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