src/tools/clippy/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::sugg::Sugg;
   9 use crate::utils::{
  10     higher, is_type_diagnostic_item, match_def_path, match_qpath, paths, snippet_with_applicability,
  11     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                     && !matches!(subject.kind, ExprKind::Call(..) | ExprKind::MethodCall(..))
  75                 {
  76                     replacement = Some(format!("{}.as_ref()?;", receiver_str));
  77                 } else {
  78                     replacement = Some(format!("{}?;", receiver_str));
  79                 }
  80
  81                 if let Some(replacement_str) = replacement {
  82                     span_lint_and_sugg(
  83                         cx,
  84                         QUESTION_MARK,
  85                         expr.span,
  86                         "this block may be rewritten with the `?` operator",
  87                         "replace it with",
  88                         replacement_str,
  89                         applicability,
  90                     )
  91                 }
  92             }
  93         }
  94     }
  95
  96     fn check_if_let_some_and_early_return_none(cx: &LateContext<'_>, expr: &Expr<'_>) {
  97         if_chain! {
  98             if let ExprKind::Match(subject, arms, source) = &expr.kind;
  99             if *source == MatchSource::IfLetDesugar { contains_else_clause: true };
 100             if Self::is_option(cx, subject);
 101
 102             if let PatKind::TupleStruct(path1, fields, None) = &arms[0].pat.kind;
 103             if match_qpath(path1, &["Some"]);
 104             if let PatKind::Binding(annot, _, bind, _) = &fields[0].kind;
 105             let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
 106
 107             if let ExprKind::Block(block, None) = &arms[0].body.kind;
 108             if block.stmts.is_empty();
 109             if let Some(trailing_expr) = &block.expr;
 110             if let ExprKind::Path(path) = &trailing_expr.kind;
 111             if match_qpath(path, &[&bind.as_str()]);
 112
 113             if let PatKind::Wild = arms[1].pat.kind;
 114             if Self::expression_returns_none(cx, arms[1].body);
 115             then {
 116                 let mut applicability = Applicability::MachineApplicable;
 117                 let receiver_str = snippet_with_applicability(cx, subject.span, "..", &mut applicability);
 118                 let replacement = format!(
 119                     "{}{}?",
 120                     receiver_str,
 121                     if by_ref { ".as_ref()" } else { "" },
 122                 );
 123
 124                 span_lint_and_sugg(
 125                     cx,
 126                     QUESTION_MARK,
 127                     expr.span,
 128                     "this if-let-else may be rewritten with the `?` operator",
 129                     "replace it with",
 130                     replacement,
 131                     applicability,
 132                 )
 133             }
 134         }
 135     }
 136
 137     fn moves_by_default(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 138         let expr_ty = cx.tables().expr_ty(expression);
 139
 140         !expr_ty.is_copy_modulo_regions(cx.tcx.at(expression.span), cx.param_env)
 141     }
 142
 143     fn is_option(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 144         let expr_ty = cx.tables().expr_ty(expression);
 145
 146         is_type_diagnostic_item(cx, expr_ty, sym!(option_type))
 147     }
 148
 149     fn expression_returns_none(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 150         match expression.kind {
 151             ExprKind::Block(ref block, _) => {
 152                 if let Some(return_expression) = Self::return_expression(block) {
 153                     return Self::expression_returns_none(cx, &return_expression);
 154                 }
 155
 156                 false
 157             },
 158             ExprKind::Ret(Some(ref expr)) => Self::expression_returns_none(cx, expr),
 159             ExprKind::Path(ref qp) => {
 160                 if let Res::Def(DefKind::Ctor(def::CtorOf::Variant, def::CtorKind::Const), def_id) =
 161                     cx.qpath_res(qp, expression.hir_id)
 162                 {
 163                     return match_def_path(cx, def_id, &paths::OPTION_NONE);
 164                 }
 165
 166                 false
 167             },
 168             _ => false,
 169         }
 170     }
 171
 172     fn return_expression<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
 173         // Check if last expression is a return statement. Then, return the expression
 174         if_chain! {
 175             if block.stmts.len() == 1;
 176             if let Some(expr) = block.stmts.iter().last();
 177             if let StmtKind::Semi(ref expr) = expr.kind;
 178             if let ExprKind::Ret(ret_expr) = expr.kind;
 179             if let Some(ret_expr) = ret_expr;
 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 }