-Znext-solver: adapt overflow rules to avoid breakage #119071

lcnr · 2023-12-18T07:47:43Z

Do not erase overflow constraints if they are from equating the impl header when normalizing¹.

This should be the minimal change to not break crates depending on the old project behavior of "apply impl constraints while only lazily evaluating any nested goals".

Fixes rust-lang/trait-system-refactor-initiative#70, see https://hackmd.io/ATf4hN0NRY-w2LIVgeFsVg for the reasoning behind this.

Only keeping constraints on overflow for normalize-to goals as that's the only thing needed for backcompat. It also allows us to not track the origin of root obligations. The issue with root goals would be something like the following:

trait Foo {}
trait Bar {}

trait FooBar {}
impl<T: Foo + Bar> FooBar for T {}

// These two should behave the same, rn we can drop constraints for both,
// but if we don't drop `Misc` goals we would only drop the constraints for
// `FooBar` unless we track origins of root obligations.
fn func1<T: Foo + Bar>() {}
fn func2<T: FooBaz>() {}

r? @compiler-errors

mostly, the actual rules are slightly different ↩

rustbot · 2023-12-18T07:47:53Z

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor

compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs

compiler-errors · 2023-12-19T14:59:50Z

r=me after adding that comment you said you would

compiler-errors · 2023-12-19T15:40:45Z

@rustbot author

lcnr · 2023-12-19T16:39:58Z

@bors r=compiler-errors rollup

bors · 2023-12-19T16:40:01Z

📌 Commit 17705ea has been approved by compiler-errors

It is now in the queue for this repository.

-Znext-solver: adapt overflow rules to avoid breakage Do not erase overflow constraints if they are from equating the impl header when normalizing[^1]. This should be the minimal change to not break crates depending on the old project behavior of "apply impl constraints while only lazily evaluating any nested goals". Fixes rust-lang/trait-system-refactor-initiative#70, see https://hackmd.io/ATf4hN0NRY-w2LIVgeFsVg for the reasoning behind this. Only keeping constraints on overflow for `normalize-to` goals as that's the only thing needed for backcompat. It also allows us to not track the origin of root obligations. The issue with root goals would be something like the following: ```rust trait Foo {} trait Bar {} trait FooBar {} impl<T: Foo + Bar> FooBar for T {} // These two should behave the same, rn we can drop constraints for both, // but if we don't drop `Misc` goals we would only drop the constraints for // `FooBar` unless we track origins of root obligations. fn func1<T: Foo + Bar>() {} fn func2<T: FooBaz>() {} ``` [^1]: mostly, the actual rules are slightly different r? `@compiler-errors`

…mpiler-errors Rollup of 7 pull requests Successful merges: - rust-lang#118691 (Add check for possible CStr literals in pre-2021) - rust-lang#118973 (rustc_codegen_ssa: Don't drop `IncorrectCguReuseType` , make `rustc_expected_cgu_reuse` attr work) - rust-lang#119071 (-Znext-solver: adapt overflow rules to avoid breakage) - rust-lang#119089 (effects: fix a comment) - rust-lang#119096 (Yeet unnecessary param envs) - rust-lang#119118 (Fix arm64e-apple-ios target) - rust-lang#119134 (resolve: Feed visibilities for unresolved trait impl items) r? `@ghost` `@rustbot` modify labels: rollup

…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#118691 (Add check for possible CStr literals in pre-2021) - rust-lang#118973 (rustc_codegen_ssa: Don't drop `IncorrectCguReuseType` , make `rustc_expected_cgu_reuse` attr work) - rust-lang#119071 (-Znext-solver: adapt overflow rules to avoid breakage) - rust-lang#119089 (effects: fix a comment) - rust-lang#119094 (Add function ABI and type layout to StableMIR) - rust-lang#119102 (Add arm-none-eabi and armv7r-none-eabi platform-support documentation.) - rust-lang#119107 (subtype_predicate: remove unnecessary probe) Failed merges: - rust-lang#119135 (Fix crash due to `CrateItem::kind()` not handling constructors) - rust-lang#119141 (Add method to get instance instantiation arguments) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#119071 - lcnr:overflowo, r=compiler-errors -Znext-solver: adapt overflow rules to avoid breakage Do not erase overflow constraints if they are from equating the impl header when normalizing[^1]. This should be the minimal change to not break crates depending on the old project behavior of "apply impl constraints while only lazily evaluating any nested goals". Fixes rust-lang/trait-system-refactor-initiative#70, see https://hackmd.io/ATf4hN0NRY-w2LIVgeFsVg for the reasoning behind this. Only keeping constraints on overflow for `normalize-to` goals as that's the only thing needed for backcompat. It also allows us to not track the origin of root obligations. The issue with root goals would be something like the following: ```rust trait Foo {} trait Bar {} trait FooBar {} impl<T: Foo + Bar> FooBar for T {} // These two should behave the same, rn we can drop constraints for both, // but if we don't drop `Misc` goals we would only drop the constraints for // `FooBar` unless we track origins of root obligations. fn func1<T: Foo + Bar>() {} fn func2<T: FooBaz>() {} ``` [^1]: mostly, the actual rules are slightly different r? ``@compiler-errors``

track the source of nested goals

ca718ff

rustbot assigned compiler-errors Dec 18, 2023

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. WG-trait-system-refactor The Rustc Trait System Refactor Initiative labels Dec 18, 2023

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dont discard overflow from normalizes-to goals

4a38442

lcnr force-pushed the overflowo branch from d9ce5b8 to 4a38442 Compare December 18, 2023 08:01

lcnr commented Dec 18, 2023

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compiler-errors approved these changes Dec 19, 2023

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 19, 2023

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17705ea

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Dec 19, 2023

compiler-errors mentioned this pull request Dec 19, 2023

Rollup of 7 pull requests #119143

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matthiaskrgr mentioned this pull request Dec 20, 2023

Rollup of 7 pull requests #119156

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bors merged commit 16a231d into rust-lang:master Dec 20, 2023
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rustbot added this to the 1.76.0 milestone Dec 20, 2023

lcnr deleted the overflowo branch December 20, 2023 14:06

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-Znext-solver: adapt overflow rules to avoid breakage #119071

-Znext-solver: adapt overflow rules to avoid breakage #119071

lcnr commented Dec 18, 2023 •

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-Znext-solver: adapt overflow rules to avoid breakage #119071

-Znext-solver: adapt overflow rules to avoid breakage #119071

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