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Allow any identifier as format arg name #66847

Merged
merged 1 commit into from
Nov 30, 2019
Merged

Allow any identifier as format arg name #66847

merged 1 commit into from
Nov 30, 2019

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dtolnay
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@dtolnay dtolnay commented Nov 28, 2019

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

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 28, 2019
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;
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break-with-value in while-loops when?

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Looks entirely reasonable to me!

@bors r+

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bors commented Nov 29, 2019

📌 Commit 423a5d3 has been approved by joshtriplett

@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 Nov 29, 2019
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@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 Nov 30, 2019
dtolnay added a commit to dtolnay/rust that referenced this pull request Nov 30, 2019
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.
@dtolnay

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@bors bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Nov 30, 2019
bors added a commit that referenced this pull request Nov 30, 2019
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
@bors bors merged commit 423a5d3 into rust-lang:master Nov 30, 2019
@dtolnay dtolnay deleted the _fmt branch November 30, 2019 19:20
@Centril Centril added the relnotes Marks issues that should be documented in the release notes of the next release. label Jan 6, 2020
@Centril Centril added this to the 1.41 milestone Jan 6, 2020
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Feb 17, 2020
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
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