src/tools/clippy/clippy_lints/src/option_if_let_else.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::sugg::Sugg;
   3 use clippy_utils::{
   4     can_move_expr_to_closure, eager_or_lazy, higher, in_constant, is_else_clause, is_lang_ctor, peel_blocks,
   5     peel_hir_expr_while, CaptureKind,
   6 };
   7 use if_chain::if_chain;
   8 use rustc_errors::Applicability;
   9 use rustc_hir::LangItem::{OptionNone, OptionSome, ResultErr, ResultOk};
  10 use rustc_hir::{
  11     def::Res, Arm, BindingAnnotation, Expr, ExprKind, MatchSource, Mutability, Pat, PatKind, Path, QPath, UnOp,
  12 };
  13 use rustc_lint::{LateContext, LateLintPass};
  14 use rustc_session::{declare_lint_pass, declare_tool_lint};
  15
  16 declare_clippy_lint! {
  17     /// ### What it does
  18     /// Lints usage of `if let Some(v) = ... { y } else { x }` and
  19     /// `match .. { Some(v) => y, None/_ => x }` which are more
  20     /// idiomatically done with `Option::map_or` (if the else bit is a pure
  21     /// expression) or `Option::map_or_else` (if the else bit is an impure
  22     /// expression).
  23     ///
  24     /// ### Why is this bad?
  25     /// Using the dedicated functions of the `Option` type is clearer and
  26     /// more concise than an `if let` expression.
  27     ///
  28     /// ### Known problems
  29     /// This lint uses a deliberately conservative metric for checking
  30     /// if the inside of either body contains breaks or continues which will
  31     /// cause it to not suggest a fix if either block contains a loop with
  32     /// continues or breaks contained within the loop.
  33     ///
  34     /// ### Example
  35     /// ```rust
  36     /// # let optional: Option<u32> = Some(0);
  37     /// # fn do_complicated_function() -> u32 { 5 };
  38     /// let _ = if let Some(foo) = optional {
  39     ///     foo
  40     /// } else {
  41     ///     5
  42     /// };
  43     /// let _ = match optional {
  44     ///     Some(val) => val + 1,
  45     ///     None => 5
  46     /// };
  47     /// let _ = if let Some(foo) = optional {
  48     ///     foo
  49     /// } else {
  50     ///     let y = do_complicated_function();
  51     ///     y*y
  52     /// };
  53     /// ```
  54     ///
  55     /// should be
  56     ///
  57     /// ```rust
  58     /// # let optional: Option<u32> = Some(0);
  59     /// # fn do_complicated_function() -> u32 { 5 };
  60     /// let _ = optional.map_or(5, |foo| foo);
  61     /// let _ = optional.map_or(5, |val| val + 1);
  62     /// let _ = optional.map_or_else(||{
  63     ///     let y = do_complicated_function();
  64     ///     y*y
  65     /// }, |foo| foo);
  66     /// ```
  67     // FIXME: Before moving this lint out of nursery, the lint name needs to be updated. It now also
  68     // covers matches and `Result`.
  69     #[clippy::version = "1.47.0"]
  70     pub OPTION_IF_LET_ELSE,
  71     nursery,
  72     "reimplementation of Option::map_or"
  73 }
  74
  75 declare_lint_pass!(OptionIfLetElse => [OPTION_IF_LET_ELSE]);
  76
  77 /// A struct containing information about occurrences of construct that this lint detects
  78 ///
  79 /// Such as:
  80 ///
  81 /// ```ignore
  82 /// if let Some(..) = {..} else {..}
  83 /// ```
  84 /// or
  85 /// ```ignore
  86 /// match x {
  87 ///     Some(..) => {..},
  88 ///     None/_ => {..}
  89 /// }
  90 /// ```
  91 struct OptionOccurence {
  92     option: String,
  93     method_sugg: String,
  94     some_expr: String,
  95     none_expr: String,
  96 }
  97
  98 fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String {
  99     format!(
 100         "{}{}",
 101         Sugg::hir_with_macro_callsite(cx, cond_expr, "..").maybe_par(),
 102         if as_mut {
 103             ".as_mut()"
 104         } else if as_ref {
 105             ".as_ref()"
 106         } else {
 107             ""
 108         }
 109     )
 110 }
 111
 112 fn try_get_option_occurence<'tcx>(
 113     cx: &LateContext<'tcx>,
 114     pat: &Pat<'tcx>,
 115     expr: &Expr<'_>,
 116     if_then: &'tcx Expr<'_>,
 117     if_else: &'tcx Expr<'_>,
 118 ) -> Option<OptionOccurence> {
 119     let cond_expr = match expr.kind {
 120         ExprKind::Unary(UnOp::Deref, inner_expr) | ExprKind::AddrOf(_, _, inner_expr) => inner_expr,
 121         _ => expr,
 122     };
 123     let inner_pat = try_get_inner_pat(cx, pat)?;
 124     if_chain! {
 125         if let PatKind::Binding(bind_annotation, _, id, None) = inner_pat.kind;
 126         if let Some(some_captures) = can_move_expr_to_closure(cx, if_then);
 127         if let Some(none_captures) = can_move_expr_to_closure(cx, if_else);
 128         if some_captures
 129             .iter()
 130             .filter_map(|(id, &c)| none_captures.get(id).map(|&c2| (c, c2)))
 131             .all(|(x, y)| x.is_imm_ref() && y.is_imm_ref());
 132         then {
 133             let capture_mut = if bind_annotation == BindingAnnotation::MUT { "mut " } else { "" };
 134             let some_body = peel_blocks(if_then);
 135             let none_body = peel_blocks(if_else);
 136             let method_sugg = if eager_or_lazy::switch_to_eager_eval(cx, none_body) { "map_or" } else { "map_or_else" };
 137             let capture_name = id.name.to_ident_string();
 138             let (as_ref, as_mut) = match &expr.kind {
 139                 ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
 140                 ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
 141                 _ => (bind_annotation == BindingAnnotation::REF, bind_annotation == BindingAnnotation::REF_MUT),
 142             };
 143
 144             // Check if captures the closure will need conflict with borrows made in the scrutinee.
 145             // TODO: check all the references made in the scrutinee expression. This will require interacting
 146             // with the borrow checker. Currently only `<local>[.<field>]*` is checked for.
 147             if as_ref || as_mut {
 148                 let e = peel_hir_expr_while(cond_expr, |e| match e.kind {
 149                     ExprKind::Field(e, _) | ExprKind::AddrOf(_, _, e) => Some(e),
 150                     _ => None,
 151                 });
 152                 if let ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(local_id), .. })) = e.kind {
 153                     match some_captures.get(local_id)
 154                         .or_else(|| (method_sugg == "map_or_else").then_some(()).and_then(|_| none_captures.get(local_id)))
 155                     {
 156                         Some(CaptureKind::Value | CaptureKind::Ref(Mutability::Mut)) => return None,
 157                         Some(CaptureKind::Ref(Mutability::Not)) if as_mut => return None,
 158                         Some(CaptureKind::Ref(Mutability::Not)) | None => (),
 159                     }
 160                 }
 161             }
 162
 163             return Some(OptionOccurence {
 164                 option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
 165                 method_sugg: method_sugg.to_string(),
 166                 some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir_with_macro_callsite(cx, some_body, "..")),
 167                 none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir_with_macro_callsite(cx, none_body, "..")),
 168             });
 169         }
 170     }
 171
 172     None
 173 }
 174
 175 fn try_get_inner_pat<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'tcx>) -> Option<&'tcx Pat<'tcx>> {
 176     if let PatKind::TupleStruct(ref qpath, [inner_pat], ..) = pat.kind {
 177         if is_lang_ctor(cx, qpath, OptionSome) || is_lang_ctor(cx, qpath, ResultOk) {
 178             return Some(inner_pat);
 179         }
 180     }
 181     None
 182 }
 183
 184 /// If this expression is the option if let/else construct we're detecting, then
 185 /// this function returns an `OptionOccurence` struct with details if
 186 /// this construct is found, or None if this construct is not found.
 187 fn detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionOccurence> {
 188     if let Some(higher::IfLet {
 189         let_pat,
 190         let_expr,
 191         if_then,
 192         if_else: Some(if_else),
 193     }) = higher::IfLet::hir(cx, expr)
 194     {
 195         if !is_else_clause(cx.tcx, expr) {
 196             return try_get_option_occurence(cx, let_pat, let_expr, if_then, if_else);
 197         }
 198     }
 199     None
 200 }
 201
 202 fn detect_option_match<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionOccurence> {
 203     if let ExprKind::Match(ex, arms, MatchSource::Normal) = expr.kind {
 204         if let Some((let_pat, if_then, if_else)) = try_convert_match(cx, arms) {
 205             return try_get_option_occurence(cx, let_pat, ex, if_then, if_else);
 206         }
 207     }
 208     None
 209 }
 210
 211 fn try_convert_match<'tcx>(
 212     cx: &LateContext<'tcx>,
 213     arms: &[Arm<'tcx>],
 214 ) -> Option<(&'tcx Pat<'tcx>, &'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
 215     if arms.len() == 2 {
 216         return if is_none_or_err_arm(cx, &arms[1]) {
 217             Some((arms[0].pat, arms[0].body, arms[1].body))
 218         } else if is_none_or_err_arm(cx, &arms[0]) {
 219             Some((arms[1].pat, arms[1].body, arms[0].body))
 220         } else {
 221             None
 222         };
 223     }
 224     None
 225 }
 226
 227 fn is_none_or_err_arm(cx: &LateContext<'_>, arm: &Arm<'_>) -> bool {
 228     match arm.pat.kind {
 229         PatKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
 230         PatKind::TupleStruct(ref qpath, [first_pat], _) => {
 231             is_lang_ctor(cx, qpath, ResultErr) && matches!(first_pat.kind, PatKind::Wild)
 232         },
 233         PatKind::Wild => true,
 234         _ => false,
 235     }
 236 }
 237
 238 impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
 239     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
 240         // Don't lint macros and constants
 241         if expr.span.from_expansion() || in_constant(cx, expr.hir_id) {
 242             return;
 243         }
 244
 245         let detection = detect_option_if_let_else(cx, expr).or_else(|| detect_option_match(cx, expr));
 246         if let Some(det) = detection {
 247             span_lint_and_sugg(
 248                 cx,
 249                 OPTION_IF_LET_ELSE,
 250                 expr.span,
 251                 format!("use Option::{} instead of an if let/else", det.method_sugg).as_str(),
 252                 "try",
 253                 format!(
 254                     "{}.{}({}, {})",
 255                     det.option, det.method_sugg, det.none_expr, det.some_expr
 256                 ),
 257                 Applicability::MaybeIncorrect,
 258             );
 259         }
 260     }
 261 }