clippy_lints/src/should_assert_eq.rs

   1 use rustc::lint::*;
   2 use rustc::hir::*;
   3 use utils::{is_direct_expn_of, is_expn_of, implements_trait, span_lint};
   4
   5 /// **What it does:** Checks for `assert!(x == y)` or `assert!(x != y)` which can be better written
   6 /// using `assert_eq` or `assert_ne` if `x` and `y` implement `Debug` trait.
   7 ///
   8 /// **Why is this bad?** `assert_eq` and `assert_ne` provide better assertion failure reporting.
   9 ///
  10 /// **Known problems:** Hopefully none.
  11 ///
  12 /// **Example:**
  13 /// ```rust
  14 /// let (x, y) = (1, 2);
  15 ///
  16 /// assert!(x == y);  // assertion failed: x == y
  17 /// assert_eq!(x, y); // assertion failed: `(left == right)` (left: `1`, right: `2`)
  18 /// ```
  19 declare_lint! {
  20     pub SHOULD_ASSERT_EQ,
  21     Warn,
  22     "using `assert` macro for asserting equality"
  23 }
  24
  25 pub struct ShouldAssertEq;
  26
  27 impl LintPass for ShouldAssertEq {
  28     fn get_lints(&self) -> LintArray {
  29         lint_array![SHOULD_ASSERT_EQ]
  30     }
  31 }
  32
  33 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ShouldAssertEq {
  34     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  35         if_let_chain! {[
  36             let ExprIf(ref cond, ..) = e.node,
  37             let ExprUnary(UnOp::UnNot, ref cond) = cond.node,
  38             let ExprBinary(ref binop, ref expr1, ref expr2) = cond.node,
  39             is_direct_expn_of(e.span, "assert").is_some(),
  40             let Some(debug_trait) = cx.tcx.lang_items.debug_trait(),
  41         ], {
  42             let debug = is_expn_of(e.span, "debug_assert").map_or("", |_| "debug_");
  43             let sugg = match binop.node {
  44                 BinOp_::BiEq => "assert_eq",
  45                 BinOp_::BiNe => "assert_ne",
  46                 _ => return,
  47             };
  48
  49             let ty1 = cx.tables.expr_ty(expr1);
  50             let ty2 = cx.tables.expr_ty(expr2);
  51
  52             let parent = cx.tcx.hir.get_parent(e.id);
  53
  54             if implements_trait(cx, ty1, debug_trait, &[], Some(parent)) &&
  55                 implements_trait(cx, ty2, debug_trait, &[], Some(parent)) {
  56                 span_lint(cx, SHOULD_ASSERT_EQ, e.span, &format!("use `{}{}` for better reporting", debug, sugg));
  57             }
  58         }}
  59     }
  60 }