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Recommend to never display zero disambiguators when demangling v0 symbols #124514

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michaelwoerister
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This PR extends the v0 symbol mangling documentation with the strong recommendation that demanglers should never display zero-disambiguators, especially when dealing with crate-root.

Being able to rely on C3foo to be rendered as foo (i.e. without explicit disambiguator value) rather than as foo[0] allows the compiler to encode things like new basic types in a backward compatible way. This idea has been originally proposed by @eddyb in the discussion around supporting f16 and f128 in the v0 mangling scheme. It is a generally useful mechanism for supporting a certain class of new elements in the v0 mangling scheme in a backward compatible way (whether as a temporary workaround until downstream tooling has picked up grammar changes or as a permanent encoding).

cc @tgross35

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rustbot commented Apr 29, 2024

r? @GuillaumeGomez

rustbot has assigned @GuillaumeGomez.
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@rustbot rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Apr 29, 2024
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cc @ehuss, as the original author of these (incredible) docs.

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r? eddyb

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@eddyb, would you like me to make any changes to this PR before it can be approved?

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@_eddyb seems to be unavailable at the moment.

r? @davidtwco maybe?

@rustbot rustbot assigned davidtwco and unassigned eddyb Jun 3, 2024
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@bors r+ rollup

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bors commented Jun 12, 2024

📌 Commit c8a3697 has been approved by davidtwco

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 Jun 12, 2024
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 12, 2024
…kingjubilee

Rollup of 16 pull requests

Successful merges:

 - rust-lang#123374 (DOC: Add FFI example for slice::from_raw_parts())
 - rust-lang#124514 (Recommend to never display zero disambiguators when demangling v0 symbols)
 - rust-lang#125978 (Cleanup: HIR ty lowering: Consolidate the places that do assoc item probing & access checking)
 - rust-lang#125980 (Nvptx remove direct passmode)
 - rust-lang#126187 (For E0277 suggest adding `Result` return type for function when using QuestionMark `?` in the body.)
 - rust-lang#126210 (docs(core): make more const_ptr doctests assert instead of printing)
 - rust-lang#126249 (Simplify `[T; N]::try_map` signature)
 - rust-lang#126256 (Add {{target}} substitution to compiletest)
 - rust-lang#126263 (Make issue-122805.rs big endian compatible)
 - rust-lang#126281 (set_env: State the conclusion upfront)
 - rust-lang#126286 (Make `storage-live.rs` robust against rustc internal changes.)
 - rust-lang#126287 (Update a cranelift patch file for formatting changes.)
 - rust-lang#126301 (Use `tidy` to sort crate attributes for all compiler crates.)
 - rust-lang#126305 (Make PathBuf less Ok with adding UTF-16 then `into_string`)
 - rust-lang#126310 (Migrate run make prefer rlib)
 - rust-lang#126314 (fix RELEASES: we do not support upcasting to auto traits)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 969056d into rust-lang:master Jun 12, 2024
10 checks passed
@rustbot rustbot added this to the 1.81.0 milestone Jun 12, 2024
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Jun 12, 2024
Rollup merge of rust-lang#124514 - michaelwoerister:zero-disambiguator-demangling-recommendation, r=davidtwco

Recommend to never display zero disambiguators when demangling v0 symbols

This PR extends the [v0 symbol mangling documentation](https://doc.rust-lang.org/rustc/symbol-mangling/v0.html) with the strong recommendation that demanglers should never display zero-disambiguators, especially when dealing with `crate-root`.

Being able to rely on `C3foo` to be rendered as `foo` (i.e. without explicit disambiguator value) rather than as `foo[0]` allows the compiler to encode things like new basic types in a backward compatible way. This idea has been originally proposed by `@eddyb` in [the discussion around supporting `f16` and `f128` in the v0 mangling scheme](rust-lang#122106). It is a generally useful mechanism for supporting a certain class of new elements in the v0 mangling scheme in a backward compatible way (whether as a temporary workaround until downstream tooling has picked up grammar changes or as a permanent encoding).

cc `@tgross35`
bjorn3 pushed a commit to bjorn3/rust that referenced this pull request Jun 30, 2024
…kingjubilee

Rollup of 16 pull requests

Successful merges:

 - rust-lang#123374 (DOC: Add FFI example for slice::from_raw_parts())
 - rust-lang#124514 (Recommend to never display zero disambiguators when demangling v0 symbols)
 - rust-lang#125978 (Cleanup: HIR ty lowering: Consolidate the places that do assoc item probing & access checking)
 - rust-lang#125980 (Nvptx remove direct passmode)
 - rust-lang#126187 (For E0277 suggest adding `Result` return type for function when using QuestionMark `?` in the body.)
 - rust-lang#126210 (docs(core): make more const_ptr doctests assert instead of printing)
 - rust-lang#126249 (Simplify `[T; N]::try_map` signature)
 - rust-lang#126256 (Add {{target}} substitution to compiletest)
 - rust-lang#126263 (Make issue-122805.rs big endian compatible)
 - rust-lang#126281 (set_env: State the conclusion upfront)
 - rust-lang#126286 (Make `storage-live.rs` robust against rustc internal changes.)
 - rust-lang#126287 (Update a cranelift patch file for formatting changes.)
 - rust-lang#126301 (Use `tidy` to sort crate attributes for all compiler crates.)
 - rust-lang#126305 (Make PathBuf less Ok with adding UTF-16 then `into_string`)
 - rust-lang#126310 (Migrate run make prefer rlib)
 - rust-lang#126314 (fix RELEASES: we do not support upcasting to auto traits)

r? `@ghost`
`@rustbot` modify labels: rollup
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6 participants