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

//! The main interface to parsing kwargs
//!
//! Generally speaking,
//! this should be considered an implementation detail of the macro.
use std::hash::Hash;
use std::fmt::Debug;

use indexmap::{IndexMap, map::Entry};

use proc_macro2::{Ident, Span};
use syn::{Token, punctuated::Punctuated, ext::IdentExt, braced};
use syn::parse::{Parse, ParseStream};

use crate::MacroArg;

/// The runtime value of a parsed argument
pub trait ParsedArgValue<Id: KeywordArgId>: Sized {
    /// Return the corresponding id
    fn id(&self) -> Id;
    /// Parse the argument with the specified id
    fn parse_with_id(
        id: Id,
        id_span: Span,
        stream: ParseStream
    ) -> syn::Result<Self>;
}
/// The unique id for a single keyword argument
pub trait KeywordArgId: Copy + Eq + Hash + Debug {
    /// The name of this argument, as a string
    fn as_str(&self) -> &'_ str;
    /// Get the argument with the specified name,
    /// returning `None` if it's unknown
    fn from_name(name: &str) -> Option<Self>;
}

/// A parsed argument,
/// along with its original name and id.
pub struct KeywordArg<K: MacroKeywordArgs> {
    /// The name of this argument,
    /// as a `Ident`
    ///
    /// This is needed in addition to `id`,
    /// because it contains a `Span`
    pub name: Ident,
    /// The id of this argument
    pub id: K::ArgId,
    /// The parsed value of this argument
    pub value: K::ParsedArg,
}
impl<K: MacroKeywordArgs> Parse for KeywordArg<K> {
    fn parse(stream: ParseStream) -> syn::Result<Self> {
        let name = stream.call(Ident::parse_any)?;
        let name_text = name.to_string();
        let id = K::ArgId::from_name(&name_text).ok_or_else(|| {
            syn::Error::new(
                name.span(),
                format!("Unknown argument name: {}", &name_text)
            )
        })?;
        stream.parse::<Token![=>]>()?;
        let value = K::ParsedArg::parse_with_id(
            id,
            name.span(),
            stream
        )?;
        Ok(KeywordArg { id, name, value })
    }
}
/// The list of parsed keyword arguments
pub struct ParsedKeywordArguments<K: MacroKeywordArgs> {
    /// A map of arguments, in the order of the declaration.
    by_name: IndexMap<K::ArgId, KeywordArg<K>>,
}
impl<K: MacroKeywordArgs> ParsedKeywordArguments<K> {
    /// Lookup a argument by its id,
    /// returning `None` if it's missing
    pub fn get(&self, id: K::ArgId) -> Option<&'_ KeywordArg<K>> {
        self.by_name.get(&id)
    }
    /// Consume the argument with the specified id,
    /// returning `None` if it's missing
    ///
    /// Implicitly shifts the ordering of the map.
    pub fn take(&mut self, id: K::ArgId) -> Option<KeywordArg<K>> {
        self.by_name.swap_remove(&id)
    }
    /// Require that the argument with the specified id exists,
    /// returning an error if it is missing
    ///
    /// Consumes the argument, as if calling `take`
    pub fn require(&mut self, id: K::ArgId) -> syn::Result<KeywordArg<K>> {
        self.take(id).ok_or_else(|| {
            syn::Error::new(
                Span::call_site(),
                format!("Missing required argument `{}`", id.as_str())
            )
        })
    }
    /// Iterate over the original list of arguments,
    /// in the order of their declaration
    #[inline]
    pub fn iter(&self) -> impl Iterator<Item=&'_ KeywordArg<K>> + '_ {
        self.by_name.values()
    }
}
impl<K: MacroKeywordArgs> Parse for ParsedKeywordArguments<K> {
    fn parse(stream: ParseStream) -> syn::Result<Self> {
        let punct: Punctuated<KeywordArg<K>, Token![,]> = stream.call(Punctuated::parse_terminated)?;
        let mut by_name = IndexMap::with_capacity(punct.len());
        let mut errors = Vec::new();
        for arg in punct.into_iter() {
            match by_name.entry(arg.id) {
                Entry::Occupied(_entry) => {
                    errors.push(syn::Error::new(
                        arg.name.span(),
                        format!(
                            "Duplicate values for argument: {}",
                            arg.name
                        )
                    ));
                },
                Entry::Vacant(entry) => {
                    entry.insert(arg);
                }
            }
        }
        if !errors.is_empty() {
            return Err(crate::combine_errors(errors))
        }
        Ok(ParsedKeywordArguments {
            by_name
        })
    }
}
impl<K: MacroKeywordArgs> MacroArg for ParsedKeywordArguments<K> {
    fn parse_macro_arg(stream: ParseStream) -> syn::Result<Self> {
        let content;
        braced!(content in stream);
        content.parse::<Self>()
    }
}

/// The whole point.
/// 
/// Defines the interface for parsing keyword args.
///
/// A set of argument can itself be nested as a `MacroArg`,
/// provided it is wrapped in braces `{ }`
pub trait MacroKeywordArgs: MacroArg + Parse {
    /// The id of an argument.
    type ArgId: KeywordArgId;
    /// The runtime value of a parsed argument
    type ParsedArg: ParsedArgValue<Self::ArgId>;
    /// Create the parsed arguments struct from
    /// its list of arguments
    fn from_keyword_args(kwargs: ParsedKeywordArguments<Self>)
        -> Result<Self, syn::Error>;
}