Auto merge of #70015 - jonas-schievink:gen-needs-drop, r=matthewjasper
Make `needs_drop` less pessimistic on generators Generators only have non-trivial drop logic when they may store (in upvars or across yields) a type that does. This prevents generation of some unnecessary MIR in simple generators. There might be some impact on compile times, but this is probably limited in real-world applications. ~~This builds off of https://github.com/rust-lang/rust/pull/69814 since that contains some fixes that are made relevant by *this* PR (see https://github.com/rust-lang/rust/pull/69814#issuecomment-599147269).~~ (this has been merged)
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commit
36b1a9296c
6 changed files with 85 additions and 44 deletions
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@ -1047,10 +1047,7 @@ pub fn needs_drop_components(
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// Foreign types can never have destructors.
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ty::Foreign(..) => Ok(SmallVec::new()),
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// Pessimistically assume that all generators will require destructors
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// as we don't know if a destructor is a noop or not until after the MIR
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// state transformation pass.
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ty::Generator(..) | ty::Dynamic(..) | ty::Error => Err(AlwaysRequiresDrop),
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ty::Dynamic(..) | ty::Error => Err(AlwaysRequiresDrop),
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ty::Slice(ty) => needs_drop_components(ty, target_layout),
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ty::Array(elem_ty, size) => {
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@ -1083,7 +1080,8 @@ pub fn needs_drop_components(
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| ty::Placeholder(..)
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| ty::Opaque(..)
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| ty::Infer(_)
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| ty::Closure(..) => Ok(smallvec![ty]),
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| ty::Closure(..)
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| ty::Generator(..) => Ok(smallvec![ty]),
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}
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}
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@ -99,6 +99,23 @@ where
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}
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}
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ty::Generator(_, substs, _) => {
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let substs = substs.as_generator();
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for upvar_ty in substs.upvar_tys() {
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queue_type(self, upvar_ty);
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}
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let witness = substs.witness();
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let interior_tys = match &witness.kind {
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ty::GeneratorWitness(tys) => tcx.erase_late_bound_regions(tys),
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_ => bug!(),
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};
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for interior_ty in interior_tys {
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queue_type(self, interior_ty);
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}
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}
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// Check for a `Drop` impl and whether this is a union or
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// `ManuallyDrop`. If it's a struct or enum without a `Drop`
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// impl then check whether the field types need `Drop`.
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@ -1,11 +1,14 @@
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#![feature(generators, generator_trait)]
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// ignore-wasm32-bare compiled with panic=abort by default
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// Regression test for #58892, generator drop shims should not have blocks
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// spuriously marked as cleanup
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// EMIT_MIR rustc.main-{{closure}}.generator_drop.0.mir
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fn main() {
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let gen = || {
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let _s = String::new();
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yield;
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};
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}
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@ -1,53 +1,80 @@
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// MIR for `main::{{closure}}#0` 0 generator_drop
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// generator_layout = GeneratorLayout { field_tys: [], variant_fields: [[], [], [], []], storage_conflicts: BitMatrix { num_rows: 0, num_columns: 0, words: [], marker: PhantomData } }
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// generator_layout = GeneratorLayout { field_tys: [std::string::String], variant_fields: [[], [], [], [_0]], storage_conflicts: BitMatrix { num_rows: 1, num_columns: 1, words: [1], marker: PhantomData } }
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fn main::{{closure}}#0(_1: *mut [generator@$DIR/generator-drop-cleanup.rs:8:15: 10:6 {()}]) -> () {
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let mut _0: (); // return place in scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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let mut _2: (); // in scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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let _3: (); // in scope 0 at $DIR/generator-drop-cleanup.rs:9:9: 9:14
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let mut _4: (); // in scope 0 at $DIR/generator-drop-cleanup.rs:9:9: 9:14
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let mut _5: (); // in scope 0 at $DIR/generator-drop-cleanup.rs:8:18: 8:18
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let mut _6: (); // in scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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let mut _7: isize; // in scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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fn main::{{closure}}#0(_1: *mut [generator@$DIR/generator-drop-cleanup.rs:10:15: 13:6 {std::string::String, ()}]) -> () {
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let mut _0: (); // return place in scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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let mut _2: (); // in scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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let _3: std::string::String; // in scope 0 at $DIR/generator-drop-cleanup.rs:11:13: 11:15
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let _4: (); // in scope 0 at $DIR/generator-drop-cleanup.rs:12:9: 12:14
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let mut _5: (); // in scope 0 at $DIR/generator-drop-cleanup.rs:12:9: 12:14
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let mut _7: (); // in scope 0 at $DIR/generator-drop-cleanup.rs:10:18: 10:18
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let mut _8: (); // in scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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let mut _9: isize; // in scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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scope 1 {
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debug _s => (((*_1) as variant#3).0: std::string::String); // in scope 1 at $DIR/generator-drop-cleanup.rs:11:13: 11:15
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}
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scope 2 {
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let mut _6: std::vec::Vec<u8>; // in scope 2 at $DIR/generator-drop-cleanup.rs:11:18: 11:31
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scope 3 {
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}
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}
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bb0: {
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_7 = discriminant((*_1)); // bb0[0]: scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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switchInt(move _7) -> [0u32: bb4, 3u32: bb7, otherwise: bb8]; // bb0[1]: scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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_9 = discriminant((*_1)); // bb0[0]: scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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switchInt(move _9) -> [0u32: bb7, 3u32: bb11, otherwise: bb12]; // bb0[1]: scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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}
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bb1: {
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StorageDead(_4); // bb1[0]: scope 0 at $DIR/generator-drop-cleanup.rs:9:13: 9:14
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StorageDead(_3); // bb1[1]: scope 0 at $DIR/generator-drop-cleanup.rs:9:14: 9:15
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goto -> bb5; // bb1[2]: scope 0 at $DIR/generator-drop-cleanup.rs:10:5: 10:6
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bb1 (cleanup): {
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resume; // bb1[0]: scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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}
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bb2: {
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return; // bb2[0]: scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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bb2 (cleanup): {
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nop; // bb2[0]: scope 0 at $DIR/generator-drop-cleanup.rs:13:5: 13:6
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goto -> bb8; // bb2[1]: scope 0 at $DIR/generator-drop-cleanup.rs:13:5: 13:6
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}
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bb3: {
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return; // bb3[0]: scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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StorageDead(_5); // bb3[0]: scope 1 at $DIR/generator-drop-cleanup.rs:12:13: 12:14
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StorageDead(_4); // bb3[1]: scope 1 at $DIR/generator-drop-cleanup.rs:12:14: 12:15
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drop((((*_1) as variant#3).0: std::string::String)) -> [return: bb4, unwind: bb2]; // bb3[2]: scope 0 at $DIR/generator-drop-cleanup.rs:13:5: 13:6
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}
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bb4: {
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goto -> bb6; // bb4[0]: scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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nop; // bb4[0]: scope 0 at $DIR/generator-drop-cleanup.rs:13:5: 13:6
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goto -> bb9; // bb4[1]: scope 0 at $DIR/generator-drop-cleanup.rs:13:5: 13:6
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}
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bb5: {
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goto -> bb2; // bb5[0]: scope 0 at $DIR/generator-drop-cleanup.rs:10:5: 10:6
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return; // bb5[0]: scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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}
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bb6: {
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goto -> bb3; // bb6[0]: scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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return; // bb6[0]: scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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}
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bb7: {
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StorageLive(_3); // bb7[0]: scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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StorageLive(_4); // bb7[1]: scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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goto -> bb1; // bb7[2]: scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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goto -> bb10; // bb7[0]: scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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}
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bb8: {
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return; // bb8[0]: scope 0 at $DIR/generator-drop-cleanup.rs:8:15: 10:6
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bb8 (cleanup): {
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goto -> bb1; // bb8[0]: scope 0 at $DIR/generator-drop-cleanup.rs:13:5: 13:6
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}
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bb9: {
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goto -> bb5; // bb9[0]: scope 0 at $DIR/generator-drop-cleanup.rs:13:5: 13:6
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}
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bb10: {
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goto -> bb6; // bb10[0]: scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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}
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bb11: {
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StorageLive(_4); // bb11[0]: scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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StorageLive(_5); // bb11[1]: scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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goto -> bb3; // bb11[2]: scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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}
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bb12: {
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return; // bb12[0]: scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
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}
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}
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@ -1,19 +1,16 @@
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error[E0597]: `a` does not live long enough
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--> $DIR/borrowing.rs:9:33
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LL | let _b = {
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| -- borrow later stored here
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LL | let a = 3;
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LL | Pin::new(&mut || yield &a).resume(())
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| ----------^
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| | |
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| | borrowed value does not live long enough
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| -- ^ borrowed value does not live long enough
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| |
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| value captured here by generator
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| a temporary with access to the borrow is created here ...
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LL |
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LL | };
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| -- ... and the borrow might be used here, when that temporary is dropped and runs the destructor for generator
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| |
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| `a` dropped here while still borrowed
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= note: The temporary is part of an expression at the end of a block. Consider forcing this temporary to be dropped sooner, before the block's local variables are dropped. For example, you could save the expression's value in a new local variable `x` and then make `x` be the expression at the end of the block.
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| - `a` dropped here while still borrowed
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error[E0597]: `a` does not live long enough
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--> $DIR/borrowing.rs:16:20
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@ -4,10 +4,9 @@ error[E0499]: cannot borrow `thing` as mutable more than once at a time
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LL | gen.as_mut().resume(&mut thing);
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| ---------- first mutable borrow occurs here
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LL | gen.as_mut().resume(&mut thing);
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| ^^^^^^^^^^ second mutable borrow occurs here
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LL |
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LL | }
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| - first borrow might be used here, when `gen` is dropped and runs the destructor for generator
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| ------ ^^^^^^^^^^ second mutable borrow occurs here
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| |
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| first borrow later used by call
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error: aborting due to previous error
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