tokel_std/
structure.rs

1//! Structural boundary and grouping [`Transformer`]s.
2
3use std::iter;
4
5use proc_macro2::{Delimiter, Group, TokenStream, TokenTree};
6use syn::parse::{Nothing, Parse, ParseStream};
7use tokel_engine::prelude::{Registry, Transformer};
8
9/// Recursively removes all `()`, `{}`, and `[]` boundaries, flattening into a 1D stream.
10#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
11pub struct Flatten;
12
13impl Flatten {
14    fn flatten_recursive(stream: TokenStream) -> TokenStream {
15        let mut output = TokenStream::new();
16        for tree in stream {
17            match tree {
18                TokenTree::Group(g) => output.extend(Self::flatten_recursive(g.stream())),
19                other => output.extend(iter::once(other)),
20            }
21        }
22        output
23    }
24}
25
26impl Transformer for Flatten {
27    fn transform(
28        &mut self,
29        input: TokenStream,
30        argument: TokenStream,
31    ) -> Result<TokenStream, syn::Error> {
32        let _: Nothing = syn::parse2(argument)?;
33
34        Ok(Self::flatten_recursive(input))
35    }
36}
37
38/// Wraps the entire input stream in the delimiter type of the provided argument [`Group`].
39#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
40pub struct Encapsulate;
41
42impl Transformer for Encapsulate {
43    fn transform(
44        &mut self,
45        input: TokenStream,
46        argument: TokenStream,
47    ) -> Result<TokenStream, syn::Error> {
48        struct Argument(Delimiter);
49
50        impl Parse for Argument {
51            fn parse(input: ParseStream) -> syn::Result<Self> {
52                let group = input.parse::<Group>()?;
53
54                let _: Nothing = syn::parse2(group.stream())?;
55
56                let _: Nothing = input.parse()?;
57
58                Ok(Self(group.delimiter()))
59            }
60        }
61
62        let Argument(delimiter) = syn::parse2(argument)?;
63
64        let group = Group::new(delimiter, input);
65
66        Ok(iter::once(TokenTree::Group(group)).collect())
67    }
68}
69
70/// Inserts all `structure`-related [`Transformer`]s into the specified [`Registry`].
71///
72/// # Errors
73///
74/// This will fail if at least one standard `structure`-related [`Transformer`] is already present by-name in the [`Registry`].
75///
76/// On failure, there is no guarantee that other non-colliding transformers have not been registered.
77#[inline]
78pub fn register(registry: &mut Registry) -> Result<(), Box<dyn Transformer>> {
79    registry
80        .try_insert("flatten", Flatten)
81        .map_err(Box::new)
82        .map_err(|target_value| target_value as Box<dyn Transformer>)?;
83
84    registry
85        .try_insert("encapsulate", Encapsulate)
86        .map_err(Box::new)
87        .map_err(|target_value| target_value as Box<dyn Transformer>)?;
88
89    Ok(())
90}
tokel_std/structure.rs

tokel_std/
structure.rs
