clippy_lints/src/question_mark.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::higher;
   3 use clippy_utils::source::snippet_with_applicability;
   4 use clippy_utils::ty::is_type_diagnostic_item;
   5 use clippy_utils::{
   6     eq_expr_value, get_parent_node, is_else_clause, is_lang_ctor, path_to_local, path_to_local_id, peel_blocks,
   7     peel_blocks_with_stmt,
   8 };
   9 use if_chain::if_chain;
  10 use rustc_errors::Applicability;
  11 use rustc_hir::LangItem::{OptionNone, OptionSome, ResultErr, ResultOk};
  12 use rustc_hir::{BindingAnnotation, Expr, ExprKind, Node, PatKind, PathSegment, QPath};
  13 use rustc_lint::{LateContext, LateLintPass};
  14 use rustc_middle::ty::Ty;
  15 use rustc_session::{declare_lint_pass, declare_tool_lint};
  16 use rustc_span::{sym, symbol::Symbol};
  17
  18 declare_clippy_lint! {
  19     /// ### What it does
  20     /// Checks for expressions that could be replaced by the question mark operator.
  21     ///
  22     /// ### Why is this bad?
  23     /// Question mark usage is more idiomatic.
  24     ///
  25     /// ### Example
  26     /// ```ignore
  27     /// if option.is_none() {
  28     ///     return None;
  29     /// }
  30     /// ```
  31     ///
  32     /// Could be written:
  33     ///
  34     /// ```ignore
  35     /// option?;
  36     /// ```
  37     #[clippy::version = "pre 1.29.0"]
  38     pub QUESTION_MARK,
  39     style,
  40     "checks for expressions that could be replaced by the question mark operator"
  41 }
  42
  43 declare_lint_pass!(QuestionMark => [QUESTION_MARK]);
  44
  45 enum IfBlockType<'hir> {
  46     /// An `if x.is_xxx() { a } else { b } ` expression.
  47     ///
  48     /// Contains: caller (x), caller_type, call_sym (is_xxx), if_then (a), if_else (b)
  49     IfIs(
  50         &'hir Expr<'hir>,
  51         Ty<'hir>,
  52         Symbol,
  53         &'hir Expr<'hir>,
  54         Option<&'hir Expr<'hir>>,
  55     ),
  56     /// An `if let Xxx(a) = b { c } else { d }` expression.
  57     ///
  58     /// Contains: let_pat_qpath (Xxx), let_pat_type, let_pat_sym (a), let_expr (b), if_then (c),
  59     /// if_else (d)
  60     IfLet(
  61         &'hir QPath<'hir>,
  62         Ty<'hir>,
  63         Symbol,
  64         &'hir Expr<'hir>,
  65         &'hir Expr<'hir>,
  66         Option<&'hir Expr<'hir>>,
  67     ),
  68 }
  69
  70 /// Checks if the given expression on the given context matches the following structure:
  71 ///
  72 /// ```ignore
  73 /// if option.is_none() {
  74 ///    return None;
  75 /// }
  76 /// ```
  77 ///
  78 /// ```ignore
  79 /// if result.is_err() {
  80 ///     return result;
  81 /// }
  82 /// ```
  83 ///
  84 /// If it matches, it will suggest to use the question mark operator instead
  85 fn check_is_none_or_err_and_early_return<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
  86     if_chain! {
  87         if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
  88         if !is_else_clause(cx.tcx, expr);
  89         if let ExprKind::MethodCall(segment, args, _) = &cond.kind;
  90         if let Some(caller) = args.get(0);
  91         let caller_ty = cx.typeck_results().expr_ty(caller);
  92         let if_block = IfBlockType::IfIs(caller, caller_ty, segment.ident.name, then, r#else);
  93         if is_early_return(sym::Option, cx, &if_block) || is_early_return(sym::Result, cx, &if_block);
  94         then {
  95             let mut applicability = Applicability::MachineApplicable;
  96             let receiver_str = snippet_with_applicability(cx, caller.span, "..", &mut applicability);
  97             let by_ref = !caller_ty.is_copy_modulo_regions(cx.tcx.at(caller.span), cx.param_env) &&
  98                 !matches!(caller.kind, ExprKind::Call(..) | ExprKind::MethodCall(..));
  99             let sugg = if let Some(else_inner) = r#else {
 100                 if eq_expr_value(cx, caller, peel_blocks(else_inner)) {
 101                     format!("Some({}?)", receiver_str)
 102                 } else {
 103                     return;
 104                 }
 105             } else {
 106                 format!("{}{}?;", receiver_str, if by_ref { ".as_ref()" } else { "" })
 107             };
 108
 109             span_lint_and_sugg(
 110                 cx,
 111                 QUESTION_MARK,
 112                 expr.span,
 113                 "this block may be rewritten with the `?` operator",
 114                 "replace it with",
 115                 sugg,
 116                 applicability,
 117             );
 118         }
 119     }
 120 }
 121
 122 fn check_if_let_some_or_err_and_early_return<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
 123     if_chain! {
 124         if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else }) = higher::IfLet::hir(cx, expr);
 125         if !is_else_clause(cx.tcx, expr);
 126         if let PatKind::TupleStruct(ref path1, fields, None) = let_pat.kind;
 127         if let PatKind::Binding(annot, bind_id, ident, _) = fields[0].kind;
 128         let caller_ty = cx.typeck_results().expr_ty(let_expr);
 129         let if_block = IfBlockType::IfLet(path1, caller_ty, ident.name, let_expr, if_then, if_else);
 130         if (is_early_return(sym::Option, cx, &if_block) && path_to_local_id(peel_blocks(if_then), bind_id))
 131             || is_early_return(sym::Result, cx, &if_block);
 132         if if_else.map(|e| eq_expr_value(cx, let_expr, peel_blocks(e))).filter(|e| *e).is_none();
 133         then {
 134             let mut applicability = Applicability::MachineApplicable;
 135             let receiver_str = snippet_with_applicability(cx, let_expr.span, "..", &mut applicability);
 136             let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
 137             let requires_semi = matches!(get_parent_node(cx.tcx, expr.hir_id), Some(Node::Stmt(_)));
 138             let sugg = format!(
 139                 "{}{}?{}",
 140                 receiver_str,
 141                 if by_ref { ".as_ref()" } else { "" },
 142                 if requires_semi { ";" } else { "" }
 143             );
 144             span_lint_and_sugg(
 145                 cx,
 146                 QUESTION_MARK,
 147                 expr.span,
 148                 "this block may be rewritten with the `?` operator",
 149                 "replace it with",
 150                 sugg,
 151                 applicability,
 152             );
 153         }
 154     }
 155 }
 156
 157 fn is_early_return(smbl: Symbol, cx: &LateContext<'_>, if_block: &IfBlockType<'_>) -> bool {
 158     match *if_block {
 159         IfBlockType::IfIs(caller, caller_ty, call_sym, if_then, _) => {
 160             // If the block could be identified as `if x.is_none()/is_err()`,
 161             // we then only need to check the if_then return to see if it is none/err.
 162             is_type_diagnostic_item(cx, caller_ty, smbl)
 163                 && expr_return_none_or_err(smbl, cx, if_then, caller, None)
 164                 && match smbl {
 165                     sym::Option => call_sym == sym!(is_none),
 166                     sym::Result => call_sym == sym!(is_err),
 167                     _ => false,
 168                 }
 169         },
 170         IfBlockType::IfLet(qpath, let_expr_ty, let_pat_sym, let_expr, if_then, if_else) => {
 171             is_type_diagnostic_item(cx, let_expr_ty, smbl)
 172                 && match smbl {
 173                     sym::Option => {
 174                         // We only need to check `if let Some(x) = option` not `if let None = option`,
 175                         // because the later one will be suggested as `if option.is_none()` thus causing conflict.
 176                         is_lang_ctor(cx, qpath, OptionSome)
 177                             && if_else.is_some()
 178                             && expr_return_none_or_err(smbl, cx, if_else.unwrap(), let_expr, None)
 179                     },
 180                     sym::Result => {
 181                         (is_lang_ctor(cx, qpath, ResultOk)
 182                             && if_else.is_some()
 183                             && expr_return_none_or_err(smbl, cx, if_else.unwrap(), let_expr, Some(let_pat_sym)))
 184                             || is_lang_ctor(cx, qpath, ResultErr)
 185                                 && expr_return_none_or_err(smbl, cx, if_then, let_expr, Some(let_pat_sym))
 186                     },
 187                     _ => false,
 188                 }
 189         },
 190     }
 191 }
 192
 193 fn expr_return_none_or_err(
 194     smbl: Symbol,
 195     cx: &LateContext<'_>,
 196     expr: &Expr<'_>,
 197     cond_expr: &Expr<'_>,
 198     err_sym: Option<Symbol>,
 199 ) -> bool {
 200     match peel_blocks_with_stmt(expr).kind {
 201         ExprKind::Ret(Some(ret_expr)) => expr_return_none_or_err(smbl, cx, ret_expr, cond_expr, err_sym),
 202         ExprKind::Path(ref qpath) => match smbl {
 203             sym::Option => is_lang_ctor(cx, qpath, OptionNone),
 204             sym::Result => path_to_local(expr).is_some() && path_to_local(expr) == path_to_local(cond_expr),
 205             _ => false,
 206         },
 207         ExprKind::Call(call_expr, args_expr) => {
 208             if_chain! {
 209                 if smbl == sym::Result;
 210                 if let ExprKind::Path(QPath::Resolved(_, path)) = &call_expr.kind;
 211                 if let Some(segment) = path.segments.first();
 212                 if let Some(err_sym) = err_sym;
 213                 if let Some(arg) = args_expr.first();
 214                 if let ExprKind::Path(QPath::Resolved(_, arg_path)) = &arg.kind;
 215                 if let Some(PathSegment { ident, .. }) = arg_path.segments.first();
 216                 then {
 217                     return segment.ident.name == sym::Err && err_sym == ident.name;
 218                 }
 219             }
 220             false
 221         },
 222         _ => false,
 223     }
 224 }
 225
 226 impl<'tcx> LateLintPass<'tcx> for QuestionMark {
 227     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 228         check_is_none_or_err_and_early_return(cx, expr);
 229         check_if_let_some_or_err_and_early_return(cx, expr);
 230     }
 231 }