clippy_lints/src/question_mark.rs

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