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

//! Value traversal traits.

// Copyright 2020 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#![warn(missing_docs)]

use crate::io::{DecodeError, PathItem};
use std::convert::Infallible;
use thiserror::Error;
pub(crate) use wasmbin_derive::Visit;

/// Error type for [Visit] traversals.
#[derive(Error, Debug)]
pub enum VisitError<E> {
    /// Decoding error occured while visiting a [`Lazy`](crate::builtins::Lazy) value.
    #[error(transparent)]
    LazyDecode(DecodeError),

    /// A custom error returned from a visitor callback.
    #[error(transparent)]
    Custom(E),
}

impl<E> VisitError<E> {
    pub(crate) fn in_path(self, item: PathItem) -> Self {
        #[allow(clippy::match_wildcard_for_single_variants)]
        match self {
            VisitError::LazyDecode(err) => VisitError::LazyDecode(err.in_path(item)),
            err => err,
        }
    }
}

impl From<VisitError<Infallible>> for DecodeError {
    fn from(err: VisitError<Infallible>) -> Self {
        match err {
            VisitError::Custom(err) => match err {},
            VisitError::LazyDecode(err) => err,
        }
    }
}

mod sealed {
    pub trait Sealed {}
}

/// A trait for results that can be returned from a visitor.
pub trait VisitResult: sealed::Sealed {
    /// The error type of the result.
    type Error;

    /// Convert this result into a standard [`Result`].
    fn into_result(self) -> Result<(), Self::Error>;
}

impl sealed::Sealed for () {}
impl VisitResult for () {
    type Error = Infallible;

    fn into_result(self) -> Result<(), Self::Error> {
        Ok(())
    }
}

impl sealed::Sealed for bool {}
impl VisitResult for bool {
    type Error = ();

    fn into_result(self) -> Result<(), Self::Error> {
        match self {
            true => Ok(()),
            false => Err(()),
        }
    }
}

impl<E> sealed::Sealed for Result<(), E> {}
impl<E> VisitResult for Result<(), E> {
    type Error = E;

    fn into_result(self) -> Result<(), Self::Error> {
        self
    }
}

/// A trait for recursively finding instances of a given type within a value.
///
/// This is particularly useful for finding and updating [indices](crate::indices).
pub trait Visit: 'static + Sized {
    /// Traverse this value with the provided callback.
    fn visit<'a, T: 'static, R: VisitResult, F: FnMut(&'a T) -> R>(
        &'a self,
        mut f: F,
    ) -> Result<(), VisitError<R::Error>> {
        self.visit_child(&mut move |item| f(item).into_result())
    }

    /// Traverse this value mutably with the provided callback.
    fn visit_mut<T: 'static, R: VisitResult, F: FnMut(&mut T) -> R>(
        &mut self,
        mut f: F,
    ) -> Result<(), VisitError<R::Error>> {
        self.visit_child_mut(&mut move |item| f(item).into_result())
    }

    #[doc(hidden)]
    /// Internal implementation of [`visit`](Visit::visit).
    ///
    /// Takes a mutable reference to the callback to avoid infinite
    /// generic recursion.
    fn visit_child<'a, T: 'static, E, F: FnMut(&'a T) -> Result<(), E>>(
        &'a self,
        f: &mut F,
    ) -> Result<(), VisitError<E>> {
        if let Some(v) = <dyn std::any::Any>::downcast_ref(self) {
            f(v).map_err(VisitError::Custom)?;
        }
        self.visit_children(f)
    }

    #[doc(hidden)]
    /// Internal implementation of [`visit_mut`](Visit::visit_mut).
    ///
    /// Takes a mutable reference to the callback to avoid infinite
    /// generic recursion.
    fn visit_child_mut<T: 'static, E, F: FnMut(&mut T) -> Result<(), E>>(
        &mut self,
        f: &mut F,
    ) -> Result<(), VisitError<E>> {
        if let Some(v) = <dyn std::any::Any>::downcast_mut(self) {
            f(v).map_err(VisitError::Custom)?;
        }
        self.visit_children_mut(f)
    }

    /// Traverse the children of this value with the provided callback.
    fn visit_children<'a, T: 'static, E, F: FnMut(&'a T) -> Result<(), E>>(
        &'a self,
        _f: &mut F,
    ) -> Result<(), VisitError<E>> {
        Ok(())
    }

    /// Traverse the children of this value mutably with the provided callback.
    fn visit_children_mut<T: 'static, E, F: FnMut(&mut T) -> Result<(), E>>(
        &mut self,
        _f: &mut F,
    ) -> Result<(), VisitError<E>> {
        Ok(())
    }
}