impl-macro-internal 0.1.0

Helper for the impl-macro crate.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153

#![allow(clippy::panic)]
#![allow(clippy::unwrap_used)]
#![allow(clippy::expect_used)]

use proc_macro2::TokenStream;
use proc_macro2::TokenTree;
use proc_macro2::Delimiter;
use quote::quote;

// ===============
// === Helpers ===
// ===============

fn is_brace(tt: &TokenTree) -> bool {
    if let TokenTree::Group(group) = tt {
        group.delimiter() == Delimiter::Brace
    } else {
        false
    }
}

fn is_for(tt: &TokenTree) -> bool {
    if let TokenTree::Ident(ident) = tt {
        ident.to_string() == "for"
    } else {
        false
    }
}

fn is_where(tt: &TokenTree) -> bool {
    if let TokenTree::Ident(ident) = tt {
        ident.to_string() == "where"
    } else {
        false
    }
}

fn is_comma(tt: &TokenTree) -> bool {
    if let TokenTree::Punct(punct) = tt {
        punct.as_char() == ','
    } else {
        false
    }
}

fn is_open_angle(tt: &TokenTree) -> bool {
    if let TokenTree::Punct(punct) = tt {
        punct.as_char() == '<'
    } else {
        false
    }
}

fn is_close_angle(tt: &TokenTree) -> bool {
    if let TokenTree::Punct(punct) = tt {
        punct.as_char() == '>'
    } else {
        false
    }
}

// =================
// === Imp Macro ===
// =================

#[proc_macro]
pub fn imp(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let input: TokenStream = input.into();

    let mut prefix = Vec::new();
    let mut targets = Vec::new();
    let mut where_clause = Vec::new();
    let mut body = TokenStream::new();
    let mut tokens = input.into_iter().peekable();

    while !tokens.peek().map(is_for).unwrap_or_default() {
        prefix.push(tokens.next().unwrap());
    }

    if tokens.peek().map(is_for).unwrap_or_default() {
        tokens.next();
    } else {
        panic!("Expected 'for' keyword");
    }

    // Extract for-targets (handle multiple "for ... where ..." patterns)
    while let Some(tt) = tokens.peek() {
        match tt {
            _ if is_where(tt) => {
                let mut clause = Vec::new();
                clause.push(tokens.next().unwrap());
                while !tokens.peek().map(is_brace).unwrap_or_default() {
                    clause.push(tokens.next().unwrap());
                }
                where_clause.push(TokenStream::from_iter(clause));
            }
            _ if is_comma(tt) => {
                tokens.next();
            }
            _ if is_for(tt) => {
                tokens.next();
            }
            _ if is_brace(tt) => {
                break;
            }
            _ => {
                let mut depth: i32 = 0;
                let mut target = Vec::new();
                target.push(tokens.next().unwrap());
                while let Some(tt2) = tokens.peek() {
                    if is_brace(tt2) || is_for(tt2) || is_where(tt2) {
                        break;
                    }
                    if is_open_angle(tt2) {
                        depth += 1;
                    } else if is_close_angle(tt2) {
                        depth -= 1;
                    }
                    if depth == 0 && is_comma(tt2) {
                        break;
                    }
                    target.push(tokens.next().unwrap());
                }
                if target.last().map(is_comma).unwrap_or_default() {
                    target.pop();
                }
                targets.push(TokenStream::from_iter(target));
            }
        }
    }

    if let Some(tt) = tokens.peek() {
        if is_brace(tt) {
            body = tt.clone().into();
            tokens.next();
        }
    } else {
        panic!("Unexpected end of input");
    }

    let prefix = TokenStream::from_iter(prefix);
    let where_clause = TokenStream::from_iter(where_clause);
    let impls = targets.iter().map(|target| {
        quote! { impl #prefix for #target #where_clause #body }
    }).collect::<Vec<_>>();

    let output = quote! {
        #(#impls)*
    };

    // println!("{}", output);
    output.into()
}