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