Allow any identifier as format arg name #66847

dtolnay · 2019-11-28T19:39:55Z

Previously:

error: invalid format string: invalid argument name `_x`
 --> src/main.rs:2:16
  |
2 |     println!("{_x}", _x=0);
  |                ^^ invalid argument name in format string
  |
  = note: argument names cannot start with an underscore

Not supporting identifiers starting with underscore appears to have been an arbitrary limitation from 2013 in code that was most likely never reviewed: https://github.com/rust-lang/rust/pull/8245/files#diff-0347868ef389c805e97636623e4a4ea6R277

The error message was dutifully improved in #50610 but is there any reason that leading underscore would be a special case?

This commit updates the format_args parser to accept identifiers with leading underscores.

Previously: error: invalid format string: invalid argument name `_x` --> src/main.rs:2:16 | 2 | println!("{_x}", a=0); | ^^ invalid argument name in format string | = note: argument names cannot start with an underscore Not supporting identifiers starting with underscore appears to have been an arbitrary limitation from 2013 in code that was most likely never reviewed: https://github.com/rust-lang/rust/pull/8245/files#diff-0347868ef389c805e97636623e4a4ea6R277 The error message was dutifully improved in rust-lang#50610 but is there any reason that leading underscore would be a special case? This commit updates the format_args parser to accept identifiers with leading underscores.

rust-highfive · 2019-11-28T19:40:06Z

r? @joshtriplett

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

dtolnay · 2019-11-28T19:43:00Z

src/libfmt_macros/lib.rs

        while let Some(&(pos, c)) = self.cur.peek() {
            if rustc_lexer::is_id_continue(c) {
                self.cur.next();
            } else {
-                return &self.input[start..pos];
+                end = Some(pos);
+                break;


break-with-value in while-loops when?

joshtriplett · 2019-11-29T06:27:43Z

Looks entirely reasonable to me!

@bors r+

bors · 2019-11-29T06:27:44Z

📌 Commit 423a5d3 has been approved by joshtriplett

Allow any identifier as format arg name Previously: ```console error: invalid format string: invalid argument name `_x` --> src/main.rs:2:16 | 2 | println!("{_x}", _x=0); | ^^ invalid argument name in format string | = note: argument names cannot start with an underscore ``` Not supporting identifiers starting with underscore appears to have been an arbitrary limitation from 2013 in code that was most likely never reviewed: https://github.com/rust-lang/rust/pull/8245/files#diff-0347868ef389c805e97636623e4a4ea6R277 The error message was dutifully improved in rust-lang#50610 but is there any reason that leading underscore would be a special case? This commit updates the format_args parser to accept identifiers with leading underscores.

@ghost

Rollup of 4 pull requests Successful merges: - #66818 (Format libstd/os with rustfmt) - #66819 (Format libstd/sys with rustfmt) - #66820 (Format libstd with rustfmt) - #66847 (Allow any identifier as format arg name) Failed merges: r? @ghost

Version 1.41.0 (2020-01-30) =========================== Language -------- - [You can now pass type parameters to foreign items when implementing traits.][65879] E.g. You can now write `impl<T> From<Foo> for Vec<T> {}`. - [You can now arbitrarily nest receiver types in the `self` position.][64325] E.g. you can now write `fn foo(self: Box<Box<Self>>) {}`. Previously only `Self`, `&Self`, `&mut Self`, `Arc<Self>`, `Rc<Self>`, and `Box<Self>` were allowed. - [You can now use any valid identifier in a `format_args` macro.][66847] Previously identifiers starting with an underscore were not allowed. - [Visibility modifiers (e.g. `pub`) are now syntactically allowed on trait items and enum variants.][66183] These are still rejected semantically, but can be seen and parsed by procedural macros and conditional compilation. Compiler -------- - [Rustc will now warn if you have unused loop `'label`s.][66325] - [Removed support for the `i686-unknown-dragonfly` target.][67255] - [Added tier 3 support\* for the `riscv64gc-unknown-linux-gnu` target.][66661] - [You can now pass an arguments file passing the `@path` syntax to rustc.][66172] Note that the format differs somewhat from what is found in other tooling; please see [the documentation][argfile-docs] for more information. - [You can now provide `--extern` flag without a path, indicating that it is available from the search path or specified with an `-L` flag.][64882] \* Refer to Rust's [platform support page][forge-platform-support] for more information on Rust's tiered platform support. [argfile-docs]: https://doc.rust-lang.org/nightly/rustc/command-line-arguments.html#path-load-command-line-flags-from-a-path Libraries --------- - [The `core::panic` module is now stable.][66771] It was already stable through `std`. - [`NonZero*` numerics now implement `From<NonZero*>` if it's a smaller integer width.][66277] E.g. `NonZeroU16` now implements `From<NonZeroU8>`. - [`MaybeUninit<T>` now implements `fmt::Debug`.][65013] Stabilized APIs --------------- - [`Result::map_or`] - [`Result::map_or_else`] - [`std::rc::Weak::weak_count`] - [`std::rc::Weak::strong_count`] - [`std::sync::Weak::weak_count`] - [`std::sync::Weak::strong_count`] Cargo ----- - [Cargo will now document all the private items for binary crates by default.][cargo/7593] - [`cargo-install` will now reinstall the package if it detects that it is out of date.][cargo/7560] - [Cargo.lock now uses a more git friendly format that should help to reduce merge conflicts.][cargo/7579] - [You can now override specific dependencies's build settings][cargo/7591] E.g. `[profile.dev.overrides.image] opt-level = 2` sets the `image` crate's optimisation level to `2` for debug builds. You can also use `[profile.<profile>.build_overrides]` to override build scripts and their dependencies. Misc ---- - [You can now specify `edition` in documentation code blocks to compile the block for that edition.][66238] E.g. `edition2018` tells rustdoc that the code sample should be compiled the 2018 edition of Rust. - [You can now provide custom themes to rustdoc with `--theme`, and check the current theme with `--check-theme`.][54733] - [You can use `#[cfg(doc)]` to compile an item when building documentation.][61351] Compatibility Notes ------------------- - [As previously announced 1.41.0 will be the last tier 1 release for 32-bit Apple targets.][apple-32bit-drop] This means that the source code is still available to build, but the targets are no longer being tested and release binaries for those platforms will no longer be distributed by the Rust project. Please refer to the linked blog post for more information. [54733]: rust-lang/rust#54733 [61351]: rust-lang/rust#61351 [67255]: rust-lang/rust#67255 [66661]: rust-lang/rust#66661 [66771]: rust-lang/rust#66771 [66847]: rust-lang/rust#66847 [66238]: rust-lang/rust#66238 [66277]: rust-lang/rust#66277 [66325]: rust-lang/rust#66325 [66172]: rust-lang/rust#66172 [66183]: rust-lang/rust#66183 [65879]: rust-lang/rust#65879 [65013]: rust-lang/rust#65013 [64882]: rust-lang/rust#64882 [64325]: rust-lang/rust#64325 [cargo/7560]: rust-lang/cargo#7560 [cargo/7579]: rust-lang/cargo#7579 [cargo/7591]: rust-lang/cargo#7591 [cargo/7593]: rust-lang/cargo#7593 [`Result::map_or_else`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.map_or_else [`Result::map_or`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.map_or [`std::rc::Weak::weak_count`]: https://doc.rust-lang.org/std/rc/struct.Weak.html#method.weak_count [`std::rc::Weak::strong_count`]: https://doc.rust-lang.org/std/rc/struct.Weak.html#method.strong_count [`std::sync::Weak::weak_count`]: https://doc.rust-lang.org/std/sync/struct.Weak.html#method.weak_count [`std::sync::Weak::strong_count`]: https://doc.rust-lang.org/std/sync/struct.Weak.html#method.strong_count [apple-32bit-drop]: https://blog.rust-lang.org/2020/01/03/reducing-support-for-32-bit-apple-targets.html

dtolnay added the T-lang Relevant to the language team, which will review and decide on the PR/issue. label Nov 28, 2019

rust-highfive assigned joshtriplett Nov 28, 2019

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 28, 2019

dtolnay commented Nov 28, 2019

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dtolnay mentioned this pull request Nov 30, 2019

Rollup of 4 pull requests #66887

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bors merged commit 423a5d3 into rust-lang:master Nov 30, 2019

dtolnay deleted the _fmt branch November 30, 2019 19:20

Centril added the relnotes Marks issues that should be documented in the release notes of the next release. label Jan 6, 2020

Centril added this to the 1.41 milestone Jan 6, 2020

ilslv mentioned this pull request Jan 20, 2022

Add support for captured identifiers JelteF/derive_more#182

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dtolnay mentioned this pull request Nov 1, 2024

Remove format var parsing workaround that targeted rustc 1.40 and older dtolnay/thiserror#334

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Allow any identifier as format arg name #66847

Allow any identifier as format arg name #66847

dtolnay commented Nov 28, 2019 •

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Allow any identifier as format arg name #66847

Allow any identifier as format arg name #66847

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dtolnay commented Nov 28, 2019 •

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