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, in_constant, is_else_clause, is_res_lang_ctor, path_to_local, path_to_local_id,
   7     peel_blocks, peel_blocks_with_stmt,
   8 };
   9 use if_chain::if_chain;
  10 use rustc_errors::Applicability;
  11 use rustc_hir::def::Res;
  12 use rustc_hir::LangItem::{OptionNone, OptionSome, ResultErr, ResultOk};
  13 use rustc_hir::{BindingAnnotation, ByRef, Expr, ExprKind, Node, PatKind, PathSegment, QPath};
  14 use rustc_lint::{LateContext, LateLintPass};
  15 use rustc_middle::ty::Ty;
  16 use rustc_session::{declare_lint_pass, declare_tool_lint};
  17 use rustc_span::{sym, symbol::Symbol};
  18
  19 declare_clippy_lint! {
  20     /// ### What it does
  21     /// Checks for expressions that could be replaced by the question mark operator.
  22     ///
  23     /// ### Why is this bad?
  24     /// Question mark usage is more idiomatic.
  25     ///
  26     /// ### Example
  27     /// ```ignore
  28     /// if option.is_none() {
  29     ///     return None;
  30     /// }
  31     /// ```
  32     ///
  33     /// Could be written:
  34     ///
  35     /// ```ignore
  36     /// option?;
  37     /// ```
  38     #[clippy::version = "pre 1.29.0"]
  39     pub QUESTION_MARK,
  40     style,
  41     "checks for expressions that could be replaced by the question mark operator"
  42 }
  43
  44 declare_lint_pass!(QuestionMark => [QUESTION_MARK]);
  45
  46 enum IfBlockType<'hir> {
  47     /// An `if x.is_xxx() { a } else { b } ` expression.
  48     ///
  49     /// Contains: caller (x), caller_type, call_sym (is_xxx), if_then (a), if_else (b)
  50     IfIs(
  51         &'hir Expr<'hir>,
  52         Ty<'hir>,
  53         Symbol,
  54         &'hir Expr<'hir>,
  55         Option<&'hir Expr<'hir>>,
  56     ),
  57     /// An `if let Xxx(a) = b { c } else { d }` expression.
  58     ///
  59     /// Contains: let_pat_qpath (Xxx), let_pat_type, let_pat_sym (a), let_expr (b), if_then (c),
  60     /// if_else (d)
  61     IfLet(
  62         Res,
  63         Ty<'hir>,
  64         Symbol,
  65         &'hir Expr<'hir>,
  66         &'hir Expr<'hir>,
  67         Option<&'hir Expr<'hir>>,
  68     ),
  69 }
  70
  71 /// Checks if the given expression on the given context matches the following structure:
  72 ///
  73 /// ```ignore
  74 /// if option.is_none() {
  75 ///    return None;
  76 /// }
  77 /// ```
  78 ///
  79 /// ```ignore
  80 /// if result.is_err() {
  81 ///     return result;
  82 /// }
  83 /// ```
  84 ///
  85 /// If it matches, it will suggest to use the question mark operator instead
  86 fn check_is_none_or_err_and_early_return<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
  87     if_chain! {
  88         if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
  89         if !is_else_clause(cx.tcx, expr);
  90         if let ExprKind::MethodCall(segment, caller, ..) = &cond.kind;
  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, 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, [field], ddpos) = let_pat.kind;
 127         if ddpos.as_opt_usize().is_none();
 128         if let PatKind::Binding(BindingAnnotation(by_ref, _), bind_id, ident, None) = field.kind;
 129         let caller_ty = cx.typeck_results().expr_ty(let_expr);
 130         let if_block = IfBlockType::IfLet(
 131             cx.qpath_res(path1, let_pat.hir_id),
 132             caller_ty,
 133             ident.name,
 134             let_expr,
 135             if_then,
 136             if_else
 137         );
 138         if (is_early_return(sym::Option, cx, &if_block) && path_to_local_id(peel_blocks(if_then), bind_id))
 139             || is_early_return(sym::Result, cx, &if_block);
 140         if if_else.map(|e| eq_expr_value(cx, let_expr, peel_blocks(e))).filter(|e| *e).is_none();
 141         then {
 142             let mut applicability = Applicability::MachineApplicable;
 143             let receiver_str = snippet_with_applicability(cx, let_expr.span, "..", &mut applicability);
 144             let requires_semi = matches!(get_parent_node(cx.tcx, expr.hir_id), Some(Node::Stmt(_)));
 145             let sugg = format!(
 146                 "{receiver_str}{}?{}",
 147                 if by_ref == ByRef::Yes { ".as_ref()" } else { "" },
 148                 if requires_semi { ";" } else { "" }
 149             );
 150             span_lint_and_sugg(
 151                 cx,
 152                 QUESTION_MARK,
 153                 expr.span,
 154                 "this block may be rewritten with the `?` operator",
 155                 "replace it with",
 156                 sugg,
 157                 applicability,
 158             );
 159         }
 160     }
 161 }
 162
 163 fn is_early_return(smbl: Symbol, cx: &LateContext<'_>, if_block: &IfBlockType<'_>) -> bool {
 164     match *if_block {
 165         IfBlockType::IfIs(caller, caller_ty, call_sym, if_then, _) => {
 166             // If the block could be identified as `if x.is_none()/is_err()`,
 167             // we then only need to check the if_then return to see if it is none/err.
 168             is_type_diagnostic_item(cx, caller_ty, smbl)
 169                 && expr_return_none_or_err(smbl, cx, if_then, caller, None)
 170                 && match smbl {
 171                     sym::Option => call_sym == sym!(is_none),
 172                     sym::Result => call_sym == sym!(is_err),
 173                     _ => false,
 174                 }
 175         },
 176         IfBlockType::IfLet(res, let_expr_ty, let_pat_sym, let_expr, if_then, if_else) => {
 177             is_type_diagnostic_item(cx, let_expr_ty, smbl)
 178                 && match smbl {
 179                     sym::Option => {
 180                         // We only need to check `if let Some(x) = option` not `if let None = option`,
 181                         // because the later one will be suggested as `if option.is_none()` thus causing conflict.
 182                         is_res_lang_ctor(cx, res, OptionSome)
 183                             && if_else.is_some()
 184                             && expr_return_none_or_err(smbl, cx, if_else.unwrap(), let_expr, None)
 185                     },
 186                     sym::Result => {
 187                         (is_res_lang_ctor(cx, res, ResultOk)
 188                             && if_else.is_some()
 189                             && expr_return_none_or_err(smbl, cx, if_else.unwrap(), let_expr, Some(let_pat_sym)))
 190                             || is_res_lang_ctor(cx, res, ResultErr)
 191                                 && expr_return_none_or_err(smbl, cx, if_then, let_expr, Some(let_pat_sym))
 192                     },
 193                     _ => false,
 194                 }
 195         },
 196     }
 197 }
 198
 199 fn expr_return_none_or_err(
 200     smbl: Symbol,
 201     cx: &LateContext<'_>,
 202     expr: &Expr<'_>,
 203     cond_expr: &Expr<'_>,
 204     err_sym: Option<Symbol>,
 205 ) -> bool {
 206     match peel_blocks_with_stmt(expr).kind {
 207         ExprKind::Ret(Some(ret_expr)) => expr_return_none_or_err(smbl, cx, ret_expr, cond_expr, err_sym),
 208         ExprKind::Path(ref qpath) => match smbl {
 209             sym::Option => is_res_lang_ctor(cx, cx.qpath_res(qpath, expr.hir_id), OptionNone),
 210             sym::Result => path_to_local(expr).is_some() && path_to_local(expr) == path_to_local(cond_expr),
 211             _ => false,
 212         },
 213         ExprKind::Call(call_expr, args_expr) => {
 214             if_chain! {
 215                 if smbl == sym::Result;
 216                 if let ExprKind::Path(QPath::Resolved(_, path)) = &call_expr.kind;
 217                 if let Some(segment) = path.segments.first();
 218                 if let Some(err_sym) = err_sym;
 219                 if let Some(arg) = args_expr.first();
 220                 if let ExprKind::Path(QPath::Resolved(_, arg_path)) = &arg.kind;
 221                 if let Some(PathSegment { ident, .. }) = arg_path.segments.first();
 222                 then {
 223                     return segment.ident.name == sym::Err && err_sym == ident.name;
 224                 }
 225             }
 226             false
 227         },
 228         _ => false,
 229     }
 230 }
 231
 232 impl<'tcx> LateLintPass<'tcx> for QuestionMark {
 233     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 234         if !in_constant(cx, expr.hir_id) {
 235             check_is_none_or_err_and_early_return(cx, expr);
 236             check_if_let_some_or_err_and_early_return(cx, expr);
 237         }
 238     }
 239 }