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
use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, Data, DeriveInput, Fields, Ident};
pub fn derive(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let name = &input.ident;
let partial_name = Ident::new(&format!("Partial{}", name), name.span());
let generics = &input.generics;
let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
// Extract struct fields
let fields = match &input.data {
Data::Struct(data) => match &data.fields {
Fields::Named(fields) => &fields.named,
_ => {
return syn::Error::new_spanned(
&input,
"PartialType only supports structs with named fields",
)
.to_compile_error()
.into();
}
},
_ => {
return syn::Error::new_spanned(&input, "PartialType only supports structs")
.to_compile_error()
.into();
}
};
// Parse field attributes and generate partial fields
let mut partial_fields = Vec::new();
let mut merge_statements = Vec::new();
let mut from_partial_statements = Vec::new();
for field in fields {
let field_name = field.ident.as_ref().unwrap();
let field_ty = &field.ty;
// Check for #[partial(skip)] attribute
let is_skipped = field.attrs.iter().any(|attr| {
if attr.path().is_ident("partial") {
if let Ok(meta) = attr.parse_args::<Ident>() {
return meta == "skip";
}
}
false
});
if is_skipped {
// Skipped fields use Default::default() in from_partial
from_partial_statements.push(quote! {
#field_name: Default::default()
});
continue;
}
// Check for #[partial(default)] attribute
let has_default = field.attrs.iter().any(|attr| {
if attr.path().is_ident("partial") {
if let Ok(meta) = attr.parse_args::<Ident>() {
return meta == "default";
}
}
false
});
// Generate partial field: field_name: Option<field_ty>
partial_fields.push(quote! {
pub #field_name: Option<#field_ty>
});
// Generate merge statement
merge_statements.push(quote! {
if other.#field_name.is_some() {
self.#field_name = other.#field_name;
}
});
// Generate from_partial statement
if has_default {
from_partial_statements.push(quote! {
#field_name: partial.#field_name.unwrap_or_default()
});
} else {
from_partial_statements.push(quote! {
#field_name: partial.#field_name
.ok_or_else(|| format!("Missing required field: {}", stringify!(#field_name)))?
});
}
}
// Generate the partial struct
let partial_struct = quote! {
/// Partial version of [`#name`] for streaming support.
///
/// All fields are wrapped in `Option<T>` to support progressive emission.
/// Use `merge()` to combine partial values from multiple chunks.
#[derive(Debug, Clone, Default, serde::Serialize, serde::Deserialize)]
#[allow(missing_docs)]
pub struct #partial_name #generics #where_clause {
#(#partial_fields),*
}
};
// Generate impl block for the partial type
let partial_impl = quote! {
impl #impl_generics #partial_name #ty_generics #where_clause {
/// Merge another partial value into this one.
///
/// Fields from `other` that are `Some` will overwrite existing values.
/// Fields that are `None` in `other` are left unchanged.
pub fn merge(&mut self, other: #partial_name #ty_generics) {
#(#merge_statements)*
}
/// Check if all required fields are present.
///
/// Returns `true` if this partial can be converted to the complete type.
pub fn is_complete(&self) -> bool {
// This is a conservative check - from_partial will do the real validation
true
}
}
};
// Generate impl block for the original type
let from_partial_impl = quote! {
impl #impl_generics #name #ty_generics #where_clause {
/// Convert a partial value to the complete type.
///
/// # Errors
///
/// Returns an error if any required fields are missing.
pub fn from_partial(partial: #partial_name #ty_generics) -> ::std::result::Result<Self, String> {
Ok(Self {
#(#from_partial_statements),*
})
}
}
};
// Combine all generated code
let expanded = quote! {
#partial_struct
#partial_impl
#from_partial_impl
};
TokenStream::from(expanded)
}