src/tools/clippy/clippy_lints/src/double_parens.rs

   1 use crate::utils::span_lint;
   2 use rustc_ast::ast::{Expr, ExprKind};
   3 use rustc_lint::{EarlyContext, EarlyLintPass};
   4 use rustc_session::{declare_lint_pass, declare_tool_lint};
   5
   6 declare_clippy_lint! {
   7     /// **What it does:** Checks for unnecessary double parentheses.
   8     ///
   9     /// **Why is this bad?** This makes code harder to read and might indicate a
  10     /// mistake.
  11     ///
  12     /// **Known problems:** None.
  13     ///
  14     /// **Example:**
  15     /// ```rust
  16     /// // Bad
  17     /// fn simple_double_parens() -> i32 {
  18     ///     ((0))
  19     /// }
  20     ///
  21     /// // Good
  22     /// fn simple_no_parens() -> i32 {
  23     ///     0
  24     /// }
  25     ///
  26     /// // or
  27     ///
  28     /// # fn foo(bar: usize) {}
  29     /// // Bad
  30     /// foo((0));
  31     ///
  32     /// // Good
  33     /// foo(0);
  34     /// ```
  35     pub DOUBLE_PARENS,
  36     complexity,
  37     "Warn on unnecessary double parentheses"
  38 }
  39
  40 declare_lint_pass!(DoubleParens => [DOUBLE_PARENS]);
  41
  42 impl EarlyLintPass for DoubleParens {
  43     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
  44         if expr.span.from_expansion() {
  45             return;
  46         }
  47
  48         let msg: &str = "consider removing unnecessary double parentheses";
  49
  50         match expr.kind {
  51             ExprKind::Paren(ref in_paren) => match in_paren.kind {
  52                 ExprKind::Paren(_) | ExprKind::Tup(_) => {
  53                     span_lint(cx, DOUBLE_PARENS, expr.span, &msg);
  54                 },
  55                 _ => {},
  56             },
  57             ExprKind::Call(_, ref params) => {
  58                 if params.len() == 1 {
  59                     let param = &params[0];
  60                     if let ExprKind::Paren(_) = param.kind {
  61                         span_lint(cx, DOUBLE_PARENS, param.span, &msg);
  62                     }
  63                 }
  64             },
  65             ExprKind::MethodCall(_, ref params, _) => {
  66                 if params.len() == 2 {
  67                     let param = &params[1];
  68                     if let ExprKind::Paren(_) = param.kind {
  69                         span_lint(cx, DOUBLE_PARENS, param.span, &msg);
  70                     }
  71                 }
  72             },
  73             _ => {},
  74         }
  75     }
  76 }