Suggest removing .unwrap() or .expect() if followed by a failed `…

…?` operator

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

@@ -374,6 +374,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
 
                         self.suggest_floating_point_literal(&obligation, &mut err, leaf_trait_ref);
                         self.suggest_dereferencing_index(&obligation, &mut err, leaf_trait_predicate);
+                        suggested |= self.suggest_remove_unwrap(&obligation, &mut err, leaf_trait_predicate);
                         suggested |= self.suggest_dereferences(&obligation, &mut err, leaf_trait_predicate);
                         suggested |= self.suggest_fn_call(&obligation, &mut err, leaf_trait_predicate);
                         let impl_candidates = self.find_similar_impl_candidates(leaf_trait_predicate);

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

@@ -1576,6 +1576,55 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         false
     }
 
+    /// When a failed try operator follows an `unwrap()` or `expect()`, suggest removing it
+    fn suggest_remove_unwrap(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+        err: &mut Diag<'_>,
+        trait_pred: ty::PolyTraitPredicate<'tcx>,
+    ) -> bool {
+        if !matches!(obligation.cause.code(), ObligationCauseCode::QuestionMark) {
+            return false;
+        }
+
+        let Some(body) = self.tcx.hir().maybe_body_owned_by(obligation.cause.body_id) else {
+            return false;
+        };
+
+        let mut expr_finder = super::FindExprBySpan::new(obligation.cause.span, self.tcx);
+        expr_finder.visit_expr(body.value);
+
+        if let Some(expr) = expr_finder.result
+            && let Some(node) = self.tcx.hir().parent_iter(expr.hir_id).nth(2)
+            && let hir::Node::Expr(expr) = node.1
+            && let hir::ExprKind::Match(expr, _, _) = expr.kind
+            && let hir::ExprKind::Call(_, args) = expr.kind
+            && let Some(expr) = args.get(0)
+            && let hir::ExprKind::MethodCall(pathsegment, receiver, _, span) = expr.kind
+            && let Some(typeck_results) = &self.typeck_results
+            && let receiver_ty = typeck_results.expr_ty_adjusted(receiver)
+            && let ty::Adt(adt, _) = receiver_ty.kind()
+            && (self.tcx.is_diagnostic_item(sym::Option, adt.did())
+                || self.tcx.is_diagnostic_item(sym::Result, adt.did()))
+            && (pathsegment.ident.name == sym::unwrap || pathsegment.ident.name == sym::expect)
+            && self.predicate_may_hold(&self.mk_trait_obligation_with_new_self_ty(
+                obligation.param_env,
+                trait_pred.map_bound(|trait_pred| (trait_pred, receiver_ty)),
+            ))
+        {
+            err.span_suggestion_verbose(
+                receiver.span.shrink_to_hi().to(span),
+                format!("remove the `.{}()`", pathsegment.ident.name),
+                "",
+                Applicability::MaybeIncorrect,
+            );
+
+            return true;
+        }
+
+        false
+    }
+
     fn suggest_remove_await(&self, obligation: &PredicateObligation<'tcx>, err: &mut Diag<'_>) {
         let hir = self.tcx.hir();
         if let ObligationCauseCode::AwaitableExpr(hir_id) = obligation.cause.code().peel_derives()

tests/ui/try-trait/try-after-unwrap-issue-127345.rs

@@ -0,0 +1,62 @@
+fn foo() -> Option<usize> {
+    let x = Some(42).expect("moop")?;
+    //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+    //~| HELP the trait `Try` is not implemented for `{integer}`
+    //~| HELP remove the `.expect()`
+    let x = Some(42).unwrap()?;
+    //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+    //~| HELP the trait `Try` is not implemented for `{integer}`
+    //~| HELP remove the `.unwrap()`
+    x
+}
+
+fn bar() -> Option<usize> {
+    foo().or(Some(43)).unwrap()?
+    //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+    //~| HELP the trait `Try` is not implemented for `usize`
+    //~| HELP remove the `.unwrap()`
+}
+
+fn baz() -> Result<usize, ()> {
+    Ok(44).unwrap()?
+    //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+    //~| HELP the trait `Try` is not implemented for `{integer}`
+    //~| HELP remove the `.unwrap()`
+}
+
+fn baz2() -> Result<String, ()> {
+    Ok(44).unwrap()?
+    //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+    //~| HELP the trait `Try` is not implemented for `{integer}`
+    //~| HELP remove the `.unwrap()`
+}
+
+fn baz3() -> Option<usize> {
+    Ok(44).unwrap()?
+    //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+    //~| HELP the trait `Try` is not implemented for `{integer}`
+    //~| HELP remove the `.unwrap()`
+}
+
+fn baz4() {
+    Ok(44).unwrap()?
+    //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+    //~| HELP the trait `Try` is not implemented for `{integer}`
+    //~| HELP remove the `.unwrap()`
+    //~| ERROR the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
+    //~| HELP the trait `FromResidual<_>` is not implemented for `()`
+}
+
+struct FakeUnwrappable;
+
+impl FakeUnwrappable {
+    fn unwrap(self) -> () {}
+}
+
+fn qux() -> Option<usize> {
+    FakeUnwrappable.unwrap()?
+    //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+    //~| HELP the trait `Try` is not implemented for `()`
+}
+
+fn main() {}

tests/ui/try-trait/try-after-unwrap-issue-127345.stderr

@@ -0,0 +1,112 @@
+error[E0277]: the `?` operator can only be applied to values that implement `Try`
+  --> $DIR/try-after-unwrap-issue-127345.rs:2:13
+   |
+LL |     let x = Some(42).expect("moop")?;
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `{integer}`
+   |
+   = help: the trait `Try` is not implemented for `{integer}`
+help: remove the `.expect()`
+   |
+LL -     let x = Some(42).expect("moop")?;
+LL +     let x = Some(42)?;
+   |
+
+error[E0277]: the `?` operator can only be applied to values that implement `Try`
+  --> $DIR/try-after-unwrap-issue-127345.rs:6:13
+   |
+LL |     let x = Some(42).unwrap()?;
+   |             ^^^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `{integer}`
+   |
+   = help: the trait `Try` is not implemented for `{integer}`
+help: remove the `.unwrap()`
+   |
+LL -     let x = Some(42).unwrap()?;
+LL +     let x = Some(42)?;
+   |
+
+error[E0277]: the `?` operator can only be applied to values that implement `Try`
+  --> $DIR/try-after-unwrap-issue-127345.rs:14:5
+   |
+LL |     foo().or(Some(43)).unwrap()?
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `usize`
+   |
+   = help: the trait `Try` is not implemented for `usize`
+help: remove the `.unwrap()`
+   |
+LL -     foo().or(Some(43)).unwrap()?
+LL +     foo().or(Some(43))?
+   |
+
+error[E0277]: the `?` operator can only be applied to values that implement `Try`
+  --> $DIR/try-after-unwrap-issue-127345.rs:21:5
+   |
+LL |     Ok(44).unwrap()?
+   |     ^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `{integer}`
+   |
+   = help: the trait `Try` is not implemented for `{integer}`
+help: remove the `.unwrap()`
+   |
+LL -     Ok(44).unwrap()?
+LL +     Ok(44)?
+   |
+
+error[E0277]: the `?` operator can only be applied to values that implement `Try`
+  --> $DIR/try-after-unwrap-issue-127345.rs:28:5
+   |
+LL |     Ok(44).unwrap()?
+   |     ^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `{integer}`
+   |
+   = help: the trait `Try` is not implemented for `{integer}`
+help: remove the `.unwrap()`
+   |
+LL -     Ok(44).unwrap()?
+LL +     Ok(44)?
+   |
+
+error[E0277]: the `?` operator can only be applied to values that implement `Try`
+  --> $DIR/try-after-unwrap-issue-127345.rs:35:5
+   |
+LL |     Ok(44).unwrap()?
+   |     ^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `{integer}`
+   |
+   = help: the trait `Try` is not implemented for `{integer}`
+help: remove the `.unwrap()`
+   |
+LL -     Ok(44).unwrap()?
+LL +     Ok(44)?
+   |
+
+error[E0277]: the `?` operator can only be applied to values that implement `Try`
+  --> $DIR/try-after-unwrap-issue-127345.rs:42:5
+   |
+LL |     Ok(44).unwrap()?
+   |     ^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `{integer}`
+   |
+   = help: the trait `Try` is not implemented for `{integer}`
+help: remove the `.unwrap()`
+   |
+LL -     Ok(44).unwrap()?
+LL +     Ok(44)?
+   |
+
+error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
+  --> $DIR/try-after-unwrap-issue-127345.rs:42:20
+   |
+LL | fn baz4() {
+   | --------- this function should return `Result` or `Option` to accept `?`
+LL |     Ok(44).unwrap()?
+   |                    ^ cannot use the `?` operator in a function that returns `()`
+   |
+   = help: the trait `FromResidual<_>` is not implemented for `()`
+
+error[E0277]: the `?` operator can only be applied to values that implement `Try`
+  --> $DIR/try-after-unwrap-issue-127345.rs:57:5
+   |
+LL |     FakeUnwrappable.unwrap()?
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `()`
+   |
+   = help: the trait `Try` is not implemented for `()`
+
+error: aborting due to 9 previous errors
+
+For more information about this error, try `rustc --explain E0277`.