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
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180

#[cfg(feature = "colours")]
use ansi_term::{Colour, Style};
use proc_macro2::{Span, TokenStream, TokenTree};
use quote::{quote, quote_spanned, ToTokens};
use std::iter::FromIterator;
use syn::{
    parse, punctuated::Punctuated, token, AttrStyle, Expr, ExprMacro, Ident, ItemFn, Macro,
    MacroDelimiter, Pat, Path, PathArguments, PathSegment, Stmt,
};

#[proc_macro_attribute]
pub fn code_tour(
    _attributes: proc_macro::TokenStream,
    input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
    if let Ok(mut function) = parse::<ItemFn>(input.clone()) {
        let block_statements = &function.block.stmts;
        let mut statements = Vec::with_capacity(block_statements.len());

        for statement in block_statements.into_iter() {
            // That's a `let` binding.
            if let Stmt::Local(local) = statement {
                // Extract the local pattern.
                if let Pat::Ident(local_pat) = &local.pat {
                    // There is attributes, which are normally `///`
                    // (outer doc) or `/** */` (outer block) comments
                    // before the `let` binding.
                    if !local.attrs.is_empty() {
                        // Write `println!("{}", ident_comment)`.
                        {
                            let formatted_comment = local
                                .attrs
                                .iter()
                                .filter_map(|attribute| match (attribute.style, &attribute.path) {
                                    (
                                        AttrStyle::Outer,
                                        Path {
                                            leading_colon: None,
                                            segments,
                                        },
                                    ) if !segments.is_empty()
                                        && segments[0].ident
                                            == Ident::new("doc", Span::call_site()) =>
                                    {
                                        if let Some(TokenTree::Literal(literal)) =
                                            attribute.tokens.clone().into_iter().nth(1)
                                        {
                                            let literal_string =
                                                literal.to_string().replace("\\\'", "'");

                                            Some(format!(
                                                "▍{:<80}",
                                                &literal_string[1..literal_string.len() - 1]
                                            ))
                                        } else {
                                            None
                                        }
                                    }

                                    _ => None,
                                })
                                .map(format_comment)
                                .collect::<Vec<String>>()
                                .join("\n ");

                            let empty_line = format_comment(format!("▍{:<80}", " "));
                            let formatted_comment = format!(
                                "\n {empty}\n {comment}\n {empty}\n",
                                empty = empty_line,
                                comment = formatted_comment
                            );

                            statements.push(println(quote!("{}", #formatted_comment)));
                        }

                        let mut local_without_attrs = local.clone();
                        local_without_attrs.attrs = vec![];

                        // Write `println!("{}", stringify!(<local>))`.
                        {
                            let statement =
                                format_statement(quote!(#local_without_attrs).to_string());

                            statements.push(println(quote!(" {}\n", #statement)));
                        }

                        // Write the original statement, without the documentation.
                        {
                            statements.push(Stmt::Local(local_without_attrs));
                        }

                        // Write `println!("{:?}", <ident>)`.
                        {
                            statements.push(println({
                                let ident = &local_pat.ident;

                                quote!(
                                    " ◀︎    {}\n\n",
                                    format!("{:#?}", #ident).replace("\n", "\n ▐    ")
                                )
                            }));
                        }

                        continue;
                    }
                }
            }

            statements.push(statement.clone());
        }

        function.block.stmts = statements;

        quote!(#function).to_token_stream().into()
    } else {
        let span = TokenStream::from(input).into_iter().nth(0).unwrap().span();
        quote_spanned!(span => compile_error!("`code_tour` works on functions only")).into()
    }
}

fn println(tokens: TokenStream) -> Stmt {
    Stmt::Semi(
        Expr::Macro(ExprMacro {
            attrs: vec![],
            mac: Macro {
                path: Path {
                    leading_colon: None,
                    segments: Punctuated::from_iter(
                        vec![PathSegment {
                            ident: Ident::new("println", Span::call_site()),
                            arguments: PathArguments::None,
                        }]
                        .into_iter(),
                    ),
                },
                bang_token: token::Bang {
                    spans: [Span::call_site()],
                },
                delimiter: MacroDelimiter::Paren(token::Paren {
                    span: Span::call_site(),
                }),
                tokens,
            },
        }),
        token::Semi {
            spans: [Span::call_site()],
        },
    )
}

fn format_comment(comment: String) -> String {
    #[cfg(feature = "colours")]
    {
        Style::new()
            .fg(Colour::Fixed(253))
            .on(Colour::Fixed(238))
            .paint(comment)
            .to_string()
    }

    #[cfg(not(feature = "colours"))]
    {
        comment
    }
}

fn format_statement(statement: String) -> String {
    #[cfg(feature = "colours")]
    {
        Style::new()
            .fg(Colour::Fixed(228))
            .paint(format!("▶︎    {}", statement))
            .to_string()
    }

    #[cfg(not(feature = "colours"))]
    {
        statement
    }
}