clippy_lints/src/question_mark.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::is_lang_ctor;
   3 use clippy_utils::source::snippet_with_applicability;
   4 use clippy_utils::sugg::Sugg;
   5 use clippy_utils::ty::is_type_diagnostic_item;
   6 use clippy_utils::{eq_expr_value, path_to_local_id};
   7 use if_chain::if_chain;
   8 use rustc_errors::Applicability;
   9 use rustc_hir::LangItem::{OptionNone, OptionSome};
  10 use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, MatchSource, PatKind, StmtKind};
  11 use rustc_lint::{LateContext, LateLintPass};
  12 use rustc_session::{declare_lint_pass, declare_tool_lint};
  13 use rustc_span::sym;
  14
  15 declare_clippy_lint! {
  16     /// ### What it does
  17     /// Checks for expressions that could be replaced by the question mark operator.
  18     ///
  19     /// ### Why is this bad?
  20     /// Question mark usage is more idiomatic.
  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 ExprKind::If(if_expr, body, else_) = &expr.kind;
  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 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(block, None) = &arms[0].body.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 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.typeck_results().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.typeck_results().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(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(expr)) => Self::expression_returns_none(cx, expr),
 159             ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
 160             _ => false,
 161         }
 162     }
 163
 164     fn return_expression<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
 165         // Check if last expression is a return statement. Then, return the expression
 166         if_chain! {
 167             if block.stmts.len() == 1;
 168             if let Some(expr) = block.stmts.iter().last();
 169             if let StmtKind::Semi(expr) = expr.kind;
 170             if let ExprKind::Ret(Some(ret_expr)) = expr.kind;
 171
 172             then {
 173                 return Some(ret_expr);
 174             }
 175         }
 176
 177         // Check for `return` without a semicolon.
 178         if_chain! {
 179             if block.stmts.is_empty();
 180             if let Some(ExprKind::Ret(Some(ret_expr))) = block.expr.as_ref().map(|e| &e.kind);
 181             then {
 182                 return Some(ret_expr);
 183             }
 184         }
 185
 186         None
 187     }
 188 }
 189
 190 impl<'tcx> LateLintPass<'tcx> for QuestionMark {
 191     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 192         Self::check_is_none_and_early_return_none(cx, expr);
 193         Self::check_if_let_some_and_early_return_none(cx, expr);
 194     }
 195 }