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std::fmt: Fix the grammar documentation

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According to the grammar documented, the format specifier `{: }` should not be
legal because of the whitespace it contains. However, in reality, this is
perfectly fine because the actual implementation allows spaces before the
closing brace. Fixes #71088.

Also, the exact meaning of most of the terminal symbols was not specified, for
example the meaning of `identifier`.
This commit is contained in:
Elias Holzmann 2022-04-30 02:39:59 +02:00
parent afd80a21b0
commit 79d9afda13
1 changed files with 7 additions and 2 deletions
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9
library/alloc/src/fmt.rs
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@ -310,7 +310,7 @@
//! ```text
//! format_string := text [ maybe_format text ] *
//! maybe_format := '{' '{' | '}' '}' | format
//! format := '{' [ argument ] [ ':' format_spec ] '}'
//! format := '{' [ argument ] [ ':' format_spec ] [ ws ] * '}'
//! argument := integer | identifier
//!
//! format_spec := [[fill]align][sign]['#']['0'][width]['.' precision]type
@ -323,7 +323,12 @@
//! count := parameter | integer
//! parameter := argument '$'
//! ```
//! In the above grammar, `text` must not contain any `'{'` or `'}'` characters.
//! In the above grammar,
//! - `text` must not contain any `'{'` or `'}'` characters,
//! - `ws` is any character for which [`char::is_whitespace`] returns `true`, has no semantic
//! meaning and is completely optional,
//! - `integer` is a decimal integer that may contain leading zeroes and
//! - `identifier` is an `IDENTIFIER_OR_KEYWORD` (not an `IDENTIFIER`) as defined by the [Rust language reference](https://doc.rust-lang.org/reference/identifiers.html).
//!
//! # Formatting traits
//!