clippy_lints/src/question_mark.rs

   1 use if_chain::if_chain;
   2 use rustc_errors::Applicability;
   3 use rustc_hir::def::{DefKind, Res};
   4 use rustc_hir::{def, BindingAnnotation, Block, Expr, ExprKind, MatchSource, PatKind, StmtKind};
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7
   8 use crate::utils::paths::{OPTION, OPTION_NONE};
   9 use crate::utils::sugg::Sugg;
  10 use crate::utils::{
  11     higher, match_def_path, match_qpath, match_type, snippet_with_applicability, span_lint_and_sugg, SpanlessEq,
  12 };
  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 mut applicability = Applicability::MachineApplicable;
  61                 let receiver_str = &Sugg::hir_with_applicability(cx, subject, "..", &mut applicability);
  62                 let mut replacement: Option<String> = None;
  63                 if let Some(else_) = else_ {
  64                     if_chain! {
  65                         if let ExprKind::Block(block, None) = &else_.kind;
  66                         if block.stmts.is_empty();
  67                         if let Some(block_expr) = &block.expr;
  68                         if SpanlessEq::new(cx).ignore_fn().eq_expr(subject, block_expr);
  69                         then {
  70                             replacement = Some(format!("Some({}?)", receiver_str));
  71                         }
  72                     }
  73                 } else if Self::moves_by_default(cx, subject) {
  74                         replacement = Some(format!("{}.as_ref()?;", receiver_str));
  75                 } else {
  76                         replacement = Some(format!("{}?;", receiver_str));
  77                 }
  78
  79                 if let Some(replacement_str) = replacement {
  80                     span_lint_and_sugg(
  81                         cx,
  82                         QUESTION_MARK,
  83                         expr.span,
  84                         "this block may be rewritten with the `?` operator",
  85                         "replace it with",
  86                         replacement_str,
  87                         applicability,
  88                     )
  89                }
  90             }
  91         }
  92     }
  93
  94     fn check_if_let_some_and_early_return_none(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
  95         if_chain! {
  96             if let ExprKind::Match(subject, arms, source) = &expr.kind;
  97             if *source == MatchSource::IfLetDesugar { contains_else_clause: true };
  98             if Self::is_option(cx, subject);
  99
 100             if let PatKind::TupleStruct(path1, fields, None) = &arms[0].pat.kind;
 101             if match_qpath(path1, &["Some"]);
 102             if let PatKind::Binding(annot, _, bind, _) = &fields[0].kind;
 103             let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
 104
 105             if let ExprKind::Block(block, None) = &arms[0].body.kind;
 106             if block.stmts.is_empty();
 107             if let Some(trailing_expr) = &block.expr;
 108             if let ExprKind::Path(path) = &trailing_expr.kind;
 109             if match_qpath(path, &[&bind.as_str()]);
 110
 111             if let PatKind::Wild = arms[1].pat.kind;
 112             if Self::expression_returns_none(cx, arms[1].body);
 113             then {
 114                 let mut applicability = Applicability::MachineApplicable;
 115                 let receiver_str = snippet_with_applicability(cx, subject.span, "..", &mut applicability);
 116                 let replacement = format!(
 117                     "{}{}?",
 118                     receiver_str,
 119                     if by_ref { ".as_ref()" } else { "" },
 120                 );
 121
 122                 span_lint_and_sugg(
 123                     cx,
 124                     QUESTION_MARK,
 125                     expr.span,
 126                     "this if-let-else may be rewritten with the `?` operator",
 127                     "replace it with",
 128                     replacement,
 129                     applicability,
 130                 )
 131             }
 132         }
 133     }
 134
 135     fn moves_by_default(cx: &LateContext<'_, '_>, expression: &Expr<'_>) -> bool {
 136         let expr_ty = cx.tables.expr_ty(expression);
 137
 138         !expr_ty.is_copy_modulo_regions(cx.tcx, cx.param_env, expression.span)
 139     }
 140
 141     fn is_option(cx: &LateContext<'_, '_>, expression: &Expr<'_>) -> bool {
 142         let expr_ty = cx.tables.expr_ty(expression);
 143
 144         match_type(cx, expr_ty, &OPTION)
 145     }
 146
 147     fn expression_returns_none(cx: &LateContext<'_, '_>, expression: &Expr<'_>) -> bool {
 148         match expression.kind {
 149             ExprKind::Block(ref block, _) => {
 150                 if let Some(return_expression) = Self::return_expression(block) {
 151                     return Self::expression_returns_none(cx, &return_expression);
 152                 }
 153
 154                 false
 155             },
 156             ExprKind::Ret(Some(ref expr)) => Self::expression_returns_none(cx, expr),
 157             ExprKind::Path(ref qp) => {
 158                 if let Res::Def(DefKind::Ctor(def::CtorOf::Variant, def::CtorKind::Const), def_id) =
 159                     cx.tables.qpath_res(qp, expression.hir_id)
 160                 {
 161                     return match_def_path(cx, def_id, &OPTION_NONE);
 162                 }
 163
 164                 false
 165             },
 166             _ => false,
 167         }
 168     }
 169
 170     fn return_expression<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
 171         // Check if last expression is a return statement. Then, return the expression
 172         if_chain! {
 173             if block.stmts.len() == 1;
 174             if let Some(expr) = block.stmts.iter().last();
 175             if let StmtKind::Semi(ref expr) = expr.kind;
 176             if let ExprKind::Ret(ret_expr) = expr.kind;
 177             if let Some(ret_expr) = ret_expr;
 178
 179             then {
 180                 return Some(ret_expr);
 181             }
 182         }
 183
 184         // Check for `return` without a semicolon.
 185         if_chain! {
 186             if block.stmts.is_empty();
 187             if let Some(ExprKind::Ret(Some(ret_expr))) = block.expr.as_ref().map(|e| &e.kind);
 188             then {
 189                 return Some(ret_expr);
 190             }
 191         }
 192
 193         None
 194     }
 195 }
 196
 197 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for QuestionMark {
 198     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
 199         Self::check_is_none_and_early_return_none(cx, expr);
 200         Self::check_if_let_some_and_early_return_none(cx, expr);
 201     }
 202 }