*index1].source_info.span);
+                FindExprBySpan::new(self.body.local_decls[*index1].source_info.span, tcx);
             expr_finder.visit_expr(hir.body(body_id).value);
             let Some(index1) = expr_finder.result else {
                 note_default_suggestion();
                 return;
             };
 
-            expr_finder = FindExprBySpan::new(self.body.local_decls[*index2].source_info.span);
+            expr_finder = FindExprBySpan::new(self.body.local_decls[*index2].source_info.span, tcx);
             expr_finder.visit_expr(hir.body(body_id).value);
             let Some(index2) = expr_finder.result else {
                 note_default_suggestion();

compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -76,7 +76,7 @@ impl<'tcx> BorrowExplanation<'tcx> {
                 && let Some(body_id) = node.body_id()
             {
                 let body = tcx.hir().body(body_id);
-                let mut expr_finder = FindExprBySpan::new(span);
+                let mut expr_finder = FindExprBySpan::new(span, tcx);
                 expr_finder.visit_expr(body.value);
                 if let Some(mut expr) = expr_finder.result {
                     while let hir::ExprKind::AddrOf(_, _, inner)

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -50,15 +50,22 @@ pub struct FindExprBySpan<'hir> {
     pub span: Span,
     pub result: Option<&'hir hir::Expr<'hir>>,
     pub ty_result: Option<&'hir hir::Ty<'hir>>,
+    pub tcx: TyCtxt<'hir>,
 }
 
 impl<'hir> FindExprBySpan<'hir> {
-    pub fn new(span: Span) -> Self {
-        Self { span, result: None, ty_result: None }
+    pub fn new(span: Span, tcx: TyCtxt<'hir>) -> Self {
+        Self { span, result: None, ty_result: None, tcx }
     }
 }
 
 impl<'v> Visitor<'v> for FindExprBySpan<'v> {
+    type NestedFilter = rustc_middle::hir::nested_filter::OnlyBodies;
+
+    fn nested_visit_map(&mut self) -> Self::Map {
+        self.tcx.hir()
+    }
+
     fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
         if self.span == ex.span {
             self.result = Some(ex);

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -903,7 +903,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             // Remove all the desugaring and macro contexts.
             span.remove_mark();
         }
-        let mut expr_finder = FindExprBySpan::new(span);
+        let mut expr_finder = FindExprBySpan::new(span, self.tcx);
         let Some(body_id) = self.tcx.hir().maybe_body_owned_by(obligation.cause.body_id) else {
             return;
         };
@@ -1369,7 +1369,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             return false;
                         };
                         let body = self.tcx.hir().body(body_id);
-                        let mut expr_finder = FindExprBySpan::new(span);
+                        let mut expr_finder = FindExprBySpan::new(span, self.tcx);
                         expr_finder.visit_expr(body.value);
                         let Some(expr) = expr_finder.result else {
                             return false;
@@ -1471,7 +1471,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             // Remove all the hir desugaring contexts while maintaining the macro contexts.
             span.remove_mark();
         }
-        let mut expr_finder = super::FindExprBySpan::new(span);
+        let mut expr_finder = super::FindExprBySpan::new(span, self.tcx);
         let Some(body_id) = self.tcx.hir().maybe_body_owned_by(obligation.cause.body_id) else {
             return false;
         };

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -2451,7 +2451,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     && let Some(body_id) =
                         self.tcx.hir().maybe_body_owned_by(obligation.cause.body_id)
                 {
-                    let mut expr_finder = FindExprBySpan::new(span);
+                    let mut expr_finder = FindExprBySpan::new(span, self.tcx);
                     expr_finder.visit_expr(self.tcx.hir().body(body_id).value);
 
                     if let Some(hir::Expr {

tests/ui/coroutine/borrowing.stderr

@@ -4,6 +4,7 @@ error[E0597]: `a` does not live long enough
 LL |     let _b = {
    |         -- borrow later stored here
 LL |         let a = 3;
+   |             - binding `a` declared here
 LL |         Pin::new(&mut || yield &a).resume(())
    |                       --        ^ borrowed value does not live long enough
    |                       |
@@ -18,6 +19,7 @@ error[E0597]: `a` does not live long enough
 LL |     let _b = {
    |         -- borrow later stored here
 LL |         let a = 3;
+   |             - binding `a` declared here
 LL |         || {
    |         -- value captured here by coroutine
 LL |             yield &a

tests/ui/coroutine/dropck.stderr

@@ -18,6 +18,9 @@ LL | }
 error[E0597]: `ref_` does not live long enough
   --> $DIR/dropck.rs:15:18
    |
+LL |     let ref_ = Box::leak(Box::new(Some(cell.borrow_mut())));
+   |         ---- binding `ref_` declared here
+...
 LL |     gen = || {
    |           -- value captured here by coroutine
 LL |         // but the coroutine can use it to drop a `Ref<'a, i32>`.

tests/ui/fn/suggest-return-closure.rs

@@ -18,6 +18,7 @@ fn fn_mut() -> _ {
     //~| NOTE for more information on `Fn` traits and closure types
     let x = String::new();
     //~^ HELP: consider changing this to be mutable
+    //~| NOTE binding `x` declared here
     |c| { //~ NOTE: value captured here
         x.push(c);
         //~^ ERROR: does not live long enough

tests/ui/fn/suggest-return-closure.stderr

@@ -21,7 +21,7 @@ LL | fn fn_mut() -> _ {
    = note: for more information on `Fn` traits and closure types, see https://doc.rust-lang.org/book/ch13-01-closures.html
 
 error[E0121]: the placeholder `_` is not allowed within types on item signatures for return types
-  --> $DIR/suggest-return-closure.rs:31:13
+  --> $DIR/suggest-return-closure.rs:32:13
    |
 LL | fn fun() -> _ {
    |             ^
@@ -32,7 +32,7 @@ LL | fn fun() -> _ {
    = note: for more information on `Fn` traits and closure types, see https://doc.rust-lang.org/book/ch13-01-closures.html
 
 error[E0596]: cannot borrow `x` as mutable, as it is not declared as mutable
-  --> $DIR/suggest-return-closure.rs:22:9
+  --> $DIR/suggest-return-closure.rs:23:9
    |
 LL |     let x = String::new();
    |         - help: consider changing this to be mutable: `mut x`
@@ -41,8 +41,11 @@ LL |         x.push(c);
    |         ^ cannot borrow as mutable
 
 error[E0597]: `x` does not live long enough
-  --> $DIR/suggest-return-closure.rs:22:9
+  --> $DIR/suggest-return-closure.rs:23:9
    |
+LL |     let x = String::new();
+   |         - binding `x` declared here
+...
 LL |     |c| {
    |     --- value captured here
 LL |         x.push(c);

tests/ui/nll/closure-borrow-spans.stderr

@@ -25,6 +25,8 @@ LL |     f.use_ref();
 error[E0597]: `x` does not live long enough
   --> $DIR/closure-borrow-spans.rs:19:16
    |
+LL |         let x = 1;
+   |             - binding `x` declared here
 LL |         f = || x;
    |             -- ^ borrowed value does not live long enough
    |             |
@@ -85,6 +87,8 @@ LL |     f.use_ref();
 error[E0597]: `x` does not live long enough
   --> $DIR/closure-borrow-spans.rs:52:16
    |
+LL |         let mut x = 1;
+   |             ----- binding `x` declared here
 LL |         f = || x = 0;
    |             -- ^ borrowed value does not live long enough
    |             |
@@ -145,6 +149,8 @@ LL |     f.use_ref();
 error[E0597]: `x` does not live long enough
   --> $DIR/closure-borrow-spans.rs:86:16
    |
+LL |         let x = &mut z;
+   |             - binding `x` declared here
 LL |         f = || *x = 0;
    |             -- ^^ borrowed value does not live long enough
    |             |