clippy_lints/src/reference.rs

   1 use crate::utils::sugg::Sugg;
   2 use crate::utils::{in_macro, snippet_opt, snippet_with_applicability, span_lint_and_sugg};
   3 use if_chain::if_chain;
   4 use rustc_ast::ast::{Expr, ExprKind, Mutability, UnOp};
   5 use rustc_errors::Applicability;
   6 use rustc_lint::{EarlyContext, EarlyLintPass};
   7 use rustc_session::{declare_lint_pass, declare_tool_lint};
   8 use rustc_span::BytePos;
   9
  10 declare_clippy_lint! {
  11     /// **What it does:** Checks for usage of `*&` and `*&mut` in expressions.
  12     ///
  13     /// **Why is this bad?** Immediately dereferencing a reference is no-op and
  14     /// makes the code less clear.
  15     ///
  16     /// **Known problems:** Multiple dereference/addrof pairs are not handled so
  17     /// the suggested fix for `x = **&&y` is `x = *&y`, which is still incorrect.
  18     ///
  19     /// **Example:**
  20     /// ```rust,ignore
  21     /// // Bad
  22     /// let a = f(*&mut b);
  23     /// let c = *&d;
  24     ///
  25     /// // Good
  26     /// let a = f(b);
  27     /// let c = d;
  28     /// ```
  29     pub DEREF_ADDROF,
  30     complexity,
  31     "use of `*&` or `*&mut` in an expression"
  32 }
  33
  34 declare_lint_pass!(DerefAddrOf => [DEREF_ADDROF]);
  35
  36 fn without_parens(mut e: &Expr) -> &Expr {
  37     while let ExprKind::Paren(ref child_e) = e.kind {
  38         e = child_e;
  39     }
  40     e
  41 }
  42
  43 impl EarlyLintPass for DerefAddrOf {
  44     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
  45         if_chain! {
  46             if let ExprKind::Unary(UnOp::Deref, ref deref_target) = e.kind;
  47             if let ExprKind::AddrOf(_, ref mutability, ref addrof_target) = without_parens(deref_target).kind;
  48             if !in_macro(addrof_target.span);
  49             then {
  50                 let mut applicability = Applicability::MachineApplicable;
  51                 let sugg = if e.span.from_expansion() {
  52                     if let Ok(macro_source) = cx.sess.source_map().span_to_snippet(e.span) {
  53                         // Remove leading whitespace from the given span
  54                         // e.g: ` $visitor` turns into `$visitor`
  55                         let trim_leading_whitespaces = |span| {
  56                             snippet_opt(cx, span).and_then(|snip| {
  57                                 #[allow(clippy::cast_possible_truncation)]
  58                                 snip.find(|c: char| !c.is_whitespace()).map(|pos| {
  59                                     span.lo() + BytePos(pos as u32)
  60                                 })
  61                             }).map_or(span, |start_no_whitespace| e.span.with_lo(start_no_whitespace))
  62                         };
  63
  64                         let mut generate_snippet = |pattern: &str| {
  65                             #[allow(clippy::cast_possible_truncation)]
  66                             macro_source.rfind(pattern).map(|pattern_pos| {
  67                                 let rpos = pattern_pos + pattern.len();
  68                                 let span_after_ref = e.span.with_lo(BytePos(e.span.lo().0 + rpos as u32));
  69                                 let span = trim_leading_whitespaces(span_after_ref);
  70                                 snippet_with_applicability(cx, span, "_", &mut applicability)
  71                             })
  72                         };
  73
  74                         if *mutability == Mutability::Mut {
  75                             generate_snippet("mut")
  76                         } else {
  77                             generate_snippet("&")
  78                         }
  79                     } else {
  80                         Some(snippet_with_applicability(cx, e.span, "_", &mut applicability))
  81                     }
  82                 } else {
  83                     Some(snippet_with_applicability(cx, addrof_target.span, "_", &mut applicability))
  84                 };
  85                 if let Some(sugg) = sugg {
  86                     span_lint_and_sugg(
  87                         cx,
  88                         DEREF_ADDROF,
  89                         e.span,
  90                         "immediately dereferencing a reference",
  91                         "try this",
  92                         sugg.to_string(),
  93                         applicability,
  94                     );
  95                 }
  96             }
  97         }
  98     }
  99 }
 100
 101 declare_clippy_lint! {
 102     /// **What it does:** Checks for references in expressions that use
 103     /// auto dereference.
 104     ///
 105     /// **Why is this bad?** The reference is a no-op and is automatically
 106     /// dereferenced by the compiler and makes the code less clear.
 107     ///
 108     /// **Example:**
 109     /// ```rust
 110     /// struct Point(u32, u32);
 111     /// let point = Point(30, 20);
 112     /// let x = (&point).0;
 113     /// ```
 114     /// Use instead:
 115     /// ```rust
 116     /// # struct Point(u32, u32);
 117     /// # let point = Point(30, 20);
 118     /// let x = point.0;
 119     /// ```
 120     pub REF_IN_DEREF,
 121     complexity,
 122     "Use of reference in auto dereference expression."
 123 }
 124
 125 declare_lint_pass!(RefInDeref => [REF_IN_DEREF]);
 126
 127 impl EarlyLintPass for RefInDeref {
 128     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
 129         if_chain! {
 130             if let ExprKind::Field(ref object, _) = e.kind;
 131             if let ExprKind::Paren(ref parened) = object.kind;
 132             if let ExprKind::AddrOf(_, _, ref inner) = parened.kind;
 133             then {
 134                 let applicability = if inner.span.from_expansion() {
 135                     Applicability::MaybeIncorrect
 136                 } else {
 137                     Applicability::MachineApplicable
 138                 };
 139                 let sugg = Sugg::ast(cx, inner, "_").maybe_par();
 140                 span_lint_and_sugg(
 141                     cx,
 142                     REF_IN_DEREF,
 143                     object.span,
 144                     "creating a reference that is immediately dereferenced",
 145                     "try this",
 146                     sugg.to_string(),
 147                     applicability,
 148                 );
 149             }
 150         }
 151     }
 152 }