patterns: reject raw pointers that are not just integers #116930

RalfJung · 2023-10-19T06:37:41Z

Matching against 0 as *const i32 is fine, matching against &42 as *const i32 is not.

This extends the existing check against function pointers and wide pointers: we now uniformly reject all these pointer types during valtree construction, and then later lint because of that. See here for some more explanation and context.

Also fixes #116929.

Cc @oli-obk @lcnr

rustbot · 2023-10-19T06:37:49Z

r? @davidtwco

(rustbot has picked a reviewer for you, use r? to override)

RalfJung · 2023-10-19T06:38:08Z

compiler/rustc_lint_defs/src/builtin.rs

    pub POINTER_STRUCTURAL_MATCH,
-    Allow,


I didn't realize this lint is still allow-by-default oO. Seems high time we make it warn-by-default?

RalfJung · 2023-10-19T06:38:50Z

The 2nd commit makes this forbid-by-default so we can crater it.
@bors try

bors · 2023-10-19T06:39:59Z

⌛ Trying commit 0787e62 with merge ebb1189...

patterns: reject raw pointers that are not just integers Matching against `0 as *const i32` is fine, matching against `&42 as *const i32` is not. Cc `@oli-obk` `@lcnr`

RalfJung · 2023-10-19T06:41:19Z

Due to #116929 this lint still has a big gap, it'll only find bad raw pointers "at the root".

I wonder if with this change to valtree construction, we can make it so that some lint always fires when a const is used as a pattern and valtree construction fails? I do think those cases should all become hard errors eventually...

bors · 2023-10-19T08:01:15Z

☀️ Try build successful - checks-actions
Build commit: ebb1189 (ebb118907fa893a392c699ddf120848fa0a8d6c2)

RalfJung · 2023-10-19T08:02:09Z

Let's see how much fallout we're getting from this weak form of the lint.
@craterbot check

craterbot · 2023-10-19T08:02:21Z

👌 Experiment pr-116930 created and queued.
🤖 Automatically detected try build ebb1189
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

rustbot · 2023-10-19T08:03:27Z

Some changes might have occurred in exhaustiveness checking

cc @Nadrieril

compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs

RalfJung · 2023-10-20T08:10:53Z

Lol, the doctest for StructuralEq uses a function pointer as a bad example.^^

RalfJung · 2023-10-20T08:31:29Z

library/core/src/marker.rs

@@ -247,6 +247,7 @@ marker_impls! {
 ///
 /// const CFN: Wrap<fn(&())> = Wrap(higher_order);
 ///
+/// #[allow(pointer_structural_match)]


FWIW these entire trait docs are outdated; that's tracked in #115881.

craterbot · 2023-10-20T11:55:53Z

🚧 Experiment pr-116930 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2023-10-22T12:29:57Z

🎉 Experiment pr-116930 is completed!
📊 876 regressed and 3 fixed (379825 total)
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the blacklist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

RalfJung · 2023-10-22T15:55:33Z

@craterbot run mode=check-only crates=https://crater-reports.s3.amazonaws.com/pr-116930/retry-regressed-list.txt

RalfJung · 2023-10-30T07:54:13Z

@rust-lang/lang this PR does three things:

it fixes our old lint that detects match on function pointers and wide pointers to also catch cases where those pointers are hidden inside other types
it makes that lint warn-by-default (but doesn't yet make it show up in dependencies)
it makes the lint also trigger when encountering a raw pointer that was not constructed via int as *const/mut T, but e.g. via &something as *const T -- those allocations don't have guarantees on their ptr equality just like function pointers and vtables, so we should reject them for the same reason.

We haven't reached a proper conclusion in the recent "match on const" meeting, but the general direction seems to have been towards "it should still work like a pattern" (and not like sugar for ==), and this PR is a crucial step towards ensuring that they do indeed behave like a pattern, with structural properties and all that. Even if the goal is just to future-proof against both options (as has been the strategy so far), we want this warning.

Crater found only 3 cases where the warning triggers, in the entire ecosystem. All of them would already warn on stable if they enabled the lint; the new cases covered by this PR were not detected at all by crater.

davidtwco

Implementation changes look good to me, r=me after decisions from t-lang.

davidtwco · 2023-11-04T01:45:03Z

compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs

-                        );
-                    }
-                    _ => {}
+                if !have_valtree {


nit: could be part of the condition on the previous line

nikomatsakis · 2023-11-08T16:47:41Z

I'm in favor of this. (I also have thoughts on the semantics of matching on constants -- tl;dr I think I'm ready to accept "match is not an extensible mechanism" and hence will not act the same as == so we can stop talking about it -- but those are best discussed elsewhere, I assume)

WaffleLapkin · 2023-11-08T16:47:43Z

T-lang meeting consensus: let's do this, no FCP needed.

RalfJung · 2023-11-08T19:39:03Z

@bors r=davidtwco

bors · 2023-11-08T19:39:06Z

📌 Commit 3058865 has been approved by davidtwco

It is now in the queue for this repository.

bors · 2023-11-08T20:42:35Z

⌛ Testing commit 3058865 with merge fdaaaf9...

bors · 2023-11-08T22:39:54Z

☀️ Test successful - checks-actions
Approved by: davidtwco
Pushing fdaaaf9 to master...

rust-timer · 2023-11-09T00:20:34Z

Finished benchmarking commit (fdaaaf9): 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

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.4%, 1.4%]	5
Regressions ❌ (secondary)	3.6%	[3.6%, 3.6%]	1
Improvements ✅ (primary)	-0.7%	[-1.1%, -0.5%]	7
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.1%	[-1.1%, 1.4%]	12

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.4%, 0.5%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-0.4%, -0.4%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[-0.4%, 0.5%]	3

Binary size

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

Bootstrap: 662.394s -> 663.159s (0.12%)
Artifact size: 308.74 MiB -> 308.75 MiB (0.00%)

patterns: reject raw pointers that are not just integers Matching against `0 as *const i32` is fine, matching against `&42 as *const i32` is not. This extends the existing check against function pointers and wide pointers: we now uniformly reject all these pointer types during valtree construction, and then later lint because of that. See [here](rust-lang/rust#116930 (comment)) for some more explanation and context. Also fixes rust-lang/rust#116929. Cc `@oli-obk` `@lcnr`

Update Rust toolchain from nightly-2023-11-08 to nightly-2023-11-09 without any other source changes. This is an automatically generated pull request. If any of the CI checks fail, manual intervention is required. In such a case, review the changes at https://github.com/rust-lang/rust from rust-lang@7adc89b up to rust-lang@fdaaaf9. The log for this commit range is: rust-lang@fdaaaf9f92 Auto merge of rust-lang#116930 - RalfJung:raw-ptr-match, r=davidtwco rust-lang@30588657b7 avoid unnecessary nested conditionals rust-lang@90fdc1fc27 Auto merge of rust-lang#117716 - GuillaumeGomez:rollup-83gnhll, r=GuillaumeGomez rust-lang@9d3c80248b Rollup merge of rust-lang#117713 - GuillaumeGomez:document-hidden-json, r=notriddle rust-lang@d8c52b378d Rollup merge of rust-lang#117702 - davidtwco:target-tier-refactors, r=petrochenkov rust-lang@5d00a5d936 Rollup merge of rust-lang#117679 - aDotInTheVoid:yes-core, r=GuillaumeGomez rust-lang@c828371179 Rollup merge of rust-lang#117282 - clubby789:recover-wrong-function-header, r=TaKO8Ki rust-lang@e05e4f38b5 Rollup merge of rust-lang#117263 - onur-ozkan:change-id-fix, r=saethlin rust-lang@341efb1017 Auto merge of rust-lang#117560 - lqd:issue-117146, r=matthewjasper rust-lang@33edea60f0 Add test for reexported hidden item with `--document-hidden-items` rust-lang@28acba3c61 Auto merge of rust-lang#115460 - zachs18:borrowedcursor_write_no_panic, r=dtolnay rust-lang@755629fe59 Auto merge of rust-lang#117706 - matthiaskrgr:rollup-lscx7dg, r=matthiaskrgr rust-lang@e0cb1cc296 bootstrap: add more detail on change-id comments rust-lang@e878100386 bootstrap: improve `fn check_version` rust-lang@ae4d18b2da handle the case when the change-id isn't found rust-lang@7e4ffa98b5 Rollup merge of rust-lang#117700 - Zalathar:rename-run-coverage, r=onur-ozkan rust-lang@55306535dd Rollup merge of rust-lang#117698 - nnethercote:space_between-2, r=petrochenkov rust-lang@b1b5a8ea9d Rollup merge of rust-lang#117667 - Alexendoo:doc-clippy-config, r=albertlarsan68 rust-lang@adf4981969 Rollup merge of rust-lang#117663 - klensy:bump-deps, r=davidtwco rust-lang@8198864377 Rollup merge of rust-lang#117650 - saethlin:inline-me-please, r=davidtwco rust-lang@ba7ec56639 Rollup merge of rust-lang#117531 - fmease:rustdoc-effects-properly-elide-x-crate-host-args, r=GuillaumeGomez rust-lang@b74a84c0bc Rollup merge of rust-lang#114316 - ecnelises:aix_doc, r=workingjubilee rust-lang@fab1054e17 Auto merge of rust-lang#117542 - compiler-errors:only-normalize-predicate, r=lcnr rust-lang@750c2ecd15 Auto merge of rust-lang#116881 - LuuuXXX:issue-110087, r=onur-ozkan rust-lang@b9b7982f72 Add AIX platform-support doc rust-lang@ef7ebaa788 rustc_target: move file for uniformity rust-lang@1af256fe8a targets: move target specs to spec/targets rust-lang@76aa83e3e1 target: move base specs to spec/base rust-lang@a573880373 coverage: Rename the `run-coverage` test mode to `coverage-run` rust-lang@7cc997d373 Auto merge of rust-lang#117699 - weihanglo:update-cargo, r=weihanglo rust-lang@0670466e2c Update cargo rust-lang@438b9a6e82 More tests for token stream pretty-printing with adjacent punctuation. rust-lang@783d4b8b26 Clarify `space_between`. rust-lang@91cfcb0219 Auto merge of rust-lang#117484 - Zalathar:tests, r=cjgillot rust-lang@97c9d8f405 Only use normalize_param_env when normalizing predicate in check_item_bounds rust-lang@1b8dee19e8 Fix issue rust-lang#110087 rust-lang@0d5ec963bb Auto merge of rust-lang#117692 - matthiaskrgr:rollup-umaf5pr, r=matthiaskrgr rust-lang@f72e974e3f Rollup merge of rust-lang#117655 - compiler-errors:method-tweaks, r=estebank rust-lang@7552dd19ad Rollup merge of rust-lang#117625 - nnethercote:clippy-perf, r=cuviper rust-lang@3c6307240c Rollup merge of rust-lang#116399 - WaffleLapkin:erase_small_things, r=cjgillot rust-lang@b724d9c90e Rollup merge of rust-lang#113925 - clubby789:const-ctor-repeat, r=estebank rust-lang@fcdd99edca Add -Zcross-crate-inline-threshold=yes rust-lang@e8cf29b584 rustdoc: minor changes suggested by clippy perf lints. rust-lang@ff0b4b6091 Auto merge of rust-lang#117672 - lqd:ci-gcc-lld, r=Kobzol rust-lang@1b3733e5a4 rustc: minor changes suggested by clippy perf lints. rust-lang@eca9a1533f Add an explanation for `transmute_unchecked` rust-lang@1d1fe9a205 add note to remember to update a url when bumping to gcc 10.1.0 rust-lang@434b69a1d6 tests/rustdoc-json: Rewrite tests no not use `#![no_core]`. rust-lang@0875f456f1 tests/rustdoc-json: Remove more needless uses of `#![no_core]`. rust-lang@f784fa7bd9 tests/rustdoc-json: Remove some needless uses of `#![no_core]`. rust-lang@d73eaaac5f ci: bump gcc on dist x64 linux builder to 9.5 rust-lang@f2fd8ad788 Document clippy_config in nightly-rustc docs rust-lang@eed89185bb bump some deps rust-lang@0add056dee Rework print_disambiguation_help rust-lang@88a37acb26 Yeet MethodCallComponents rust-lang@4e6f438d2a coverage: Register `test::Coverage` as the test suite for `tests/coverage` rust-lang@49127c64d6 coverage: Migrate `tests/coverage-map` into `tests/coverage` rust-lang@e9d04c5e24 coverage: Migrate `tests/run-coverage` into `tests/coverage` rust-lang@aea7c27eae coverage: Set up a macro for declaring unified coverage test suites rust-lang@3509aed632 coverage: Add `./x.py test coverage`, an alias for `coverage-map` and `run-coverage` rust-lang@e585a99230 coverage: Give each coverage test mode a separate output directory rust-lang@211d4cee8e coverage: Copy all remaining run-coverage tests into coverage-map rust-lang@4b76b97bc8 coverage: Copy all remaining coverage-map tests into run-coverage rust-lang@f5df56b26b coverage: Flatten `coverage-map/status-quo/` into its parent directory rust-lang@8eef39f082 coverage: Remove `tests/coverage-map/if.rs` rust-lang@7f8a6de72c coverage: Use `-Copt-level=2` by default in run-coverage tests rust-lang@1dcdf83927 rustdoc: properly elide cross-crate host effect args rust-lang@2dff90dc23 add test for issue 117146 rust-lang@de7a8305ae traverse region graph instead of SCCs to compute polonius loan scopes rust-lang@03b24f2756 remove some dead code rust-lang@70a8e157ab make pointer_structural_match warn-by-default rust-lang@af6c7e0ca1 also lint against fn ptr and raw ptr nested inside the const rust-lang@bec88ad4aa patterns: reject raw pointers that are not just integers rust-lang@be0b42fabe Recover from incorrectly ordered/duplicated function keywords rust-lang@b3d50255d9 Use consisntent style of `size_of` in query type erasure rust-lang@61361bb212 Use `transmute_unchecked` and make the types explicit in query type erasure rust-lang@11a64a1834 don't panic in BorrowedCursor::write rust-lang@86b112204a Improve diagnostic for const ctors in array repeat expressions Co-authored-by: celinval <celinval@users.noreply.github.com>

rustbot assigned davidtwco Oct 19, 2023

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remove some dead code

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avoid unnecessary nested conditionals

3058865

bors added the merged-by-bors This PR was explicitly merged by bors. label Nov 8, 2023

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This was referenced Nov 8, 2023

make matching on NaN a hard error, and remove the rest of illegal_floating_point_literal_pattern #116284

Merged

mark ty::Const::Error when meet unsupport ty for const generic params #117176

Merged

matthiaskrgr mentioned this pull request Nov 11, 2023

ICE: Got a scalar pair where a scalar was expected #117806

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RalfJung deleted the raw-ptr-match branch November 11, 2023 09:58

matthiaskrgr mentioned this pull request Dec 24, 2023

ICE: shouldn't have created a ValTree for *const .. #119270

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RalfJung mentioned this pull request Jan 28, 2024

update indirect_structural_match and pointer_structural_match lints to match RFC and to show up for dependencies #120423

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apiraino removed the I-lang-nominated Nominated for discussion during a lang team meeting. label Apr 10, 2025

patterns: reject raw pointers that are not just integers #116930

patterns: reject raw pointers that are not just integers #116930

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Overall result: no relevant changes - no action needed

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