document Closure capture precision by tshepang · Pull Request #698 · rust-lang/fls

tshepang · 2026-04-20T15:05:46Z

This captures some gaps FLS has compared to Reference, and the content is adjusted from Closure capture precision section.

kirtchev-adacore

This is it for now. I will have to revisit the remaining rules once the "place" business has been cleared up. I think we can find better wording/grouping of the remaining rules, as they feel somewhat randomly sprinkled.

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tshepang · 2026-04-21T13:37:06Z

all addressed but #698 (comment)

kirtchev-adacore

I will probably need to read Capture precision to ensure that no rules have been omitted.

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PLeVasseur

Thanks for pulling this material into 6.22. The remaining comments are mainly about semantic completeness and alignment with the Rust Reference so the new section lands as dependable spec text.

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PLeVasseur · 2026-04-22T17:55:10Z

 - `Const blocks are no longer evaluated to determine if expressions involving fallible operations can implicitly be constant-promoted <https://github.com/rust-lang/rust/pull/150557>`_
 - `Make operational semantics of pattern matching independent of crate and module <https://github.com/rust-lang/rust/pull/150681>`_

+  Changed paragraphs:


The paragraph-ID list itself looks fine, but this changelog attribution still seems too broad.

The changed capture-mode paragraphs fit rust-lang/rust#150681, but the new capture-precision block spans multiple sources: some items align with the later pattern/discriminant work in rust-lang/rust#138961 and rust-lang/reference#1837, while others are pre-existing Reference behavior now being documented here.

Could this entry be split, or reworded so #150681 is not presented as introducing the whole block? The note that these paragraphs mostly document behavior that existed before this release already points in that direction.

Support:

Make closure capturing have consistent and correct behaviour around patterns rust#138961

Document how closure capturing interacts with discriminant reads reference#1837

Make operational semantics of pattern matching independent of crate and module rust#150681

I can go find where each behavior was added, but am not sure it's worth the time

maybe a good compromise is having a different heading, like "Pre-existing behavior before 1.95", or just "FLS maintenance"

@tshepang So far we have used the following headings:

FLS fixes/improvements FLS corrections

I think those should be changed to "FLS maintenance" (as it is more general), and you should use that heading to split the pre-release changes.

done through a rebase

kirtchev-adacore · 2026-05-06T10:49:11Z

This is it for now. I will have to revisit the remaining rules once the "place" business has been cleared up. I think we can find better wording/grouping of the remaining rules, as they feel somewhat randomly sprinkled.

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Just to clarify, after reading the Reference's Capture precision, I think "place" is indeed the proper term.

all done (I think)

Co-authored-by: Ana Hobden <operator@hoverbear.org>

Co-authored-by: Hristian Kirtchev <60669983+kirtchev-adacore@users.noreply.github.com>

…tions

…erload the term) Co-authored-by: Hristian Kirtchev <60669983+kirtchev-adacore@users.noreply.github.com>

Co-authored-by: Hristian Kirtchev <60669983+kirtchev-adacore@users.noreply.github.com>

Also, sort by alphabet

In an FLS call, we decided that it's not important after all... my thinking is that mentioning a read is not exactly relevant, as FLS is not a place to explain mechanics of rustc. It should be enough to only explain surface behavior, and not why that behavior is so. This reverts commit a3d7be4.

rustbot · 2026-07-24T06:47:42Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

This avoids the entry getting missed, due to the much larger "New paragraphs" entry

tshepang · 2026-07-24T09:02:25Z

rebased due to divergence from main

hristian took over, and review now handled

Hoverbear reviewed Apr 20, 2026

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tshepang force-pushed the tshepang/capture-precision branch from e3ed8e9 to 7be2ad5 Compare April 21, 2026 09:49

tshepang requested a review from kirtchev-adacore April 21, 2026 13:36

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tshepang mentioned this pull request Apr 27, 2026

FLS scope #700

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tshepang force-pushed the tshepang/capture-precision branch from dcd9707 to 550f10d Compare May 2, 2026 17:24

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tshepang mentioned this pull request Jun 26, 2026

define "uninhabited type" #705

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tshepang and others added 10 commits July 24, 2026 08:38

document Closure capture precision

e78a79b

typo

c386039

Co-authored-by: Ana Hobden <operator@hoverbear.org>

use a defined term

1ae776e

Co-authored-by: Hristian Kirtchev <60669983+kirtchev-adacore@users.noreply.github.com>

remove a redundancy, and add some links

1ca67a5

Co-authored-by: Hristian Kirtchev <60669983+kirtchev-adacore@users.noreply.github.com>

grammar and consistency fix

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link-it

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Co-authored-by: Hristian Kirtchev <60669983+kirtchev-adacore@users.noreply.github.com>

define the term before using it

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be more consise and clear, remove redundancy, and link to a definition

6eb57a3

be more consise and clear, remove redundancy, and link to some defini…

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…tions

clarity

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tshepang and others added 19 commits July 24, 2026 08:43

be less verbose (and nearly all the paragraphs are rules, so don't ov…

f6d88b0

…erload the term) Co-authored-by: Hristian Kirtchev <60669983+kirtchev-adacore@users.noreply.github.com>

link-it

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match FLS style, and re-oder one rule

cc832e5

Co-authored-by: Hristian Kirtchev <60669983+kirtchev-adacore@users.noreply.github.com>

fix links

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these should not be conflated

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add some clarity

b6440a5

add pattern destructing rules

e8b422a

clarity

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Co-authored-by: Hristian Kirtchev <60669983+kirtchev-adacore@users.noreply.github.com>

sort

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Co-authored-by: Hristian Kirtchev <60669983+kirtchev-adacore@users.noreply.github.com>

more sorting

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Co-authored-by: Hristian Kirtchev <60669983+kirtchev-adacore@users.noreply.github.com>

create section for pattern destructuring

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link-it

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fix

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remove misapplied plurality

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make more clear that this is recursive

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it is important to mention the "read"

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include autoderef in definition

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Also, sort by alphabet

a more a more specific term

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tshepang force-pushed the tshepang/capture-precision branch from 529319e to c14483e Compare July 24, 2026 06:47

re-order

3149c0d

This avoids the entry getting missed, due to the much larger "New paragraphs" entry

point to new behavior introduced by release note entry

74f0b28

kirtchev-adacore approved these changes Jul 24, 2026

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kirtchev-adacore added this pull request to the merge queue Jul 24, 2026

Merged via the queue into main with commit 51b7879 Jul 24, 2026
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kirtchev-adacore deleted the tshepang/capture-precision branch July 24, 2026 10:18

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