clippy_lints/src/default_trait_access.rs

   1 use if_chain::if_chain;
   2 use rustc::hir::*;
   3 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   4 use rustc::ty;
   5 use rustc::{declare_tool_lint, lint_array};
   6 use rustc_errors::Applicability;
   7
   8 use crate::utils::{any_parent_is_automatically_derived, match_def_path, paths, span_lint_and_sugg};
   9
  10 declare_clippy_lint! {
  11     /// **What it does:** Checks for literal calls to `Default::default()`.
  12     ///
  13     /// **Why is this bad?** It's more clear to the reader to use the name of the type whose default is
  14     /// being gotten than the generic `Default`.
  15     ///
  16     /// **Known problems:** None.
  17     ///
  18     /// **Example:**
  19     /// ```rust
  20     /// // Bad
  21     /// let s: String = Default::default();
  22     ///
  23     /// // Good
  24     /// let s = String::default();
  25     /// ```
  26     pub DEFAULT_TRAIT_ACCESS,
  27     pedantic,
  28     "checks for literal calls to Default::default()"
  29 }
  30
  31 #[derive(Copy, Clone)]
  32 pub struct DefaultTraitAccess;
  33
  34 impl LintPass for DefaultTraitAccess {
  35     fn get_lints(&self) -> LintArray {
  36         lint_array!(DEFAULT_TRAIT_ACCESS)
  37     }
  38
  39     fn name(&self) -> &'static str {
  40         "DefaultTraitAccess"
  41     }
  42 }
  43
  44 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DefaultTraitAccess {
  45     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  46         if_chain! {
  47             if let ExprKind::Call(ref path, ..) = expr.node;
  48             if !any_parent_is_automatically_derived(cx.tcx, expr.hir_id);
  49             if let ExprKind::Path(ref qpath) = path.node;
  50             if let Some(def_id) = cx.tables.qpath_def(qpath, path.hir_id).opt_def_id();
  51             if match_def_path(cx.tcx, def_id, &paths::DEFAULT_TRAIT_METHOD);
  52             then {
  53                 match qpath {
  54                     QPath::Resolved(..) => {
  55                         if_chain! {
  56                             // Detect and ignore <Foo as Default>::default() because these calls do
  57                             // explicitly name the type.
  58                             if let ExprKind::Call(ref method, ref _args) = expr.node;
  59                             if let ExprKind::Path(ref p) = method.node;
  60                             if let QPath::Resolved(Some(_ty), _path) = p;
  61                             then {
  62                                 return;
  63                             }
  64                         }
  65
  66                         // TODO: Work out a way to put "whatever the imported way of referencing
  67                         // this type in this file" rather than a fully-qualified type.
  68                         let expr_ty = cx.tables.expr_ty(expr);
  69                         if let ty::Adt(..) = expr_ty.sty {
  70                             let replacement = format!("{}::default()", expr_ty);
  71                             span_lint_and_sugg(
  72                                 cx,
  73                                 DEFAULT_TRAIT_ACCESS,
  74                                 expr.span,
  75                                 &format!("Calling {} is more clear than this expression", replacement),
  76                                 "try",
  77                                 replacement,
  78                                 Applicability::Unspecified, // First resolve the TODO above
  79                             );
  80                          }
  81                     },
  82                     QPath::TypeRelative(..) => {},
  83                 }
  84             }
  85         }
  86     }
  87 }