glib_macros/
closure.rs

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
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
// Take a look at the license at the top of the repository in the LICENSE file.

use proc_macro2::{Ident, Span, TokenStream};
use quote::{quote, ToTokens};
use syn::{
    parse::{Parse, ParseStream},
    spanned::Spanned,
    Attribute, ExprClosure, Token,
};

use crate::{
    clone::{Capture, CaptureKind, UpgradeBehaviour},
    utils::crate_ident_new,
};

struct Closure {
    captures: Vec<Capture>,
    args: Vec<Ident>,
    upgrade_behaviour: UpgradeBehaviour,
    closure: ExprClosure,
    constructor: &'static str,
}

impl Parse for Closure {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let mut captures: Vec<Capture> = vec![];
        let mut upgrade_behaviour: Option<(UpgradeBehaviour, Span)> = None;

        loop {
            // There must either be one or no attributes here. Multiple attributes are not
            // supported.
            //
            // If this is a capture attribute, it must be followed by an identifier.
            // If this is an upgrade failure attribute, it might be followed by a closure. After the
            // upgrade failure attribute there must not be any further attributes.
            //
            // If this is not an attribute then it is a closure, async closure or async block which
            // is handled outside the loop
            let attrs = input.call(Attribute::parse_outer)?;
            if attrs.is_empty() {
                break;
            };

            if let Some(capture) = Capture::maybe_parse(&attrs, input)? {
                if capture.kind == CaptureKind::Watch
                    && captures.iter().any(|c| c.kind == CaptureKind::Watch)
                {
                    return Err(syn::Error::new_spanned(
                        &attrs[0],
                        "only one `watch` capture is allowed per closure",
                    ));
                }

                captures.push(capture);
            } else if let Some(behaviour) = UpgradeBehaviour::maybe_parse(&attrs, input)? {
                if upgrade_behaviour.is_some() {
                    return Err(syn::Error::new_spanned(
                        &attrs[0],
                        "multiple upgrade failure attributes are not supported",
                    ));
                }

                upgrade_behaviour = Some((behaviour, attrs[0].span()));
                break;
            } else if let Some(ident) = attrs[0].path().get_ident() {
                return Err(syn::Error::new_spanned(
                        &attrs[0],
                        format!(
                            "unsupported attribute `{ident}`: only `watch`, `strong`, `weak`, `weak_allow_none`, `to_owned`, `upgrade_or`, `upgrade_or_else`, `upgrade_or_default` and `upgrade_or_panic` are supported",
                        ),
                ));
            } else {
                return Err(syn::Error::new_spanned(
                        &attrs[0],
                        "unsupported attribute: only `strong`, `weak`, `weak_allow_none`, `to_owned`, `upgrade_or_else`, `upgrade_or_default` and `upgrade_or_panic` are supported",
                ));
            }
        }

        if let Some((_, ref span)) = upgrade_behaviour {
            if captures.iter().all(|c| c.kind != CaptureKind::Weak) {
                return Err(syn::Error::new(
                    *span,
                    "upgrade failure attribute can only be used together with weak variable captures",
                ));
            }
        }

        let upgrade_behaviour = upgrade_behaviour.map(|x| x.0).unwrap_or_default();

        let mut closure = input.parse::<ExprClosure>()?;
        if closure.asyncness.is_some() {
            return Err(syn::Error::new_spanned(
                closure,
                "async closures not supported",
            ));
        }
        if !captures.is_empty() && closure.capture.is_none() {
            return Err(syn::Error::new_spanned(
                closure,
                "closures need to capture variables by move. Please add the `move` keyword",
            ));
        }
        closure.capture = None;

        let args = closure
            .inputs
            .iter()
            .enumerate()
            .map(|(i, _)| Ident::new(&format!("____value{i}"), Span::call_site()))
            .collect();

        // Trailing comma, if any
        if input.peek(Token![,]) {
            input.parse::<Token![,]>()?;
        }

        Ok(Closure {
            captures,
            args,
            upgrade_behaviour,
            closure,
            constructor: "new",
        })
    }
}

impl ToTokens for Closure {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        let crate_ident = crate_ident_new();

        let closure_ident = Ident::new("____closure", Span::call_site());
        let values_ident = Ident::new("____values", Span::call_site());
        let upgrade_failure_closure_ident =
            Ident::new("____upgrade_failure_closure", Span::call_site());
        let upgrade_failure_closure_wrapped_ident =
            Ident::new("____upgrade_failure_closure_wrapped", Span::call_site());

        let outer_before = self
            .captures
            .iter()
            .map(|c| c.outer_before_tokens(&crate_ident));
        let inner_before = self.captures.iter().map(|c| {
            c.inner_before_tokens(
                &crate_ident,
                &self.upgrade_behaviour,
                &upgrade_failure_closure_wrapped_ident,
                Some(quote! {
                    return #crate_ident::closure::IntoClosureReturnValue::into_closure_return_value(());
                }),
            )
        });
        let outer_after = self
            .captures
            .iter()
            .map(|c| c.outer_after_tokens(&crate_ident, &closure_ident));

        let arg_values = self.args.iter().enumerate().map(|(index, arg)| {
            let err_msg = format!("Wrong type for argument {index}: {{:?}}");
            quote! {
                let #arg = ::core::result::Result::unwrap_or_else(
                    #crate_ident::Value::get(&#values_ident[#index]),
                    |e| panic!(#err_msg, e),
                );
            }
        });
        let arg_names = &self.args;
        let args_len = self.args.len();
        let closure = &self.closure;
        let constructor = Ident::new(self.constructor, Span::call_site());

        let upgrade_failure_closure = match self.upgrade_behaviour {
            UpgradeBehaviour::Default => Some(quote! {
                let #upgrade_failure_closure_ident = ::std::default::Default::default;
                let #upgrade_failure_closure_wrapped_ident = ||
                    #crate_ident::closure::IntoClosureReturnValue::into_closure_return_value(
                        (#upgrade_failure_closure_ident)()
                    );
            }),
            UpgradeBehaviour::Expression(ref expr) => Some(quote! {
                let #upgrade_failure_closure_ident = move || {
                    #expr
                };
                let #upgrade_failure_closure_wrapped_ident = ||
                    #crate_ident::closure::IntoClosureReturnValue::into_closure_return_value(
                        (#upgrade_failure_closure_ident)()
                    );
            }),
            UpgradeBehaviour::Closure(ref closure_2) => Some(quote! {
                    let #upgrade_failure_closure_ident = #closure_2;
                    let #upgrade_failure_closure_wrapped_ident = ||
                        #crate_ident::closure::IntoClosureReturnValue::into_closure_return_value(
                            (#upgrade_failure_closure_ident)()
                        );
            }),
            _ => None,
        };

        let assert_return_type = upgrade_failure_closure.is_some().then(|| {
            quote! {
                fn ____same<T>(_a: &T, _b: impl Fn() -> T) {}
                ____same(&____res, #upgrade_failure_closure_ident);
            }
        });

        tokens.extend(quote! {
            {
                let #closure_ident = {
                    #(#outer_before)*
                    #crate_ident::closure::RustClosure::#constructor(move |#values_ident| {
                        assert_eq!(
                            #values_ident.len(),
                            #args_len,
                            "Expected {} arguments but got {}",
                            #args_len,
                            #values_ident.len(),
                        );
                        #upgrade_failure_closure
                        #(#inner_before)*
                        #(#arg_values)*
                        #crate_ident::closure::IntoClosureReturnValue::into_closure_return_value({
                            let ____res = (#closure)(#(#arg_names),*);
                            #assert_return_type
                            ____res
                        })
                    }
                    )
                };
                #(#outer_after)*
                #closure_ident
            }
        });
    }
}

pub(crate) fn closure_inner(
    input: proc_macro::TokenStream,
    constructor: &'static str,
) -> proc_macro::TokenStream {
    let mut closure = syn::parse_macro_input!(input as Closure);
    closure.constructor = constructor;
    closure.into_token_stream().into()
}