Suggest boxed trait objects in tail `match` and `if` expressions
When encountering a `match` or `if` as a tail expression where the different arms do not have the same type *and* the return type of that `fn` is an `impl Trait`, check whether those arms can implement `Trait` and if so, suggest using boxed trait objects.
This commit is contained in:
parent
c8ee33714b
commit
fd9133b9c3
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@ -617,11 +617,20 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
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ref prior_arms,
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ref prior_arms,
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last_ty,
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last_ty,
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scrut_hir_id,
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scrut_hir_id,
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suggest_box,
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arm_span,
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..
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..
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}) => match source {
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}) => match source {
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hir::MatchSource::IfLetDesugar { .. } => {
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hir::MatchSource::IfLetDesugar { .. } => {
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let msg = "`if let` arms have incompatible types";
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let msg = "`if let` arms have incompatible types";
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err.span_label(cause.span, msg);
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err.span_label(cause.span, msg);
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if let Some(ret_sp) = suggest_box {
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self.suggest_boxing_for_return_impl_trait(
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err,
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ret_sp,
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prior_arms.iter().chain(std::iter::once(&arm_span)).map(|s| *s),
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);
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}
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}
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}
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hir::MatchSource::TryDesugar => {
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hir::MatchSource::TryDesugar => {
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if let Some(ty::error::ExpectedFound { expected, .. }) = exp_found {
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if let Some(ty::error::ExpectedFound { expected, .. }) = exp_found {
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@ -675,9 +684,23 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
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Applicability::MachineApplicable,
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Applicability::MachineApplicable,
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);
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);
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}
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}
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if let Some(ret_sp) = suggest_box {
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// Get return type span and point to it.
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self.suggest_boxing_for_return_impl_trait(
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err,
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ret_sp,
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prior_arms.iter().chain(std::iter::once(&arm_span)).map(|s| *s),
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);
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}
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}
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}
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},
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},
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ObligationCauseCode::IfExpression(box IfExpressionCause { then, outer, semicolon }) => {
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ObligationCauseCode::IfExpression(box IfExpressionCause {
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then,
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else_sp,
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outer,
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semicolon,
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suggest_box,
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}) => {
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err.span_label(then, "expected because of this");
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err.span_label(then, "expected because of this");
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if let Some(sp) = outer {
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if let Some(sp) = outer {
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err.span_label(sp, "`if` and `else` have incompatible types");
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err.span_label(sp, "`if` and `else` have incompatible types");
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@ -690,11 +713,52 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
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Applicability::MachineApplicable,
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Applicability::MachineApplicable,
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);
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);
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}
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}
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if let Some(ret_sp) = suggest_box {
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self.suggest_boxing_for_return_impl_trait(
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err,
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ret_sp,
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vec![then, else_sp].into_iter(),
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);
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}
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}
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}
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_ => (),
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_ => (),
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}
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}
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}
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}
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fn suggest_boxing_for_return_impl_trait(
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&self,
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err: &mut DiagnosticBuilder<'tcx>,
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return_sp: Span,
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arm_spans: impl Iterator<Item = Span>,
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) {
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let snippet = self
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.tcx
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.sess
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.source_map()
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.span_to_snippet(return_sp)
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.unwrap_or_else(|_| "dyn Trait".to_string());
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err.span_suggestion_verbose(
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return_sp,
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"you could change the return type to be a boxed trait object",
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format!("Box<dyn {}>", &snippet[5..]),
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Applicability::MaybeIncorrect,
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);
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let sugg = arm_spans
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.flat_map(|sp| {
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vec![
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(sp.shrink_to_lo(), "Box::new(".to_string()),
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(sp.shrink_to_hi(), ")".to_string()),
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]
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.into_iter()
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})
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.collect::<Vec<_>>();
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err.multipart_suggestion(
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"if you change the return type to expect trait objects box the returned expressions",
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sugg,
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Applicability::MaybeIncorrect,
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);
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}
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/// Given that `other_ty` is the same as a type argument for `name` in `sub`, populate `value`
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/// Given that `other_ty` is the same as a type argument for `name` in `sub`, populate `value`
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/// highlighting `name` and every type argument that isn't at `pos` (which is `other_ty`), and
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/// highlighting `name` and every type argument that isn't at `pos` (which is `other_ty`), and
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/// populate `other_value` with `other_ty`.
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/// populate `other_value` with `other_ty`.
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@ -350,13 +350,16 @@ pub struct MatchExpressionArmCause<'tcx> {
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pub prior_arms: Vec<Span>,
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pub prior_arms: Vec<Span>,
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pub last_ty: Ty<'tcx>,
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pub last_ty: Ty<'tcx>,
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pub scrut_hir_id: hir::HirId,
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pub scrut_hir_id: hir::HirId,
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pub suggest_box: Option<Span>,
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}
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}
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#[derive(Clone, Debug, PartialEq, Eq, Hash)]
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#[derive(Clone, Debug, PartialEq, Eq, Hash)]
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pub struct IfExpressionCause {
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pub struct IfExpressionCause {
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pub then: Span,
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pub then: Span,
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pub else_sp: Span,
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pub outer: Option<Span>,
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pub outer: Option<Span>,
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pub semicolon: Option<Span>,
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pub semicolon: Option<Span>,
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pub suggest_box: Option<Span>,
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}
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}
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#[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
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#[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
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@ -1,12 +1,15 @@
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use crate::check::coercion::CoerceMany;
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use crate::check::coercion::CoerceMany;
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use crate::check::{Diverges, Expectation, FnCtxt, Needs};
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use crate::check::{Diverges, Expectation, FnCtxt, Needs};
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use rustc_hir as hir;
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use rustc_hir::{self as hir, ExprKind};
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use rustc_hir::ExprKind;
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use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
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use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
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use rustc_middle::ty::Ty;
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use rustc_infer::traits::Obligation;
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use rustc_middle::ty::{self, ToPredicate, Ty};
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use rustc_span::Span;
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use rustc_span::Span;
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use rustc_trait_selection::traits::ObligationCauseCode;
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use rustc_trait_selection::opaque_types::InferCtxtExt as _;
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use rustc_trait_selection::traits::{IfExpressionCause, MatchExpressionArmCause, ObligationCause};
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use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
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use rustc_trait_selection::traits::{
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IfExpressionCause, MatchExpressionArmCause, ObligationCause, ObligationCauseCode,
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};
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impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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pub fn check_match(
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pub fn check_match(
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@ -14,7 +17,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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expr: &'tcx hir::Expr<'tcx>,
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expr: &'tcx hir::Expr<'tcx>,
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scrut: &'tcx hir::Expr<'tcx>,
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scrut: &'tcx hir::Expr<'tcx>,
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arms: &'tcx [hir::Arm<'tcx>],
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arms: &'tcx [hir::Arm<'tcx>],
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expected: Expectation<'tcx>,
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orig_expected: Expectation<'tcx>,
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match_src: hir::MatchSource,
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match_src: hir::MatchSource,
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) -> Ty<'tcx> {
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) -> Ty<'tcx> {
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let tcx = self.tcx;
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let tcx = self.tcx;
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@ -22,7 +25,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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use hir::MatchSource::*;
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use hir::MatchSource::*;
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let (source_if, if_no_else, force_scrutinee_bool) = match match_src {
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let (source_if, if_no_else, force_scrutinee_bool) = match match_src {
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IfDesugar { contains_else_clause } => (true, !contains_else_clause, true),
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IfDesugar { contains_else_clause } => (true, !contains_else_clause, true),
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IfLetDesugar { contains_else_clause } => (true, !contains_else_clause, false),
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IfLetDesugar { contains_else_clause, .. } => (true, !contains_else_clause, false),
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WhileDesugar => (false, false, true),
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WhileDesugar => (false, false, true),
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_ => (false, false, false),
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_ => (false, false, false),
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};
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};
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@ -69,7 +72,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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// type in that case)
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// type in that case)
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let mut all_arms_diverge = Diverges::WarnedAlways;
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let mut all_arms_diverge = Diverges::WarnedAlways;
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let expected = expected.adjust_for_branches(self);
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let expected = orig_expected.adjust_for_branches(self);
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let mut coercion = {
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let mut coercion = {
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let coerce_first = match expected {
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let coerce_first = match expected {
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@ -112,6 +115,59 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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self.check_expr_with_expectation(&arm.body, expected)
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self.check_expr_with_expectation(&arm.body, expected)
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};
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};
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all_arms_diverge &= self.diverges.get();
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all_arms_diverge &= self.diverges.get();
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// When we have a `match` as a tail expression in a `fn` with a returned `impl Trait`
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// we check if the different arms would work with boxed trait objects instead and
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// provide a structured suggestion in that case.
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let suggest_box = match (
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orig_expected,
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self.body_id
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.owner
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.to_def_id()
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.as_local()
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.and_then(|id| self.ret_coercion_impl_trait.map(|ty| (id, ty))),
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) {
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(Expectation::ExpectHasType(expected), Some((id, ty)))
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if self.in_tail_expr && self.can_coerce(arm_ty, expected) =>
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{
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let impl_trait_ret_ty = self.infcx.instantiate_opaque_types(
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id,
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self.body_id,
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self.param_env,
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&ty,
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arm.body.span,
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);
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let mut suggest_box = !impl_trait_ret_ty.obligations.is_empty();
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for o in impl_trait_ret_ty.obligations {
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match o.predicate.skip_binders_unchecked() {
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ty::PredicateAtom::Trait(t, constness) => {
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let pred = ty::PredicateAtom::Trait(
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ty::TraitPredicate {
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trait_ref: ty::TraitRef {
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def_id: t.def_id(),
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substs: self.infcx.tcx.mk_substs_trait(arm_ty, &[]),
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},
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},
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constness,
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);
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let obl = Obligation::new(
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o.cause.clone(),
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self.param_env,
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pred.to_predicate(self.infcx.tcx),
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);
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suggest_box &= self.infcx.predicate_must_hold_modulo_regions(&obl);
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if !suggest_box {
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break;
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}
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}
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_ => {}
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}
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}
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if suggest_box { self.ret_type_span.clone() } else { None }
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}
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_ => None,
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};
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if source_if {
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if source_if {
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let then_expr = &arms[0].body;
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let then_expr = &arms[0].body;
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match (i, if_no_else) {
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match (i, if_no_else) {
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@ -119,7 +175,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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(_, true) => {} // Handled above to avoid duplicated type errors (#60254).
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(_, true) => {} // Handled above to avoid duplicated type errors (#60254).
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(_, _) => {
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(_, _) => {
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let then_ty = prior_arm_ty.unwrap();
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let then_ty = prior_arm_ty.unwrap();
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let cause = self.if_cause(expr.span, then_expr, &arm.body, then_ty, arm_ty);
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let cause = self.if_cause(
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expr.span,
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then_expr,
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&arm.body,
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then_ty,
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arm_ty,
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suggest_box,
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);
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coercion.coerce(self, &cause, &arm.body, arm_ty);
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coercion.coerce(self, &cause, &arm.body, arm_ty);
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}
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}
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}
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}
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@ -142,6 +205,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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prior_arms: other_arms.clone(),
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prior_arms: other_arms.clone(),
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last_ty: prior_arm_ty.unwrap(),
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last_ty: prior_arm_ty.unwrap(),
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scrut_hir_id: scrut.hir_id,
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scrut_hir_id: scrut.hir_id,
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suggest_box,
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}),
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}),
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),
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),
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};
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};
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@ -266,6 +330,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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else_expr: &'tcx hir::Expr<'tcx>,
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else_expr: &'tcx hir::Expr<'tcx>,
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then_ty: Ty<'tcx>,
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then_ty: Ty<'tcx>,
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else_ty: Ty<'tcx>,
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else_ty: Ty<'tcx>,
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suggest_box: Option<Span>,
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) -> ObligationCause<'tcx> {
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) -> ObligationCause<'tcx> {
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let mut outer_sp = if self.tcx.sess.source_map().is_multiline(span) {
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let mut outer_sp = if self.tcx.sess.source_map().is_multiline(span) {
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// The `if`/`else` isn't in one line in the output, include some context to make it
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// The `if`/`else` isn't in one line in the output, include some context to make it
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@ -353,8 +418,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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error_sp,
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error_sp,
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ObligationCauseCode::IfExpression(box IfExpressionCause {
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ObligationCauseCode::IfExpression(box IfExpressionCause {
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then: then_sp,
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then: then_sp,
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else_sp: error_sp,
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outer: outer_sp,
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outer: outer_sp,
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semicolon: remove_semicolon,
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semicolon: remove_semicolon,
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suggest_box,
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}),
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}),
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)
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)
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}
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}
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|
|
|
@ -570,6 +570,14 @@ pub struct FnCtxt<'a, 'tcx> {
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/// any).
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/// any).
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ret_coercion: Option<RefCell<DynamicCoerceMany<'tcx>>>,
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ret_coercion: Option<RefCell<DynamicCoerceMany<'tcx>>>,
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|
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ret_coercion_impl_trait: Option<Ty<'tcx>>,
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ret_type_span: Option<Span>,
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/// Used exclusively to reduce cost of advanced evaluation used for
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/// more helpful diagnostics.
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in_tail_expr: bool,
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|
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/// First span of a return site that we find. Used in error messages.
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/// First span of a return site that we find. Used in error messages.
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ret_coercion_span: RefCell<Option<Span>>,
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ret_coercion_span: RefCell<Option<Span>>,
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|
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@ -1302,10 +1310,15 @@ fn check_fn<'a, 'tcx>(
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let hir = tcx.hir();
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let hir = tcx.hir();
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|
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let declared_ret_ty = fn_sig.output();
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let declared_ret_ty = fn_sig.output();
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|
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let revealed_ret_ty =
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let revealed_ret_ty =
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fcx.instantiate_opaque_types_from_value(fn_id, &declared_ret_ty, decl.output.span());
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fcx.instantiate_opaque_types_from_value(fn_id, &declared_ret_ty, decl.output.span());
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debug!("check_fn: declared_ret_ty: {}, revealed_ret_ty: {}", declared_ret_ty, revealed_ret_ty);
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debug!("check_fn: declared_ret_ty: {}, revealed_ret_ty: {}", declared_ret_ty, revealed_ret_ty);
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fcx.ret_coercion = Some(RefCell::new(CoerceMany::new(revealed_ret_ty)));
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fcx.ret_coercion = Some(RefCell::new(CoerceMany::new(revealed_ret_ty)));
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fcx.ret_type_span = Some(decl.output.span());
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if let ty::Opaque(..) = declared_ret_ty.kind() {
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fcx.ret_coercion_impl_trait = Some(declared_ret_ty);
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}
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fn_sig = tcx.mk_fn_sig(
|
fn_sig = tcx.mk_fn_sig(
|
||||||
fn_sig.inputs().iter().cloned(),
|
fn_sig.inputs().iter().cloned(),
|
||||||
revealed_ret_ty,
|
revealed_ret_ty,
|
||||||
|
@ -1366,6 +1379,7 @@ fn check_fn<'a, 'tcx>(
|
||||||
|
|
||||||
inherited.typeck_results.borrow_mut().liberated_fn_sigs_mut().insert(fn_id, fn_sig);
|
inherited.typeck_results.borrow_mut().liberated_fn_sigs_mut().insert(fn_id, fn_sig);
|
||||||
|
|
||||||
|
fcx.in_tail_expr = true;
|
||||||
if let ty::Dynamic(..) = declared_ret_ty.kind() {
|
if let ty::Dynamic(..) = declared_ret_ty.kind() {
|
||||||
// FIXME: We need to verify that the return type is `Sized` after the return expression has
|
// FIXME: We need to verify that the return type is `Sized` after the return expression has
|
||||||
// been evaluated so that we have types available for all the nodes being returned, but that
|
// been evaluated so that we have types available for all the nodes being returned, but that
|
||||||
|
@ -1385,6 +1399,7 @@ fn check_fn<'a, 'tcx>(
|
||||||
fcx.require_type_is_sized(declared_ret_ty, decl.output.span(), traits::SizedReturnType);
|
fcx.require_type_is_sized(declared_ret_ty, decl.output.span(), traits::SizedReturnType);
|
||||||
fcx.check_return_expr(&body.value);
|
fcx.check_return_expr(&body.value);
|
||||||
}
|
}
|
||||||
|
fcx.in_tail_expr = false;
|
||||||
|
|
||||||
// We insert the deferred_generator_interiors entry after visiting the body.
|
// We insert the deferred_generator_interiors entry after visiting the body.
|
||||||
// This ensures that all nested generators appear before the entry of this generator.
|
// This ensures that all nested generators appear before the entry of this generator.
|
||||||
|
@ -3084,6 +3099,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
|
||||||
param_env,
|
param_env,
|
||||||
err_count_on_creation: inh.tcx.sess.err_count(),
|
err_count_on_creation: inh.tcx.sess.err_count(),
|
||||||
ret_coercion: None,
|
ret_coercion: None,
|
||||||
|
ret_coercion_impl_trait: None,
|
||||||
|
ret_type_span: None,
|
||||||
|
in_tail_expr: false,
|
||||||
ret_coercion_span: RefCell::new(None),
|
ret_coercion_span: RefCell::new(None),
|
||||||
resume_yield_tys: None,
|
resume_yield_tys: None,
|
||||||
ps: RefCell::new(UnsafetyState::function(hir::Unsafety::Normal, hir::CRATE_HIR_ID)),
|
ps: RefCell::new(UnsafetyState::function(hir::Unsafety::Normal, hir::CRATE_HIR_ID)),
|
||||||
|
|
|
@ -54,6 +54,12 @@ fn cat() -> impl std::fmt::Display {
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
fn dog() -> impl std::fmt::Display {
|
||||||
|
match 13 {
|
||||||
|
0 => 0i32,
|
||||||
|
1 => 1u32, //~ ERROR `match` arms have incompatible types
|
||||||
|
_ => 2u32,
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
|
|
@ -72,6 +72,17 @@ LL | | 1u32
|
||||||
| | ^^^^ expected `i32`, found `u32`
|
| | ^^^^ expected `i32`, found `u32`
|
||||||
LL | | }
|
LL | | }
|
||||||
| |_____- `if` and `else` have incompatible types
|
| |_____- `if` and `else` have incompatible types
|
||||||
|
|
|
||||||
|
help: you could change the return type to be a boxed trait object
|
||||||
|
|
|
||||||
|
LL | fn qux() -> Box<dyn std::fmt::Display> {
|
||||||
|
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||||
|
help: if you change the return type to expect trait objects box the returned expressions
|
||||||
|
|
|
||||||
|
LL | Box::new(0i32)
|
||||||
|
LL | } else {
|
||||||
|
LL | Box::new(1u32)
|
||||||
|
|
|
||||||
|
|
||||||
error[E0308]: mismatched types
|
error[E0308]: mismatched types
|
||||||
--> $DIR/point-to-type-err-cause-on-impl-trait-return.rs:35:14
|
--> $DIR/point-to-type-err-cause-on-impl-trait-return.rs:35:14
|
||||||
|
@ -136,6 +147,28 @@ help: you could change the return type to be a boxed trait object
|
||||||
LL | fn cat() -> Box<dyn std::fmt::Display> {
|
LL | fn cat() -> Box<dyn std::fmt::Display> {
|
||||||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
|
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||||
|
|
||||||
error: aborting due to 7 previous errors
|
error[E0308]: `match` arms have incompatible types
|
||||||
|
--> $DIR/point-to-type-err-cause-on-impl-trait-return.rs:61:14
|
||||||
|
|
|
||||||
|
LL | / match 13 {
|
||||||
|
LL | | 0 => 0i32,
|
||||||
|
| | ---- this is found to be of type `i32`
|
||||||
|
LL | | 1 => 1u32,
|
||||||
|
| | ^^^^ expected `i32`, found `u32`
|
||||||
|
LL | | _ => 2u32,
|
||||||
|
LL | | }
|
||||||
|
| |_____- `match` arms have incompatible types
|
||||||
|
|
|
||||||
|
help: you could change the return type to be a boxed trait object
|
||||||
|
|
|
||||||
|
LL | fn dog() -> Box<dyn std::fmt::Display> {
|
||||||
|
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||||
|
help: if you change the return type to expect trait objects box the returned expressions
|
||||||
|
|
|
||||||
|
LL | 0 => Box::new(0i32),
|
||||||
|
LL | 1 => Box::new(1u32),
|
||||||
|
|
|
||||||
|
|
||||||
|
error: aborting due to 8 previous errors
|
||||||
|
|
||||||
For more information about this error, try `rustc --explain E0308`.
|
For more information about this error, try `rustc --explain E0308`.
|
||||||
|
|
Loading…
Reference in New Issue