Allow fmt::Arguments::as_str() to return more Some(_). #106823

m-ou-se · 2023-01-13T18:49:14Z

This adjusts the documentation to allow optimization of format_args!() to be visible through fmt::Arguments::as_str().

This allows for future changes like #106824.

m-ou-se · 2023-01-13T18:49:45Z

rfcbot · 2023-01-13T18:49:46Z

Team member @m-ou-se has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

nbdd0121 · 2023-01-13T19:20:57Z

Does this cover case like const BAR: &str = "bar"; format_args!("foo{}", BAR), or just literals?

If constants involving CTFE can also be "optimized", I feel this makes formatting machinery more integrated with language/compiler, in a way that (even without considering panicking) non-std implementations would not be able to replicate, and thus would need ACK from both language and compiler teams.

nbdd0121 · 2023-01-13T19:26:51Z

Note that in the compiler team MCP discussion of rust-lang/compiler-team#541 on Zulip (https://rust-lang.zulipchat.com/#narrow/stream/233931-xxx/topic/Make.20format_args.21.28.29.20its.20own.20AST.20node.20.28ast.E2.80.A6.20compiler-team.23541), it is unclear whether there is a consensus about whether as_str can return the "optimized version".

m-ou-se · 2023-01-13T20:33:37Z

Does this cover case like const BAR: &str = "bar"; format_args!("foo{}", BAR), or just literals?

Yes and no.

This FCP itself is just about clearly saying 'there are no guarantees' in the API documentation. This allows us to change a None to Some (and back) in future versions. So even for format_args!("foo{}", BAR) we will not guarantee as_str() returns None.

Separately from this API change/clarification, any future implementation change (like #106824) that does anything that couldn't be done with a regular proc macro should probably be carefully considered by the language and/or compiler team. But before we have that discussion, it'd be good to first agree that as_str() has (almost) no guarantees, so we can separate the 'library API stability discussion' from the 'builtin macro abilities discussion'.

rfcbot · 2023-01-13T21:02:26Z

🔔 This is now entering its final comment period, as per the review above. 🔔

rfcbot · 2023-01-23T21:06:26Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

dtolnay · 2023-01-23T21:40:27Z

@bors r+ rollup

bors · 2023-01-23T21:40:29Z

📌 Commit a37b484 has been approved by dtolnay

It is now in the queue for this repository.

…ees, r=dtolnay Allow fmt::Arguments::as_str() to return more Some(_). This adjusts the documentation to allow optimization of format_args!() to be visible through fmt::Arguments::as_str(). This allows for future changes like rust-lang#106824.

Rollup of 9 pull requests Successful merges: - rust-lang#105552 (Add help message about function pointers) - rust-lang#106583 (Suggest coercion of `Result` using `?`) - rust-lang#106767 (Allow setting CFG_DISABLE_UNSTABLE_FEATURES to 0) - rust-lang#106823 (Allow fmt::Arguments::as_str() to return more Some(_).) - rust-lang#107166 (rustc_metadata: Support non-`Option` nullable values in metadata tables) - rust-lang#107213 (Add suggestion to remove if in let..else block) - rust-lang#107223 (`sub_ptr()` is equivalent to `usize::try_from().unwrap_unchecked()`, not `usize::from().unwrap_unchecked()`) - rust-lang#107227 (`new_outside_solver` -> `evaluate_root_goal`) - rust-lang#107232 (rustdoc: simplify settings popover DOM, CSS, JS) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

Enable flatten-format-args by default. Part of rust-lang#99012. This enables the `flatten-format-args` feature that was added by rust-lang#106824: > This change inlines string literals, integer literals and nested format_args!() into format_args!() during ast lowering, making all of the following pairs result in equivalent hir: > > ```rust > println!("Hello, {}!", "World"); > println!("Hello, World!"); > ``` > > ```rust > println!("[info] {}", format_args!("error")); > println!("[info] error"); > ``` > > ```rust > println!("[{}] {}", status, format_args!("error: {}", msg)); > println!("[{}] error: {}", status, msg); > ``` > > ```rust > println!("{} + {} = {}", 1, 2, 1 + 2); > println!("1 + 2 = {}", 1 + 2); > ``` > > And so on. > > This is useful for macros. E.g. a `log::info!()` macro could just pass the tokens from the user directly into a `format_args!()` that gets efficiently flattened/inlined into a `format_args!("info: {}")`. > > It also means that `dbg!(x)` will have its file, line, and expression name inlined: > > ```rust > eprintln!("[{}:{}] {} = {:#?}", file!(), line!(), stringify!(x), x); // before > eprintln!("[example.rs:1] x = {:#?}", x); // after > ``` > > Which can be nice in some cases, but also means a lot more unique static strings than before if dbg!() is used a lot. This is mostly an optimization, except that it will be visible through [`fmt::Arguments::as_str()`](https://doc.rust-lang.org/nightly/std/fmt/struct.Arguments.html#method.as_str). In rust-lang#106823, there was already a libs-api FCP about the documentation of `fmt::Arguments::as_str()` to allow it to give `Some` rather than `None` depending on optimizations like this. That was just a documentation update though. This PR is the one that actually makes the user visible change: ```rust assert_eq!(format_args!("abc").as_str(), Some("abc")); // Unchanged. assert_eq!(format_args!("ab{}", "c").as_str(), Some("abc")); // Was `None` before! ```

Enable flatten-format-args by default. Part of rust-lang/rust#99012. This enables the `flatten-format-args` feature that was added by rust-lang/rust#106824: > This change inlines string literals, integer literals and nested format_args!() into format_args!() during ast lowering, making all of the following pairs result in equivalent hir: > > ```rust > println!("Hello, {}!", "World"); > println!("Hello, World!"); > ``` > > ```rust > println!("[info] {}", format_args!("error")); > println!("[info] error"); > ``` > > ```rust > println!("[{}] {}", status, format_args!("error: {}", msg)); > println!("[{}] error: {}", status, msg); > ``` > > ```rust > println!("{} + {} = {}", 1, 2, 1 + 2); > println!("1 + 2 = {}", 1 + 2); > ``` > > And so on. > > This is useful for macros. E.g. a `log::info!()` macro could just pass the tokens from the user directly into a `format_args!()` that gets efficiently flattened/inlined into a `format_args!("info: {}")`. > > It also means that `dbg!(x)` will have its file, line, and expression name inlined: > > ```rust > eprintln!("[{}:{}] {} = {:#?}", file!(), line!(), stringify!(x), x); // before > eprintln!("[example.rs:1] x = {:#?}", x); // after > ``` > > Which can be nice in some cases, but also means a lot more unique static strings than before if dbg!() is used a lot. This is mostly an optimization, except that it will be visible through [`fmt::Arguments::as_str()`](https://doc.rust-lang.org/nightly/std/fmt/struct.Arguments.html#method.as_str). In rust-lang/rust#106823, there was already a libs-api FCP about the documentation of `fmt::Arguments::as_str()` to allow it to give `Some` rather than `None` depending on optimizations like this. That was just a documentation update though. This PR is the one that actually makes the user visible change: ```rust assert_eq!(format_args!("abc").as_str(), Some("abc")); // Unchanged. assert_eq!(format_args!("ab{}", "c").as_str(), Some("abc")); // Was `None` before! ```

Pkgsrc changes: * Adjust patches and cargo checksums to new versions. * Sadly, the patch to reduce the cargo verbosity no longer applies, so I've asked upstream about the proper way to get the old result. (so the build log becomes Quite Bloated for now). Upstream changes: Version 1.69.0 (2023-04-20) ========================== Language -------- - [Deriving built-in traits on packed structs works with `Copy` fields.] (rust-lang/rust#104429) - [Stabilize the `cmpxchg16b` target feature on x86 and x86_64.] (rust-lang/rust#106774) - [Improve analysis of trait bounds for associated types.] (rust-lang/rust#103695) - [Allow associated types to be used as union fields.] (rust-lang/rust#106938) - [Allow `Self: Autotrait` bounds on dyn-safe trait methods.] (rust-lang/rust#107082) - [Treat `str` as containing `[u8]` for auto trait purposes.] (rust-lang/rust#107941) Compiler -------- - [Upgrade `*-pc-windows-gnu` on CI to mingw-w64 v10 and GCC 12.2.] (rust-lang/rust#100178) - [Rework min_choice algorithm of member constraints.] (rust-lang/rust#105300) - [Support `true` and `false` as boolean flags in compiler arguments.] (rust-lang/rust#107043) - [Default `repr(C)` enums to `c_int` size.] (rust-lang/rust#107592) Libraries --------- - [Implement the unstable `DispatchFromDyn` for cell types, allowing downstream experimentation with custom method receivers.] (rust-lang/rust#97373) - [Document that `fmt::Arguments::as_str()` may return `Some(_)` in more cases after optimization, subject to change.] (rust-lang/rust#106823) - [Implement `AsFd` and `AsRawFd` for `Rc`.] (rust-lang/rust#107317) Stabilized APIs --------------- - [`CStr::from_bytes_until_nul`] (https://doc.rust-lang.org/stable/core/ffi/struct.CStr.html#method.from_bytes_until_nul) - [`core::ffi::FromBytesUntilNulError`] (https://doc.rust-lang.org/stable/core/ffi/struct.FromBytesUntilNulError.html) These APIs are now stable in const contexts: - [`SocketAddr::new`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.new) - [`SocketAddr::ip`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.ip) - [`SocketAddr::port`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.port) - [`SocketAddr::is_ipv4`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.is_ipv4) - [`SocketAddr::is_ipv6`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.is_ipv6) - [`SocketAddrV4::new`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV4.html#method.new) - [`SocketAddrV4::ip`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV4.html#method.ip) - [`SocketAddrV4::port`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV4.html#method.port) - [`SocketAddrV6::new`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.new) - [`SocketAddrV6::ip`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.ip) - [`SocketAddrV6::port`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.port) - [`SocketAddrV6::flowinfo`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.flowinfo) - [`SocketAddrV6::scope_id`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.scope_id) Cargo ----- - [Cargo now suggests `cargo fix` or `cargo clippy --fix` when compilation warnings are auto-fixable.] (rust-lang/cargo#11558) - [Cargo now suggests `cargo add` if you try to install a library crate.] (rust-lang/cargo#11410) - [Cargo now sets the `CARGO_BIN_NAME` environment variable also for binary examples.] (rust-lang/cargo#11705) Rustdoc ----- - [Vertically compact trait bound formatting.] (rust-lang/rust#102842) - [Only include stable lints in `rustdoc::all` group.] (rust-lang/rust#106316) - [Compute maximum Levenshtein distance based on the query.] (rust-lang/rust#107141) - [Remove inconsistently-present sidebar tooltips.] (rust-lang/rust#107490) - [Search by macro when query ends with `!`.] (rust-lang/rust#108143) Compatibility Notes ------------------- - [The `rust-analysis` component from `rustup` now only contains a warning placeholder.] (rust-lang/rust#101841) This was primarily intended for RLS, and the corresponding `-Zsave-analysis` flag has been removed from the compiler as well. - [Unaligned references to packed fields are now a hard error.] (rust-lang/rust#102513) This has been a warning since 1.53, and denied by default with a future-compatibility warning since 1.62. - [Update the minimum external LLVM to 14.] (rust-lang/rust#107573) - [Cargo now emits errors on invalid characters in a registry token.] (rust-lang/cargo#11600) - [When `default-features` is set to false of a workspace dependency, and an inherited dependency of a member has `default-features = true`, Cargo will enable default features of that dependency.] (rust-lang/cargo#11409) - [Cargo denies `CARGO_HOME` in the `[env]` configuration table. Cargo itself doesn't pick up this value, but recursive calls to cargo would, which was not intended.] (rust-lang/cargo#11644) - [Debuginfo for build dependencies is now off if not explicitly set. This is expected to improve the overall build time.] (rust-lang/cargo#11252) Internal Changes ---------------- These changes do not affect any public interfaces of Rust, but they represent significant improvements to the performance or internals of rustc and related tools. - [Move `format_args!()` into AST (and expand it during AST lowering)] (rust-lang/rust#106745)

Pkgsrc changes: * Adjust patches and cargo checksums to new versions. Upstream changes: Version 1.69.0 (2023-04-20) ========================== Language -------- - [Deriving built-in traits on packed structs works with `Copy` fields.] (rust-lang/rust#104429) - [Stabilize the `cmpxchg16b` target feature on x86 and x86_64.] (rust-lang/rust#106774) - [Improve analysis of trait bounds for associated types.] (rust-lang/rust#103695) - [Allow associated types to be used as union fields.] (rust-lang/rust#106938) - [Allow `Self: Autotrait` bounds on dyn-safe trait methods.] (rust-lang/rust#107082) - [Treat `str` as containing `[u8]` for auto trait purposes.] (rust-lang/rust#107941) Compiler -------- - [Upgrade `*-pc-windows-gnu` on CI to mingw-w64 v10 and GCC 12.2.] (rust-lang/rust#100178) - [Rework min_choice algorithm of member constraints.] (rust-lang/rust#105300) - [Support `true` and `false` as boolean flags in compiler arguments.] (rust-lang/rust#107043) - [Default `repr(C)` enums to `c_int` size.] (rust-lang/rust#107592) Libraries --------- - [Implement the unstable `DispatchFromDyn` for cell types, allowing downstream experimentation with custom method receivers.] (rust-lang/rust#97373) - [Document that `fmt::Arguments::as_str()` may return `Some(_)` in more cases after optimization, subject to change.] (rust-lang/rust#106823) - [Implement `AsFd` and `AsRawFd` for `Rc`.] (rust-lang/rust#107317) Stabilized APIs --------------- - [`CStr::from_bytes_until_nul`] (https://doc.rust-lang.org/stable/core/ffi/struct.CStr.html#method.from_bytes_until_nul) - [`core::ffi::FromBytesUntilNulError`] (https://doc.rust-lang.org/stable/core/ffi/struct.FromBytesUntilNulError.html) These APIs are now stable in const contexts: - [`SocketAddr::new`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.new) - [`SocketAddr::ip`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.ip) - [`SocketAddr::port`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.port) - [`SocketAddr::is_ipv4`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.is_ipv4) - [`SocketAddr::is_ipv6`] (https://doc.rust-lang.org/stable/std/net/enum.SocketAddr.html#method.is_ipv6) - [`SocketAddrV4::new`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV4.html#method.new) - [`SocketAddrV4::ip`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV4.html#method.ip) - [`SocketAddrV4::port`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV4.html#method.port) - [`SocketAddrV6::new`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.new) - [`SocketAddrV6::ip`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.ip) - [`SocketAddrV6::port`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.port) - [`SocketAddrV6::flowinfo`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.flowinfo) - [`SocketAddrV6::scope_id`] (https://doc.rust-lang.org/stable/std/net/struct.SocketAddrV6.html#method.scope_id) Cargo ----- - [Cargo now suggests `cargo fix` or `cargo clippy --fix` when compilation warnings are auto-fixable.] (rust-lang/cargo#11558) - [Cargo now suggests `cargo add` if you try to install a library crate.] (rust-lang/cargo#11410) - [Cargo now sets the `CARGO_BIN_NAME` environment variable also for binary examples.] (rust-lang/cargo#11705) Rustdoc ----- - [Vertically compact trait bound formatting.] (rust-lang/rust#102842) - [Only include stable lints in `rustdoc::all` group.] (rust-lang/rust#106316) - [Compute maximum Levenshtein distance based on the query.] (rust-lang/rust#107141) - [Remove inconsistently-present sidebar tooltips.] (rust-lang/rust#107490) - [Search by macro when query ends with `!`.] (rust-lang/rust#108143) Compatibility Notes ------------------- - [The `rust-analysis` component from `rustup` now only contains a warning placeholder.] (rust-lang/rust#101841) This was primarily intended for RLS, and the corresponding `-Zsave-analysis` flag has been removed from the compiler as well. - [Unaligned references to packed fields are now a hard error.] (rust-lang/rust#102513) This has been a warning since 1.53, and denied by default with a future-compatibility warning since 1.62. - [Update the minimum external LLVM to 14.] (rust-lang/rust#107573) - [Cargo now emits errors on invalid characters in a registry token.] (rust-lang/cargo#11600) - [When `default-features` is set to false of a workspace dependency, and an inherited dependency of a member has `default-features = true`, Cargo will enable default features of that dependency.] (rust-lang/cargo#11409) - [Cargo denies `CARGO_HOME` in the `[env]` configuration table. Cargo itself doesn't pick up this value, but recursive calls to cargo would, which was not intended.] (rust-lang/cargo#11644) - [Debuginfo for build dependencies is now off if not explicitly set. This is expected to improve the overall build time.] (rust-lang/cargo#11252) Internal Changes ---------------- These changes do not affect any public interfaces of Rust, but they represent significant improvements to the performance or internals of rustc and related tools. - [Move `format_args!()` into AST (and expand it during AST lowering)] (rust-lang/rust#106745)

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Flatten/inline format_args!() and (string and int) literal arguments into format_args!() #106824

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format_args!() could 'inline' literal arguments #78356

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rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Jan 13, 2023

Allow fmt::Arguments::as_str() to return more Some(_).

a37b484

m-ou-se force-pushed the format-args-as-str-guarantees branch from acdc3d4 to a37b484 Compare January 13, 2023 21:42

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Tracking issue for improving std::fmt::Arguments and format_args!() #99012

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Rollup of 7 pull requests #107249

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Rollup of 9 pull requests #107290

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Enable flatten-format-args by default. #109999

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Allow fmt::Arguments::as_str() to return more Some(_). #106823

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