diff --git a/compiler/rustc_mir_build/src/build/matches/mod.rs b/compiler/rustc_mir_build/src/build/matches/mod.rs index 1ea671a4f791e..367c391b45a49 100644 --- a/compiler/rustc_mir_build/src/build/matches/mod.rs +++ b/compiler/rustc_mir_build/src/build/matches/mod.rs @@ -214,12 +214,77 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { /// /// ## False edges /// - /// We don't want to have the exact structure of the decision tree be - /// visible through borrow checking. False edges ensure that the CFG as - /// seen by borrow checking doesn't encode this. False edges are added: + /// We don't want to have the exact structure of the decision tree be visible through borrow + /// checking. Specifically we want borrowck to think that: + /// - at any point, any or none of the patterns and guards seen so far may have been tested; + /// - after the match, any of the patterns may have matched. /// - /// * From each pre-binding block to the next pre-binding block. - /// * From each otherwise block to the next pre-binding block. + /// For example, all of these would fail to error if borrowck could see the real CFG (examples + /// taken from `tests/ui/nll/match-cfg-fake-edges.rs`): + /// ```ignore (too many errors, this is already in the test suite) + /// let x = String::new(); + /// let _ = match true { + /// _ => {}, + /// _ => drop(x), + /// }; + /// // Borrowck must not know the second arm is never run. + /// drop(x); //~ ERROR use of moved value + /// + /// let x; + /// # let y = true; + /// match y { + /// _ if { x = 2; true } => {}, + /// // Borrowck must not know the guard is always run. + /// _ => drop(x), //~ ERROR used binding `x` is possibly-uninitialized + /// }; + /// + /// let x = String::new(); + /// # let y = true; + /// match y { + /// false if { drop(x); true } => {}, + /// // Borrowck must not know the guard is not run in the `true` case. + /// true => drop(x), //~ ERROR use of moved value: `x` + /// false => {}, + /// }; + /// + /// # let mut y = (true, true); + /// let r = &mut y.1; + /// match y { + /// //~^ ERROR cannot use `y.1` because it was mutably borrowed + /// (false, true) => {} + /// // Borrowck must not know we don't test `y.1` when `y.0` is `true`. + /// (true, _) => drop(r), + /// (false, _) => {} + /// }; + /// ``` + /// + /// We add false edges to act as if we were naively matching each arm in order. What we need is + /// a (fake) path from each candidate to the next, specifically from candidate C's pre-binding + /// block to next candidate D's pre-binding block. For maximum precision (needed for deref + /// patterns), we choose the earliest node on D's success path that doesn't also lead to C (to + /// avoid loops). + /// + /// This turns out to be easy to compute: that block is the `start_block` of the first call to + /// `match_candidates` where D is the first candidate in the list. + /// + /// For example: + /// ```rust + /// # let (x, y) = (true, true); + /// match (x, y) { + /// (true, true) => 1, + /// (false, true) => 2, + /// (true, false) => 3, + /// _ => 4, + /// } + /// # ; + /// ``` + /// In this example, the pre-binding block of arm 1 has a false edge to the block for result + /// `false` of the first test on `x`. The other arms have false edges to the pre-binding blocks + /// of the next arm. + /// + /// On top of this, we also add a false edge from the otherwise_block of each guard to the + /// aforementioned start block of the next candidate, to ensure borrock doesn't rely on which + /// guards may have run. #[instrument(level = "debug", skip(self, arms))] pub(crate) fn match_expr( &mut self, @@ -365,7 +430,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { for candidate in candidates { candidate.visit_leaves(|leaf_candidate| { if let Some(ref mut prev) = previous_candidate { - prev.next_candidate_pre_binding_block = leaf_candidate.pre_binding_block; + assert!(leaf_candidate.false_edge_start_block.is_some()); + prev.next_candidate_start_block = leaf_candidate.false_edge_start_block; } previous_candidate = Some(leaf_candidate); }); @@ -1010,8 +1076,12 @@ struct Candidate<'pat, 'tcx> { /// The block before the `bindings` have been established. pre_binding_block: Option, - /// The pre-binding block of the next candidate. - next_candidate_pre_binding_block: Option, + + /// The earliest block that has only candidates >= this one as descendents. Used for false + /// edges, see the doc for [`Builder::match_expr`]. + false_edge_start_block: Option, + /// The `false_edge_start_block` of the next candidate. + next_candidate_start_block: Option, } impl<'tcx, 'pat> Candidate<'pat, 'tcx> { @@ -1033,7 +1103,8 @@ impl<'tcx, 'pat> Candidate<'pat, 'tcx> { or_span: None, otherwise_block: None, pre_binding_block: None, - next_candidate_pre_binding_block: None, + false_edge_start_block: None, + next_candidate_start_block: None, } } @@ -1325,6 +1396,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { otherwise_block: BasicBlock, candidates: &mut [&mut Candidate<'_, 'tcx>], ) { + if let [first, ..] = candidates { + if first.false_edge_start_block.is_none() { + first.false_edge_start_block = Some(start_block); + } + } + match candidates { [] => { // If there are no candidates that still need testing, we're done. Since all matches are @@ -1545,6 +1622,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { .into_iter() .map(|flat_pat| Candidate::from_flat_pat(flat_pat, candidate.has_guard)) .collect(); + candidate.subcandidates[0].false_edge_start_block = candidate.false_edge_start_block; } /// Try to merge all of the subcandidates of the given candidate into one. This avoids @@ -1564,6 +1642,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { let any_matches = self.cfg.start_new_block(); let or_span = candidate.or_span.take().unwrap(); let source_info = self.source_info(or_span); + if candidate.false_edge_start_block.is_none() { + candidate.false_edge_start_block = + candidate.subcandidates[0].false_edge_start_block; + } for subcandidate in mem::take(&mut candidate.subcandidates) { let or_block = subcandidate.pre_binding_block.unwrap(); self.cfg.goto(or_block, source_info, any_matches); @@ -1979,12 +2061,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { let mut block = candidate.pre_binding_block.unwrap(); - if candidate.next_candidate_pre_binding_block.is_some() { + if candidate.next_candidate_start_block.is_some() { let fresh_block = self.cfg.start_new_block(); self.false_edges( block, fresh_block, - candidate.next_candidate_pre_binding_block, + candidate.next_candidate_start_block, candidate_source_info, ); block = fresh_block; @@ -2132,7 +2214,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { self.false_edges( otherwise_post_guard_block, otherwise_block, - candidate.next_candidate_pre_binding_block, + candidate.next_candidate_start_block, source_info, ); diff --git a/tests/mir-opt/building/match/match_false_edges.main.built.after.mir b/tests/mir-opt/building/match/match_false_edges.main.built.after.mir index b71b2412cdf47..dfa31cfff6b2c 100644 --- a/tests/mir-opt/building/match/match_false_edges.main.built.after.mir +++ b/tests/mir-opt/building/match/match_false_edges.main.built.after.mir @@ -48,7 +48,7 @@ fn main() -> () { } bb2: { - falseEdge -> [real: bb15, imaginary: bb6]; + falseEdge -> [real: bb15, imaginary: bb3]; } bb3: { diff --git a/tests/mir-opt/building/match/sort_candidates.constant_eq.SimplifyCfg-initial.after.mir b/tests/mir-opt/building/match/sort_candidates.constant_eq.SimplifyCfg-initial.after.mir index e95a97b5b87fc..c3497c6989d77 100644 --- a/tests/mir-opt/building/match/sort_candidates.constant_eq.SimplifyCfg-initial.after.mir +++ b/tests/mir-opt/building/match/sort_candidates.constant_eq.SimplifyCfg-initial.after.mir @@ -40,7 +40,7 @@ fn constant_eq(_1: &str, _2: bool) -> u32 { } bb4: { - falseEdge -> [real: bb12, imaginary: bb9]; + falseEdge -> [real: bb12, imaginary: bb7]; } bb5: { @@ -48,7 +48,7 @@ fn constant_eq(_1: &str, _2: bool) -> u32 { } bb6: { - falseEdge -> [real: bb16, imaginary: bb3]; + falseEdge -> [real: bb16, imaginary: bb1]; } bb7: { @@ -60,7 +60,7 @@ fn constant_eq(_1: &str, _2: bool) -> u32 { } bb9: { - falseEdge -> [real: bb15, imaginary: bb6]; + falseEdge -> [real: bb15, imaginary: bb5]; } bb10: { @@ -89,7 +89,7 @@ fn constant_eq(_1: &str, _2: bool) -> u32 { bb14: { StorageDead(_10); - falseEdge -> [real: bb5, imaginary: bb9]; + falseEdge -> [real: bb5, imaginary: bb7]; } bb15: { diff --git a/tests/mir-opt/building/match/sort_candidates.disjoint_ranges.SimplifyCfg-initial.after.mir b/tests/mir-opt/building/match/sort_candidates.disjoint_ranges.SimplifyCfg-initial.after.mir index 80d3c2e5c23e8..4a1e4fb9ec56f 100644 --- a/tests/mir-opt/building/match/sort_candidates.disjoint_ranges.SimplifyCfg-initial.after.mir +++ b/tests/mir-opt/building/match/sort_candidates.disjoint_ranges.SimplifyCfg-initial.after.mir @@ -23,7 +23,7 @@ fn disjoint_ranges(_1: i32, _2: bool) -> u32 { } bb2: { - falseEdge -> [real: bb9, imaginary: bb4]; + falseEdge -> [real: bb9, imaginary: bb3]; } bb3: { @@ -32,7 +32,7 @@ fn disjoint_ranges(_1: i32, _2: bool) -> u32 { } bb4: { - falseEdge -> [real: bb12, imaginary: bb6]; + falseEdge -> [real: bb12, imaginary: bb5]; } bb5: { @@ -69,7 +69,7 @@ fn disjoint_ranges(_1: i32, _2: bool) -> u32 { bb11: { StorageDead(_8); - falseEdge -> [real: bb1, imaginary: bb4]; + falseEdge -> [real: bb1, imaginary: bb3]; } bb12: { diff --git a/tests/mir-opt/match_arm_scopes.complicated_match.panic-abort.SimplifyCfg-initial.after-ElaborateDrops.after.diff b/tests/mir-opt/match_arm_scopes.complicated_match.panic-abort.SimplifyCfg-initial.after-ElaborateDrops.after.diff index 307f7105dd2f1..ba333ba1a5866 100644 --- a/tests/mir-opt/match_arm_scopes.complicated_match.panic-abort.SimplifyCfg-initial.after-ElaborateDrops.after.diff +++ b/tests/mir-opt/match_arm_scopes.complicated_match.panic-abort.SimplifyCfg-initial.after-ElaborateDrops.after.diff @@ -60,11 +60,11 @@ } - bb5: { -- falseEdge -> [real: bb13, imaginary: bb3]; +- falseEdge -> [real: bb13, imaginary: bb2]; - } - - bb6: { -- falseEdge -> [real: bb8, imaginary: bb5]; +- falseEdge -> [real: bb8, imaginary: bb1]; - } - - bb7: { @@ -127,7 +127,7 @@ StorageDead(_9); StorageDead(_8); StorageDead(_6); -- falseEdge -> [real: bb1, imaginary: bb5]; +- falseEdge -> [real: bb1, imaginary: bb1]; + goto -> bb1; } @@ -184,7 +184,7 @@ StorageDead(_12); StorageDead(_8); StorageDead(_6); -- falseEdge -> [real: bb2, imaginary: bb3]; +- falseEdge -> [real: bb2, imaginary: bb2]; + goto -> bb2; } diff --git a/tests/mir-opt/match_arm_scopes.complicated_match.panic-unwind.SimplifyCfg-initial.after-ElaborateDrops.after.diff b/tests/mir-opt/match_arm_scopes.complicated_match.panic-unwind.SimplifyCfg-initial.after-ElaborateDrops.after.diff index 307f7105dd2f1..ba333ba1a5866 100644 --- a/tests/mir-opt/match_arm_scopes.complicated_match.panic-unwind.SimplifyCfg-initial.after-ElaborateDrops.after.diff +++ b/tests/mir-opt/match_arm_scopes.complicated_match.panic-unwind.SimplifyCfg-initial.after-ElaborateDrops.after.diff @@ -60,11 +60,11 @@ } - bb5: { -- falseEdge -> [real: bb13, imaginary: bb3]; +- falseEdge -> [real: bb13, imaginary: bb2]; - } - - bb6: { -- falseEdge -> [real: bb8, imaginary: bb5]; +- falseEdge -> [real: bb8, imaginary: bb1]; - } - - bb7: { @@ -127,7 +127,7 @@ StorageDead(_9); StorageDead(_8); StorageDead(_6); -- falseEdge -> [real: bb1, imaginary: bb5]; +- falseEdge -> [real: bb1, imaginary: bb1]; + goto -> bb1; } @@ -184,7 +184,7 @@ StorageDead(_12); StorageDead(_8); StorageDead(_6); -- falseEdge -> [real: bb2, imaginary: bb3]; +- falseEdge -> [real: bb2, imaginary: bb2]; + goto -> bb2; } diff --git a/tests/ui/nll/match-cfg-fake-edges.rs b/tests/ui/nll/match-cfg-fake-edges.rs index 1afc7931a6b62..e349c2c8e2a5f 100644 --- a/tests/ui/nll/match-cfg-fake-edges.rs +++ b/tests/ui/nll/match-cfg-fake-edges.rs @@ -3,15 +3,57 @@ #![feature(if_let_guard)] +#[rustfmt::skip] +fn all_patterns_are_tested() { + // Even though `x` is never actually moved out of, we don't want borrowck results to be based on + // whether MIR lowering reveals which patterns are unreachable. + let x = String::new(); + match true { + _ => {}, + _ => drop(x), + } + // Borrowck must not know the second arm is never run. + drop(x); //~ ERROR use of moved value + + let x = String::new(); + if let _ = true { //~ WARN irrefutable + } else { + drop(x) + } + // Borrowck must not know the else branch is never run. + drop(x); //~ ERROR use of moved value + + let x = (String::new(), String::new()); + match x { + (y, _) | (_, y) => (), + } + &x.0; //~ ERROR borrow of moved value + // Borrowck must not know the second pattern never matches. + &x.1; //~ ERROR borrow of moved value + + let x = (String::new(), String::new()); + let ((y, _) | (_, y)) = x; + &x.0; //~ ERROR borrow of moved value + // Borrowck must not know the second pattern never matches. + &x.1; //~ ERROR borrow of moved value +} + +#[rustfmt::skip] fn guard_always_precedes_arm(y: i32) { - let mut x; // x should always be initialized, as the only way to reach the arm is // through the guard. + let mut x; match y { 0 | 2 if { x = 2; true } => x, _ => 2, }; + let mut x; + match y { + _ => 2, + 0 | 2 if { x = 2; true } => x, + }; + let mut x; match y { 0 | 2 if let Some(()) = { x = 2; Some(()) } => x, @@ -19,51 +61,58 @@ fn guard_always_precedes_arm(y: i32) { }; } +#[rustfmt::skip] fn guard_may_be_skipped(y: i32) { + // Even though x *is* always initialized, we don't want to have borrowck results be based on + // whether MIR lowering reveals which patterns are exhaustive. + let x; + match y { + _ if { x = 2; true } => {}, + // Borrowck must not know the guard is always run. + _ => drop(x), //~ ERROR used binding `x` is possibly-uninitialized + }; + let x; - // Even though x *is* always initialized, we don't want to have borrowck - // results be based on whether patterns are exhaustive. match y { _ if { x = 2; true } => 1, - _ if { - x; //~ ERROR E0381 - false - } => 2, + // Borrowck must not know the guard is always run. + _ if { x; false } => 2, //~ ERROR used binding `x` isn't initialized _ => 3, }; let x; match y { _ if let Some(()) = { x = 2; Some(()) } => 1, - _ if let Some(()) = { - x; //~ ERROR E0381 - None - } => 2, + _ if let Some(()) = { x; None } => 2, //~ ERROR used binding `x` isn't initialized _ => 3, }; } +#[rustfmt::skip] fn guard_may_be_taken(y: bool) { - let x = String::new(); // Even though x *is* never moved before the use, we don't want to have // borrowck results be based on whether patterns are disjoint. + let x = String::new(); + match y { + false if { drop(x); true } => {}, + // Borrowck must not know the guard is not run in the `true` case. + true => drop(x), //~ ERROR use of moved value: `x` + false => {}, + }; + + // Fine in the other order. + let x = String::new(); match y { - false if { drop(x); true } => 1, - true => { - x; //~ ERROR use of moved value: `x` - 2 - } - false => 3, + true => drop(x), + false if { drop(x); true } => {}, + false => {}, }; let x = String::new(); match y { - false if let Some(()) = { drop(x); Some(()) } => 1, - true => { - x; //~ ERROR use of moved value: `x` - 2 - } - false => 3, + false if let Some(()) = { drop(x); Some(()) } => {}, + true => drop(x), //~ ERROR use of moved value: `x` + false => {}, }; } diff --git a/tests/ui/nll/match-cfg-fake-edges.stderr b/tests/ui/nll/match-cfg-fake-edges.stderr index a6261345ceac7..d692ded36fa49 100644 --- a/tests/ui/nll/match-cfg-fake-edges.stderr +++ b/tests/ui/nll/match-cfg-fake-edges.stderr @@ -1,14 +1,128 @@ -error[E0381]: used binding `x` isn't initialized - --> $DIR/match-cfg-fake-edges.rs:29:13 +warning: irrefutable `if let` pattern + --> $DIR/match-cfg-fake-edges.rs:19:8 + | +LL | if let _ = true { + | ^^^^^^^^^^^^ + | + = note: this pattern will always match, so the `if let` is useless + = help: consider replacing the `if let` with a `let` + = note: `#[warn(irrefutable_let_patterns)]` on by default + +error[E0382]: use of moved value: `x` + --> $DIR/match-cfg-fake-edges.rs:16:10 + | +LL | let x = String::new(); + | - move occurs because `x` has type `String`, which does not implement the `Copy` trait +... +LL | _ => drop(x), + | - value moved here +... +LL | drop(x); + | ^ value used here after move + | +help: consider cloning the value if the performance cost is acceptable + | +LL | _ => drop(x.clone()), + | ++++++++ + +error[E0382]: use of moved value: `x` + --> $DIR/match-cfg-fake-edges.rs:24:10 + | +LL | let x = String::new(); + | - move occurs because `x` has type `String`, which does not implement the `Copy` trait +... +LL | drop(x) + | - value moved here +... +LL | drop(x); + | ^ value used here after move + | +help: consider cloning the value if the performance cost is acceptable + | +LL | drop(x.clone()) + | ++++++++ + +error[E0382]: borrow of moved value: `x.0` + --> $DIR/match-cfg-fake-edges.rs:30:5 + | +LL | (y, _) | (_, y) => (), + | - value moved here +LL | } +LL | &x.0; + | ^^^^ value borrowed here after move + | + = note: move occurs because `x.0` has type `String`, which does not implement the `Copy` trait +help: borrow this binding in the pattern to avoid moving the value + | +LL | (ref y, _) | (_, y) => (), + | +++ + +error[E0382]: borrow of moved value: `x.1` + --> $DIR/match-cfg-fake-edges.rs:32:5 + | +LL | (y, _) | (_, y) => (), + | - value moved here +... +LL | &x.1; + | ^^^^ value borrowed here after move + | + = note: move occurs because `x.1` has type `String`, which does not implement the `Copy` trait +help: borrow this binding in the pattern to avoid moving the value + | +LL | (y, _) | (_, ref y) => (), + | +++ + +error[E0382]: borrow of moved value: `x.0` + --> $DIR/match-cfg-fake-edges.rs:36:5 + | +LL | let ((y, _) | (_, y)) = x; + | - value moved here +LL | &x.0; + | ^^^^ value borrowed here after move + | + = note: move occurs because `x.0` has type `String`, which does not implement the `Copy` trait +help: borrow this binding in the pattern to avoid moving the value + | +LL | let ((ref y, _) | (_, y)) = x; + | +++ + +error[E0382]: borrow of moved value: `x.1` + --> $DIR/match-cfg-fake-edges.rs:38:5 + | +LL | let ((y, _) | (_, y)) = x; + | - value moved here +... +LL | &x.1; + | ^^^^ value borrowed here after move + | + = note: move occurs because `x.1` has type `String`, which does not implement the `Copy` trait +help: borrow this binding in the pattern to avoid moving the value + | +LL | let ((y, _) | (_, ref y)) = x; + | +++ + +error[E0381]: used binding `x` is possibly-uninitialized + --> $DIR/match-cfg-fake-edges.rs:72:19 | LL | let x; | - binding declared here but left uninitialized ... +LL | _ => drop(x), + | - ^ `x` used here but it is possibly-uninitialized + | | + | if this pattern is matched, `x` is not initialized + +error[E0381]: used binding `x` isn't initialized + --> $DIR/match-cfg-fake-edges.rs:79:16 + | +LL | let x; + | - binding declared here but left uninitialized +LL | match y { LL | _ if { x = 2; true } => 1, | ----- binding initialized here in some conditions -LL | _ if { -LL | x; - | ^ `x` used here but it isn't initialized +LL | // Borrowck must not know the guard is always run. +LL | _ if { x; false } => 2, + | ^ `x` used here but it isn't initialized | help: consider assigning a value | @@ -16,16 +130,15 @@ LL | let x = 0; | +++ error[E0381]: used binding `x` isn't initialized - --> $DIR/match-cfg-fake-edges.rs:39:13 + --> $DIR/match-cfg-fake-edges.rs:86:31 | LL | let x; | - binding declared here but left uninitialized LL | match y { LL | _ if let Some(()) = { x = 2; Some(()) } => 1, | ----- binding initialized here in some conditions -LL | _ if let Some(()) = { -LL | x; - | ^ `x` used here but it isn't initialized +LL | _ if let Some(()) = { x; None } => 2, + | ^ `x` used here but it isn't initialized | help: consider assigning a value | @@ -33,40 +146,39 @@ LL | let x = 0; | +++ error[E0382]: use of moved value: `x` - --> $DIR/match-cfg-fake-edges.rs:53:13 + --> $DIR/match-cfg-fake-edges.rs:99:22 | LL | let x = String::new(); | - move occurs because `x` has type `String`, which does not implement the `Copy` trait -... -LL | false if { drop(x); true } => 1, +LL | match y { +LL | false if { drop(x); true } => {}, | - value moved here -LL | true => { -LL | x; - | ^ value used here after move +LL | // Borrowck must not know the guard is not run in the `true` case. +LL | true => drop(x), + | ^ value used here after move | help: consider cloning the value if the performance cost is acceptable | -LL | false if { drop(x.clone()); true } => 1, +LL | false if { drop(x.clone()); true } => {}, | ++++++++ error[E0382]: use of moved value: `x` - --> $DIR/match-cfg-fake-edges.rs:63:13 + --> $DIR/match-cfg-fake-edges.rs:114:22 | LL | let x = String::new(); | - move occurs because `x` has type `String`, which does not implement the `Copy` trait LL | match y { -LL | false if let Some(()) = { drop(x); Some(()) } => 1, +LL | false if let Some(()) = { drop(x); Some(()) } => {}, | - value moved here -LL | true => { -LL | x; - | ^ value used here after move +LL | true => drop(x), + | ^ value used here after move | help: consider cloning the value if the performance cost is acceptable | -LL | false if let Some(()) = { drop(x.clone()); Some(()) } => 1, +LL | false if let Some(()) = { drop(x.clone()); Some(()) } => {}, | ++++++++ -error: aborting due to 4 previous errors +error: aborting due to 11 previous errors; 1 warning emitted Some errors have detailed explanations: E0381, E0382. For more information about an error, try `rustc --explain E0381`. diff --git a/tests/ui/nll/match-cfg-fake-edges2.rs b/tests/ui/nll/match-cfg-fake-edges2.rs index 48f95e03b78ca..ac90fb9cd1e76 100644 --- a/tests/ui/nll/match-cfg-fake-edges2.rs +++ b/tests/ui/nll/match-cfg-fake-edges2.rs @@ -5,13 +5,20 @@ fn all_previous_tests_may_be_done(y: &mut (bool, bool)) { let r = &mut y.1; // We don't actually test y.1 to select the second arm, but we don't want // borrowck results to be based on the order we match patterns. - match y { //~ ERROR cannot use `y.1` because it was mutably borrowed - (false, true) => 1, - (true, _) => { - r; - 2 - } - (false, _) => 3, + match y { + //~^ ERROR cannot use `y.1` because it was mutably borrowed + (false, true) => {} + // Borrowck must not know we don't test `y.1` when `y.0` is `true`. + (true, _) => drop(r), + (false, _) => {} + }; + + // Fine in the other order. + let r = &mut y.1; + match y { + (true, _) => drop(r), + (false, true) => {} + (false, _) => {} }; } diff --git a/tests/ui/nll/match-cfg-fake-edges2.stderr b/tests/ui/nll/match-cfg-fake-edges2.stderr index 639cba1406aef..0a228d62b9237 100644 --- a/tests/ui/nll/match-cfg-fake-edges2.stderr +++ b/tests/ui/nll/match-cfg-fake-edges2.stderr @@ -7,8 +7,8 @@ LL | let r = &mut y.1; LL | match y { | ^^^^^^^ use of borrowed `y.1` ... -LL | r; - | - borrow later used here +LL | (true, _) => drop(r), + | - borrow later used here error: aborting due to 1 previous error