time/format_description/parse/
mod.rs

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1//! Parser for format descriptions.
2
3use alloc::boxed::Box;
4use alloc::vec::Vec;
5
6pub use self::strftime::{parse_strftime_borrowed, parse_strftime_owned};
7use crate::{error, format_description};
8
9/// A helper macro to make version restrictions simpler to read and write.
10macro_rules! version {
11    ($range:expr) => {
12        $range.contains(&VERSION)
13    };
14}
15
16/// A helper macro to statically validate the version (when used as a const parameter).
17macro_rules! validate_version {
18    ($version:ident) => {
19        #[allow(clippy::let_unit_value)]
20        let _ = $crate::format_description::parse::Version::<$version>::IS_VALID;
21    };
22}
23
24mod ast;
25mod format_item;
26mod lexer;
27mod strftime;
28
29/// A struct that is used to ensure that the version is valid.
30struct Version<const N: usize>;
31impl<const N: usize> Version<N> {
32    /// A constant that panics if the version is not valid. This results in a post-monomorphization
33    /// error.
34    const IS_VALID: () = assert!(N >= 1 && N <= 2);
35}
36
37/// Parse a sequence of items from the format description.
38///
39/// The syntax for the format description can be found in [the
40/// book](https://time-rs.github.io/book/api/format-description.html).
41///
42/// This function exists for backward compatibility reasons. It is equivalent to calling
43/// `parse_borrowed::<1>(s)`. In the future, this function will be deprecated in favor of
44/// `parse_borrowed`.
45pub fn parse(
46    s: &str,
47) -> Result<Vec<format_description::BorrowedFormatItem<'_>>, error::InvalidFormatDescription> {
48    parse_borrowed::<1>(s)
49}
50
51/// Parse a sequence of items from the format description.
52///
53/// The syntax for the format description can be found in [the
54/// book](https://time-rs.github.io/book/api/format-description.html). The version of the format
55/// description is provided as the const parameter. **It is recommended to use version 2.**
56pub fn parse_borrowed<const VERSION: usize>(
57    s: &str,
58) -> Result<Vec<format_description::BorrowedFormatItem<'_>>, error::InvalidFormatDescription> {
59    validate_version!(VERSION);
60    let mut lexed = lexer::lex::<VERSION>(s.as_bytes());
61    let ast = ast::parse::<_, VERSION>(&mut lexed);
62    let format_items = format_item::parse(ast);
63    Ok(format_items
64        .map(|res| res.and_then(TryInto::try_into))
65        .collect::<Result<_, _>>()?)
66}
67
68/// Parse a sequence of items from the format description.
69///
70/// The syntax for the format description can be found in [the
71/// book](https://time-rs.github.io/book/api/format-description.html). The version of the format
72/// description is provided as the const parameter.
73///
74/// Unlike [`parse`], this function returns [`OwnedFormatItem`], which owns its contents. This means
75/// that there is no lifetime that needs to be handled. **It is recommended to use version 2.**
76///
77/// [`OwnedFormatItem`]: crate::format_description::OwnedFormatItem
78pub fn parse_owned<const VERSION: usize>(
79    s: &str,
80) -> Result<format_description::OwnedFormatItem, error::InvalidFormatDescription> {
81    validate_version!(VERSION);
82    let mut lexed = lexer::lex::<VERSION>(s.as_bytes());
83    let ast = ast::parse::<_, VERSION>(&mut lexed);
84    let format_items = format_item::parse(ast);
85    let items = format_items.collect::<Result<Box<_>, _>>()?;
86    Ok(items.into())
87}
88
89/// Attach [`Location`] information to each byte in the iterator.
90fn attach_location<'item>(
91    iter: impl Iterator<Item = &'item u8>,
92) -> impl Iterator<Item = (&'item u8, Location)> {
93    let mut byte_pos = 0;
94
95    iter.map(move |byte| {
96        let location = Location { byte: byte_pos };
97        byte_pos += 1;
98        (byte, location)
99    })
100}
101
102/// A location within a string.
103#[derive(Clone, Copy)]
104struct Location {
105    /// The zero-indexed byte of the string.
106    byte: u32,
107}
108
109impl Location {
110    /// Create a new [`Span`] from `self` to `other`.
111    const fn to(self, end: Self) -> Span {
112        Span { start: self, end }
113    }
114
115    /// Create a new [`Span`] consisting entirely of `self`.
116    const fn to_self(self) -> Span {
117        Span {
118            start: self,
119            end: self,
120        }
121    }
122
123    /// Offset the location by the provided amount.
124    ///
125    /// Note that this assumes the resulting location is on the same line as the original location.
126    #[must_use = "this does not modify the original value"]
127    const fn offset(&self, offset: u32) -> Self {
128        Self {
129            byte: self.byte + offset,
130        }
131    }
132
133    /// Create an error with the provided message at this location.
134    const fn error(self, message: &'static str) -> ErrorInner {
135        ErrorInner {
136            _message: message,
137            _span: Span {
138                start: self,
139                end: self,
140            },
141        }
142    }
143}
144
145/// A start and end point within a string.
146#[derive(Clone, Copy)]
147struct Span {
148    #[allow(clippy::missing_docs_in_private_items)]
149    start: Location,
150    #[allow(clippy::missing_docs_in_private_items)]
151    end: Location,
152}
153
154impl Span {
155    /// Obtain a `Span` pointing at the start of the pre-existing span.
156    #[must_use = "this does not modify the original value"]
157    const fn shrink_to_start(&self) -> Self {
158        Self {
159            start: self.start,
160            end: self.start,
161        }
162    }
163
164    /// Obtain a `Span` pointing at the end of the pre-existing span.
165    #[must_use = "this does not modify the original value"]
166    const fn shrink_to_end(&self) -> Self {
167        Self {
168            start: self.end,
169            end: self.end,
170        }
171    }
172
173    /// Obtain a `Span` that ends before the provided position of the pre-existing span.
174    #[must_use = "this does not modify the original value"]
175    const fn shrink_to_before(&self, pos: u32) -> Self {
176        Self {
177            start: self.start,
178            end: Location {
179                byte: self.start.byte + pos - 1,
180            },
181        }
182    }
183
184    /// Obtain a `Span` that starts after provided position to the end of the pre-existing span.
185    #[must_use = "this does not modify the original value"]
186    const fn shrink_to_after(&self, pos: u32) -> Self {
187        Self {
188            start: Location {
189                byte: self.start.byte + pos + 1,
190            },
191            end: self.end,
192        }
193    }
194
195    /// Create an error with the provided message at this span.
196    const fn error(self, message: &'static str) -> ErrorInner {
197        ErrorInner {
198            _message: message,
199            _span: self,
200        }
201    }
202}
203
204/// A value with an associated [`Span`].
205#[derive(Clone, Copy)]
206struct Spanned<T> {
207    /// The value.
208    value: T,
209    /// Where the value was in the format string.
210    span: Span,
211}
212
213impl<T> core::ops::Deref for Spanned<T> {
214    type Target = T;
215
216    fn deref(&self) -> &Self::Target {
217        &self.value
218    }
219}
220
221/// Helper trait to attach a [`Span`] to a value.
222trait SpannedValue: Sized {
223    /// Attach a [`Span`] to a value.
224    fn spanned(self, span: Span) -> Spanned<Self>;
225}
226
227impl<T> SpannedValue for T {
228    fn spanned(self, span: Span) -> Spanned<Self> {
229        Spanned { value: self, span }
230    }
231}
232
233/// The internal error type.
234struct ErrorInner {
235    /// The message displayed to the user.
236    _message: &'static str,
237    /// Where the error originated.
238    _span: Span,
239}
240
241/// A complete error description.
242struct Error {
243    /// The internal error.
244    _inner: Unused<ErrorInner>,
245    /// The error needed for interoperability with the rest of `time`.
246    public: error::InvalidFormatDescription,
247}
248
249impl From<Error> for error::InvalidFormatDescription {
250    fn from(error: Error) -> Self {
251        error.public
252    }
253}
254
255/// A value that may be used in the future, but currently is not.
256///
257/// This struct exists so that data can semantically be passed around without _actually_ passing it
258/// around. This way the data still exists if it is needed in the future.
259// `PhantomData` is not used directly because we don't want to introduce any trait implementations.
260struct Unused<T>(core::marker::PhantomData<T>);
261
262/// Indicate that a value is currently unused.
263fn unused<T>(_: T) -> Unused<T> {
264    Unused(core::marker::PhantomData)
265}
time/format_description/parse/mod.rs

time/format_description/parse/
mod.rs
