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, path_to_local_id};
   8 use if_chain::if_chain;
   9 use rustc_errors::Applicability;
  10 use rustc_hir::LangItem::{OptionNone, OptionSome, ResultOk};
  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     /// ```ignore
  52     /// if result.is_err() {
  53     ///     return result;
  54     /// }
  55     /// ```
  56     ///
  57     /// If it matches, it will suggest to use the question mark operator instead
  58     fn check_is_none_or_err_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>) {
  59         if_chain! {
  60             if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
  61             if let ExprKind::MethodCall(segment, _, args, _) = &cond.kind;
  62             if let Some(subject) = args.get(0);
  63             if (Self::is_option(cx, subject)
  64                 && Self::expression_returns_none(cx, then)
  65                 && segment.ident.name == sym!(is_none))
  66                 ||
  67                 (Self::is_result(cx, subject)
  68                 && Self::expression_returns_unmodified_err(cx, then, subject)
  69                 && segment.ident.name == sym!(is_err));
  70             then {
  71                 let mut applicability = Applicability::MachineApplicable;
  72                 let receiver_str = &Sugg::hir_with_applicability(cx, subject, "..", &mut applicability);
  73                 let mut replacement: Option<String> = None;
  74                 if let Some(else_inner) = r#else {
  75                     if_chain! {
  76                         if let ExprKind::Block(block, None) = &else_inner.kind;
  77                         if block.stmts.is_empty();
  78                         if let Some(block_expr) = &block.expr;
  79                         if eq_expr_value(cx, subject, block_expr);
  80                         then {
  81                             replacement = Some(format!("Some({}?)", receiver_str));
  82                         }
  83                     }
  84                 } else if Self::moves_by_default(cx, subject)
  85                     && !matches!(subject.kind, ExprKind::Call(..) | ExprKind::MethodCall(..))
  86                 {
  87                     replacement = Some(format!("{}.as_ref()?;", receiver_str));
  88                 } else {
  89                     replacement = Some(format!("{}?;", receiver_str));
  90                 }
  91
  92                 if let Some(replacement_str) = replacement {
  93                     span_lint_and_sugg(
  94                         cx,
  95                         QUESTION_MARK,
  96                         expr.span,
  97                         "this block may be rewritten with the `?` operator",
  98                         "replace it with",
  99                         replacement_str,
 100                         applicability,
 101                     );
 102                 }
 103             }
 104         }
 105     }
 106
 107     fn check_if_let_some_or_err_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>) {
 108         if_chain! {
 109             if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: Some(if_else) })
 110                 = higher::IfLet::hir(cx, expr);
 111             if let PatKind::TupleStruct(ref path1, fields, None) = let_pat.kind;
 112             if (Self::is_option(cx, let_expr)
 113                 && Self::expression_returns_none(cx, if_else)
 114                 && is_lang_ctor(cx, path1, OptionSome))
 115                 ||
 116                 (Self::is_result(cx, let_expr)
 117                  && Self::expression_returns_unmodified_err(cx, if_else, let_expr)
 118                  && is_lang_ctor(cx, path1, ResultOk));
 119
 120             if let PatKind::Binding(annot, bind_id, _, _) = fields[0].kind;
 121             let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
 122             if let ExprKind::Block(block, None) = if_then.kind;
 123             if block.stmts.is_empty();
 124             if let Some(trailing_expr) = &block.expr;
 125             if path_to_local_id(trailing_expr, bind_id);
 126             then {
 127                 let mut applicability = Applicability::MachineApplicable;
 128                 let receiver_str = snippet_with_applicability(cx, let_expr.span, "..", &mut applicability);
 129                 let replacement = format!("{}{}?", receiver_str, if by_ref { ".as_ref()" } else { "" },);
 130
 131                 span_lint_and_sugg(
 132                     cx,
 133                     QUESTION_MARK,
 134                     expr.span,
 135                     "this if-let-else may be rewritten with the `?` operator",
 136                     "replace it with",
 137                     replacement,
 138                     applicability,
 139                 );
 140             }
 141         }
 142     }
 143
 144     fn moves_by_default(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 145         let expr_ty = cx.typeck_results().expr_ty(expression);
 146
 147         !expr_ty.is_copy_modulo_regions(cx.tcx.at(expression.span), cx.param_env)
 148     }
 149
 150     fn is_option(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 151         let expr_ty = cx.typeck_results().expr_ty(expression);
 152
 153         is_type_diagnostic_item(cx, expr_ty, sym::Option)
 154     }
 155
 156     fn is_result(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 157         let expr_ty = cx.typeck_results().expr_ty(expression);
 158
 159         is_type_diagnostic_item(cx, expr_ty, sym::Result)
 160     }
 161
 162     fn expression_returns_none(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 163         match expression.kind {
 164             ExprKind::Block(block, _) => {
 165                 if let Some(return_expression) = Self::return_expression(block) {
 166                     return Self::expression_returns_none(cx, return_expression);
 167                 }
 168
 169                 false
 170             },
 171             ExprKind::Ret(Some(expr)) => Self::expression_returns_none(cx, expr),
 172             ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
 173             _ => false,
 174         }
 175     }
 176
 177     fn expression_returns_unmodified_err(
 178         cx: &LateContext<'_>,
 179         expression: &Expr<'_>,
 180         origin_hir_id: &Expr<'_>,
 181     ) -> bool {
 182         match expression.kind {
 183             ExprKind::Block(block, _) => {
 184                 if let Some(return_expression) = Self::return_expression(block) {
 185                     return Self::expression_returns_unmodified_err(cx, return_expression, origin_hir_id);
 186                 }
 187
 188                 false
 189             },
 190             ExprKind::Ret(Some(expr)) | ExprKind::Call(expr, _) => {
 191                 Self::expression_returns_unmodified_err(cx, expr, origin_hir_id)
 192             },
 193             ExprKind::Path(_) => path_to_local(expression) == path_to_local(origin_hir_id),
 194             _ => false,
 195         }
 196     }
 197
 198     fn return_expression<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
 199         // Check if last expression is a return statement. Then, return the expression
 200         if_chain! {
 201             if block.stmts.len() == 1;
 202             if let Some(expr) = block.stmts.iter().last();
 203             if let StmtKind::Semi(expr) = expr.kind;
 204             if let ExprKind::Ret(Some(ret_expr)) = expr.kind;
 205
 206             then {
 207                 return Some(ret_expr);
 208             }
 209         }
 210
 211         // Check for `return` without a semicolon.
 212         if_chain! {
 213             if block.stmts.is_empty();
 214             if let Some(ExprKind::Ret(Some(ret_expr))) = block.expr.as_ref().map(|e| &e.kind);
 215             then {
 216                 return Some(ret_expr);
 217             }
 218         }
 219
 220         None
 221     }
 222 }
 223
 224 impl<'tcx> LateLintPass<'tcx> for QuestionMark {
 225     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 226         Self::check_is_none_or_err_and_early_return(cx, expr);
 227         Self::check_if_let_some_or_err_and_early_return(cx, expr);
 228     }
 229 }