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use syn::spanned::Spanned;
use super::{self_type_of, single_return_expr, trait_name_of, BoilerplateFind};
use crate::config::sections::BoilerplateConfig;
/// Detect trivial `impl From<T> for U` that just wraps a value.
/// Operation: AST pattern matching logic; helper calls in closures.
// qual:allow(complexity) reason: "AST pattern matching with nested closures"
pub(super) fn check_trivial_from(
parsed: &[(String, String, syn::File)],
config: &BoilerplateConfig,
) -> Vec<BoilerplateFind> {
pattern_guard!("BP-001", config);
let suggest = if config.suggest_crates {
"Consider using derive_more::From"
} else {
"Consider using a derive macro for trivial conversions"
};
parsed
.iter()
.flat_map(|(file, _, syntax)| {
syntax.items.iter().filter_map({
let file = file.clone();
let suggest = suggest.to_string();
move |item| {
let imp = if let syn::Item::Impl(imp) = item {
imp
} else {
return None;
};
if trait_name_of(imp).as_deref() != Some("From") {
return None;
}
let methods: Vec<_> = imp
.items
.iter()
.filter_map(|i| {
if let syn::ImplItem::Fn(m) = i {
Some(m)
} else {
None
}
})
.collect();
if methods.len() != 1 || methods[0].sig.ident != "from" {
return None;
}
let expr = single_return_expr(&methods[0].block)?;
// Trivial: constructor call with simple args, or struct literal with simple fields
let is_trivial = match expr {
syn::Expr::Call(c) => {
c.args.iter().all(|a| matches!(a, syn::Expr::Path(_)))
}
syn::Expr::Struct(s) => {
s.rest.is_none()
&& s.fields
.iter()
.all(|f| matches!(f.expr, syn::Expr::Path(_)))
}
_ => false,
};
if !is_trivial {
return None;
}
Some(BoilerplateFind {
pattern_id: "BP-001".to_string(),
file: file.clone(),
line: imp.self_ty.span().start().line,
struct_name: self_type_of(imp),
description: "Trivial From implementation that just wraps a value"
.to_string(),
suggestion: suggest.clone(),
})
}
})
})
.collect()
}