Rollup merge of #153888 - MaximilianAzendorf:issue-153583, r=Kivooeo

Avoid stack overflow in FindExprBySpan

Fixes rust-lang/rust#153583.

Deeply nested `?` desugarings can build a very deep HIR expression spine.
When `FindExprBySpan` walks that expression during error reporting, the
recursive `visit_expr` traversal can overflow the stack before rustc emits the
actual diagnostic.

This wraps the recursive expression walk in `ensure_sufficient_stack`, which
lets the compiler report the expected E0277 instead of crashing.

Added a UI regression test for a deeply nested `?` chain.

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

@@ -8,6 +8,7 @@
 use std::{fmt, iter};
 
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
+use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_data_structures::unord::UnordSet;
 use rustc_errors::{Applicability, Diag, E0038, E0276, MultiSpan, struct_span_code_err};
 use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
@@ -74,18 +75,20 @@ fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
     }
 
     fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
-        if self.span == ex.span {
-            self.result = Some(ex);
-        } else {
-            if let hir::ExprKind::Closure(..) = ex.kind
-                && self.include_closures
-                && let closure_header_sp = self.span.with_hi(ex.span.hi())
-                && closure_header_sp == ex.span
-            {
+        ensure_sufficient_stack(|| {
+            if self.span == ex.span {
                 self.result = Some(ex);
+            } else {
+                if let hir::ExprKind::Closure(..) = ex.kind
+                    && self.include_closures
+                    && let closure_header_sp = self.span.with_hi(ex.span.hi())
+                    && closure_header_sp == ex.span
+                {
+                    self.result = Some(ex);
+                }
+                hir::intravisit::walk_expr(self, ex);
             }
-            hir::intravisit::walk_expr(self, ex);
-        }
+        });
     }
 
     fn visit_ty(&mut self, ty: &'v hir::Ty<'v, AmbigArg>) {

tests/ui/try-trait/deep-try-chain-issue-153583.rs

@@ -0,0 +1,8 @@
+// Regression test for #153583: deeply nested `?` operators should not overflow
+// the error-reporting visitor.
+// ignore-tidy-linelength
+
+fn main() -> Result<(), ()> {
+    0????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????; //~ ERROR the `?` operator can only be applied to values that implement `Try`
+    Ok(())
+}

tests/ui/try-trait/deep-try-chain-issue-153583.stderr

@@ -0,0 +1,11 @@
+error[E0277]: the `?` operator can only be applied to values that implement `Try`
+  --> $DIR/deep-try-chain-issue-153583.rs:6:5
+   |
+LL |     0???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????...
+   |     ^^ the `?` operator cannot be applied to type `{integer}`
+   |
+   = help: the nightly-only, unstable trait `Try` is not implemented for `{integer}`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.