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use rustc::hir::*;
use rustc::lint::*;
use rustc::ty::TypeVariants;
use crate::utils::{any_parent_is_automatically_derived, match_def_path, opt_def_id, paths, span_lint_and_sugg};
/// **What it does:** Checks for literal calls to `Default::default()`.
///
/// **Why is this bad?** It's more clear to the reader to use the name of the type whose default is
/// being gotten than the generic `Default`.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// // Bad
/// let s: String = Default::default();
///
/// // Good
/// let s = String::default();
/// ```
declare_clippy_lint! {
pub DEFAULT_TRAIT_ACCESS,
pedantic,
"checks for literal calls to Default::default()"
}
#[derive(Copy, Clone)]
pub struct DefaultTraitAccess;
impl LintPass for DefaultTraitAccess {
fn get_lints(&self) -> LintArray {
lint_array!(DEFAULT_TRAIT_ACCESS)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DefaultTraitAccess {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if_chain! {
if let ExprCall(ref path, ..) = expr.node;
if !any_parent_is_automatically_derived(cx.tcx, expr.id);
if let ExprPath(ref qpath) = path.node;
if let Some(def_id) = opt_def_id(cx.tables.qpath_def(qpath, path.hir_id));
if match_def_path(cx.tcx, def_id, &paths::DEFAULT_TRAIT_METHOD);
then {
match qpath {
QPath::Resolved(..) => {
// TODO: Work out a way to put "whatever the imported way of referencing
// this type in this file" rather than a fully-qualified type.
let expr_ty = cx.tables.expr_ty(expr);
if let TypeVariants::TyAdt(..) = expr_ty.sty {
let replacement = format!("{}::default()", expr_ty);
span_lint_and_sugg(
cx,
DEFAULT_TRAIT_ACCESS,
expr.span,
&format!("Calling {} is more clear than this expression", replacement),
"try",
replacement);
}
},
QPath::TypeRelative(..) => {},
}
}
}
}
}