88 lines
3.5 KiB
Markdown
88 lines
3.5 KiB
Markdown
# `litrs`: parsing and inspecting Rust literals
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[<img alt="CI status of main" src="https://img.shields.io/github/actions/workflow/status/LukasKalbertodt/litrs/ci.yml?branch=main&label=CI&logo=github&logoColor=white&style=for-the-badge" height="23">](https://github.com/LukasKalbertodt/litrs/actions/workflows/ci.yml)
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[<img alt="Crates.io Version" src="https://img.shields.io/crates/v/litrs?logo=rust&style=for-the-badge" height="23">](https://crates.io/crates/litrs)
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[<img alt="docs.rs" src="https://img.shields.io/crates/v/litrs?color=blue&label=docs&style=for-the-badge" height="23">](https://docs.rs/litrs)
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`litrs` offers functionality to parse Rust literals, i.e. tokens in the Rust programming language that represent fixed values.
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For example: `27`, `"crab"`, `bool`.
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This is particularly useful for proc macros, but can also be used outside of a proc-macro context.
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**Why this library?**
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Unfortunately, the `proc_macro` API shipped with the compiler offers no easy way to inspect literals.
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There are mainly two libraries for this purpose:
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[`syn`](https://github.com/dtolnay/syn) and [`literalext`](https://github.com/mystor/literalext).
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The latter is deprecated.
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And `syn` is oftentimes overkill for the task at hand, especially when developing function-like proc-macros (e.g. `foo!(..)`).
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This crate is a lightweight alternative.
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Also, when it comes to literals, `litrs` offers a bit more flexibility and a few more features compared to `syn`.
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I'm interested in community feedback!
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If you consider using this, please speak your mind [in this issue](https://github.com/LukasKalbertodt/litrs/issues/1).
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## Example
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### In proc macro
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```rust
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use std::convert::TryFrom;
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use proc_macro::TokenStream;
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use litrs::Literal;
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#[proc_macro]
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pub fn foo(input: TokenStream) -> TokenStream {
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// Please do proper error handling in your real code!
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let first_token = input.into_iter().next().expect("no input");
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// `try_from` will return an error if the token is not a literal.
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match Literal::try_from(first_token) {
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// Convenient methods to produce decent errors via `compile_error!`.
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Err(e) => return e.to_compile_error(),
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// You can now inspect your literal!
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Ok(Literal::Integer(i)) => {
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println!("Got an integer specified in base {:?}", i.base());
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let value = i.value::<u64>().expect("integer literal too large");
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println!("Is your integer even? {}", value % 2 == 0);
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}
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Ok(other) => {
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println!("Got a non-integer literal");
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}
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}
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TokenStream::new() // dummy output
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}
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```
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If you are expecting a specific kind of literal, you can also use this, which will return an error if the token is not a float literal.
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```rust
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FloatLit::try_from(first_token)
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```
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### Parsing from a `&str`
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Outside of a proc macro context you might want to parse a string directly.
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```rust
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use litrs::{FloatLit, Literal};
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let lit = Literal::parse("'🦀'").expect("failed to parse literal");
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let float_lit = FloatLit::parse("2.7e3").expect("failed to parse as float literal");
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```
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See [**the documentation**](https://docs.rs/litrs) or the `examples/` directory for more examples and information.
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<br />
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---
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## License
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Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
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2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
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Unless you explicitly state otherwise, any contribution intentionally submitted
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for inclusion in this project by you, as defined in the Apache-2.0 license,
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shall be dual licensed as above, without any additional terms or conditions.
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