clippy_lints/src/reference.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::source::{snippet_opt, snippet_with_applicability};
   3 use clippy_utils::sugg::Sugg;
   4 use if_chain::if_chain;
   5 use rustc_ast::ast::{Expr, ExprKind, Mutability, UnOp};
   6 use rustc_errors::Applicability;
   7 use rustc_lint::{EarlyContext, EarlyLintPass};
   8 use rustc_session::{declare_lint_pass, declare_tool_lint};
   9 use rustc_span::BytePos;
  10
  11 declare_clippy_lint! {
  12     /// ### What it does
  13     /// Checks for usage of `*&` and `*&mut` in expressions.
  14     ///
  15     /// ### Why is this bad?
  16     /// Immediately dereferencing a reference is no-op and
  17     /// makes the code less clear.
  18     ///
  19     /// ### Known problems
  20     /// Multiple dereference/addrof pairs are not handled so
  21     /// the suggested fix for `x = **&&y` is `x = *&y`, which is still incorrect.
  22     ///
  23     /// ### Example
  24     /// ```rust,ignore
  25     /// // Bad
  26     /// let a = f(*&mut b);
  27     /// let c = *&d;
  28     ///
  29     /// // Good
  30     /// let a = f(b);
  31     /// let c = d;
  32     /// ```
  33     #[clippy::version = "pre 1.29.0"]
  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 deref_target.span.ctxt() == e.span.ctxt();
  54             if !addrof_target.span.from_expansion();
  55             then {
  56                 let mut applicability = Applicability::MachineApplicable;
  57                 let sugg = if e.span.from_expansion() {
  58                     #[allow(clippy::option_if_let_else)]
  59                     if let Some(macro_source) = snippet_opt(cx, e.span) {
  60                         // Remove leading whitespace from the given span
  61                         // e.g: ` $visitor` turns into `$visitor`
  62                         let trim_leading_whitespaces = |span| {
  63                             snippet_opt(cx, span).and_then(|snip| {
  64                                 #[allow(clippy::cast_possible_truncation)]
  65                                 snip.find(|c: char| !c.is_whitespace()).map(|pos| {
  66                                     span.lo() + BytePos(pos as u32)
  67                                 })
  68                             }).map_or(span, |start_no_whitespace| e.span.with_lo(start_no_whitespace))
  69                         };
  70
  71                         let mut generate_snippet = |pattern: &str| {
  72                             #[allow(clippy::cast_possible_truncation)]
  73                             macro_source.rfind(pattern).map(|pattern_pos| {
  74                                 let rpos = pattern_pos + pattern.len();
  75                                 let span_after_ref = e.span.with_lo(BytePos(e.span.lo().0 + rpos as u32));
  76                                 let span = trim_leading_whitespaces(span_after_ref);
  77                                 snippet_with_applicability(cx, span, "_", &mut applicability)
  78                             })
  79                         };
  80
  81                         if *mutability == Mutability::Mut {
  82                             generate_snippet("mut")
  83                         } else {
  84                             generate_snippet("&")
  85                         }
  86                     } else {
  87                         Some(snippet_with_applicability(cx, e.span, "_", &mut applicability))
  88                     }
  89                 } else {
  90                     Some(snippet_with_applicability(cx, addrof_target.span, "_", &mut applicability))
  91                 };
  92                 if let Some(sugg) = sugg {
  93                     span_lint_and_sugg(
  94                         cx,
  95                         DEREF_ADDROF,
  96                         e.span,
  97                         "immediately dereferencing a reference",
  98                         "try this",
  99                         sugg.to_string(),
 100                         applicability,
 101                     );
 102                 }
 103             }
 104         }
 105     }
 106 }
 107
 108 declare_clippy_lint! {
 109     /// ### What it does
 110     /// Checks for references in expressions that use
 111     /// auto dereference.
 112     ///
 113     /// ### Why is this bad?
 114     /// The reference is a no-op and is automatically
 115     /// dereferenced by the compiler and makes the code less clear.
 116     ///
 117     /// ### Example
 118     /// ```rust
 119     /// struct Point(u32, u32);
 120     /// let point = Point(30, 20);
 121     /// let x = (&point).0;
 122     /// ```
 123     /// Use instead:
 124     /// ```rust
 125     /// # struct Point(u32, u32);
 126     /// # let point = Point(30, 20);
 127     /// let x = point.0;
 128     /// ```
 129     #[clippy::version = "pre 1.29.0"]
 130     pub REF_IN_DEREF,
 131     complexity,
 132     "Use of reference in auto dereference expression."
 133 }
 134
 135 declare_lint_pass!(RefInDeref => [REF_IN_DEREF]);
 136
 137 impl EarlyLintPass for RefInDeref {
 138     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
 139         if_chain! {
 140             if let ExprKind::Field(ref object, _) = e.kind;
 141             if let ExprKind::Paren(ref parened) = object.kind;
 142             if let ExprKind::AddrOf(_, _, ref inner) = parened.kind;
 143             then {
 144                 let applicability = if inner.span.from_expansion() {
 145                     Applicability::MaybeIncorrect
 146                 } else {
 147                     Applicability::MachineApplicable
 148                 };
 149                 let sugg = Sugg::ast(cx, inner, "_").maybe_par();
 150                 span_lint_and_sugg(
 151                     cx,
 152                     REF_IN_DEREF,
 153                     object.span,
 154                     "creating a reference that is immediately dereferenced",
 155                     "try this",
 156                     sugg.to_string(),
 157                     applicability,
 158                 );
 159             }
 160         }
 161     }
 162 }