diff --git a/src/librustc_borrowck/borrowck/mir/elaborate_drops.rs b/src/librustc_borrowck/borrowck/mir/elaborate_drops.rs index 4f49bfc9725..88e5bae483d 100644 --- a/src/librustc_borrowck/borrowck/mir/elaborate_drops.rs +++ b/src/librustc_borrowck/borrowck/mir/elaborate_drops.rs @@ -481,54 +481,55 @@ fn drop_halfladder<'a>(&mut self, is_cleanup: bool) -> Vec { - let mut succ = succ; let mut unwind_succ = if is_cleanup { None } else { c.unwind }; - let mut update_drop_flag = true; + + let mut succ = self.new_block( + c, c.is_cleanup, TerminatorKind::Goto { target: succ } + ); + + // Always clear the "master" drop flag at the bottom of the + // ladder. This is needed because the "master" drop flag + // protects the ADT's discriminant, which is invalidated + // after the ADT is dropped. + self.set_drop_flag( + Location { block: succ, statement_index: 0 }, + c.path, + DropFlagState::Absent + ); fields.iter().rev().enumerate().map(|(i, &(ref lv, path))| { - let drop_block = match path { - Some(path) => { - debug!("drop_ladder: for std field {} ({:?})", i, lv); + succ = if let Some(path) = path { + debug!("drop_ladder: for std field {} ({:?})", i, lv); - self.elaborated_drop_block(&DropCtxt { - source_info: c.source_info, - is_cleanup: is_cleanup, - init_data: c.init_data, - lvalue: lv, - path: path, - succ: succ, - unwind: unwind_succ, - }) - } - None => { - debug!("drop_ladder: for rest field {} ({:?})", i, lv); + self.elaborated_drop_block(&DropCtxt { + source_info: c.source_info, + is_cleanup: is_cleanup, + init_data: c.init_data, + lvalue: lv, + path: path, + succ: succ, + unwind: unwind_succ, + }) + } else { + debug!("drop_ladder: for rest field {} ({:?})", i, lv); - let blk = self.complete_drop(&DropCtxt { - source_info: c.source_info, - is_cleanup: is_cleanup, - init_data: c.init_data, - lvalue: lv, - path: c.path, - succ: succ, - unwind: unwind_succ, - }, update_drop_flag); - - // the drop flag has been updated - updating - // it again would clobber it. - update_drop_flag = false; - - blk - } + self.complete_drop(&DropCtxt { + source_info: c.source_info, + is_cleanup: is_cleanup, + init_data: c.init_data, + lvalue: lv, + path: c.path, + succ: succ, + unwind: unwind_succ, + }, false) }; - succ = drop_block; unwind_succ = unwind_ladder.as_ref().map(|p| p[i]); - - drop_block + succ }).collect() } diff --git a/src/test/run-pass/issue-38437.rs b/src/test/run-pass/issue-38437.rs new file mode 100644 index 00000000000..a6e7df1c010 --- /dev/null +++ b/src/test/run-pass/issue-38437.rs @@ -0,0 +1,54 @@ +// Copyright 2016 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +// Check that drop elaboration clears the "master" discriminant +// drop flag even if it protects no fields. + +struct Good(usize); +impl Drop for Good { + #[inline(never)] + fn drop(&mut self) { + println!("dropping Good({})", self.0); + } +} + +struct Void; +impl Drop for Void { + #[inline(never)] + fn drop(&mut self) { + panic!("Suddenly, a Void appears."); + } +} + +enum E { + Never(Void), + Fine(Good) +} + +fn main() { + let mut go = true; + + loop { + let next; + match go { + true => next = E::Fine(Good(123)), + false => return, + } + + match next { + E::Never(_) => return, + E::Fine(_good) => go = false, + } + + // `next` is dropped and StorageDead'd here. We must reset the + // discriminant's drop flag to avoid random variants being + // dropped. + } +}