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use crate::ARBITRARY_ATTRIBUTE_NAME;
use proc_macro2::{Group, Span, TokenStream, TokenTree};
use quote::quote;
use syn::{spanned::Spanned, *};
/// Determines how a value for a field should be constructed.
#[cfg_attr(test, derive(Debug))]
pub enum FieldConstructor {
/// Assume that Arbitrary is defined for the type of this field and use it (default)
Arbitrary,
/// Places `Default::default()` as a field value.
Default,
/// Use custom function or closure to generate a value for a field.
With(TokenStream),
/// Set a field always to the given value.
Value(TokenStream),
}
pub fn determine_field_constructor(field: &Field) -> Result<FieldConstructor> {
let opt_attr = fetch_attr_from_field(field)?;
let ctor = match opt_attr {
Some(attr) => parse_attribute(attr)?,
None => FieldConstructor::Arbitrary,
};
Ok(ctor)
}
fn fetch_attr_from_field(field: &Field) -> Result<Option<&Attribute>> {
let found_attributes: Vec<_> = field
.attrs
.iter()
.filter(|a| {
let path = &a.path;
let name = quote!(#path).to_string();
name == ARBITRARY_ATTRIBUTE_NAME
})
.collect();
if found_attributes.len() > 1 {
let name = field.ident.as_ref().unwrap();
let msg = format!(
"Multiple conflicting #[{ARBITRARY_ATTRIBUTE_NAME}] attributes found on field `{name}`"
);
return Err(syn::Error::new(field.span(), msg));
}
Ok(found_attributes.into_iter().next())
}
fn parse_attribute(attr: &Attribute) -> Result<FieldConstructor> {
let group = {
let mut tokens_iter = attr.clone().tokens.into_iter();
let token = tokens_iter.next().ok_or_else(|| {
let msg = format!("#[{ARBITRARY_ATTRIBUTE_NAME}] cannot be empty.");
syn::Error::new(attr.span(), msg)
})?;
match token {
TokenTree::Group(g) => g,
t => {
let msg = format!("#[{ARBITRARY_ATTRIBUTE_NAME}] must contain a group, got: {t})");
return Err(syn::Error::new(attr.span(), msg));
}
}
};
parse_attribute_internals(group)
}
fn parse_attribute_internals(group: Group) -> Result<FieldConstructor> {
let stream = group.stream();
let mut tokens_iter = stream.into_iter();
let token = tokens_iter.next().ok_or_else(|| {
let msg = format!("#[{ARBITRARY_ATTRIBUTE_NAME}] cannot be empty.");
syn::Error::new(group.span(), msg)
})?;
match token.to_string().as_ref() {
"default" => Ok(FieldConstructor::Default),
"with" => {
let func_path = parse_assigned_value("with", tokens_iter, group.span())?;
Ok(FieldConstructor::With(func_path))
}
"value" => {
let value = parse_assigned_value("value", tokens_iter, group.span())?;
Ok(FieldConstructor::Value(value))
}
_ => {
let msg = format!("Unknown option for #[{ARBITRARY_ATTRIBUTE_NAME}]: `{token}`");
Err(syn::Error::new(token.span(), msg))
}
}
}
// Input:
// = 2 + 2
// Output:
// 2 + 2
fn parse_assigned_value(
opt_name: &str,
mut tokens_iter: impl Iterator<Item = TokenTree>,
default_span: Span,
) -> Result<TokenStream> {
let eq_sign = tokens_iter.next().ok_or_else(|| {
let msg = format!(
"Invalid syntax for #[{ARBITRARY_ATTRIBUTE_NAME}], `{opt_name}` is missing assignment."
);
syn::Error::new(default_span, msg)
})?;
if eq_sign.to_string() == "=" {
Ok(tokens_iter.collect())
} else {
let msg = format!("Invalid syntax for #[{ARBITRARY_ATTRIBUTE_NAME}], expected `=` after `{opt_name}`, got: `{eq_sign}`");
Err(syn::Error::new(eq_sign.span(), msg))
}
}
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