clippy_lints/src/question_mark.rs

   1 use if_chain::if_chain;
   2 use rustc::hir::def::Def;
   3 use rustc::hir::*;
   4 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   5 use rustc::{declare_tool_lint, lint_array};
   6 use rustc_errors::Applicability;
   7 use syntax::ptr::P;
   8
   9 use crate::utils::paths::*;
  10 use crate::utils::sugg::Sugg;
  11 use crate::utils::{match_def_path, match_type, span_lint_and_then, SpanlessEq};
  12
  13 declare_clippy_lint! {
  14     /// **What it does:** Checks for expressions that could be replaced by the question mark operator.
  15     ///
  16     /// **Why is this bad?** Question mark usage is more idiomatic.
  17     ///
  18     /// **Known problems:** None
  19     ///
  20     /// **Example:**
  21     /// ```ignore
  22     /// if option.is_none() {
  23     ///     return None;
  24     /// }
  25     /// ```
  26     ///
  27     /// Could be written:
  28     ///
  29     /// ```ignore
  30     /// option?;
  31     /// ```
  32     pub QUESTION_MARK,
  33     style,
  34     "checks for expressions that could be replaced by the question mark operator"
  35 }
  36
  37 #[derive(Copy, Clone)]
  38 pub struct Pass;
  39
  40 impl LintPass for Pass {
  41     fn get_lints(&self) -> LintArray {
  42         lint_array!(QUESTION_MARK)
  43     }
  44
  45     fn name(&self) -> &'static str {
  46         "QuestionMark"
  47     }
  48 }
  49
  50 impl Pass {
  51     /// Checks if the given expression on the given context matches the following structure:
  52     ///
  53     /// ```ignore
  54     /// if option.is_none() {
  55     ///    return None;
  56     /// }
  57     /// ```
  58     ///
  59     /// If it matches, it will suggest to use the question mark operator instead
  60     fn check_is_none_and_early_return_none(cx: &LateContext<'_, '_>, expr: &Expr) {
  61         if_chain! {
  62             if let ExprKind::If(if_expr, body, else_) = &expr.node;
  63             if let ExprKind::MethodCall(segment, _, args) = &if_expr.node;
  64             if segment.ident.name == "is_none";
  65             if Self::expression_returns_none(cx, body);
  66             if let Some(subject) = args.get(0);
  67             if Self::is_option(cx, subject);
  68
  69             then {
  70                 let receiver_str = &Sugg::hir(cx, subject, "..");
  71                 let mut replacement: Option<String> = None;
  72                 if let Some(else_) = else_ {
  73                     if_chain! {
  74                         if let ExprKind::Block(block, None) = &else_.node;
  75                         if block.stmts.len() == 0;
  76                         if let Some(block_expr) = &block.expr;
  77                         if SpanlessEq::new(cx).ignore_fn().eq_expr(subject, block_expr);
  78                         then {
  79                             replacement = Some(format!("Some({}?)", receiver_str));
  80                         }
  81                     }
  82                 } else if Self::moves_by_default(cx, subject) {
  83                         replacement = Some(format!("{}.as_ref()?;", receiver_str));
  84                 } else {
  85                         replacement = Some(format!("{}?;", receiver_str));
  86                 }
  87
  88                 if let Some(replacement_str) = replacement {
  89                     span_lint_and_then(
  90                         cx,
  91                         QUESTION_MARK,
  92                         expr.span,
  93                         "this block may be rewritten with the `?` operator",
  94                         |db| {
  95                             db.span_suggestion(
  96                                 expr.span,
  97                                 "replace_it_with",
  98                                 replacement_str,
  99                                 Applicability::MaybeIncorrect, // snippet
 100                             );
 101                         }
 102                     )
 103                }
 104             }
 105         }
 106     }
 107
 108     fn moves_by_default(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
 109         let expr_ty = cx.tables.expr_ty(expression);
 110
 111         !expr_ty.is_copy_modulo_regions(cx.tcx, cx.param_env, expression.span)
 112     }
 113
 114     fn is_option(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
 115         let expr_ty = cx.tables.expr_ty(expression);
 116
 117         match_type(cx, expr_ty, &OPTION)
 118     }
 119
 120     fn expression_returns_none(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
 121         match expression.node {
 122             ExprKind::Block(ref block, _) => {
 123                 if let Some(return_expression) = Self::return_expression(block) {
 124                     return Self::expression_returns_none(cx, &return_expression);
 125                 }
 126
 127                 false
 128             },
 129             ExprKind::Ret(Some(ref expr)) => Self::expression_returns_none(cx, expr),
 130             ExprKind::Path(ref qp) => {
 131                 if let Def::VariantCtor(def_id, _) = cx.tables.qpath_def(qp, expression.hir_id) {
 132                     return match_def_path(cx.tcx, def_id, &OPTION_NONE);
 133                 }
 134
 135                 false
 136             },
 137             _ => false,
 138         }
 139     }
 140
 141     fn return_expression(block: &Block) -> Option<P<Expr>> {
 142         // Check if last expression is a return statement. Then, return the expression
 143         if_chain! {
 144             if block.stmts.len() == 1;
 145             if let Some(expr) = block.stmts.iter().last();
 146             if let StmtKind::Semi(ref expr) = expr.node;
 147             if let ExprKind::Ret(ref ret_expr) = expr.node;
 148             if let &Some(ref ret_expr) = ret_expr;
 149
 150             then {
 151                 return Some(ret_expr.clone());
 152             }
 153         }
 154
 155         // Check for `return` without a semicolon.
 156         if_chain! {
 157             if block.stmts.len() == 0;
 158             if let Some(ExprKind::Ret(Some(ret_expr))) = block.expr.as_ref().map(|e| &e.node);
 159             then {
 160                 return Some(ret_expr.clone());
 161             }
 162         }
 163
 164         None
 165     }
 166 }
 167
 168 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
 169     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
 170         Self::check_is_none_and_early_return_none(cx, expr);
 171     }
 172 }