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