clippy_lints/src/reference.rs

   1 use crate::utils::{in_macro, snippet_opt, snippet_with_applicability, span_lint_and_sugg};
   2 use if_chain::if_chain;
   3 use rustc_ast::ast::{Expr, ExprKind, Mutability, UnOp};
   4 use rustc_errors::Applicability;
   5 use rustc_lint::{EarlyContext, EarlyLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7 use rustc_span::BytePos;
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** Checks for usage of `*&` and `*&mut` in expressions.
  11     ///
  12     /// **Why is this bad?** Immediately dereferencing a reference is no-op and
  13     /// makes the code less clear.
  14     ///
  15     /// **Known problems:** Multiple dereference/addrof pairs are not handled so
  16     /// the suggested fix for `x = **&&y` is `x = *&y`, which is still incorrect.
  17     ///
  18     /// **Example:**
  19     /// ```rust,ignore
  20     /// // Bad
  21     /// let a = f(*&mut b);
  22     /// let c = *&d;
  23     ///
  24     /// // Good
  25     /// let a = f(b);
  26     /// let c = d;
  27     /// ```
  28     pub DEREF_ADDROF,
  29     complexity,
  30     "use of `*&` or `*&mut` in an expression"
  31 }
  32
  33 declare_lint_pass!(DerefAddrOf => [DEREF_ADDROF]);
  34
  35 fn without_parens(mut e: &Expr) -> &Expr {
  36     while let ExprKind::Paren(ref child_e) = e.kind {
  37         e = child_e;
  38     }
  39     e
  40 }
  41
  42 impl EarlyLintPass for DerefAddrOf {
  43     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
  44         if_chain! {
  45             if let ExprKind::Unary(UnOp::Deref, ref deref_target) = e.kind;
  46             if let ExprKind::AddrOf(_, ref mutability, ref addrof_target) = without_parens(deref_target).kind;
  47             if !in_macro(addrof_target.span);
  48             then {
  49                 let mut applicability = Applicability::MachineApplicable;
  50                 let sugg = if e.span.from_expansion() {
  51                     if let Ok(macro_source) = cx.sess.source_map().span_to_snippet(e.span) {
  52                         // Remove leading whitespace from the given span
  53                         // e.g: ` $visitor` turns into `$visitor`
  54                         let trim_leading_whitespaces = |span| {
  55                             snippet_opt(cx, span).and_then(|snip| {
  56                                 #[allow(clippy::cast_possible_truncation)]
  57                                 snip.find(|c: char| !c.is_whitespace()).map(|pos| {
  58                                     span.lo() + BytePos(pos as u32)
  59                                 })
  60                             }).map_or(span, |start_no_whitespace| e.span.with_lo(start_no_whitespace))
  61                         };
  62
  63                         let rpos = if *mutability == Mutability::Mut {
  64                             macro_source.rfind("mut").expect("already checked this is a mutable reference") + "mut".len()
  65                         } else {
  66                             macro_source.rfind('&').expect("already checked this is a reference") + "&".len()
  67                         };
  68                         #[allow(clippy::cast_possible_truncation)]
  69                         let span_after_ref = e.span.with_lo(BytePos(e.span.lo().0 + rpos as u32));
  70                         let span = trim_leading_whitespaces(span_after_ref);
  71                         snippet_with_applicability(cx, span, "_", &mut applicability)
  72                     } else {
  73                         snippet_with_applicability(cx, e.span, "_", &mut applicability)
  74                     }
  75                 } else {
  76                     snippet_with_applicability(cx, addrof_target.span, "_", &mut applicability)
  77                 }.to_string();
  78                 span_lint_and_sugg(
  79                     cx,
  80                     DEREF_ADDROF,
  81                     e.span,
  82                     "immediately dereferencing a reference",
  83                     "try this",
  84                     sugg,
  85                     applicability,
  86                 );
  87             }
  88         }
  89     }
  90 }
  91
  92 declare_clippy_lint! {
  93     /// **What it does:** Checks for references in expressions that use
  94     /// auto dereference.
  95     ///
  96     /// **Why is this bad?** The reference is a no-op and is automatically
  97     /// dereferenced by the compiler and makes the code less clear.
  98     ///
  99     /// **Example:**
 100     /// ```rust
 101     /// struct Point(u32, u32);
 102     /// let point = Point(30, 20);
 103     /// let x = (&point).0;
 104     /// ```
 105     pub REF_IN_DEREF,
 106     complexity,
 107     "Use of reference in auto dereference expression."
 108 }
 109
 110 declare_lint_pass!(RefInDeref => [REF_IN_DEREF]);
 111
 112 impl EarlyLintPass for RefInDeref {
 113     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
 114         if_chain! {
 115             if let ExprKind::Field(ref object, _) = e.kind;
 116             if let ExprKind::Paren(ref parened) = object.kind;
 117             if let ExprKind::AddrOf(_, _, ref inner) = parened.kind;
 118             then {
 119                 let mut applicability = Applicability::MachineApplicable;
 120                 span_lint_and_sugg(
 121                     cx,
 122                     REF_IN_DEREF,
 123                     object.span,
 124                     "creating a reference that is immediately dereferenced",
 125                     "try this",
 126                     snippet_with_applicability(cx, inner.span, "_", &mut applicability).to_string(),
 127                     applicability,
 128                 );
 129             }
 130         }
 131     }
 132 }