clippy_lints/src/default_trait_access.rs

   1 use if_chain::if_chain;
   2 use rustc::declare_lint_pass;
   3 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   4 use rustc::ty;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::*;
   7 use rustc_session::declare_tool_lint;
   8
   9 use crate::utils::{any_parent_is_automatically_derived, match_def_path, paths, span_lint_and_sugg};
  10
  11 declare_clippy_lint! {
  12     /// **What it does:** Checks for literal calls to `Default::default()`.
  13     ///
  14     /// **Why is this bad?** It's more clear to the reader to use the name of the type whose default is
  15     /// being gotten than the generic `Default`.
  16     ///
  17     /// **Known problems:** None.
  18     ///
  19     /// **Example:**
  20     /// ```rust
  21     /// // Bad
  22     /// let s: String = Default::default();
  23     ///
  24     /// // Good
  25     /// let s = String::default();
  26     /// ```
  27     pub DEFAULT_TRAIT_ACCESS,
  28     pedantic,
  29     "checks for literal calls to Default::default()"
  30 }
  31
  32 declare_lint_pass!(DefaultTraitAccess => [DEFAULT_TRAIT_ACCESS]);
  33
  34 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DefaultTraitAccess {
  35     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
  36         if_chain! {
  37             if let ExprKind::Call(ref path, ..) = expr.kind;
  38             if !any_parent_is_automatically_derived(cx.tcx, expr.hir_id);
  39             if let ExprKind::Path(ref qpath) = path.kind;
  40             if let Some(def_id) = cx.tables.qpath_res(qpath, path.hir_id).opt_def_id();
  41             if match_def_path(cx, def_id, &paths::DEFAULT_TRAIT_METHOD);
  42             then {
  43                 match qpath {
  44                     QPath::Resolved(..) => {
  45                         if_chain! {
  46                             // Detect and ignore <Foo as Default>::default() because these calls do
  47                             // explicitly name the type.
  48                             if let ExprKind::Call(ref method, ref _args) = expr.kind;
  49                             if let ExprKind::Path(ref p) = method.kind;
  50                             if let QPath::Resolved(Some(_ty), _path) = p;
  51                             then {
  52                                 return;
  53                             }
  54                         }
  55
  56                         // TODO: Work out a way to put "whatever the imported way of referencing
  57                         // this type in this file" rather than a fully-qualified type.
  58                         let expr_ty = cx.tables.expr_ty(expr);
  59                         if let ty::Adt(..) = expr_ty.kind {
  60                             let replacement = format!("{}::default()", expr_ty);
  61                             span_lint_and_sugg(
  62                                 cx,
  63                                 DEFAULT_TRAIT_ACCESS,
  64                                 expr.span,
  65                                 &format!("Calling {} is more clear than this expression", replacement),
  66                                 "try",
  67                                 replacement,
  68                                 Applicability::Unspecified, // First resolve the TODO above
  69                             );
  70                          }
  71                     },
  72                     QPath::TypeRelative(..) => {},
  73                 }
  74             }
  75         }
  76     }
  77 }