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Implement selection via new trait solver #112869

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merged 2 commits into from
Jul 3, 2023
Merged

Implement selection via new trait solver #112869

merged 2 commits into from
Jul 3, 2023

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@compiler-errors compiler-errors commented Jun 21, 2023 •
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Implements selection via the new solver by calling into assemble_and_evaluate_candidates, doing a very light-weight "winnow" to choose one candidate over the others, and then re-confirming that candidate outside of the EvalCtxt in order to compute the information necessary for the ImplSource.

This selection routine is best effort -- if it receives an ambiguous response from the EvalCtxt, then it may return ambiguity if the work to re-confirm the goal is not "easy" -- right now, that means everything except for object and impl goals. Since we don't want to reimplement all of the work of the compute_builtin_* methods in the solver internals, we bail out if we encounter ambiguity more often than the old solver. This should only barely affect method selection and not codegen. It can be made more precise later if needed.

r? @lcnr

@rustbot 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 (-Znext-solver) labels Jun 21, 2023
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bors commented Jun 27, 2023

☔ The latest upstream changes (presumably #112938) made this pull request unmergeable. Please resolve the merge conflicts.

@lcnr lcnr mentioned this pull request Jun 27, 2023
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@rust-cloud-vms rust-cloud-vms bot force-pushed the sketchy-new-select branch from 412c831 to deadc39 Compare June 27, 2023 17:22
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r=me after nits and updating description

compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs Outdated Show resolved Hide resolved
compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs Outdated Show resolved Hide resolved
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@rust-cloud-vms rust-cloud-vms bot force-pushed the sketchy-new-select branch from deadc39 to 2c4b85d Compare June 29, 2023 21:20
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@rust-cloud-vms rust-cloud-vms bot force-pushed the sketchy-new-select branch from 2c4b85d to 4905bc8 Compare June 29, 2023 23:36
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BoxyUwU commented Jun 30, 2023

Are we intending on having a flag for only enabling the new solver for selection?

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compiler-errors commented Jun 30, 2023 •
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No, the intention is just for this PR (and the deep normalization PR that lcnr has open) to remove the remaining entrypoints into old solver code when the new solver is enabled, since right now we still call into old solver logic during codegen and manual calls to SelectionContext::select (which ideally we'd remove12).

Footnotes

  1. https://github.com/rust-lang/rust/blob/97279e91d8d3973da9c1fc606a2b773213ed54e5/compiler/rustc_hir_typeck/src/method/probe.rs#L1447 ↩

  2. https://github.com/rust-lang/rust/blob/97279e91d8d3973da9c1fc606a2b773213ed54e5/compiler/rustc_hir_typeck/src/coercion.rs#L659C11-L659C11 ↩

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BoxyUwU commented Jun 30, 2023

So this select stuff ideally only exists for codegen to figure out impls?

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compiler-errors commented Jun 30, 2023 •
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Yes, that's the primary usecase, but we also use selection during the method probe and coercion logic I linked in the footnotes in my comment above (edited to include those).

(Also in other things like const checking, but that's broken in the new solver anyways so shrug)

bors added a commit to rust-lang-ci/rust that referenced this pull request Jul 3, 2023
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Auto merge of rust-lang#113086 - lcnr:rust8, r=compiler-errors
737b461 
implement deep normalization via the new solver

together with rust-lang#112869 this should remove all uses of the old solver with `-Ztrait-solver=next`.

see https://hackmd.io/V0qsUB_fTxexfQO_pcOcrg for a description of this PR. Will move that doc to the `rustc-dev-guide` after merging this.

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@rust-cloud-vms rust-cloud-vms bot force-pushed the sketchy-new-select branch from 4905bc8 to 4bb5a25 Compare July 3, 2023 15:00
@compiler-errors compiler-errors marked this pull request as ready for review July 3, 2023 15:07
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rustbot commented Jul 3, 2023

Some changes occurred to the core trait solver

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

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@rust-cloud-vms rust-cloud-vms bot force-pushed the sketchy-new-select branch from 4bb5a25 to f3f8793 Compare July 3, 2023 15:58
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lcnr commented Jul 3, 2023

@bors r+ rollup (affects only new solver)

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bors commented Jul 3, 2023

📌 Commit f3f8793 has been approved by lcnr

It is now in the queue for this repository.

@bors 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-review Status: Awaiting review from the assignee but also interested parties. labels Jul 3, 2023
@GuillaumeGomez GuillaumeGomez mentioned this pull request Jul 3, 2023
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bors added a commit to rust-lang-ci/rust that referenced this pull request Jul 3, 2023
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Auto merge of rust-lang#113293 - GuillaumeGomez:rollup-2395uw0, r=Gui…
8931edf 
…llaumeGomez

Rollup of 3 pull requests

Successful merges:

 - rust-lang#112869 (Implement selection via new trait solver)
 - rust-lang#113285 ([rustdoc] Fix display of long inline cfg labels)
 - rust-lang#113286 (Don't perform selection if inherent associated types are not enabled)

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`@rustbot` modify labels: rollup
@bors bors merged commit 4668d3e into rust-lang:master Jul 3, 2023
@rustbot rustbot added this to the 1.72.0 milestone Jul 3, 2023
@lcnr lcnr mentioned this pull request Jul 4, 2023
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@compiler-errors compiler-errors deleted the sketchy-new-select branch August 11, 2023 20:19
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S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. 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 (-Znext-solver)
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