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rust-clippy/clippy_lints/src/default_trait_access.rs

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use if_chain::if_chain;
use rustc::hir::*;
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::ty;
use rustc::{declare_tool_lint, lint_array};
use rustc_errors::Applicability;
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use crate::utils::{any_parent_is_automatically_derived, match_def_path, opt_def_id, paths, span_lint_and_sugg};
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/// **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,
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pedantic,
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"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)
}
fn name(&self) -> &'static str {
"DefaultTraitAccess"
}
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}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DefaultTraitAccess {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if_chain! {
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if let ExprKind::Call(ref path, ..) = expr.node;
if !any_parent_is_automatically_derived(cx.tcx, expr.id);
if let ExprKind::Path(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(..) => {
if_chain! {
// Detect and ignore <Foo as Default>::default() because these calls do
// explicitly name the type.
if let ExprKind::Call(ref method, ref _args) = expr.node;
if let ExprKind::Path(ref p) = method.node;
if let QPath::Resolved(Some(_ty), _path) = p;
then {
return;
}
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}
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// 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);
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if let ty::Adt(..) = expr_ty.sty {
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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,
Applicability::Unspecified, // First resolve the TODO above
);
}
},
QPath::TypeRelative(..) => {},
}
}
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}
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}
}