From 3b383fe7ca6edf58329aa187699caba9c145fa71 Mon Sep 17 00:00:00 2001 From: sgasho Date: Tue, 6 Oct 2026 00:26:42 +0900 Subject: [PATCH 1/3] Fix check_expr_if to point to a more accurate location of the compilation error --- compiler/rustc_hir_typeck/src/_if.rs | 231 ++++++++++++++++++ compiler/rustc_hir_typeck/src/coercion.rs | 35 ++- compiler/rustc_hir_typeck/src/expr.rs | 130 +++------- compiler/rustc_hir_typeck/src/lib.rs | 1 + compiler/rustc_middle/src/traits/mod.rs | 16 ++ .../src/error_reporting/infer/mod.rs | 66 ++++- .../src/error_reporting/traits/suggestions.rs | 1 + tests/ui/inference/deref-suggestion.rs | 2 +- tests/ui/inference/deref-suggestion.stderr | 22 +- .../ui/typeck/consider-borrowing-141810-1.rs | 5 +- .../typeck/consider-borrowing-141810-1.stderr | 22 +- .../if-else-type-mismatch-chain-nested.rs | 21 ++ .../if-else-type-mismatch-chain-nested.stderr | 43 ++++ .../ui/typeck/if-else-type-mismatch-chain.rs | 11 + .../typeck/if-else-type-mismatch-chain.stderr | 26 ++ 15 files changed, 515 insertions(+), 117 deletions(-) create mode 100644 compiler/rustc_hir_typeck/src/_if.rs create mode 100644 tests/ui/typeck/if-else-type-mismatch-chain-nested.rs create mode 100644 tests/ui/typeck/if-else-type-mismatch-chain-nested.stderr create mode 100644 tests/ui/typeck/if-else-type-mismatch-chain.rs create mode 100644 tests/ui/typeck/if-else-type-mismatch-chain.stderr diff --git a/compiler/rustc_hir_typeck/src/_if.rs b/compiler/rustc_hir_typeck/src/_if.rs new file mode 100644 index 0000000000000..d7d9dc748a308 --- /dev/null +++ b/compiler/rustc_hir_typeck/src/_if.rs @@ -0,0 +1,231 @@ +use rustc_hir as hir; +use rustc_hir::{ExprKind, HirId}; +use rustc_infer::traits::{IfChainCoerceCause, ObligationCauseCode}; +use rustc_middle::ty::{Ty, TypeVisitableExt}; +use rustc_span::def_id::LocalDefId; +use rustc_span::{Span, bug}; + +use crate::Expectation; +use crate::coercion::CoerceMany; +use crate::diverges::Diverges; +use crate::fn_ctxt::FnCtxt; + +/// State shared across all branches of an `else if` chain check. +struct ElseIfChainCx<'a, 'tcx> { + coerce: &'a mut CoerceMany<'tcx>, + outer_if_expr_id: HirId, + orig_expected: Expectation<'tcx>, + tail_defines_return_position_impl_trait: Option, +} + +#[derive(Copy, Clone)] +struct PrevBranch<'tcx> { + hir_id: HirId, + ty: Ty<'tcx>, +} + +fn chain_has_terminal_else_block(expr: &hir::Expr<'_>) -> bool { + let mut cur = expr; + loop { + match cur.kind { + ExprKind::If(_, _, Some(next)) => cur = next, + ExprKind::If(_, _, None) => return false, + _ => return true, + } + } +} + +fn has_empty_block_chains(expr: &hir::Expr<'_>) -> bool { + let mut cur = expr; + loop { + match cur.kind { + ExprKind::If(_, then, opt_else) => { + let ExprKind::Block(then_block, _) = then.kind else { + return true; + }; + if then_block.expr.is_none() { + return true; + } + match opt_else { + Some(next) => cur = next, + None => return false, + } + } + ExprKind::Block(block, _) => return block.expr.is_none(), + _ => return false, + } + } +} + +impl<'a, 'tcx> FnCtxt<'a, 'tcx> { + // A generic function for checking the 'then' and 'else' clauses in an 'if' + // or 'if-else' expression. + pub(crate) fn check_expr_if( + &self, + expr_id: HirId, + cond_expr: &'tcx hir::Expr<'tcx>, + then_expr: &'tcx hir::Expr<'tcx>, + opt_else_expr: Option<&'tcx hir::Expr<'tcx>>, + sp: Span, + orig_expected: Expectation<'tcx>, + ) -> Ty<'tcx> { + let cond_ty = self.check_expr_has_type_or_error(cond_expr, self.tcx.types.bool, |_| {}); + + let (expected, then_ty, cond_diverges, then_diverges) = + self.check_current_if_branch(cond_expr, then_expr, orig_expected); + + // We've already taken the expected type's preferences + // into account when typing the `then` branch. To figure + // out the initial shot at a LUB, we thus only consider + // `expected` if it represents a *hard* constraint + // (`only_has_type`); otherwise, we just go with a + // fresh type variable. + let coerce_to_ty = expected.coercion_target_type(self, sp); + let mut coerce = CoerceMany::with_capacity(coerce_to_ty, 2); + + coerce.coerce(self, &self.misc(sp), then_expr, then_ty); + + if let Some(else_expr) = opt_else_expr { + let else_diverges = if chain_has_terminal_else_block(else_expr) + && let ExprKind::If(..) = else_expr.kind + // Chains containing `{}` arms go to the path below. + // Otherwise for code like + // let x = if c1 { &() } else if c2 {} else {}; + // the "consider borrowing here" suggestion comes out as + // } else if c2 &{ + // which isn't valid syntax. Having an empty block in an if chain is an edge + // case in real code, so the fallback is harmless. + && !has_empty_block_chains(else_expr) + { + let mut cx = ElseIfChainCx { + coerce: &mut coerce, + outer_if_expr_id: expr_id, + orig_expected, + tail_defines_return_position_impl_trait: self + .return_position_impl_trait_from_match_expectation(orig_expected), + }; + self.check_expr_with_check_fn(else_expr, expected, |this| { + this.check_else_if_branch( + &mut cx, + PrevBranch { hir_id: then_expr.hir_id, ty: then_ty }, + else_expr, + ) + }); + self.diverges.get() + } else { + let else_ty = self.check_expr_with_expectation(else_expr, expected); + let else_diverges = self.diverges.get(); + let if_cause = self.if_cause( + expr_id, + else_expr, + self.return_position_impl_trait_from_match_expectation(orig_expected), + ); + coerce.coerce(self, &if_cause, else_expr, else_ty); + else_diverges + }; + + // We won't diverge unless both branches do (or the condition does). + self.diverges.set(cond_diverges | then_diverges & else_diverges); + } else { + self.if_fallback_coercion(sp, cond_expr, then_expr, &mut coerce); + + // If the condition is false we can't diverge. + self.diverges.set(cond_diverges); + } + + let result_ty = coerce.complete(self); + if let Err(guar) = cond_ty.error_reported() { + Ty::new_error(self.tcx, guar) + } else { + result_ty + } + } + + fn check_current_if_branch( + &self, + cond_expr: &'tcx hir::Expr<'tcx>, + then_expr: &'tcx hir::Expr<'tcx>, + orig_expected: Expectation<'tcx>, + ) -> (Expectation<'tcx>, Ty<'tcx>, Diverges, Diverges) { + self.warn_if_unreachable( + cond_expr.hir_id, + then_expr.span, + "block in `if` or `while` expression", + ); + + let cond_diverges = self.diverges.get(); + self.diverges.set(Diverges::Maybe); + + let expected = orig_expected.try_structurally_resolve_and_adjust_for_branches(self); + let then_ty = self.check_expr_with_expectation(then_expr, expected); + let then_diverges = self.diverges.get(); + self.diverges.set(Diverges::Maybe); + + (expected, then_ty, cond_diverges, then_diverges) + } + + fn check_else_if_branch( + &self, + cx: &mut ElseIfChainCx<'_, 'tcx>, + prev_branch: PrevBranch<'tcx>, + current_expr: &'tcx hir::Expr<'tcx>, + ) -> Ty<'tcx> { + let ExprKind::If(cond_expr, then_expr, opt_else_expr) = current_expr.kind else { + bug!("check_else_if_branch called on non-`if` expr"); + }; + self.check_expr_has_type_or_error(cond_expr, self.tcx.types.bool, |_| {}); + + let (expected, then_ty, cond_diverges, then_diverges) = + self.check_current_if_branch(cond_expr, then_expr, cx.orig_expected); + + self.coerce_branch_against_prev(cx, prev_branch, then_expr, then_ty); + + let next_prev = PrevBranch { hir_id: then_expr.hir_id, ty: then_ty }; + + let else_diverges = match opt_else_expr { + Some(else_expr) if let ExprKind::If(..) = else_expr.kind => { + self.check_expr_with_check_fn(else_expr, expected, |this| { + this.check_else_if_branch(cx, next_prev, else_expr) + }); + self.diverges.get() + } + Some(else_expr) => { + let else_ty = self.check_expr_with_expectation(else_expr, expected); + let else_diverges = self.diverges.get(); + self.coerce_branch_against_prev(cx, next_prev, else_expr, else_ty); + else_diverges + } + None => bug!("chain entered without a final else; broken `has_final_else_arm`"), + }; + + // We won't diverge unless cond does, or both then and else do. + self.diverges.set(cond_diverges | then_diverges & else_diverges); + + cx.coerce.merged_ty() + } + + fn coerce_branch_against_prev( + &self, + cx: &mut ElseIfChainCx<'_, 'tcx>, + prev: PrevBranch<'tcx>, + current_branch_expr: &'tcx hir::Expr<'tcx>, + current_branch_ty: Ty<'tcx>, + ) { + let prev_branch_span = self.find_block_span_from_hir_id(prev.hir_id); + let branch_span = self.find_block_span_from_hir_id(current_branch_expr.hir_id); + let cause = self.cause( + branch_span, + ObligationCauseCode::IfChainCoerce(Box::new(IfChainCoerceCause { + outer_if_expr_id: cx.outer_if_expr_id, + source_branch_expr_id: prev.hir_id, + source_branch_ty: prev.ty, + source_branch_span: prev_branch_span, + target_branch_expr_id: current_branch_expr.hir_id, + target_branch_ty: current_branch_ty, + target_branch_span: branch_span, + tail_defines_return_position_impl_trait: cx.tail_defines_return_position_impl_trait, + })), + ); + cx.coerce.coerce(self, &cause, current_branch_expr, current_branch_ty); + } +} diff --git a/compiler/rustc_hir_typeck/src/coercion.rs b/compiler/rustc_hir_typeck/src/coercion.rs index af00194a95bf0..1c9b73ede7b31 100644 --- a/compiler/rustc_hir_typeck/src/coercion.rs +++ b/compiler/rustc_hir_typeck/src/coercion.rs @@ -47,7 +47,8 @@ use rustc_hir_analysis::hir_ty_lowering::HirTyLowerer; use rustc_infer::infer::relate::RelateResult; use rustc_infer::infer::{DefineOpaqueTypes, InferOk, InferResult, RegionVariableOrigin}; use rustc_infer::traits::{ - MatchExpressionArmCause, Obligation, PredicateObligation, PredicateObligations, SelectionError, + IfChainCoerceCause, MatchExpressionArmCause, Obligation, PredicateObligation, + PredicateObligations, SelectionError, }; use rustc_middle::ty::adjustment::{ Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability, DerefAdjustKind, @@ -1865,6 +1866,38 @@ impl<'tcx> CoerceMany<'tcx> { ); } } + ObligationCauseCode::IfChainCoerce(IfChainCoerceCause { + source_branch_expr_id: prev_branch_expr_id, + source_branch_ty: prev_branch_ty, + source_branch_span: prev_branch_span, + target_branch_expr_id: branch_expr_id, + target_branch_ty: branch_ty, + target_branch_span: branch_span, + tail_defines_return_position_impl_trait: Some(rpit_def_id), + .. + }) => { + err = fcx.err_ctxt().report_mismatched_types( + cause, + fcx.param_env, + expected, + found, + coercion_error, + ); + let prev_expr_span = + fcx.tcx.hir_node(prev_branch_expr_id).expect_expr().span; + let branch_expr_span = fcx.tcx.hir_node(branch_expr_id).expect_expr().span; + // Don't suggest wrapping whole block in `Box::new`. + if prev_branch_span != prev_expr_span && branch_span != branch_expr_span { + self.suggest_boxing_tail_for_return_position_impl_trait( + fcx, + &mut err, + rpit_def_id, + prev_branch_ty, + branch_ty, + [prev_branch_span, branch_span].into_iter(), + ); + } + } _ => { err = fcx.err_ctxt().report_mismatched_types( cause, diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs index 9f0d00d5274fa..79b574a23ba9d 100644 --- a/compiler/rustc_hir_typeck/src/expr.rs +++ b/compiler/rustc_hir_typeck/src/expr.rs @@ -205,27 +205,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { self.check_expr_with_expectation_and_needs(expr, NoExpectation, needs) } - /// Check an expr with an expectation type which may be used to eagerly - /// guide inference when evaluating that expr. - #[instrument(skip(self, expr), level = "debug")] - pub(super) fn check_expr_with_expectation( - &self, - expr: &'tcx hir::Expr<'tcx>, - expected: Expectation<'tcx>, - ) -> Ty<'tcx> { - self.check_expr_with_expectation_and_args(expr, expected, None) - } - - /// Same as [`Self::check_expr_with_expectation`], but allows us to pass in - /// the arguments of a [`ExprKind::Call`] when evaluating its callee that - /// is an [`ExprKind::Path`]. We use this to refine the spans for certain - /// well-formedness guarantees for the path expr. - pub(super) fn check_expr_with_expectation_and_args( + /// Run the per-expression framing (`write_ty`, divergence handling, + /// unreachable warnings) around `check`. + pub(super) fn check_expr_with_check_fn( &self, expr: &'tcx hir::Expr<'tcx>, expected: Expectation<'tcx>, - call_expr_and_args: Option<(&'tcx hir::Expr<'tcx>, &'tcx [hir::Expr<'tcx>])>, - ) -> Ty<'tcx> { + check: F, + ) -> Ty<'tcx> + where + F: FnOnce(&Self) -> Ty<'tcx>, + { if self.tcx().sess.verbose_internals() { // make this code only run with -Zverbose-internals because it is probably slow if let Ok(lint_str) = self.tcx.sess.source_map().span_to_snippet(expr.span) { @@ -268,13 +258,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { self.diverges.set(self.function_diverges_because_of_empty_arguments.get()) }; - let ty = match &expr.kind { - // Intercept the callee path expr and give it better spans. - hir::ExprKind::Path( - qpath @ (hir::QPath::Resolved(..) | hir::QPath::TypeRelative(..)), - ) => self.check_expr_path(qpath, expr, call_expr_and_args), - _ => self.check_expr_kind(expr, expected), - }; + let ty = check(self); let ty = self.deeply_resolve_ignoring_regions(ty); // Warn for non-block expressions with diverging children. @@ -324,6 +308,36 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { ty } + /// Check an expr with an expectation type which may be used to eagerly + /// guide inference when evaluating that expr. + #[instrument(skip(self, expr), level = "debug")] + pub(super) fn check_expr_with_expectation( + &self, + expr: &'tcx hir::Expr<'tcx>, + expected: Expectation<'tcx>, + ) -> Ty<'tcx> { + self.check_expr_with_expectation_and_args(expr, expected, None) + } + + /// Same as [`Self::check_expr_with_expectation`], but allows us to pass in + /// the arguments of a [`ExprKind::Call`] when evaluating its callee that + /// is an [`ExprKind::Path`]. We use this to refine the spans for certain + /// well-formedness guarantees for the path expr. + pub(super) fn check_expr_with_expectation_and_args( + &self, + expr: &'tcx hir::Expr<'tcx>, + expected: Expectation<'tcx>, + call_expr_and_args: Option<(&'tcx hir::Expr<'tcx>, &'tcx [hir::Expr<'tcx>])>, + ) -> Ty<'tcx> { + self.check_expr_with_check_fn(expr, expected, |this| match &expr.kind { + // Intercept the callee path expr and give it better spans. + hir::ExprKind::Path( + qpath @ (hir::QPath::Resolved(..) | hir::QPath::TypeRelative(..)), + ) => this.check_expr_path(qpath, expr, call_expr_and_args), + _ => this.check_expr_kind(expr, expected), + }) + } + #[instrument(skip(self, expr), level = "debug")] fn check_expr_kind( &self, @@ -1192,72 +1206,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { } } - // A generic function for checking the 'then' and 'else' clauses in an 'if' - // or 'if-else' expression. - fn check_expr_if( - &self, - expr_id: HirId, - cond_expr: &'tcx hir::Expr<'tcx>, - then_expr: &'tcx hir::Expr<'tcx>, - opt_else_expr: Option<&'tcx hir::Expr<'tcx>>, - sp: Span, - orig_expected: Expectation<'tcx>, - ) -> Ty<'tcx> { - let cond_ty = self.check_expr_has_type_or_error(cond_expr, self.tcx.types.bool, |_| {}); - - self.warn_if_unreachable( - cond_expr.hir_id, - then_expr.span, - "block in `if` or `while` expression", - ); - - let cond_diverges = self.diverges.get(); - self.diverges.set(Diverges::Maybe); - - let expected = orig_expected.try_structurally_resolve_and_adjust_for_branches(self); - let then_ty = self.check_expr_with_expectation(then_expr, expected); - let then_diverges = self.diverges.get(); - self.diverges.set(Diverges::Maybe); - - // We've already taken the expected type's preferences - // into account when typing the `then` branch. To figure - // out the initial shot at a LUB, we thus only consider - // `expected` if it represents a *hard* constraint - // (`only_has_type`); otherwise, we just go with a - // fresh type variable. - let coerce_to_ty = expected.coercion_target_type(self, sp); - let mut coerce = CoerceMany::with_capacity(coerce_to_ty, 2); - - coerce.coerce(self, &self.misc(sp), then_expr, then_ty); - - if let Some(else_expr) = opt_else_expr { - let else_ty = self.check_expr_with_expectation(else_expr, expected); - let else_diverges = self.diverges.get(); - - let tail_defines_return_position_impl_trait = - self.return_position_impl_trait_from_match_expectation(orig_expected); - let if_cause = - self.if_cause(expr_id, else_expr, tail_defines_return_position_impl_trait); - - coerce.coerce(self, &if_cause, else_expr, else_ty); - - // We won't diverge unless both branches do (or the condition does). - self.diverges.set(cond_diverges | then_diverges & else_diverges); - } else { - self.if_fallback_coercion(sp, cond_expr, then_expr, &mut coerce); - - // If the condition is false we can't diverge. - self.diverges.set(cond_diverges); - } - - let result_ty = coerce.complete(self); - if let Err(guar) = cond_ty.error_reported() { - Ty::new_error(self.tcx, guar) - } else { - result_ty - } - } - /// Type check assignment expression `expr` of form `lhs = rhs`. /// The expected type is `()` and is passed to the function for the purposes of diagnostics. fn check_expr_assign( diff --git a/compiler/rustc_hir_typeck/src/lib.rs b/compiler/rustc_hir_typeck/src/lib.rs index 5efb2775c77fe..db205c7d33358 100644 --- a/compiler/rustc_hir_typeck/src/lib.rs +++ b/compiler/rustc_hir_typeck/src/lib.rs @@ -6,6 +6,7 @@ #![feature(option_reference_flattening)] // tidy-alphabetical-end +mod _if; mod _match; mod autoderef; mod callee; diff --git a/compiler/rustc_middle/src/traits/mod.rs b/compiler/rustc_middle/src/traits/mod.rs index 493f6989f342c..a8a5752406e37 100644 --- a/compiler/rustc_middle/src/traits/mod.rs +++ b/compiler/rustc_middle/src/traits/mod.rs @@ -339,6 +339,8 @@ pub enum ObligationCauseCode<'tcx> { tail_defines_return_position_impl_trait: Option, }, + IfChainCoerce(Box>), + /// Computing common supertype of an if expression with no else counter-part IfExpressionWithNoElse, @@ -551,6 +553,20 @@ pub struct MatchExpressionArmCause<'tcx> { pub tail_defines_return_position_impl_trait: Option, } +#[derive(Clone, Debug, PartialEq, Eq, StableHash, TyEncodable, TyDecodable)] +#[derive(TypeVisitable, TypeFoldable)] +pub struct IfChainCoerceCause<'tcx> { + /// Outermost `if` of the chain, for the outer "incompatible types" label. + pub outer_if_expr_id: HirId, + pub source_branch_expr_id: HirId, + pub source_branch_ty: Ty<'tcx>, + pub source_branch_span: Span, + pub target_branch_expr_id: HirId, + pub target_branch_ty: Ty<'tcx>, + pub target_branch_span: Span, + pub tail_defines_return_position_impl_trait: Option, +} + /// Information about the origin expression of a pattern, relevant to diagnostics. /// Fields here refer to the scrutinee of a pattern. /// If the scrutinee isn't given in the diagnostic, then this won't exist. diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs index b2b57e018a7cf..f0518d5205f7e 100644 --- a/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs +++ b/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs @@ -59,6 +59,7 @@ use rustc_hir as hir; use rustc_hir::def_id::{CRATE_DEF_ID, DefId}; use rustc_hir::intravisit::Visitor; use rustc_infer::infer::DefineOpaqueTypes; +use rustc_infer::traits::IfChainCoerceCause; use rustc_macros::extension; use rustc_middle::traits::PatternOriginExpr; use rustc_middle::ty::consts::ConstExt; @@ -506,6 +507,69 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> { } } }, + ObligationCauseCode::IfChainCoerce(IfChainCoerceCause { + outer_if_expr_id, + source_branch_expr_id: prev_branch_expr_id, + source_branch_ty: prev_branch_ty, + source_branch_span: prev_branch_span, + target_branch_expr_id: branch_expr_id, + target_branch_ty: branch_ty, + target_branch_span: branch_span, + .. + }) => { + err.span_label(prev_branch_span, "expected because of this"); + + if let hir::Node::Expr(&hir::Expr { span: expr_span, .. }) = + self.tcx.hir_node(outer_if_expr_id) + && let hir::Node::Expr(&hir::Expr { kind: hir::ExprKind::If(cond, ..), .. }) = + self.tcx.hir_node(outer_if_expr_id) + { + let outer_span = if self.tcx.sess.source_map().is_multiline(expr_span) { + if prev_branch_span.hi() == expr_span.hi() + || branch_span.hi() == expr_span.hi() + { + // Avoid overlapping arrows: shrink to `if `. + Some(expr_span.shrink_to_lo().to(cond.peel_drop_temps().span)) + } else { + Some(expr_span) + } + } else { + None + }; + if let Some(sp) = outer_span { + err.span_label(sp, "`if` and `else` have incompatible types"); + } + } + + let prev_id = if let hir::Node::Expr(hir::Expr { + kind: hir::ExprKind::Block(blk, _), + .. + }) = self.tcx.hir_node(prev_branch_expr_id) + { + blk.hir_id + } else { + prev_branch_expr_id + }; + let new_id = if let hir::Node::Expr(hir::Expr { + kind: hir::ExprKind::Block(blk, _), + .. + }) = self.tcx.hir_node(branch_expr_id) + { + blk.hir_id + } else { + branch_expr_id + }; + if let Some(subdiag) = self.suggest_remove_semi_or_return_binding( + Some(prev_id), + prev_branch_ty, + prev_branch_span, + Some(new_id), + branch_ty, + branch_span, + ) { + err.subdiagnostic(subdiag); + } + } ObligationCauseCode::IfExpression { expr_id, .. } => { let hir::Node::Expr(&hir::Expr { kind: hir::ExprKind::If(cond_expr, then_expr, Some(else_expr)), @@ -2623,7 +2687,7 @@ impl<'tcx> ObligationCause<'tcx> { _ => ObligationCauseFailureCode::MatchCompat { span, subdiags }, } } - ObligationCauseCode::IfExpression { .. } => { + ObligationCauseCode::IfExpression { .. } | ObligationCauseCode::IfChainCoerce(_) => { ObligationCauseFailureCode::IfElseDifferent { span, subdiags } } ObligationCauseCode::IfExpressionWithNoElse => { diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs index 76755eb481db7..90ef6b8432c0f 100644 --- a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs +++ b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs @@ -3897,6 +3897,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> { ObligationCauseCode::ExprAssignable | ObligationCauseCode::MatchExpressionArm { .. } | ObligationCauseCode::Pattern { .. } + | ObligationCauseCode::IfChainCoerce(_) | ObligationCauseCode::IfExpression { .. } | ObligationCauseCode::IfExpressionWithNoElse | ObligationCauseCode::MainFunctionType diff --git a/tests/ui/inference/deref-suggestion.rs b/tests/ui/inference/deref-suggestion.rs index dc39cc9dbffb0..bed8a9d9ef637 100644 --- a/tests/ui/inference/deref-suggestion.rs +++ b/tests/ui/inference/deref-suggestion.rs @@ -67,8 +67,8 @@ fn main() { let val = if true { *a } else if true { - //~^ ERROR incompatible types b + //~^ ERROR incompatible types } else { &0 }; diff --git a/tests/ui/inference/deref-suggestion.stderr b/tests/ui/inference/deref-suggestion.stderr index 027902a9f31e2..48ad7d11975cf 100644 --- a/tests/ui/inference/deref-suggestion.stderr +++ b/tests/ui/inference/deref-suggestion.stderr @@ -165,20 +165,24 @@ LL | *b | + error[E0308]: `if` and `else` have incompatible types - --> $DIR/deref-suggestion.rs:69:12 + --> $DIR/deref-suggestion.rs:70:9 | LL | let val = if true { - | ------- `if` and `else` have incompatible types -LL | *a - | -- expected because of this -LL | } else if true { - | ____________^ -LL | | + | _______________- +LL | | *a + | | -- expected because of this +LL | | } else if true { LL | | b -LL | | } else { + | | ^ expected `i32`, found `&{integer}` +... | LL | | &0 LL | | }; - | |_____^ expected `i32`, found `&{integer}` + | |_____- `if` and `else` have incompatible types + | +help: consider dereferencing the borrow + | +LL | *b + | + error[E0308]: mismatched types --> $DIR/deref-suggestion.rs:81:15 diff --git a/tests/ui/typeck/consider-borrowing-141810-1.rs b/tests/ui/typeck/consider-borrowing-141810-1.rs index 94c2d69091517..1b1d4312b4e3c 100644 --- a/tests/ui/typeck/consider-borrowing-141810-1.rs +++ b/tests/ui/typeck/consider-borrowing-141810-1.rs @@ -1,8 +1,9 @@ fn main() { let x = if true { &true - } else if false { //~ ERROR `if` and `else` have incompatible types [E0308] - true //~ HELP consider borrowing here + } else if false { + true //~ ERROR `if` and `else` have incompatible types [E0308] + //~^ HELP consider borrowing here } else { true }; diff --git a/tests/ui/typeck/consider-borrowing-141810-1.stderr b/tests/ui/typeck/consider-borrowing-141810-1.stderr index 35ca6793eee0d..3de8ccea0bfb9 100644 --- a/tests/ui/typeck/consider-borrowing-141810-1.stderr +++ b/tests/ui/typeck/consider-borrowing-141810-1.stderr @@ -1,24 +1,22 @@ error[E0308]: `if` and `else` have incompatible types - --> $DIR/consider-borrowing-141810-1.rs:4:12 + --> $DIR/consider-borrowing-141810-1.rs:5:9 | LL | let x = if true { - | ------- `if` and `else` have incompatible types -LL | &true - | ----- expected because of this -LL | } else if false { - | ____________^ + | _____________- +LL | | &true + | | ----- expected because of this +LL | | } else if false { LL | | true -LL | | } else { + | | ^^^^ expected `&bool`, found `bool` +... | LL | | true LL | | }; - | |_____^ expected `&bool`, found `bool` + | |_____- `if` and `else` have incompatible types | help: consider borrowing here | -LL ~ &true -LL | } else { -LL ~ &true - | +LL | &true + | + error: aborting due to 1 previous error diff --git a/tests/ui/typeck/if-else-type-mismatch-chain-nested.rs b/tests/ui/typeck/if-else-type-mismatch-chain-nested.rs new file mode 100644 index 0000000000000..52bd4c12bd7a9 --- /dev/null +++ b/tests/ui/typeck/if-else-type-mismatch-chain-nested.rs @@ -0,0 +1,21 @@ +fn main() { + let oa = Some(1); + let oa2 = Some(1); + let _v = if let Some(a) = oa { + Some(&a) + } else if let Some(a) = oa2 { + let _f = 1; + + let _h = if true { + 1 + } else if true { + "2" //~ ERROR `if` and `else` have incompatible types [E0308] + } else { + 3 + }; + + &Some(a) //~ ERROR `if` and `else` have incompatible types [E0308] + } else { + None + }; +} diff --git a/tests/ui/typeck/if-else-type-mismatch-chain-nested.stderr b/tests/ui/typeck/if-else-type-mismatch-chain-nested.stderr new file mode 100644 index 0000000000000..c002a18699095 --- /dev/null +++ b/tests/ui/typeck/if-else-type-mismatch-chain-nested.stderr @@ -0,0 +1,43 @@ +error[E0308]: `if` and `else` have incompatible types + --> $DIR/if-else-type-mismatch-chain-nested.rs:12:13 + | +LL | let _h = if true { + | __________________- +LL | | 1 + | | - expected because of this +LL | | } else if true { +LL | | "2" + | | ^^^ expected integer, found `&str` +LL | | } else { +LL | | 3 +LL | | }; + | |_________- `if` and `else` have incompatible types + +error[E0308]: `if` and `else` have incompatible types + --> $DIR/if-else-type-mismatch-chain-nested.rs:17:9 + | +LL | let _v = if let Some(a) = oa { + | ______________- +LL | | Some(&a) + | | -------- expected because of this +LL | | } else if let Some(a) = oa2 { +LL | | let _f = 1; +... | +LL | | &Some(a) + | | ^^^^^^^^ expected `Option<&{integer}>`, found `&Option<{integer}>` +LL | | } else { +LL | | None +LL | | }; + | |_____- `if` and `else` have incompatible types + | + = note: expected enum `Option<&{integer}>` + found reference `&Option<{integer}>` +help: try using `.as_ref()` to convert `&Option<{integer}>` to `Option<&{integer}>` + | +LL - &Some(a) +LL + Some(a).as_ref() + | + +error: aborting due to 2 previous errors + +For more information about this error, try `rustc --explain E0308`. diff --git a/tests/ui/typeck/if-else-type-mismatch-chain.rs b/tests/ui/typeck/if-else-type-mismatch-chain.rs new file mode 100644 index 0000000000000..7a4c14f9acb76 --- /dev/null +++ b/tests/ui/typeck/if-else-type-mismatch-chain.rs @@ -0,0 +1,11 @@ +fn main() { + let oa = Some(1); + let oa2 = Some(1); + let _v = if let Some(a) = oa { + Some(&a) + } else if let Some(a) = oa2 { + &Some(a) //~ ERROR `if` and `else` have incompatible types [E0308] + } else { + None + }; +} diff --git a/tests/ui/typeck/if-else-type-mismatch-chain.stderr b/tests/ui/typeck/if-else-type-mismatch-chain.stderr new file mode 100644 index 0000000000000..890a7186e0c37 --- /dev/null +++ b/tests/ui/typeck/if-else-type-mismatch-chain.stderr @@ -0,0 +1,26 @@ +error[E0308]: `if` and `else` have incompatible types + --> $DIR/if-else-type-mismatch-chain.rs:7:9 + | +LL | let _v = if let Some(a) = oa { + | ______________- +LL | | Some(&a) + | | -------- expected because of this +LL | | } else if let Some(a) = oa2 { +LL | | &Some(a) + | | ^^^^^^^^ expected `Option<&{integer}>`, found `&Option<{integer}>` +LL | | } else { +LL | | None +LL | | }; + | |_____- `if` and `else` have incompatible types + | + = note: expected enum `Option<&{integer}>` + found reference `&Option<{integer}>` +help: try using `.as_ref()` to convert `&Option<{integer}>` to `Option<&{integer}>` + | +LL - &Some(a) +LL + Some(a).as_ref() + | + +error: aborting due to 1 previous error + +For more information about this error, try `rustc --explain E0308`. From 318302ca73b3f5d9f7f5724cc7f955ea0ecacdc6 Mon Sep 17 00:00:00 2001 From: sgasho Date: Mon, 12 Oct 2026 16:11:15 +0900 Subject: [PATCH 2/3] refactor: simplify _if.rs and remove IfCoerceChain --- compiler/rustc_hir_typeck/src/_if.rs | 234 ++++++------------ compiler/rustc_hir_typeck/src/_match.rs | 12 +- compiler/rustc_hir_typeck/src/coercion.rs | 64 ++--- .../src/fn_ctxt/suggestions.rs | 10 + compiler/rustc_middle/src/traits/mod.rs | 24 +- .../src/error_reporting/infer/mod.rs | 138 ++++------- .../error_reporting/infer/note_and_explain.rs | 10 +- .../src/error_reporting/infer/suggest.rs | 58 ++--- .../src/error_reporting/traits/suggestions.rs | 1 - .../ui/expr/if/if-else-chain-missing-else.rs | 2 +- .../expr/if/if-else-chain-missing-else.stderr | 10 +- .../typeck/consider-borrowing-141810-2.stderr | 21 +- .../typeck/consider-borrowing-141810-3.stderr | 4 +- 13 files changed, 206 insertions(+), 382 deletions(-) diff --git a/compiler/rustc_hir_typeck/src/_if.rs b/compiler/rustc_hir_typeck/src/_if.rs index d7d9dc748a308..c6755df9ce52b 100644 --- a/compiler/rustc_hir_typeck/src/_if.rs +++ b/compiler/rustc_hir_typeck/src/_if.rs @@ -1,9 +1,8 @@ use rustc_hir as hir; use rustc_hir::{ExprKind, HirId}; -use rustc_infer::traits::{IfChainCoerceCause, ObligationCauseCode}; use rustc_middle::ty::{Ty, TypeVisitableExt}; +use rustc_span::Span; use rustc_span::def_id::LocalDefId; -use rustc_span::{Span, bug}; use crate::Expectation; use crate::coercion::CoerceMany; @@ -11,52 +10,13 @@ use crate::diverges::Diverges; use crate::fn_ctxt::FnCtxt; /// State shared across all branches of an `else if` chain check. -struct ElseIfChainCx<'a, 'tcx> { +struct IfChainCx<'a, 'tcx> { coerce: &'a mut CoerceMany<'tcx>, outer_if_expr_id: HirId, orig_expected: Expectation<'tcx>, tail_defines_return_position_impl_trait: Option, } -#[derive(Copy, Clone)] -struct PrevBranch<'tcx> { - hir_id: HirId, - ty: Ty<'tcx>, -} - -fn chain_has_terminal_else_block(expr: &hir::Expr<'_>) -> bool { - let mut cur = expr; - loop { - match cur.kind { - ExprKind::If(_, _, Some(next)) => cur = next, - ExprKind::If(_, _, None) => return false, - _ => return true, - } - } -} - -fn has_empty_block_chains(expr: &hir::Expr<'_>) -> bool { - let mut cur = expr; - loop { - match cur.kind { - ExprKind::If(_, then, opt_else) => { - let ExprKind::Block(then_block, _) = then.kind else { - return true; - }; - if then_block.expr.is_none() { - return true; - } - match opt_else { - Some(next) => cur = next, - None => return false, - } - } - ExprKind::Block(block, _) => return block.expr.is_none(), - _ => return false, - } - } -} - impl<'a, 'tcx> FnCtxt<'a, 'tcx> { // A generic function for checking the 'then' and 'else' clauses in an 'if' // or 'if-else' expression. @@ -69,84 +29,45 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { sp: Span, orig_expected: Expectation<'tcx>, ) -> Ty<'tcx> { - let cond_ty = self.check_expr_has_type_or_error(cond_expr, self.tcx.types.bool, |_| {}); - - let (expected, then_ty, cond_diverges, then_diverges) = - self.check_current_if_branch(cond_expr, then_expr, orig_expected); + let expected = orig_expected.try_structurally_resolve_and_adjust_for_branches(self); - // We've already taken the expected type's preferences - // into account when typing the `then` branch. To figure - // out the initial shot at a LUB, we thus only consider - // `expected` if it represents a *hard* constraint - // (`only_has_type`); otherwise, we just go with a - // fresh type variable. let coerce_to_ty = expected.coercion_target_type(self, sp); let mut coerce = CoerceMany::with_capacity(coerce_to_ty, 2); - coerce.coerce(self, &self.misc(sp), then_expr, then_ty); - - if let Some(else_expr) = opt_else_expr { - let else_diverges = if chain_has_terminal_else_block(else_expr) - && let ExprKind::If(..) = else_expr.kind - // Chains containing `{}` arms go to the path below. - // Otherwise for code like - // let x = if c1 { &() } else if c2 {} else {}; - // the "consider borrowing here" suggestion comes out as - // } else if c2 &{ - // which isn't valid syntax. Having an empty block in an if chain is an edge - // case in real code, so the fallback is harmless. - && !has_empty_block_chains(else_expr) - { - let mut cx = ElseIfChainCx { - coerce: &mut coerce, - outer_if_expr_id: expr_id, - orig_expected, - tail_defines_return_position_impl_trait: self - .return_position_impl_trait_from_match_expectation(orig_expected), - }; - self.check_expr_with_check_fn(else_expr, expected, |this| { - this.check_else_if_branch( - &mut cx, - PrevBranch { hir_id: then_expr.hir_id, ty: then_ty }, - else_expr, - ) - }); - self.diverges.get() - } else { - let else_ty = self.check_expr_with_expectation(else_expr, expected); - let else_diverges = self.diverges.get(); - let if_cause = self.if_cause( - expr_id, - else_expr, - self.return_position_impl_trait_from_match_expectation(orig_expected), - ); - coerce.coerce(self, &if_cause, else_expr, else_ty); - else_diverges - }; - - // We won't diverge unless both branches do (or the condition does). - self.diverges.set(cond_diverges | then_diverges & else_diverges); - } else { - self.if_fallback_coercion(sp, cond_expr, then_expr, &mut coerce); - - // If the condition is false we can't diverge. - self.diverges.set(cond_diverges); - } + let mut cx = IfChainCx { + coerce: &mut coerce, + outer_if_expr_id: expr_id, + orig_expected, + tail_defines_return_position_impl_trait: self + .return_position_impl_trait_from_match_expectation(orig_expected), + }; + let branch_ty = + self.check_if_branch(&mut cx, None, cond_expr, then_expr, opt_else_expr, sp); let result_ty = coerce.complete(self); - if let Err(guar) = cond_ty.error_reported() { + if let Err(guar) = branch_ty.error_reported() { Ty::new_error(self.tcx, guar) } else { result_ty } } - fn check_current_if_branch( + /// Checks one `if` of an `if`/`else if` chain and recurses into the next `else if`. + /// + /// `prev_branch` is `None` for the outermost `if`. + /// Every later branch is coerced against the preceding one (`prev_branch`), + /// so a mismatch is reported at that branch rather than at the whole `else` chain. + fn check_if_branch( &self, + cx: &mut IfChainCx<'_, 'tcx>, + prev_branch: Option, cond_expr: &'tcx hir::Expr<'tcx>, then_expr: &'tcx hir::Expr<'tcx>, - orig_expected: Expectation<'tcx>, - ) -> (Expectation<'tcx>, Ty<'tcx>, Diverges, Diverges) { + opt_else_expr: Option<&'tcx hir::Expr<'tcx>>, + sp: Span, + ) -> Ty<'tcx> { + let cond_ty = self.check_expr_has_type_or_error(cond_expr, self.tcx.types.bool, |_| {}); + self.warn_if_unreachable( cond_expr.hir_id, then_expr.span, @@ -156,76 +77,65 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { let cond_diverges = self.diverges.get(); self.diverges.set(Diverges::Maybe); - let expected = orig_expected.try_structurally_resolve_and_adjust_for_branches(self); + let expected = cx.orig_expected.try_structurally_resolve_and_adjust_for_branches(self); let then_ty = self.check_expr_with_expectation(then_expr, expected); let then_diverges = self.diverges.get(); self.diverges.set(Diverges::Maybe); - (expected, then_ty, cond_diverges, then_diverges) - } - - fn check_else_if_branch( - &self, - cx: &mut ElseIfChainCx<'_, 'tcx>, - prev_branch: PrevBranch<'tcx>, - current_expr: &'tcx hir::Expr<'tcx>, - ) -> Ty<'tcx> { - let ExprKind::If(cond_expr, then_expr, opt_else_expr) = current_expr.kind else { - bug!("check_else_if_branch called on non-`if` expr"); - }; - self.check_expr_has_type_or_error(cond_expr, self.tcx.types.bool, |_| {}); - - let (expected, then_ty, cond_diverges, then_diverges) = - self.check_current_if_branch(cond_expr, then_expr, cx.orig_expected); - - self.coerce_branch_against_prev(cx, prev_branch, then_expr, then_ty); - - let next_prev = PrevBranch { hir_id: then_expr.hir_id, ty: then_ty }; + if let Some(prev_hir_id) = prev_branch { + let cause = self.if_cause( + cx.outer_if_expr_id, + prev_hir_id, + then_expr.hir_id, + cx.tail_defines_return_position_impl_trait, + ); + cx.coerce.coerce(self, &cause, then_expr, then_ty); + } else { + cx.coerce.coerce(self, &self.misc(sp), then_expr, then_ty); + } - let else_diverges = match opt_else_expr { - Some(else_expr) if let ExprKind::If(..) = else_expr.kind => { + match opt_else_expr { + Some(else_expr) + if let ExprKind::If(next_cond_expr, next_then_expr, next_opt_else_expr) = + else_expr.kind => + { self.check_expr_with_check_fn(else_expr, expected, |this| { - this.check_else_if_branch(cx, next_prev, else_expr) + this.check_if_branch( + cx, + Some(then_expr.hir_id), + next_cond_expr, + next_then_expr, + next_opt_else_expr, + else_expr.span, + ) }); - self.diverges.get() + + let else_diverges = self.diverges.get(); + self.diverges.set(cond_diverges | then_diverges & else_diverges); } Some(else_expr) => { let else_ty = self.check_expr_with_expectation(else_expr, expected); let else_diverges = self.diverges.get(); - self.coerce_branch_against_prev(cx, next_prev, else_expr, else_ty); - else_diverges + let cause = self.if_cause( + cx.outer_if_expr_id, + then_expr.hir_id, + else_expr.hir_id, + cx.tail_defines_return_position_impl_trait, + ); + cx.coerce.coerce(self, &cause, else_expr, else_ty); + self.diverges.set(cond_diverges | then_diverges & else_diverges); } - None => bug!("chain entered without a final else; broken `has_final_else_arm`"), - }; - - // We won't diverge unless cond does, or both then and else do. - self.diverges.set(cond_diverges | then_diverges & else_diverges); + None => { + self.if_fallback_coercion(sp, cond_expr, then_expr, cx.coerce); - cx.coerce.merged_ty() - } + self.diverges.set(cond_diverges); + } + }; - fn coerce_branch_against_prev( - &self, - cx: &mut ElseIfChainCx<'_, 'tcx>, - prev: PrevBranch<'tcx>, - current_branch_expr: &'tcx hir::Expr<'tcx>, - current_branch_ty: Ty<'tcx>, - ) { - let prev_branch_span = self.find_block_span_from_hir_id(prev.hir_id); - let branch_span = self.find_block_span_from_hir_id(current_branch_expr.hir_id); - let cause = self.cause( - branch_span, - ObligationCauseCode::IfChainCoerce(Box::new(IfChainCoerceCause { - outer_if_expr_id: cx.outer_if_expr_id, - source_branch_expr_id: prev.hir_id, - source_branch_ty: prev.ty, - source_branch_span: prev_branch_span, - target_branch_expr_id: current_branch_expr.hir_id, - target_branch_ty: current_branch_ty, - target_branch_span: branch_span, - tail_defines_return_position_impl_trait: cx.tail_defines_return_position_impl_trait, - })), - ); - cx.coerce.coerce(self, &cause, current_branch_expr, current_branch_ty); + if let Err(guar) = cond_ty.error_reported() { + Ty::new_error(self.tcx, guar) + } else { + cx.coerce.merged_ty() + } } } diff --git a/compiler/rustc_hir_typeck/src/_match.rs b/compiler/rustc_hir_typeck/src/_match.rs index a1ff036574fdc..3b6c6339e0f39 100644 --- a/compiler/rustc_hir_typeck/src/_match.rs +++ b/compiler/rustc_hir_typeck/src/_match.rs @@ -437,15 +437,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { pub(crate) fn if_cause( &self, expr_id: HirId, - else_expr: &'tcx hir::Expr<'tcx>, + expected_branch_id: HirId, + found_branch_id: HirId, tail_defines_return_position_impl_trait: Option, ) -> ObligationCause<'tcx> { - let error_sp = self.find_block_span_from_hir_id(else_expr.hir_id); + let error_sp = self.find_block_span_from_hir_id(found_branch_id); // Finally construct the cause: self.cause( error_sp, - ObligationCauseCode::IfExpression { expr_id, tail_defines_return_position_impl_trait }, + ObligationCauseCode::IfExpression { + outermost_if_expr_id: expr_id, + expected_branch_id, + found_branch_id, + tail_defines_return_position_impl_trait, + }, ) } diff --git a/compiler/rustc_hir_typeck/src/coercion.rs b/compiler/rustc_hir_typeck/src/coercion.rs index 1c9b73ede7b31..fb2b0d43c076c 100644 --- a/compiler/rustc_hir_typeck/src/coercion.rs +++ b/compiler/rustc_hir_typeck/src/coercion.rs @@ -47,8 +47,7 @@ use rustc_hir_analysis::hir_ty_lowering::HirTyLowerer; use rustc_infer::infer::relate::RelateResult; use rustc_infer::infer::{DefineOpaqueTypes, InferOk, InferResult, RegionVariableOrigin}; use rustc_infer::traits::{ - IfChainCoerceCause, MatchExpressionArmCause, Obligation, PredicateObligation, - PredicateObligations, SelectionError, + MatchExpressionArmCause, Obligation, PredicateObligation, PredicateObligations, SelectionError, }; use rustc_middle::ty::adjustment::{ Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability, DerefAdjustKind, @@ -1833,49 +1832,11 @@ impl<'tcx> CoerceMany<'tcx> { } } ObligationCauseCode::IfExpression { - expr_id, - tail_defines_return_position_impl_trait: Some(rpit_def_id), - } => { - let hir::Node::Expr(hir::Expr { - kind: hir::ExprKind::If(_, then_expr, Some(else_expr)), - .. - }) = fcx.tcx.hir_node(expr_id) - else { - unreachable!(); - }; - err = fcx.err_ctxt().report_mismatched_types( - cause, - fcx.param_env, - expected, - found, - coercion_error, - ); - let then_span = fcx.find_block_span_from_hir_id(then_expr.hir_id); - let else_span = fcx.find_block_span_from_hir_id(else_expr.hir_id); - // Don't suggest wrapping whole block in `Box::new`. - if then_span != then_expr.span && else_span != else_expr.span { - let then_ty = fcx.typeck_results.borrow().expr_ty(then_expr); - let else_ty = fcx.typeck_results.borrow().expr_ty(else_expr); - self.suggest_boxing_tail_for_return_position_impl_trait( - fcx, - &mut err, - rpit_def_id, - then_ty, - else_ty, - [then_span, else_span].into_iter(), - ); - } - } - ObligationCauseCode::IfChainCoerce(IfChainCoerceCause { - source_branch_expr_id: prev_branch_expr_id, - source_branch_ty: prev_branch_ty, - source_branch_span: prev_branch_span, - target_branch_expr_id: branch_expr_id, - target_branch_ty: branch_ty, - target_branch_span: branch_span, + expected_branch_id, + found_branch_id, tail_defines_return_position_impl_trait: Some(rpit_def_id), .. - }) => { + } => { err = fcx.err_ctxt().report_mismatched_types( cause, fcx.param_env, @@ -1883,18 +1844,21 @@ impl<'tcx> CoerceMany<'tcx> { found, coercion_error, ); - let prev_expr_span = - fcx.tcx.hir_node(prev_branch_expr_id).expect_expr().span; - let branch_expr_span = fcx.tcx.hir_node(branch_expr_id).expect_expr().span; + let expected_expr = fcx.tcx.hir_node(expected_branch_id).expect_expr(); + let found_expr = fcx.tcx.hir_node(found_branch_id).expect_expr(); + let expected_span = fcx.find_block_span_from_hir_id(expected_branch_id); + let found_span = fcx.find_block_span_from_hir_id(found_branch_id); // Don't suggest wrapping whole block in `Box::new`. - if prev_branch_span != prev_expr_span && branch_span != branch_expr_span { + if expected_span != expected_expr.span && found_span != found_expr.span { + let expected_ty = fcx.typeck_results.borrow().expr_ty(expected_expr); + let found_ty = fcx.typeck_results.borrow().expr_ty(found_expr); self.suggest_boxing_tail_for_return_position_impl_trait( fcx, &mut err, rpit_def_id, - prev_branch_ty, - branch_ty, - [prev_branch_span, branch_span].into_iter(), + expected_ty, + found_ty, + [expected_span, found_span].into_iter(), ); } } diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs index 116bbf6280642..60e0fa780674e 100644 --- a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs +++ b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs @@ -3135,6 +3135,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { return Some((suggs, help, app, mutref)); } + // Don't suggest borrowing a tail-less block that is an arm of + // an `if`: `else &{ ... }` is not valid syntax, and the block has type `()`. + if let hir::ExprKind::Block(block, _) = expr.kind + && block.expr.is_none() + && let hir::Node::Expr(hir::Expr { kind: hir::ExprKind::If(..), .. }) = + self.tcx.parent_hir_node(expr.hir_id) + { + return None; + } + if let Some((sugg, msg)) = self.can_use_as_ref_or_mut(expr, mutability) { return Some(( sugg, diff --git a/compiler/rustc_middle/src/traits/mod.rs b/compiler/rustc_middle/src/traits/mod.rs index a8a5752406e37..19e112a1d7746 100644 --- a/compiler/rustc_middle/src/traits/mod.rs +++ b/compiler/rustc_middle/src/traits/mod.rs @@ -334,13 +334,17 @@ pub enum ObligationCauseCode<'tcx> { /// Computing common supertype in an if expression IfExpression { - expr_id: HirId, + outermost_if_expr_id: HirId, + /// The branch that established the expected type: the `then` block of a plain + /// `if`/`else`, or the preceding branch of an `else if` chain. + expected_branch_id: HirId, + /// The branch whose type did not match: the `else` block, or the current + /// `else if` branch. + found_branch_id: HirId, // Is the expectation of this match expression an RPIT? tail_defines_return_position_impl_trait: Option, }, - IfChainCoerce(Box>), - /// Computing common supertype of an if expression with no else counter-part IfExpressionWithNoElse, @@ -553,20 +557,6 @@ pub struct MatchExpressionArmCause<'tcx> { pub tail_defines_return_position_impl_trait: Option, } -#[derive(Clone, Debug, PartialEq, Eq, StableHash, TyEncodable, TyDecodable)] -#[derive(TypeVisitable, TypeFoldable)] -pub struct IfChainCoerceCause<'tcx> { - /// Outermost `if` of the chain, for the outer "incompatible types" label. - pub outer_if_expr_id: HirId, - pub source_branch_expr_id: HirId, - pub source_branch_ty: Ty<'tcx>, - pub source_branch_span: Span, - pub target_branch_expr_id: HirId, - pub target_branch_ty: Ty<'tcx>, - pub target_branch_span: Span, - pub tail_defines_return_position_impl_trait: Option, -} - /// Information about the origin expression of a pattern, relevant to diagnostics. /// Fields here refer to the scrutinee of a pattern. /// If the scrutinee isn't given in the diagnostic, then this won't exist. diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs index f0518d5205f7e..cec185b34ecbe 100644 --- a/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs +++ b/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs @@ -59,7 +59,6 @@ use rustc_hir as hir; use rustc_hir::def_id::{CRATE_DEF_ID, DefId}; use rustc_hir::intravisit::Visitor; use rustc_infer::infer::DefineOpaqueTypes; -use rustc_infer::traits::IfChainCoerceCause; use rustc_macros::extension; use rustc_middle::traits::PatternOriginExpr; use rustc_middle::ty::consts::ConstExt; @@ -507,101 +506,45 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> { } } }, - ObligationCauseCode::IfChainCoerce(IfChainCoerceCause { - outer_if_expr_id, - source_branch_expr_id: prev_branch_expr_id, - source_branch_ty: prev_branch_ty, - source_branch_span: prev_branch_span, - target_branch_expr_id: branch_expr_id, - target_branch_ty: branch_ty, - target_branch_span: branch_span, + ObligationCauseCode::IfExpression { + outermost_if_expr_id: expr_id, + expected_branch_id: expected_branch, + found_branch_id: found_branch, .. - }) => { - err.span_label(prev_branch_span, "expected because of this"); - - if let hir::Node::Expr(&hir::Expr { span: expr_span, .. }) = - self.tcx.hir_node(outer_if_expr_id) - && let hir::Node::Expr(&hir::Expr { kind: hir::ExprKind::If(cond, ..), .. }) = - self.tcx.hir_node(outer_if_expr_id) - { - let outer_span = if self.tcx.sess.source_map().is_multiline(expr_span) { - if prev_branch_span.hi() == expr_span.hi() - || branch_span.hi() == expr_span.hi() - { - // Avoid overlapping arrows: shrink to `if `. - Some(expr_span.shrink_to_lo().to(cond.peel_drop_temps().span)) - } else { - Some(expr_span) - } - } else { - None - }; - if let Some(sp) = outer_span { - err.span_label(sp, "`if` and `else` have incompatible types"); - } - } - - let prev_id = if let hir::Node::Expr(hir::Expr { - kind: hir::ExprKind::Block(blk, _), - .. - }) = self.tcx.hir_node(prev_branch_expr_id) - { - blk.hir_id - } else { - prev_branch_expr_id - }; - let new_id = if let hir::Node::Expr(hir::Expr { - kind: hir::ExprKind::Block(blk, _), - .. - }) = self.tcx.hir_node(branch_expr_id) - { - blk.hir_id - } else { - branch_expr_id - }; - if let Some(subdiag) = self.suggest_remove_semi_or_return_binding( - Some(prev_id), - prev_branch_ty, - prev_branch_span, - Some(new_id), - branch_ty, - branch_span, - ) { - err.subdiagnostic(subdiag); - } - } - ObligationCauseCode::IfExpression { expr_id, .. } => { - let hir::Node::Expr(&hir::Expr { - kind: hir::ExprKind::If(cond_expr, then_expr, Some(else_expr)), - span: expr_span, - .. - }) = self.tcx.hir_node(expr_id) + } => { + let hir::Node::Expr( + outer_if @ &hir::Expr { + kind: hir::ExprKind::If(cond_expr, ..), + span: expr_span, + .. + }, + ) = self.tcx.hir_node(expr_id) else { return; }; - let then_span = self.find_block_span_from_hir_id(then_expr.hir_id); - let then_ty = self + let expected_expr = self.tcx.hir_node(expected_branch).expect_expr(); + let found_expr = self.tcx.hir_node(found_branch).expect_expr(); + let expected_span = self.find_block_span_from_hir_id(expected_branch); + let expected_ty = self .typeck_results .as_ref() .expect("if expression only expected inside FnCtxt") - .expr_ty(then_expr); - let else_span = self.find_block_span_from_hir_id(else_expr.hir_id); - let else_ty = self + .expr_ty(expected_expr); + let found_span = self.find_block_span_from_hir_id(found_branch); + let found_ty = self .typeck_results .as_ref() .expect("if expression only expected inside FnCtxt") - .expr_ty(else_expr); - if let hir::ExprKind::If(_cond, _then, None) = else_expr.kind - && else_ty.is_unit() - { - // Account for `let x = if a { 1 } else if b { 2 };` + .expr_ty(found_expr); + if !expected_ty.is_unit() && if_chain_lacks_final_else(outer_if) { + // Account for `if a { &() } else if b { }` err.note("`if` expressions without `else` evaluate to `()`"); err.note("consider adding an `else` block that evaluates to the expected type"); } - err.span_label(then_span, "expected because of this"); + err.span_label(expected_span, "expected because of this"); let outer_span = if self.tcx.sess.source_map().is_multiline(expr_span) { - if then_span.hi() == expr_span.hi() || else_span.hi() == expr_span.hi() { + if expected_span.hi() == expr_span.hi() || found_span.hi() == expr_span.hi() { // Point at condition only if either block has the same end point as // the whole expression, since that'll cause awkward overlapping spans. Some(expr_span.shrink_to_lo().to(cond_expr.peel_drop_temps().span)) @@ -615,23 +558,23 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> { err.span_label(sp, "`if` and `else` have incompatible types"); } - let then_id = if let hir::ExprKind::Block(then_blk, _) = then_expr.kind { + let expected_id = if let hir::ExprKind::Block(then_blk, _) = expected_expr.kind { then_blk.hir_id } else { - then_expr.hir_id + expected_expr.hir_id }; - let else_id = if let hir::ExprKind::Block(else_blk, _) = else_expr.kind { + let found_id = if let hir::ExprKind::Block(else_blk, _) = found_expr.kind { else_blk.hir_id } else { - else_expr.hir_id + found_expr.hir_id }; if let Some(subdiag) = self.suggest_remove_semi_or_return_binding( - Some(then_id), - then_ty, - then_span, - Some(else_id), - else_ty, - else_span, + Some(expected_id), + expected_ty, + expected_span, + Some(found_id), + found_ty, + found_span, ) { err.subdiagnostic(subdiag); } @@ -2687,7 +2630,7 @@ impl<'tcx> ObligationCause<'tcx> { _ => ObligationCauseFailureCode::MatchCompat { span, subdiags }, } } - ObligationCauseCode::IfExpression { .. } | ObligationCauseCode::IfChainCoerce(_) => { + ObligationCauseCode::IfExpression { .. } => { ObligationCauseFailureCode::IfElseDifferent { span, subdiags } } ObligationCauseCode::IfExpressionWithNoElse => { @@ -2815,3 +2758,14 @@ impl TyCategory { } } } + +fn if_chain_lacks_final_else(expr: &hir::Expr<'_>) -> bool { + let mut cur = expr; + loop { + match cur.kind { + hir::ExprKind::If(_, _, Some(next)) => cur = next, + hir::ExprKind::If(_, _, None) => return true, + _ => return false, + } + } +} diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs index 7b5bd350fe8f9..b55129d568201 100644 --- a/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs +++ b/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs @@ -485,7 +485,10 @@ impl Trait for X { } // If two if arms can be coerced to a trait object, provide a structured // suggestion. - let ObligationCauseCode::IfExpression { expr_id, .. } = cause.code() else { + let ObligationCauseCode::IfExpression { + outermost_if_expr_id: expr_id, .. + } = cause.code() + else { return; }; let hir::Node::Expr(&hir::Expr { @@ -565,7 +568,10 @@ impl Trait for X { } } (ty::Adt(_, _), ty::Adt(def, args)) - if let ObligationCauseCode::IfExpression { expr_id, .. } = cause.code() + if let ObligationCauseCode::IfExpression { + outermost_if_expr_id: expr_id, + .. + } = cause.code() && let hir::Node::Expr(if_expr) = self.tcx.hir_node(*expr_id) && let hir::ExprKind::If(_, then_expr, _) = if_expr.kind && let hir::ExprKind::Block(blk, _) = then_expr.kind diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs index 4ccc7ab986f1e..b1e548b1dd411 100644 --- a/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs +++ b/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs @@ -197,37 +197,31 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> { self.tcx.get_impl_future_output_ty(exp_found.expected), self.tcx.get_impl_future_output_ty(exp_found.found), ) { - (Some(exp), Some(found)) if self.same_type_modulo_infer(exp, found) => match cause - .code() - { - ObligationCauseCode::IfExpression { expr_id, .. } => { - let hir::Node::Expr(hir::Expr { - kind: hir::ExprKind::If(_, then_expr, _), .. - }) = self.tcx.hir_node(*expr_id) - else { - return; - }; - let then_span = self.find_block_span_from_hir_id(then_expr.hir_id); - Some(ConsiderAddingAwait::BothFuturesSugg { - first: then_span.shrink_to_hi(), - second: exp_span.shrink_to_hi(), - }) - } - ObligationCauseCode::MatchExpressionArm(MatchExpressionArmCause { - prior_non_diverging_arms, - .. - }) => { - if let [.., arm_span] = &prior_non_diverging_arms[..] { + (Some(exp), Some(found)) if self.same_type_modulo_infer(exp, found) => { + match cause.code() { + ObligationCauseCode::IfExpression { expected_branch_id, .. } => { + let expected_span = self.find_block_span_from_hir_id(*expected_branch_id); Some(ConsiderAddingAwait::BothFuturesSugg { - first: arm_span.shrink_to_hi(), + first: expected_span.shrink_to_hi(), second: exp_span.shrink_to_hi(), }) - } else { - Some(ConsiderAddingAwait::BothFuturesHelp) } + ObligationCauseCode::MatchExpressionArm(MatchExpressionArmCause { + prior_non_diverging_arms, + .. + }) => { + if let [.., arm_span] = &prior_non_diverging_arms[..] { + Some(ConsiderAddingAwait::BothFuturesSugg { + first: arm_span.shrink_to_hi(), + second: exp_span.shrink_to_hi(), + }) + } else { + Some(ConsiderAddingAwait::BothFuturesHelp) + } + } + _ => Some(ConsiderAddingAwait::BothFuturesHelp), } - _ => Some(ConsiderAddingAwait::BothFuturesHelp), - }, + } (_, Some(ty)) if self.same_type_modulo_infer(exp_found.expected, ty) => { // FIXME: Seems like we can't have a suggestion and a note with different spans in a single subdiagnostic diag.subdiagnostic(ConsiderAddingAwait::FutureSugg { @@ -242,15 +236,9 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> { span: then_span.shrink_to_hi(), }) } - ObligationCauseCode::IfExpression { expr_id, .. } => { - let hir::Node::Expr(hir::Expr { - kind: hir::ExprKind::If(_, then_expr, _), .. - }) = self.tcx.hir_node(*expr_id) - else { - return; - }; - let then_span = self.find_block_span_from_hir_id(then_expr.hir_id); - Some(ConsiderAddingAwait::FutureSugg { span: then_span.shrink_to_hi() }) + ObligationCauseCode::IfExpression { expected_branch_id, .. } => { + let expected_span = self.find_block_span_from_hir_id(*expected_branch_id); + Some(ConsiderAddingAwait::FutureSugg { span: expected_span.shrink_to_hi() }) } ObligationCauseCode::MatchExpressionArm(MatchExpressionArmCause { prior_non_diverging_arms, diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs index 90ef6b8432c0f..76755eb481db7 100644 --- a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs +++ b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs @@ -3897,7 +3897,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> { ObligationCauseCode::ExprAssignable | ObligationCauseCode::MatchExpressionArm { .. } | ObligationCauseCode::Pattern { .. } - | ObligationCauseCode::IfChainCoerce(_) | ObligationCauseCode::IfExpression { .. } | ObligationCauseCode::IfExpressionWithNoElse | ObligationCauseCode::MainFunctionType diff --git a/tests/ui/expr/if/if-else-chain-missing-else.rs b/tests/ui/expr/if/if-else-chain-missing-else.rs index 995aac07f2f76..f78701383601f 100644 --- a/tests/ui/expr/if/if-else-chain-missing-else.rs +++ b/tests/ui/expr/if/if-else-chain-missing-else.rs @@ -9,7 +9,7 @@ fn f() -> Result { let res = could_fail(); let x = if let Ok(x) = res { x - } else if let Err(e) = res { //~ ERROR `if` and `else` + } else if let Err(e) = res { //~ ERROR `if` may be missing an `else` clause return Err(e); }; Ok(x) diff --git a/tests/ui/expr/if/if-else-chain-missing-else.stderr b/tests/ui/expr/if/if-else-chain-missing-else.stderr index 6c437120d391d..f6bcbe2c1094f 100644 --- a/tests/ui/expr/if/if-else-chain-missing-else.stderr +++ b/tests/ui/expr/if/if-else-chain-missing-else.stderr @@ -1,10 +1,6 @@ -error[E0308]: `if` and `else` have incompatible types +error[E0317]: `if` may be missing an `else` clause --> $DIR/if-else-chain-missing-else.rs:12:12 | -LL | let x = if let Ok(x) = res { - | ------------------ `if` and `else` have incompatible types -LL | x - | - expected because of this LL | } else if let Err(e) = res { | ____________^ LL | | return Err(e); @@ -12,8 +8,8 @@ LL | | }; | |_____^ expected `i32`, found `()` | = note: `if` expressions without `else` evaluate to `()` - = note: consider adding an `else` block that evaluates to the expected type + = help: consider adding an `else` block that evaluates to the expected type error: aborting due to 1 previous error -For more information about this error, try `rustc --explain E0308`. +For more information about this error, try `rustc --explain E0317`. diff --git a/tests/ui/typeck/consider-borrowing-141810-2.stderr b/tests/ui/typeck/consider-borrowing-141810-2.stderr index 44ecb5a4a945a..ff3da9e04c2fe 100644 --- a/tests/ui/typeck/consider-borrowing-141810-2.stderr +++ b/tests/ui/typeck/consider-borrowing-141810-2.stderr @@ -1,15 +1,16 @@ error[E0308]: `if` and `else` have incompatible types - --> $DIR/consider-borrowing-141810-2.rs:4:12 + --> $DIR/consider-borrowing-141810-2.rs:4:21 | -LL | let x = if true { - | ------- `if` and `else` have incompatible types -LL | &() - | --- expected because of this -LL | } else if false { - | ____________^ -LL | | } else { -LL | | }; - | |_____^ expected `&()`, found `()` +LL | let x = if true { + | ______________- +LL | | &() + | | --- expected because of this +LL | | } else if false { + | | _____________________^ +LL | || } else { + | ||_____^ expected `&()`, found `()` +LL | | }; + | |______- `if` and `else` have incompatible types error: aborting due to 1 previous error diff --git a/tests/ui/typeck/consider-borrowing-141810-3.stderr b/tests/ui/typeck/consider-borrowing-141810-3.stderr index 3adf8ba1a8924..4c79b8499f279 100644 --- a/tests/ui/typeck/consider-borrowing-141810-3.stderr +++ b/tests/ui/typeck/consider-borrowing-141810-3.stderr @@ -1,12 +1,12 @@ error[E0308]: `if` and `else` have incompatible types - --> $DIR/consider-borrowing-141810-3.rs:4:12 + --> $DIR/consider-borrowing-141810-3.rs:4:21 | LL | let x = if true { | ------- `if` and `else` have incompatible types LL | &() | --- expected because of this LL | } else if false { - | ____________^ + | _____________________^ LL | | LL | | }; | |_____^ expected `&()`, found `()` From 4afcd7ad51e075604f1c304ea8dcac6461a3a399 Mon Sep 17 00:00:00 2001 From: sgasho Date: Mon, 12 Oct 2026 16:42:03 +0900 Subject: [PATCH 3/3] fixed a outdated comment --- compiler/rustc_hir_typeck/src/_if.rs | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/compiler/rustc_hir_typeck/src/_if.rs b/compiler/rustc_hir_typeck/src/_if.rs index c6755df9ce52b..e1517caae272a 100644 --- a/compiler/rustc_hir_typeck/src/_if.rs +++ b/compiler/rustc_hir_typeck/src/_if.rs @@ -9,7 +9,7 @@ use crate::coercion::CoerceMany; use crate::diverges::Diverges; use crate::fn_ctxt::FnCtxt; -/// State shared across all branches of an `else if` chain check. +/// State shared across all branches of an `if`/`else if` chain check. struct IfChainCx<'a, 'tcx> { coerce: &'a mut CoerceMany<'tcx>, outer_if_expr_id: HirId,