Fix trans coercions of Box<[T]> and Box<Trait> in match arms #21692
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…s original L-/R-value state. This fixes a subtle issue where temporaries were being allocated (but not necessarily initialized) to the (parent) terminating scope of a match expression; in particular, the code to zero out the temporary emitted by `datum.store_to` is only attached to the particular match-arm for that temporary, but when going down other arms of the match expression, the temporary may falsely appear to have been initialized, depending on what the stack held at that location, and thus may have its destructor erroneously run at the end of the terminating scope. Test cases to appear in a follow-up commit. Fix rust-lang#20055
Note that I have not yet managed to expose any bug in `trans::expr::into_fat_ptr`; it would be good to try to do so (or show that the use of `.to_lvalue_datum` there is sound).
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r? @eddyb (rust_highfive has picked a reviewer for you, use r? to override) |
This was referenced Jan 27, 2015
Fix the issue-20055-box-trait.rs test to actually test `Box<Trait>`. Fix rust-lang#21695.
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trans: When coercing to `Box<Trait>` or `Box<[T]>`, leave datum in it's original L-/R-value state. This fixes a subtle issue where temporaries were being allocated (but not necessarily initialized) to the (parent) terminating scope of a match expression; in particular, the code to zero out the temporary emitted by `datum.store_to` is only attached to the particular match-arm for that temporary, but when going down other arms of the match expression, the temporary may falsely appear to have been initialized, depending on what the stack held at that location, and thus may have its destructor erroneously run at the end of the terminating scope. FIx #20055. (There may be a latent bug still remaining in `fn into_fat_ptr`, but I am so annoyed by the test/run-pass/coerce_match.rs failures that I want to land this now.)
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ooc, is this related to the failure I've been seeing on OSX for a while? (There's no output, it just fails). |
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@richo yes, this is meant to fix that. |
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trans: When coercing to
Box<Trait>orBox<[T]>, leave datum in it's original L-/R-value state.This fixes a subtle issue where temporaries were being allocated (but not necessarily initialized) to the (parent) terminating scope of a match expression; in particular, the code to zero out the temporary emitted by
datum.store_tois only attached to the particular match-arm for that temporary, but when going down other arms of the match expression, the temporary may falsely appear to have been initialized, depending on what the stack held at that location, and thus may have its destructor erroneously run at the end of the terminating scope.FIx #20055.
(There may be a latent bug still remaining in
fn into_fat_ptr, but I am so annoyed by the test/run-pass/coerce_match.rs failures that I want to land this now.)