transmutability: Support char, NonZeroXxx #140215

joshlf · 2025-04-23T18:41:13Z

Note that NonZero support is not wired up, as the author encountered
bugs while attempting this. A future commit will wire up NonZero
support.

r? @jswrenn

compiler/rustc_transmute/src/layout/tree.rs

compiler/rustc_transmute/src/maybe_transmutable/tests.rs

bors · 2025-04-24T09:59:19Z

☔ The latest upstream changes (presumably #140168) made this pull request unmergeable. Please resolve the merge conflicts.

joshlf · 2025-04-24T16:49:07Z

@tmiasko Since you've expressed an interest in this, maybe you have a few cycles to poke at a bug that's been stumping me? Running the UI test transmutability/nonzero.rs is causing rustc to segfault. It appears to be somewhere in this match arm. No worries if not, obviously, but I figured that maybe something would jump out to you that isn't jumping out to me (as someone without much familiarity with the rustc codebase).

jswrenn · 2025-04-24T16:58:16Z

@joshlf I recommend doing an rr trace of the stage1 rustc.

joshlf · 2025-04-24T19:17:13Z

@jswrenn I'll work on that in parallel. In the meantime, this is ready for review (without wiring up NonZero types).

tmiasko · 2025-04-25T06:54:41Z

Running the UI test transmutability/nonzero.rs is causing rustc to segfault. It appears to be somewhere in this match arm.

There is an infinite recursion in ty::Alias match arm. AliasTy::to_ty reconstructs ty::Alias, and then recurses without making any progress. The actual problem is probably missing normalization when computing a field type.

jswrenn · 2025-04-25T14:56:37Z

compiler/rustc_transmute/src/layout/tree.rs

+                            Self::from_struct((ty, layout), *adt_def, cx)
+                        }
+                        (AdtKind::Struct, Included(1), Included(_hi)) if is_transparent => {
+                            // FIXME: Uncomment the code below and get it


Do you want to tackle this in this PR, or a follow up?

In a follow-up. I've removed the commented-out code for now.

jswrenn · 2025-04-25T15:55:07Z

compiler/rustc_transmute/src/layout/tree.rs

@@ -268,6 +384,10 @@ pub(crate) mod rustc {
                    }))
                }

+                ty::Char => Ok(Self::char(cx.tcx().data_layout.endian.into())),
+
+                ty::Alias(_kind, ty) => Self::from_ty(ty.to_ty(cx.tcx()), cx),


Suggested change

ty::Alias(_kind, ty) => Self::from_ty(ty.to_ty(cx.tcx()), cx),

ty::Alias(_kind, ty) => Self::from_ty(/* normalize ty */),

@tmiasko / @compiler-errors, what's the current way to normalize a type when we do care about regions?

If we're punting on normalization, can you remove this branch so we don't regress projections to an infinite loop?

If we're punting on normalization, can you remove this branch so we don't regress projections to an infinite loop?

Done.

@tmiasko / @compiler-errors, what's the current way to normalize a type when we do care about regions?

Maybe, for the time being (but in a separate PR), we could at least support 'static types by normalizing without caring about regions and returning an error when the type is non-'static? That would at least cover the NonZero case.

jswrenn · 2025-04-25T16:28:18Z

@joshlf Happy for us to punt NonZeroXxx and aliases to a future PR, but can you edit the commit message and PR title accordingly?

Note that `NonZero` support is not wired up, as the author encountered bugs while attempting this. A future commit will wire up `NonZero` support.

joshlf · 2025-04-25T19:56:17Z

@joshlf Happy for us to punt NonZeroXxx and aliases to a future PR, but can you edit the commit message and PR title accordingly?

Done.

jswrenn · 2025-04-26T00:14:07Z

Thanks! I'll follow up with a normalization fix as soon as I unbork my devbox...

@bors r+

bors · 2025-04-26T00:14:09Z

📌 Commit ae0c2fe has been approved by jswrenn

It is now in the queue for this repository.

…o, r=jswrenn transmutability: Support char, NonZeroXxx Note that `NonZero` support is not wired up, as the author encountered bugs while attempting this. A future commit will wire up `NonZero` support. r? `@jswrenn`

…o, r=jswrenn transmutability: Support char, NonZeroXxx Note that `NonZero` support is not wired up, as the author encountered bugs while attempting this. A future commit will wire up `NonZero` support. r? ``@jswrenn``

…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#123239 (Implement a lint for implicit autoref of raw pointer dereference - take 2) - rust-lang#140215 (transmutability: Support char, NonZeroXxx) - rust-lang#140226 (Update wasm-component-ld to 0.5.13) - rust-lang#140302 (Move inline asm check to typeck, properly handle aliases) - rust-lang#140317 (Remove redundant check) - rust-lang#140318 (Simply try to unpeel AsyncFnKindHelper goal in `emit_specialized_closure_kind_error`) - rust-lang#140325 (Grammar fixes for BufRead::has_data_left docs) r? `@ghost` `@rustbot` modify labels: rollup

…o, r=jswrenn transmutability: Support char, NonZeroXxx Note that `NonZero` support is not wired up, as the author encountered bugs while attempting this. A future commit will wire up `NonZero` support. r? ```@jswrenn```

…iaskrgr Rollup of 6 pull requests Successful merges: - rust-lang#123239 (Implement a lint for implicit autoref of raw pointer dereference - take 2) - rust-lang#140215 (transmutability: Support char, NonZeroXxx) - rust-lang#140226 (Update wasm-component-ld to 0.5.13) - rust-lang#140317 (Remove redundant check) - rust-lang#140318 (Simply try to unpeel AsyncFnKindHelper goal in `emit_specialized_closure_kind_error`) - rust-lang#140325 (Grammar fixes for BufRead::has_data_left docs) r? `@ghost` `@rustbot` modify labels: rollup

…iaskrgr Rollup of 6 pull requests Successful merges: - rust-lang#140215 (transmutability: Support char, NonZeroXxx) - rust-lang#140226 (Update wasm-component-ld to 0.5.13) - rust-lang#140317 (Remove redundant check) - rust-lang#140318 (Simply try to unpeel AsyncFnKindHelper goal in `emit_specialized_closure_kind_error`) - rust-lang#140320 (replace `GenericArg` with `Term` where applicable) - rust-lang#140325 (Grammar fixes for BufRead::has_data_left docs) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#140215 - joshlf:transmutability-char-nonzero, r=jswrenn transmutability: Support char, NonZeroXxx Note that `NonZero` support is not wired up, as the author encountered bugs while attempting this. A future commit will wire up `NonZero` support. r? ````@jswrenn````

rustbot assigned jswrenn Apr 23, 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 Apr 23, 2025

joshlf commented Apr 23, 2025

View reviewed changes

compiler/rustc_transmute/src/layout/tree.rs Outdated Show resolved Hide resolved

joshlf force-pushed the transmutability-char-nonzero branch 2 times, most recently from a6671a7 to b4af1e4 Compare April 23, 2025 18:45