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 use rustc_span::sym;
   8
   9 use crate::utils::sugg::Sugg;
  10 use crate::utils::{
  11     eq_expr_value, higher, is_type_diagnostic_item, match_def_path, match_qpath, paths, snippet_with_applicability,
  12     span_lint_and_sugg,
  13 };
  14
  15 declare_clippy_lint! {
  16     /// **What it does:** Checks for expressions that could be replaced by the question mark operator.
  17     ///
  18     /// **Why is this bad?** Question mark usage is more idiomatic.
  19     ///
  20     /// **Known problems:** None
  21     ///
  22     /// **Example:**
  23     /// ```ignore
  24     /// if option.is_none() {
  25     ///     return None;
  26     /// }
  27     /// ```
  28     ///
  29     /// Could be written:
  30     ///
  31     /// ```ignore
  32     /// option?;
  33     /// ```
  34     pub QUESTION_MARK,
  35     style,
  36     "checks for expressions that could be replaced by the question mark operator"
  37 }
  38
  39 declare_lint_pass!(QuestionMark => [QUESTION_MARK]);
  40
  41 impl QuestionMark {
  42     /// Checks if the given expression on the given context matches the following structure:
  43     ///
  44     /// ```ignore
  45     /// if option.is_none() {
  46     ///    return None;
  47     /// }
  48     /// ```
  49     ///
  50     /// If it matches, it will suggest to use the question mark operator instead
  51     fn check_is_none_and_early_return_none(cx: &LateContext<'_>, expr: &Expr<'_>) {
  52         if_chain! {
  53             if let Some((if_expr, body, else_)) = higher::if_block(&expr);
  54             if let ExprKind::MethodCall(segment, _, args, _) = &if_expr.kind;
  55             if segment.ident.name == sym!(is_none);
  56             if Self::expression_returns_none(cx, body);
  57             if let Some(subject) = args.get(0);
  58             if Self::is_option(cx, subject);
  59
  60             then {
  61                 let mut applicability = Applicability::MachineApplicable;
  62                 let receiver_str = &Sugg::hir_with_applicability(cx, subject, "..", &mut applicability);
  63                 let mut replacement: Option<String> = None;
  64                 if let Some(else_) = else_ {
  65                     if_chain! {
  66                         if let ExprKind::Block(block, None) = &else_.kind;
  67                         if block.stmts.is_empty();
  68                         if let Some(block_expr) = &block.expr;
  69                         if eq_expr_value(cx, subject, block_expr);
  70                         then {
  71                             replacement = Some(format!("Some({}?)", receiver_str));
  72                         }
  73                     }
  74                 } else if Self::moves_by_default(cx, subject)
  75                     && !matches!(subject.kind, ExprKind::Call(..) | ExprKind::MethodCall(..))
  76                 {
  77                     replacement = Some(format!("{}.as_ref()?;", receiver_str));
  78                 } else {
  79                     replacement = Some(format!("{}?;", receiver_str));
  80                 }
  81
  82                 if let Some(replacement_str) = replacement {
  83                     span_lint_and_sugg(
  84                         cx,
  85                         QUESTION_MARK,
  86                         expr.span,
  87                         "this block may be rewritten with the `?` operator",
  88                         "replace it with",
  89                         replacement_str,
  90                         applicability,
  91                     )
  92                 }
  93             }
  94         }
  95     }
  96
  97     fn check_if_let_some_and_early_return_none(cx: &LateContext<'_>, expr: &Expr<'_>) {
  98         if_chain! {
  99             if let ExprKind::Match(subject, arms, source) = &expr.kind;
 100             if *source == MatchSource::IfLetDesugar { contains_else_clause: true };
 101             if Self::is_option(cx, subject);
 102
 103             if let PatKind::TupleStruct(path1, fields, None) = &arms[0].pat.kind;
 104             if match_qpath(path1, &["Some"]);
 105             if let PatKind::Binding(annot, _, bind, _) = &fields[0].kind;
 106             let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
 107
 108             if let ExprKind::Block(block, None) = &arms[0].body.kind;
 109             if block.stmts.is_empty();
 110             if let Some(trailing_expr) = &block.expr;
 111             if let ExprKind::Path(path) = &trailing_expr.kind;
 112             if match_qpath(path, &[&bind.as_str()]);
 113
 114             if let PatKind::Wild = arms[1].pat.kind;
 115             if Self::expression_returns_none(cx, arms[1].body);
 116             then {
 117                 let mut applicability = Applicability::MachineApplicable;
 118                 let receiver_str = snippet_with_applicability(cx, subject.span, "..", &mut applicability);
 119                 let replacement = format!(
 120                     "{}{}?",
 121                     receiver_str,
 122                     if by_ref { ".as_ref()" } else { "" },
 123                 );
 124
 125                 span_lint_and_sugg(
 126                     cx,
 127                     QUESTION_MARK,
 128                     expr.span,
 129                     "this if-let-else may be rewritten with the `?` operator",
 130                     "replace it with",
 131                     replacement,
 132                     applicability,
 133                 )
 134             }
 135         }
 136     }
 137
 138     fn moves_by_default(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 139         let expr_ty = cx.typeck_results().expr_ty(expression);
 140
 141         !expr_ty.is_copy_modulo_regions(cx.tcx.at(expression.span), cx.param_env)
 142     }
 143
 144     fn is_option(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 145         let expr_ty = cx.typeck_results().expr_ty(expression);
 146
 147         is_type_diagnostic_item(cx, expr_ty, sym::option_type)
 148     }
 149
 150     fn expression_returns_none(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 151         match expression.kind {
 152             ExprKind::Block(ref block, _) => {
 153                 if let Some(return_expression) = Self::return_expression(block) {
 154                     return Self::expression_returns_none(cx, &return_expression);
 155                 }
 156
 157                 false
 158             },
 159             ExprKind::Ret(Some(ref expr)) => Self::expression_returns_none(cx, expr),
 160             ExprKind::Path(ref qp) => {
 161                 if let Res::Def(DefKind::Ctor(def::CtorOf::Variant, def::CtorKind::Const), def_id) =
 162                     cx.qpath_res(qp, expression.hir_id)
 163                 {
 164                     return match_def_path(cx, def_id, &paths::OPTION_NONE);
 165                 }
 166
 167                 false
 168             },
 169             _ => false,
 170         }
 171     }
 172
 173     fn return_expression<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
 174         // Check if last expression is a return statement. Then, return the expression
 175         if_chain! {
 176             if block.stmts.len() == 1;
 177             if let Some(expr) = block.stmts.iter().last();
 178             if let StmtKind::Semi(ref expr) = expr.kind;
 179             if let ExprKind::Ret(Some(ret_expr)) = expr.kind;
 180
 181             then {
 182                 return Some(ret_expr);
 183             }
 184         }
 185
 186         // Check for `return` without a semicolon.
 187         if_chain! {
 188             if block.stmts.is_empty();
 189             if let Some(ExprKind::Ret(Some(ret_expr))) = block.expr.as_ref().map(|e| &e.kind);
 190             then {
 191                 return Some(ret_expr);
 192             }
 193         }
 194
 195         None
 196     }
 197 }
 198
 199 impl<'tcx> LateLintPass<'tcx> for QuestionMark {
 200     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 201         Self::check_is_none_and_early_return_none(cx, expr);
 202         Self::check_if_let_some_and_early_return_none(cx, expr);
 203     }
 204 }