Do leak check after function pointer coercion #97206
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May 20, 2022
| // want the coerced type to be the actual supertype of these two, | ||
| // but for now, we want to just error to ensure we don't lock | ||
| // ourselves into a specific behavior with NLL. | ||
| self.leak_check(false, snapshot)?; |
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I will admit that I have no idea if this should be false or true.
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The name is not very good. It only affects diagnostics. I think the idea is that you say true if the "placeholders" result from the "actual type" and false if they come from the expected type.
In this instance, B is the expected type, I think, and the placeholders would come from B, so I guess that makes false the proper value. (i.e., the value you are supplying is insufficiently polymorphic to be cast to the type required).
| @@ -11,23 +11,20 @@ fn b<'a, 'b>(x: &mut &'a isize, y: &mut &'b isize) { | |||
| // Illegal now because there is no `'b:'a` declaration. | |||
| *x = *y; | |||
| //[base]~^ ERROR E0623 | |||
| //[nll]~^^ ERROR lifetime may not live long enough | |||
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I think these errors disappear because they are borrowck errors, but we now error and bail in typeck.
| @@ -11,23 +11,20 @@ fn b<'a, 'b>(x: &mut &'a isize, y: &mut &'b isize) { | |||
| // Illegal now because there is no `'b:'a` declaration. | |||
| *x = *y; | |||
| //[base]~^ ERROR lifetime mismatch [E0623] | |||
| //[nll]~^^ ERROR lifetime may not live long enough | |||
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| found fn pointer `for<'r, 's, 't0> fn(&'r mut &isize, &'s mut &isize, &'t0 mut &isize)` | ||
| found fn item `for<'r, 's, 't0> fn(&'r mut &isize, &'s mut &isize, &'t0 mut &isize) {a::<'_, '_, '_>}` |
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| note: function defined here | ||
| --> $DIR/regions-fn-subtyping-return-static-fail.rs:24:4 | ||
| | | ||
| LL | fn want_G(f: G) {} | ||
| | ^^^^^^ ---- |
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nikomatsakis
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Do leak check after function pointer coercion cc rust-lang#73154 I still need to clean diagnostics just a tad, but figured I would put this up anyways. This change is made in order to make match arm coercion order-independent. Basically, any time we do function pointer coercion, we follow it by doing a leak check. This is necessary because the LUB code doesn't handler higher-ranked things correctly, leading us to "coerce", but use the wrong type. A proper fix is to actually fix that code (so the type returned by `unify_and` is a supertype of both `a` and `b` if `Ok`). However, that requires a more in-depth fix, likely heavily overlapping with the new subtyping changes. Here, I've been conservative and error early if we generate unsatisfiable constraints. Note, this should *mostly* only affect NLL, since migrate mode falls back to the LUB implementation (followed by leak check), whereas NLL only does sub. There could be other coercion code that has an order-dependence where a leak check in the coercion code might be useful. However, this is more of a spot-fix for rust-lang#73154 than a "permanent" fix, since we likely want to go the other way long-term, and allow this pattern without error. r? `@nikomatsakis`
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☔ The latest upstream changes (presumably #97239) made this pull request unmergeable. Please resolve the merge conflicts. |
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Oh thanks @lcnr :) missed that |
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⌛ Testing commit baf1966b3c75fff6174c31da4a0574793bc2ace8 with merge 66e5c5953352dd6ce2a6cbae77dd187880e38510... |
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Rollup of 5 pull requests Successful merges: - rust-lang#97043 (Move some tests to more reasonable directories) - rust-lang#97206 (Do leak check after function pointer coercion) - rust-lang#97275 (small change) - rust-lang#97277 (Avoid accidentally enabling unstable features in compilers (take 2)) - rust-lang#97280 (Quote replace target in bootstrap configure) Failed merges: - rust-lang#97214 (Finish bumping stage0) r? `@ghost` `@rustbot` modify labels: rollup
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Move remaining tests with NLL differences to revisions Based on rust-lang#97206 I've already filed issues for any important differences that I've spotted: rust-lang#97252 rust-lang#97253 rust-lang#97256 rust-lang#97267 There is a lot here, but each commit is self-contained as a separate directory. I can split into separate PRs as wanted or needed.
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cc #73154
I still need to clean diagnostics just a tad, but figured I would put this up anyways.
This change is made in order to make match arm coercion order-independent.
Basically, any time we do function pointer coercion, we follow it by doing a leak check. This is necessary because the LUB code doesn't handler higher-ranked things correctly, leading us to "coerce", but use the wrong type. A proper fix is to actually fix that code (so the type returned by
unify_andis a supertype of bothaandbifOk). However, that requires a more in-depth fix, likely heavily overlapping with the new subtyping changes.Here, I've been conservative and error early if we generate unsatisfiable constraints. Note, this should mostly only affect NLL, since migrate mode falls back to the LUB implementation (followed by leak check), whereas NLL only does sub.
There could be other coercion code that has an order-dependence where a leak check in the coercion code might be useful. However, this is more of a spot-fix for #73154 than a "permanent" fix, since we likely want to go the other way long-term, and allow this pattern without error.
r? @nikomatsakis