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use clippy_utils::{diagnostics::span_lint_and_sugg, ty::is_type_lang_item};
use clippy_utils::{match_def_path, paths};
use if_chain::if_chain;
use rustc_ast::ast::LitKind;
use rustc_errors::Applicability;
use rustc_hir::{BorrowKind, Expr, ExprKind, LangItem, Mutability};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
///
/// Detects cases of owned empty strings being passed as an argument to a function expecting `&str`
///
/// ### Why is this bad?
///
/// This results in longer and less readable code
///
/// ### Example
/// ```rust
/// vec!["1", "2", "3"].join(&String::new());
/// ```
/// Use instead:
/// ```rust
/// vec!["1", "2", "3"].join("");
/// ```
#[clippy::version = "1.62.0"]
pub UNNECESSARY_OWNED_EMPTY_STRINGS,
style,
"detects cases of references to owned empty strings being passed as an argument to a function expecting `&str`"
}
declare_lint_pass!(UnnecessaryOwnedEmptyStrings => [UNNECESSARY_OWNED_EMPTY_STRINGS]);
impl<'tcx> LateLintPass<'tcx> for UnnecessaryOwnedEmptyStrings {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
if_chain! {
if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, inner_expr) = expr.kind;
if let ExprKind::Call(fun, args) = inner_expr.kind;
if let ExprKind::Path(ref qpath) = fun.kind;
if let Some(fun_def_id) = cx.qpath_res(qpath, fun.hir_id).opt_def_id();
if let ty::Ref(_, inner_str, _) = cx.typeck_results().expr_ty_adjusted(expr).kind();
if inner_str.is_str();
then {
if match_def_path(cx, fun_def_id, &paths::STRING_NEW) {
span_lint_and_sugg(
cx,
UNNECESSARY_OWNED_EMPTY_STRINGS,
expr.span,
"usage of `&String::new()` for a function expecting a `&str` argument",
"try",
"\"\"".to_owned(),
Applicability::MachineApplicable,
);
} else {
if_chain! {
if Some(fun_def_id) == cx.tcx.lang_items().from_fn();
if let [.., last_arg] = args;
if let ExprKind::Lit(spanned) = &last_arg.kind;
if let LitKind::Str(symbol, _) = spanned.node;
if symbol.is_empty();
let inner_expr_type = cx.typeck_results().expr_ty(inner_expr);
if is_type_lang_item(cx, inner_expr_type, LangItem::String);
then {
span_lint_and_sugg(
cx,
UNNECESSARY_OWNED_EMPTY_STRINGS,
expr.span,
"usage of `&String::from(\"\")` for a function expecting a `&str` argument",
"try",
"\"\"".to_owned(),
Applicability::MachineApplicable,
);
}
}
}
}
}
}
}
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