clippy_lints/src/question_mark.rs

   1 use if_chain::if_chain;
   2 use rustc::declare_lint_pass;
   3 use rustc::hir::def::{DefKind, Res};
   4 use rustc::hir::ptr::P;
   5 use rustc::hir::*;
   6 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   7 use rustc_errors::Applicability;
   8 use rustc_session::declare_tool_lint;
   9
  10 use crate::utils::paths::*;
  11 use crate::utils::sugg::Sugg;
  12 use crate::utils::{higher, match_def_path, match_type, span_lint_and_then, SpanlessEq};
  13
  14 declare_clippy_lint! {
  15     /// **What it does:** Checks for expressions that could be replaced by the question mark operator.
  16     ///
  17     /// **Why is this bad?** Question mark usage is more idiomatic.
  18     ///
  19     /// **Known problems:** None
  20     ///
  21     /// **Example:**
  22     /// ```ignore
  23     /// if option.is_none() {
  24     ///     return None;
  25     /// }
  26     /// ```
  27     ///
  28     /// Could be written:
  29     ///
  30     /// ```ignore
  31     /// option?;
  32     /// ```
  33     pub QUESTION_MARK,
  34     style,
  35     "checks for expressions that could be replaced by the question mark operator"
  36 }
  37
  38 declare_lint_pass!(QuestionMark => [QUESTION_MARK]);
  39
  40 impl QuestionMark {
  41     /// Checks if the given expression on the given context matches the following structure:
  42     ///
  43     /// ```ignore
  44     /// if option.is_none() {
  45     ///    return None;
  46     /// }
  47     /// ```
  48     ///
  49     /// If it matches, it will suggest to use the question mark operator instead
  50     fn check_is_none_and_early_return_none(cx: &LateContext<'_, '_>, expr: &Expr) {
  51         if_chain! {
  52             if let Some((if_expr, body, else_)) = higher::if_block(&expr);
  53             if let ExprKind::MethodCall(segment, _, args) = &if_expr.kind;
  54             if segment.ident.name == sym!(is_none);
  55             if Self::expression_returns_none(cx, body);
  56             if let Some(subject) = args.get(0);
  57             if Self::is_option(cx, subject);
  58
  59             then {
  60                 let receiver_str = &Sugg::hir(cx, subject, "..");
  61                 let mut replacement: Option<String> = None;
  62                 if let Some(else_) = else_ {
  63                     if_chain! {
  64                         if let ExprKind::Block(block, None) = &else_.kind;
  65                         if block.stmts.len() == 0;
  66                         if let Some(block_expr) = &block.expr;
  67                         if SpanlessEq::new(cx).ignore_fn().eq_expr(subject, block_expr);
  68                         then {
  69                             replacement = Some(format!("Some({}?)", receiver_str));
  70                         }
  71                     }
  72                 } else if Self::moves_by_default(cx, subject) {
  73                         replacement = Some(format!("{}.as_ref()?;", receiver_str));
  74                 } else {
  75                         replacement = Some(format!("{}?;", receiver_str));
  76                 }
  77
  78                 if let Some(replacement_str) = replacement {
  79                     span_lint_and_then(
  80                         cx,
  81                         QUESTION_MARK,
  82                         expr.span,
  83                         "this block may be rewritten with the `?` operator",
  84                         |db| {
  85                             db.span_suggestion(
  86                                 expr.span,
  87                                 "replace_it_with",
  88                                 replacement_str,
  89                                 Applicability::MaybeIncorrect, // snippet
  90                             );
  91                         }
  92                     )
  93                }
  94             }
  95         }
  96     }
  97
  98     fn moves_by_default(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
  99         let expr_ty = cx.tables.expr_ty(expression);
 100
 101         !expr_ty.is_copy_modulo_regions(cx.tcx, cx.param_env, expression.span)
 102     }
 103
 104     fn is_option(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
 105         let expr_ty = cx.tables.expr_ty(expression);
 106
 107         match_type(cx, expr_ty, &OPTION)
 108     }
 109
 110     fn expression_returns_none(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
 111         match expression.kind {
 112             ExprKind::Block(ref block, _) => {
 113                 if let Some(return_expression) = Self::return_expression(block) {
 114                     return Self::expression_returns_none(cx, &return_expression);
 115                 }
 116
 117                 false
 118             },
 119             ExprKind::Ret(Some(ref expr)) => Self::expression_returns_none(cx, expr),
 120             ExprKind::Path(ref qp) => {
 121                 if let Res::Def(DefKind::Ctor(def::CtorOf::Variant, def::CtorKind::Const), def_id) =
 122                     cx.tables.qpath_res(qp, expression.hir_id)
 123                 {
 124                     return match_def_path(cx, def_id, &OPTION_NONE);
 125                 }
 126
 127                 false
 128             },
 129             _ => false,
 130         }
 131     }
 132
 133     fn return_expression(block: &Block) -> Option<&P<Expr>> {
 134         // Check if last expression is a return statement. Then, return the expression
 135         if_chain! {
 136             if block.stmts.len() == 1;
 137             if let Some(expr) = block.stmts.iter().last();
 138             if let StmtKind::Semi(ref expr) = expr.kind;
 139             if let ExprKind::Ret(ref ret_expr) = expr.kind;
 140             if let &Some(ref ret_expr) = ret_expr;
 141
 142             then {
 143                 return Some(ret_expr);
 144             }
 145         }
 146
 147         // Check for `return` without a semicolon.
 148         if_chain! {
 149             if block.stmts.len() == 0;
 150             if let Some(ExprKind::Ret(Some(ret_expr))) = block.expr.as_ref().map(|e| &e.kind);
 151             then {
 152                 return Some(ret_expr);
 153             }
 154         }
 155
 156         None
 157     }
 158 }
 159
 160 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for QuestionMark {
 161     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
 162         Self::check_is_none_and_early_return_none(cx, expr);
 163     }
 164 }