From 34f4f3da4f3e2ac8fa086c4d3a3c89d49d23a263 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Esteban=20K=C3=BCber?= Date: Tue, 23 Jan 2024 04:42:26 +0000 Subject: [PATCH] Suggest boxing both arms of if expr if that solves divergent arms involving `impl Trait` When encountering the following ```rust // run-rustfix trait Trait {} struct Struct; impl Trait for Struct {} fn foo() -> Box { Box::new(Struct) } fn bar() -> impl Trait { Struct } fn main() { let _ = if true { Struct } else { foo() //~ ERROR E0308 }; let _ = if true { foo() } else { Struct //~ ERROR E0308 }; let _ = if true { Struct } else { bar() // impl Trait }; let _ = if true { bar() // impl Trait } else { Struct }; } ``` suggest boxing both arms ```rust let _ = if true { Box::new(Struct) as Box } else { Box::new(bar()) }; let _ = if true { Box::new(bar()) as Box } else { Box::new(Struct) }; ``` --- .../infer/error_reporting/note_and_explain.rs | 86 +++++++++++++++---- ...uggest-box-on-divergent-if-else-arms.fixed | 13 +++ .../suggest-box-on-divergent-if-else-arms.rs | 13 +++ ...ggest-box-on-divergent-if-else-arms.stderr | 56 +++++++++++- 4 files changed, 149 insertions(+), 19 deletions(-) diff --git a/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs b/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs index a0dfaf33a6e..01cd3c57925 100644 --- a/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs +++ b/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs @@ -294,8 +294,9 @@ impl Trait for X { ); } } - (ty::Alias(ty::Opaque, alias), _) | (_, ty::Alias(ty::Opaque, alias)) - if alias.def_id.is_local() + (_, ty::Alias(ty::Opaque, opaque_ty)) + | (ty::Alias(ty::Opaque, opaque_ty), _) => { + if opaque_ty.def_id.is_local() && matches!( tcx.def_kind(body_owner_def_id), DefKind::Fn @@ -303,21 +304,74 @@ impl Trait for X { | DefKind::Const | DefKind::AssocFn | DefKind::AssocConst - ) => - { - if tcx.is_type_alias_impl_trait(alias.def_id) { - if !tcx + ) + && tcx.is_type_alias_impl_trait(opaque_ty.def_id) + && !tcx .opaque_types_defined_by(body_owner_def_id.expect_local()) - .contains(&alias.def_id.expect_local()) - { - let sp = tcx - .def_ident_span(body_owner_def_id) - .unwrap_or_else(|| tcx.def_span(body_owner_def_id)); - diag.span_note( - sp, - "\ - this item must have the opaque type in its signature \ - in order to be able to register hidden types", + .contains(&opaque_ty.def_id.expect_local()) + { + let sp = tcx + .def_ident_span(body_owner_def_id) + .unwrap_or_else(|| tcx.def_span(body_owner_def_id)); + diag.span_note( + sp, + "this item must have the opaque type in its signature in order to \ + be able to register hidden types", + ); + } + // If two if arms can be coerced to a trait object, provide a structured + // suggestion. + let ObligationCauseCode::IfExpression(cause) = cause.code() else { + return; + }; + let hir::Node::Block(blk) = self.tcx.hir_node(cause.then_id) else { + return; + }; + let Some(then) = blk.expr else { + return; + }; + let hir::Node::Block(blk) = self.tcx.hir_node(cause.else_id) else { + return; + }; + let Some(else_) = blk.expr else { + return; + }; + let expected = match values.found.kind() { + ty::Alias(..) => values.expected, + _ => values.found, + }; + let preds = tcx.explicit_item_bounds(opaque_ty.def_id); + for (pred, _span) in preds.skip_binder() { + let ty::ClauseKind::Trait(trait_predicate) = pred.kind().skip_binder() + else { + continue; + }; + if trait_predicate.polarity != ty::ImplPolarity::Positive { + continue; + } + let def_id = trait_predicate.def_id(); + let mut impl_def_ids = vec![]; + tcx.for_each_relevant_impl(def_id, expected, |did| { + impl_def_ids.push(did) + }); + if let [_] = &impl_def_ids[..] { + let trait_name = tcx.item_name(def_id); + diag.multipart_suggestion( + format!( + "`{expected}` implements `{trait_name}` so you can box \ + both arms and coerce to the trait object \ + `Box`", + ), + vec![ + (then.span.shrink_to_lo(), "Box::new(".to_string()), + ( + then.span.shrink_to_hi(), + format!(") as Box", tcx.def_path_str(def_id)), + ), + (else_.span.shrink_to_lo(), "Box::new(".to_string()), + (else_.span.shrink_to_hi(), ")".to_string()), + ], + MachineApplicable, ); } } diff --git a/tests/ui/typeck/suggest-box-on-divergent-if-else-arms.fixed b/tests/ui/typeck/suggest-box-on-divergent-if-else-arms.fixed index dfdf6b24bf7..9ce46bc1a65 100644 --- a/tests/ui/typeck/suggest-box-on-divergent-if-else-arms.fixed +++ b/tests/ui/typeck/suggest-box-on-divergent-if-else-arms.fixed @@ -5,6 +5,9 @@ impl Trait for Struct {} fn foo() -> Box { Box::new(Struct) } +fn bar() -> impl Trait { + Struct +} fn main() { let _ = if true { Box::new(Struct) @@ -16,4 +19,14 @@ fn main() { } else { Box::new(Struct) //~ ERROR E0308 }; + let _ = if true { + Box::new(Struct) as Box + } else { + Box::new(bar()) //~ ERROR E0308 + }; + let _ = if true { + Box::new(bar()) as Box + } else { + Box::new(Struct) //~ ERROR E0308 + }; } diff --git a/tests/ui/typeck/suggest-box-on-divergent-if-else-arms.rs b/tests/ui/typeck/suggest-box-on-divergent-if-else-arms.rs index e138ad9b336..7f65a3bb59d 100644 --- a/tests/ui/typeck/suggest-box-on-divergent-if-else-arms.rs +++ b/tests/ui/typeck/suggest-box-on-divergent-if-else-arms.rs @@ -5,6 +5,9 @@ impl Trait for Struct {} fn foo() -> Box { Box::new(Struct) } +fn bar() -> impl Trait { + Struct +} fn main() { let _ = if true { Struct @@ -16,4 +19,14 @@ fn main() { } else { Struct //~ ERROR E0308 }; + let _ = if true { + Struct + } else { + bar() //~ ERROR E0308 + }; + let _ = if true { + bar() + } else { + Struct //~ ERROR E0308 + }; } diff --git a/tests/ui/typeck/suggest-box-on-divergent-if-else-arms.stderr b/tests/ui/typeck/suggest-box-on-divergent-if-else-arms.stderr index 98c9d880f97..c58bf60e7d6 100644 --- a/tests/ui/typeck/suggest-box-on-divergent-if-else-arms.stderr +++ b/tests/ui/typeck/suggest-box-on-divergent-if-else-arms.stderr @@ -1,5 +1,5 @@ error[E0308]: `if` and `else` have incompatible types - --> $DIR/suggest-box-on-divergent-if-else-arms.rs:12:9 + --> $DIR/suggest-box-on-divergent-if-else-arms.rs:15:9 | LL | let _ = if true { | _____________- @@ -19,7 +19,7 @@ LL | Box::new(Struct) | +++++++++ + error[E0308]: `if` and `else` have incompatible types - --> $DIR/suggest-box-on-divergent-if-else-arms.rs:17:9 + --> $DIR/suggest-box-on-divergent-if-else-arms.rs:20:9 | LL | let _ = if true { | _____________- @@ -39,6 +39,56 @@ help: store this in the heap by calling `Box::new` LL | Box::new(Struct) | +++++++++ + -error: aborting due to 2 previous errors +error[E0308]: `if` and `else` have incompatible types + --> $DIR/suggest-box-on-divergent-if-else-arms.rs:25:9 + | +LL | fn bar() -> impl Trait { + | ---------- the found opaque type +... +LL | let _ = if true { + | _____________- +LL | | Struct + | | ------ expected because of this +LL | | } else { +LL | | bar() + | | ^^^^^ expected `Struct`, found opaque type +LL | | }; + | |_____- `if` and `else` have incompatible types + | + = note: expected struct `Struct` + found opaque type `impl Trait` +help: `Struct` implements `Trait` so you can box both arms and coerce to the trait object `Box` + | +LL ~ Box::new(Struct) as Box +LL | } else { +LL ~ Box::new(bar()) + | + +error[E0308]: `if` and `else` have incompatible types + --> $DIR/suggest-box-on-divergent-if-else-arms.rs:30:9 + | +LL | fn bar() -> impl Trait { + | ---------- the expected opaque type +... +LL | let _ = if true { + | _____________- +LL | | bar() + | | ----- expected because of this +LL | | } else { +LL | | Struct + | | ^^^^^^ expected opaque type, found `Struct` +LL | | }; + | |_____- `if` and `else` have incompatible types + | + = note: expected opaque type `impl Trait` + found struct `Struct` +help: `Struct` implements `Trait` so you can box both arms and coerce to the trait object `Box` + | +LL ~ Box::new(bar()) as Box +LL | } else { +LL ~ Box::new(Struct) + | + +error: aborting due to 4 previous errors For more information about this error, try `rustc --explain E0308`.