src/tools/clippy/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 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
  12     /// Checks for usage of `*&` and `*&mut` in expressions.
  13     ///
  14     /// ### Why is this bad?
  15     /// Immediately dereferencing a reference is no-op and
  16     /// makes the code less clear.
  17     ///
  18     /// ### Known problems
  19     /// Multiple dereference/addrof pairs are not handled so
  20     /// the suggested fix for `x = **&&y` is `x = *&y`, which is still incorrect.
  21     ///
  22     /// ### Example
  23     /// ```rust,ignore
  24     /// // Bad
  25     /// let a = f(*&mut b);
  26     /// let c = *&d;
  27     ///
  28     /// // Good
  29     /// let a = f(b);
  30     /// let c = d;
  31     /// ```
  32     #[clippy::version = "pre 1.29.0"]
  33     pub DEREF_ADDROF,
  34     complexity,
  35     "use of `*&` or `*&mut` in an expression"
  36 }
  37
  38 declare_lint_pass!(DerefAddrOf => [DEREF_ADDROF]);
  39
  40 fn without_parens(mut e: &Expr) -> &Expr {
  41     while let ExprKind::Paren(ref child_e) = e.kind {
  42         e = child_e;
  43     }
  44     e
  45 }
  46
  47 impl EarlyLintPass for DerefAddrOf {
  48     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
  49         if_chain! {
  50             if let ExprKind::Unary(UnOp::Deref, ref deref_target) = e.kind;
  51             if let ExprKind::AddrOf(_, ref mutability, ref addrof_target) = without_parens(deref_target).kind;
  52             if deref_target.span.ctxt() == e.span.ctxt();
  53             if !addrof_target.span.from_expansion();
  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 }