clippy_lints/src/reference.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::in_macro;
   3 use clippy_utils::source::{snippet_opt, snippet_with_applicability};
   4 use clippy_utils::sugg::Sugg;
   5 use if_chain::if_chain;
   6 use rustc_ast::ast::{Expr, ExprKind, Mutability, UnOp};
   7 use rustc_errors::Applicability;
   8 use rustc_lint::{EarlyContext, EarlyLintPass};
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10 use rustc_span::BytePos;
  11
  12 declare_clippy_lint! {
  13     /// ### What it does
  14     /// Checks for usage of `*&` and `*&mut` in expressions.
  15     ///
  16     /// ### Why is this bad?
  17     /// Immediately dereferencing a reference is no-op and
  18     /// makes the code less clear.
  19     ///
  20     /// ### Known problems
  21     /// Multiple dereference/addrof pairs are not handled so
  22     /// the suggested fix for `x = **&&y` is `x = *&y`, which is still incorrect.
  23     ///
  24     /// ### Example
  25     /// ```rust,ignore
  26     /// // Bad
  27     /// let a = f(*&mut b);
  28     /// let c = *&d;
  29     ///
  30     /// // Good
  31     /// let a = f(b);
  32     /// let c = d;
  33     /// ```
  34     pub DEREF_ADDROF,
  35     complexity,
  36     "use of `*&` or `*&mut` in an expression"
  37 }
  38
  39 declare_lint_pass!(DerefAddrOf => [DEREF_ADDROF]);
  40
  41 fn without_parens(mut e: &Expr) -> &Expr {
  42     while let ExprKind::Paren(ref child_e) = e.kind {
  43         e = child_e;
  44     }
  45     e
  46 }
  47
  48 impl EarlyLintPass for DerefAddrOf {
  49     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
  50         if_chain! {
  51             if let ExprKind::Unary(UnOp::Deref, ref deref_target) = e.kind;
  52             if let ExprKind::AddrOf(_, ref mutability, ref addrof_target) = without_parens(deref_target).kind;
  53             if !in_macro(addrof_target.span);
  54             then {
  55                 let mut applicability = Applicability::MachineApplicable;
  56                 let sugg = if e.span.from_expansion() {
  57                     #[allow(clippy::option_if_let_else)]
  58                     if let Some(macro_source) = snippet_opt(cx, e.span) {
  59                         // Remove leading whitespace from the given span
  60                         // e.g: ` $visitor` turns into `$visitor`
  61                         let trim_leading_whitespaces = |span| {
  62                             snippet_opt(cx, span).and_then(|snip| {
  63                                 #[allow(clippy::cast_possible_truncation)]
  64                                 snip.find(|c: char| !c.is_whitespace()).map(|pos| {
  65                                     span.lo() + BytePos(pos as u32)
  66                                 })
  67                             }).map_or(span, |start_no_whitespace| e.span.with_lo(start_no_whitespace))
  68                         };
  69
  70                         let mut generate_snippet = |pattern: &str| {
  71                             #[allow(clippy::cast_possible_truncation)]
  72                             macro_source.rfind(pattern).map(|pattern_pos| {
  73                                 let rpos = pattern_pos + pattern.len();
  74                                 let span_after_ref = e.span.with_lo(BytePos(e.span.lo().0 + rpos as u32));
  75                                 let span = trim_leading_whitespaces(span_after_ref);
  76                                 snippet_with_applicability(cx, span, "_", &mut applicability)
  77                             })
  78                         };
  79
  80                         if *mutability == Mutability::Mut {
  81                             generate_snippet("mut")
  82                         } else {
  83                             generate_snippet("&")
  84                         }
  85                     } else {
  86                         Some(snippet_with_applicability(cx, e.span, "_", &mut applicability))
  87                     }
  88                 } else {
  89                     Some(snippet_with_applicability(cx, addrof_target.span, "_", &mut applicability))
  90                 };
  91                 if let Some(sugg) = sugg {
  92                     span_lint_and_sugg(
  93                         cx,
  94                         DEREF_ADDROF,
  95                         e.span,
  96                         "immediately dereferencing a reference",
  97                         "try this",
  98                         sugg.to_string(),
  99                         applicability,
 100                     );
 101                 }
 102             }
 103         }
 104     }
 105 }
 106
 107 declare_clippy_lint! {
 108     /// ### What it does
 109     /// Checks for references in expressions that use
 110     /// auto dereference.
 111     ///
 112     /// ### Why is this bad?
 113     /// The reference is a no-op and is automatically
 114     /// dereferenced by the compiler and makes the code less clear.
 115     ///
 116     /// ### Example
 117     /// ```rust
 118     /// struct Point(u32, u32);
 119     /// let point = Point(30, 20);
 120     /// let x = (&point).0;
 121     /// ```
 122     /// Use instead:
 123     /// ```rust
 124     /// # struct Point(u32, u32);
 125     /// # let point = Point(30, 20);
 126     /// let x = point.0;
 127     /// ```
 128     pub REF_IN_DEREF,
 129     complexity,
 130     "Use of reference in auto dereference expression."
 131 }
 132
 133 declare_lint_pass!(RefInDeref => [REF_IN_DEREF]);
 134
 135 impl EarlyLintPass for RefInDeref {
 136     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
 137         if_chain! {
 138             if let ExprKind::Field(ref object, _) = e.kind;
 139             if let ExprKind::Paren(ref parened) = object.kind;
 140             if let ExprKind::AddrOf(_, _, ref inner) = parened.kind;
 141             then {
 142                 let applicability = if inner.span.from_expansion() {
 143                     Applicability::MaybeIncorrect
 144                 } else {
 145                     Applicability::MachineApplicable
 146                 };
 147                 let sugg = Sugg::ast(cx, inner, "_").maybe_par();
 148                 span_lint_and_sugg(
 149                     cx,
 150                     REF_IN_DEREF,
 151                     object.span,
 152                     "creating a reference that is immediately dereferenced",
 153                     "try this",
 154                     sugg.to_string(),
 155                     applicability,
 156                 );
 157             }
 158         }
 159     }
 160 }