clippy_lints/src/question_mark.rs

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