Remove let_chains unstable feature #143214

camsteffen · 2025-06-29T20:44:23Z

Per #53667 (comment) (but then I also noticed #140722)

This replaces the feature gate with a parser error that says let chains require 2024.

A lot of tests were using the unstable feature. I either added edition:2024 to the test or split out the parts that require 2024.

rustbot · 2025-06-29T20:44:27Z

r? @WaffleLapkin

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rustbot · 2025-06-29T20:44:29Z

Some changes occurred in coverage tests.

cc @Zalathar

Kivooeo · 2025-06-29T21:00:51Z

i believe it should not be removed according to this

#132833 (comment)

but may be wrong

camsteffen · 2025-06-29T21:07:23Z

@Kivooeo Oh right, this is planned in #140722

I think that would only be a slight modification of this PR.

est31

I'm a bit sad about not being able to test the behaviour of let chains drop order on different editions like done in drop-order-comparisons.rs. But I suppose it's not worth it to keep around an unstable feature just for that.

tests/ui/macros/stringify.rs

compiler/rustc_feature/src/unstable.rs

est31 · 2025-06-30T01:45:51Z

Thanks for taking this over @camsteffen !

rustbot · 2025-06-30T12:49:36Z

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

camsteffen · 2025-06-30T12:59:51Z

Addressed comments and fixed a rustfmt test.

I'm a bit sad about not being able to test the behaviour of let chains drop order on different editions like done in drop-order-comparisons.rs. But I suppose it's not worth it to keep around an unstable feature just for that.

Yeah, agreed. It would only be a source of historical record rather than testing actual behavior of rustc.

est31 · 2025-06-30T15:57:21Z

only be a source of historical record

I did look at those tests when trying to figure out if let chains in match guards can be stabilized on all editions or not. I adapted some of those tests to match guards and they worked on edition 2021. Them failing on edition 2021 for if let chains assured me that the tests are indeed showcasing the edition relevant changes. But I suppose one can always use an older version of the compiler. Or just bring it back in the future.

est31 · 2025-06-30T15:57:36Z

r? @est31

est31 · 2025-06-30T15:57:47Z

@bors r+ rollup

bors · 2025-06-30T15:57:50Z

📌 Commit dc9879c has been approved by est31

It is now in the queue for this repository.

est31 · 2025-06-30T15:58:38Z

@bors rollup- for the rustfmt subtree changes. maybe better to have them separate.

est31 · 2025-06-30T16:02:12Z

@bors rollup=never (meant that one instead)

bors · 2025-07-02T17:18:50Z

⌛ Testing commit dc9879c with merge 1ce9c97...

bors · 2025-07-02T20:24:15Z

☀️ Test successful - checks-actions
Approved by: est31
Pushing 1ce9c97 to master...

github-actions · 2025-07-02T20:26:59Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing b94bd12 (parent) -> 1ce9c97 (this PR)

Test differences

Show 259 test diffs

Stage 1

errors::verify_parse_asm_expected_comma_180: [missing] -> pass (J0)
errors::verify_parse_asm_expected_string_literal_182: pass -> [missing] (J0)
errors::verify_parse_asm_non_abi_182: [missing] -> pass (J0)
errors::verify_parse_asm_sym_no_path_177: pass -> [missing] (J0)
errors::verify_parse_asm_sym_no_path_178: [missing] -> pass (J0)
errors::verify_parse_asm_underscore_input_176: pass -> [missing] (J0)
errors::verify_parse_asm_underscore_input_177: [missing] -> pass (J0)
errors::verify_parse_at_dot_dot_in_struct_pattern_124: pass -> [missing] (J0)
errors::verify_parse_attr_after_generic_140: pass -> [missing] (J0)
errors::verify_parse_attr_without_generics_141: pass -> [missing] (J0)
errors::verify_parse_bad_assoc_type_bounds_139: pass -> [missing] (J0)
errors::verify_parse_bad_item_kind_152: [missing] -> pass (J0)
errors::verify_parse_binder_and_polarity_173: pass -> [missing] (J0)
errors::verify_parse_binder_and_polarity_174: [missing] -> pass (J0)
errors::verify_parse_binder_before_modifiers_172: pass -> [missing] (J0)
errors::verify_parse_box_not_pat_157: pass -> [missing] (J0)
errors::verify_parse_cannot_be_raw_ident_102: pass -> [missing] (J0)
errors::verify_parse_const_global_cannot_be_mutable_87: [missing] -> pass (J0)
errors::verify_parse_cr_doc_comment_107: [missing] -> pass (J0)
errors::verify_parse_dot_dot_dot_for_remaining_fields_126: pass -> [missing] (J0)
errors::verify_parse_dot_dot_dot_range_to_pattern_not_allowed_122: pass -> [missing] (J0)
errors::verify_parse_dotdotdot_rest_pattern_115: pass -> [missing] (J0)
errors::verify_parse_dyn_after_mut_133: pass -> [missing] (J0)
errors::verify_parse_empty_exponent_float_109: pass -> [missing] (J0)
errors::verify_parse_enum_pattern_instead_of_identifier_124: [missing] -> pass (J0)
errors::verify_parse_expect_label_found_ident_147: pass -> [missing] (J0)
errors::verify_parse_expected_binding_left_of_at_118: [missing] -> pass (J0)
errors::verify_parse_expr_rarrow_call_169: pass -> [missing] (J0)
errors::verify_parse_extern_item_cannot_be_const_85: pass -> [missing] (J0)
errors::verify_parse_extra_impl_keyword_in_trait_impl_81: [missing] -> pass (J0)
errors::verify_parse_float_literal_unsupported_base_111: [missing] -> pass (J0)
errors::verify_parse_fn_pointer_cannot_be_async_135: pass -> [missing] (J0)
errors::verify_parse_fn_pointer_cannot_be_const_135: [missing] -> pass (J0)
errors::verify_parse_generic_args_in_pat_require_turbofish_syntax_165: pass -> [missing] (J0)
errors::verify_parse_generics_in_path_143: pass -> [missing] (J0)
errors::verify_parse_inappropriate_default_148: pass -> [missing] (J0)
errors::verify_parse_inappropriate_default_149: [missing] -> pass (J0)
errors::verify_parse_invalid_attr_unsafe_171: pass -> [missing] (J0)
errors::verify_parse_invalid_attr_unsafe_172: [missing] -> pass (J0)
errors::verify_parse_invalid_digit_literal_108: pass -> [missing] (J0)
errors::verify_parse_invalid_offset_of_167: pass -> [missing] (J0)
errors::verify_parse_invalid_path_sep_in_fn_definition_76: pass -> [missing] (J0)
errors::verify_parse_keyword_lifetime_104: pass -> [missing] (J0)
errors::verify_parse_keyword_lifetime_105: [missing] -> pass (J0)
errors::verify_parse_kw_bad_case_160: pass -> [missing] (J0)
errors::verify_parse_lifetime_after_mut_132: pass -> [missing] (J0)
errors::verify_parse_lifetime_after_mut_133: [missing] -> pass (J0)
errors::verify_parse_lifetime_in_eq_constraint_144: pass -> [missing] (J0)
errors::verify_parse_macro_invocation_visibility_156: [missing] -> pass (J0)
errors::verify_parse_macro_name_remove_bang_153: pass -> [missing] (J0)
errors::verify_parse_malformed_cfg_attr_161: pass -> [missing] (J0)
errors::verify_parse_missing_const_type_87: pass -> [missing] (J0)
errors::verify_parse_missing_trait_in_trait_impl_77: pass -> [missing] (J0)
errors::verify_parse_modifiers_and_polarity_174: pass -> [missing] (J0)
errors::verify_parse_multiple_where_clauses_98: [missing] -> pass (J0)
errors::verify_parse_mut_on_nested_ident_pattern_119: pass -> [missing] (J0)
errors::verify_parse_need_plus_after_trait_object_lifetime_130: pass -> [missing] (J0)
errors::verify_parse_need_plus_after_trait_object_lifetime_131: [missing] -> pass (J0)
errors::verify_parse_nested_adt_156: pass -> [missing] (J0)
errors::verify_parse_nested_c_variadic_type_137: [missing] -> pass (J0)
errors::verify_parse_no_digits_literal_108: [missing] -> pass (J0)
errors::verify_parse_nonterminal_expected_ident_100: pass -> [missing] (J0)
errors::verify_parse_nonterminal_expected_ident_101: [missing] -> pass (J0)
errors::verify_parse_nonterminal_expected_item_keyword_99: [missing] -> pass (J0)
errors::verify_parse_nonterminal_expected_lifetime_101: pass -> [missing] (J0)
errors::verify_parse_nonterminal_expected_lifetime_102: [missing] -> pass (J0)
errors::verify_parse_nonterminal_expected_statement_99: pass -> [missing] (J0)
errors::verify_parse_pattern_on_wrong_side_of_at_116: pass -> [missing] (J0)
errors::verify_parse_return_types_use_thin_arrow_129: pass -> [missing] (J0)
errors::verify_parse_self_argument_pointer_71: pass -> [missing] (J0)
errors::verify_parse_static_with_generics_165: [missing] -> pass (J0)
errors::verify_parse_trailing_vert_not_allowed_114: pass -> [missing] (J0)
errors::verify_parse_trait_alias_cannot_be_auto_82: pass -> [missing] (J0)
errors::verify_parse_underscore_literal_suffix_146: pass -> [missing] (J0)
errors::verify_parse_unexpected_expr_in_pat_128: pass -> [missing] (J0)
errors::verify_parse_unexpected_token_after_struct_name_found_doc_comment_93: [missing] -> pass (J0)
errors::verify_parse_unexpected_token_after_struct_name_found_keyword_90: pass -> [missing] (J0)
errors::verify_parse_unexpected_token_after_struct_name_found_other_95: [missing] -> pass (J0)
errors::verify_parse_unexpected_token_after_struct_name_found_reserved_identifier_89: pass -> [missing] (J0)
errors::verify_parse_unexpected_token_after_struct_name_found_reserved_keyword_91: pass -> [missing] (J0)
errors::verify_parse_unexpected_token_after_struct_name_found_reserved_keyword_92: [missing] -> pass (J0)
errors::verify_parse_unexpected_vert_vert_before_function_parameter_113: [missing] -> pass (J0)
errors::verify_parse_unexpected_vert_vert_in_pattern_113: pass -> [missing] (J0)
errors::verify_parse_unknown_builtin_construct_162: pass -> [missing] (J0)
errors::verify_parse_unmatched_angle_158: pass -> [missing] (J0)
errors::verify_parse_unmatched_angle_159: [missing] -> pass (J0)
errors::verify_parse_visibility_not_followed_by_item_73: pass -> [missing] (J0)
errors::verify_parse_where_generics_143: [missing] -> pass (J0)
[ui] tests/ui/drop/issue-100276.rs#edition2024: pass -> [missing] (J2)
[ui] tests/ui/mir/mir_let_chains_drop_order.rs: [missing] -> pass (J2)
[ui] tests/ui/mir/mir_let_chains_drop_order.rs#edition2021: pass -> [missing] (J2)
[ui] tests/ui/mir/mir_let_chains_drop_order.rs#edition2024: pass -> [missing] (J2)
[ui] tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions.rs#e2021: [missing] -> pass (J2)
[ui] tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions.rs#e2024: [missing] -> pass (J2)

Stage 2

[ui] tests/ui/drop/issue-100276.rs: [missing] -> pass (J1)
[ui] tests/ui/mir/mir_let_chains_drop_order.rs: [missing] -> pass (J1)
[ui] tests/ui/mir/mir_let_chains_drop_order.rs#edition2024: pass -> [missing] (J1)
[ui] tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions.rs#e2021: [missing] -> pass (J1)
[ui] tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions.rs#e2024: [missing] -> pass (J1)
[ui] tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions.rs#feature: pass -> [missing] (J1)

(and 157 additional test diffs)

Additionally, 2 doctest diffs were found. These are ignored, as they are noisy.

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 1ce9c977ffcff7c3b12bfe5629a682da0e74a7a1 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

x86_64-apple-1: 7843.5s -> 10223.2s (30.3%)
x86_64-apple-2: 4932.0s -> 5449.5s (10.5%)
dist-powerpc64-linux: 5318.7s -> 4930.5s (-7.3%)
dist-arm-linux-musl: 5083.0s -> 5443.9s (7.1%)
dist-aarch64-linux: 5457.5s -> 5838.9s (7.0%)
dist-x86_64-apple: 8957.6s -> 8339.1s (-6.9%)
aarch64-apple: 5011.4s -> 4683.3s (-6.5%)
i686-gnu-1: 8606.9s -> 8058.8s (-6.4%)
dist-arm-linux-gnueabi: 4881.7s -> 4575.7s (-6.3%)
x86_64-msvc-ext2: 5386.3s -> 5666.1s (5.2%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2025-07-03T09:51:20Z

Finished benchmarking commit (1ce9c97): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results (primary 3.0%, secondary 2.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	3.0%	[3.0%, 3.0%]	1
Regressions ❌ (secondary)	2.2%	[0.7%, 3.6%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.0%	[3.0%, 3.0%]	1

Cycles

Results (primary -1.1%, secondary -0.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.9%	[1.9%, 1.9%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.7%	[-2.2%, -1.1%]	5
Improvements ✅ (secondary)	-0.6%	[-0.7%, -0.5%]	2
All ❌✅ (primary)	-1.1%	[-2.2%, 1.9%]	6

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 462.452s -> 460.331s (-0.46%)
Artifact size: 372.20 MiB -> 372.27 MiB (0.02%)

Upstream change rust-lang/rust#143214 (Remove let_chains unstable feature) requires us to either remove the use of `let` in several places or wholesale update to Rust edition 2024. Doing this edition update seems worthwhile to keep accessing more recent features, but required code changes in several places. Resolves: model-checking#4196

Upstream change rust-lang/rust#143214 (Remove let_chains unstable feature) requires us to either remove the use of `let` in several places or wholesale update to Rust edition 2024. Doing this edition update seems worthwhile to keep accessing more recent features, but required code changes in several places. This is in preparation of the toolchain upgrade to 2025-07-03, but does not actually do this upgrade for it will require other, unrelated changes. By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses. --------- Co-authored-by: Carolyn Zech <[email protected]>

Relevant upstream PRs: - rust-lang/rust#143214 (Remove let_chains unstable feature) - rust-lang/rust#143036 (Remove support for `dyn*` from the compiler) The latter was tracked as an unsupported feature in Kani, whereby we can resolve one of our own issues as well. Resolves: model-checking#4196 Resolves: model-checking#1784

rustbot assigned WaffleLapkin Jun 29, 2025

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. labels Jun 29, 2025

camsteffen force-pushed the remove-let-chains-feature branch from d58ccd4 to bd8ed03 Compare June 29, 2025 20:46

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camsteffen force-pushed the remove-let-chains-feature branch from bd8ed03 to 3ff44da Compare June 29, 2025 21:01

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camsteffen force-pushed the remove-let-chains-feature branch from 3ff44da to d701341 Compare June 29, 2025 21:53

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est31 reviewed Jun 30, 2025

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tests/ui/macros/stringify.rs Outdated Show resolved Hide resolved

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inquisitivecrystal mentioned this pull request Jun 30, 2025

Tracking issue for eRFC 2497, "if- and while-let-chains, take 2" #53667

Closed

17 tasks

Remove let_chains feature

dc9879c

camsteffen force-pushed the remove-let-chains-feature branch from d701341 to dc9879c Compare June 30, 2025 12:49

rustbot assigned est31 and unassigned WaffleLapkin Jun 30, 2025

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 Jun 30, 2025

est31 mentioned this pull request Jun 30, 2025

let_chains stabilization followups #140722

Open

8 tasks

kpreid mentioned this pull request Jun 30, 2025

let expressions in this position are unstable #142111

Closed

bors added the merged-by-bors This PR was explicitly merged by bors. label Jul 2, 2025

bors merged commit 1ce9c97 into rust-lang:master Jul 2, 2025
11 checks passed

rustbot added this to the 1.90.0 milestone Jul 2, 2025

camsteffen deleted the remove-let-chains-feature branch July 2, 2025 22:22

tautschnig mentioned this pull request Jul 3, 2025

Update to Rust edition 2024 model-checking/kani#4197

Merged

tautschnig mentioned this pull request Jul 4, 2025

Upgrade Rust toolchain to 2025-07-04 model-checking/kani#4199

Open

Remove let_chains unstable feature #143214

Remove let_chains unstable feature #143214

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Test differences

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Overall result: no relevant changes - no action needed

Instruction count

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camsteffen commented Jun 29, 2025 •

edited by rustbot

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