Rollup merge of #58204 - estebank:impl-trait-semi, r=zackmdavis
On return type `impl Trait` for block with no expr point at last semi Partial solution, doesn't actually validate that the last statement in the function body can satisfy the trait bound, but it's a good incremental improvement over the status quo. ``` error[E0277]: the trait bound `(): Bar` is not satisfied --> $DIR/impl-trait-return-trailing-semicolon.rs:3:13 | LL | fn foo() -> impl Bar { | ^^^^^^^^ the trait `Bar` is not implemented for `()` LL | 5; | - consider removing this semicolon | = note: the return type of a function must have a statically known size ``` Partially addresses #54771.
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commit
479756802a
@ -599,11 +599,12 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
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}
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}
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pub fn report_selection_error(&self,
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obligation: &PredicateObligation<'tcx>,
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error: &SelectionError<'tcx>,
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fallback_has_occurred: bool)
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{
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pub fn report_selection_error(
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&self,
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obligation: &PredicateObligation<'tcx>,
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error: &SelectionError<'tcx>,
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fallback_has_occurred: bool,
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) {
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let span = obligation.cause.span;
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let mut err = match *error {
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@ -673,6 +674,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
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self.suggest_borrow_on_unsized_slice(&obligation.cause.code, &mut err);
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self.suggest_remove_reference(&obligation, &mut err, &trait_ref);
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self.suggest_semicolon_removal(&obligation, &mut err, span, &trait_ref);
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// Try to report a help message
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if !trait_ref.has_infer_types() &&
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@ -901,9 +903,11 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
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/// When encountering an assignment of an unsized trait, like `let x = ""[..];`, provide a
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/// suggestion to borrow the initializer in order to use have a slice instead.
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fn suggest_borrow_on_unsized_slice(&self,
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code: &ObligationCauseCode<'tcx>,
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err: &mut DiagnosticBuilder<'tcx>) {
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fn suggest_borrow_on_unsized_slice(
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&self,
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code: &ObligationCauseCode<'tcx>,
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err: &mut DiagnosticBuilder<'tcx>,
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) {
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if let &ObligationCauseCode::VariableType(node_id) = code {
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let parent_node = self.tcx.hir().get_parent_node(node_id);
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if let Some(Node::Local(ref local)) = self.tcx.hir().find(parent_node) {
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@ -925,10 +929,12 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
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/// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`,
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/// suggest removing these references until we reach a type that implements the trait.
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fn suggest_remove_reference(&self,
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obligation: &PredicateObligation<'tcx>,
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err: &mut DiagnosticBuilder<'tcx>,
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trait_ref: &ty::Binder<ty::TraitRef<'tcx>>) {
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fn suggest_remove_reference(
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&self,
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obligation: &PredicateObligation<'tcx>,
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err: &mut DiagnosticBuilder<'tcx>,
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trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
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) {
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let trait_ref = trait_ref.skip_binder();
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let span = obligation.cause.span;
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@ -970,6 +976,40 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
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}
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}
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fn suggest_semicolon_removal(
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&self,
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obligation: &PredicateObligation<'tcx>,
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err: &mut DiagnosticBuilder<'tcx>,
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span: Span,
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trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
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) {
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let hir = self.tcx.hir();
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let parent_node = hir.get_parent_node(
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hir.hir_to_node_id(obligation.cause.body_id),
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);
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let node = hir.find(parent_node);
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if let Some(hir::Node::Item(hir::Item {
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node: hir::ItemKind::Fn(decl, _, _, body_id),
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..
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})) = node {
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let body = hir.body(*body_id);
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if let hir::ExprKind::Block(blk, _) = &body.value.node {
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if decl.output.span().overlaps(span) && blk.expr.is_none() &&
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"()" == &trait_ref.self_ty().to_string()
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{
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// FIXME(estebank): When encountering a method with a trait
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// bound not satisfied in the return type with a body that has
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// no return, suggest removal of semicolon on last statement.
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// Once that is added, close #54771.
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if let Some(ref stmt) = blk.stmts.last() {
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let sp = self.tcx.sess.source_map().end_point(stmt.span);
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err.span_label(sp, "consider removing this semicolon");
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}
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}
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}
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}
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}
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/// Given some node representing a fn-like thing in the HIR map,
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/// returns a span and `ArgKind` information that describes the
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/// arguments it expects. This can be supplied to
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@ -0,0 +1,7 @@
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trait Bar {}
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impl Bar for u8 {}
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fn foo() -> impl Bar {
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5; //~^ ERROR the trait bound `(): Bar` is not satisfied
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}
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fn main() {}
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@ -0,0 +1,13 @@
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error[E0277]: the trait bound `(): Bar` is not satisfied
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--> $DIR/impl-trait-return-trailing-semicolon.rs:3:13
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LL | fn foo() -> impl Bar {
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| ^^^^^^^^ the trait `Bar` is not implemented for `()`
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LL | 5; //~^ ERROR the trait bound `(): Bar` is not satisfied
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| - consider removing this semicolon
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= note: the return type of a function must have a statically known size
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error: aborting due to previous error
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For more information about this error, try `rustc --explain E0277`.
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