src/tools/clippy/clippy_lints/src/question_mark.rs

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