clippy_lints/src/manual_map.rs

   1 use crate::{map_unit_fn::OPTION_MAP_UNIT_FN, matches::MATCH_AS_REF};
   2 use clippy_utils::diagnostics::span_lint_and_sugg;
   3 use clippy_utils::source::{snippet_with_applicability, snippet_with_context};
   4 use clippy_utils::ty::{can_partially_move_ty, is_type_diagnostic_item, peel_mid_ty_refs_is_mutable};
   5 use clippy_utils::{is_allowed, match_def_path, match_var, paths, peel_hir_expr_refs};
   6 use rustc_ast::util::parser::PREC_POSTFIX;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::{
   9     def::Res,
  10     intravisit::{walk_expr, ErasedMap, NestedVisitorMap, Visitor},
  11     Arm, BindingAnnotation, Block, Expr, ExprKind, Mutability, Pat, PatKind, Path, QPath,
  12 };
  13 use rustc_lint::{LateContext, LateLintPass, LintContext};
  14 use rustc_middle::lint::in_external_macro;
  15 use rustc_session::{declare_lint_pass, declare_tool_lint};
  16 use rustc_span::{
  17     symbol::{sym, Ident},
  18     SyntaxContext,
  19 };
  20
  21 declare_clippy_lint! {
  22     /// **What it does:** Checks for usages of `match` which could be implemented using `map`
  23     ///
  24     /// **Why is this bad?** Using the `map` method is clearer and more concise.
  25     ///
  26     /// **Known problems:** None.
  27     ///
  28     /// **Example:**
  29     ///
  30     /// ```rust
  31     /// match Some(0) {
  32     ///     Some(x) => Some(x + 1),
  33     ///     None => None,
  34     /// };
  35     /// ```
  36     /// Use instead:
  37     /// ```rust
  38     /// Some(0).map(|x| x + 1);
  39     /// ```
  40     pub MANUAL_MAP,
  41     style,
  42     "reimplementation of `map`"
  43 }
  44
  45 declare_lint_pass!(ManualMap => [MANUAL_MAP]);
  46
  47 impl LateLintPass<'_> for ManualMap {
  48     #[allow(clippy::too_many_lines)]
  49     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  50         if in_external_macro(cx.sess(), expr.span) {
  51             return;
  52         }
  53
  54         if let ExprKind::Match(scrutinee, [arm1 @ Arm { guard: None, .. }, arm2 @ Arm { guard: None, .. }], _) =
  55             expr.kind
  56         {
  57             let (scrutinee_ty, ty_ref_count, ty_mutability) =
  58                 peel_mid_ty_refs_is_mutable(cx.typeck_results().expr_ty(scrutinee));
  59             if !(is_type_diagnostic_item(cx, scrutinee_ty, sym::option_type)
  60                 && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::option_type))
  61             {
  62                 return;
  63             }
  64
  65             let expr_ctxt = expr.span.ctxt();
  66             let (some_expr, some_pat, pat_ref_count, is_wild_none) = match (
  67                 try_parse_pattern(cx, arm1.pat, expr_ctxt),
  68                 try_parse_pattern(cx, arm2.pat, expr_ctxt),
  69             ) {
  70                 (Some(OptionPat::Wild), Some(OptionPat::Some { pattern, ref_count }))
  71                     if is_none_expr(cx, arm1.body) =>
  72                 {
  73                     (arm2.body, pattern, ref_count, true)
  74                 },
  75                 (Some(OptionPat::None), Some(OptionPat::Some { pattern, ref_count }))
  76                     if is_none_expr(cx, arm1.body) =>
  77                 {
  78                     (arm2.body, pattern, ref_count, false)
  79                 },
  80                 (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::Wild))
  81                     if is_none_expr(cx, arm2.body) =>
  82                 {
  83                     (arm1.body, pattern, ref_count, true)
  84                 },
  85                 (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::None))
  86                     if is_none_expr(cx, arm2.body) =>
  87                 {
  88                     (arm1.body, pattern, ref_count, false)
  89                 },
  90                 _ => return,
  91             };
  92
  93             // Top level or patterns aren't allowed in closures.
  94             if matches!(some_pat.kind, PatKind::Or(_)) {
  95                 return;
  96             }
  97
  98             let some_expr = match get_some_expr(cx, some_expr, expr_ctxt) {
  99                 Some(expr) => expr,
 100                 None => return,
 101             };
 102
 103             if cx.typeck_results().expr_ty(some_expr) == cx.tcx.types.unit
 104                 && !is_allowed(cx, OPTION_MAP_UNIT_FN, expr.hir_id)
 105             {
 106                 return;
 107             }
 108
 109             if !can_move_expr_to_closure(cx, some_expr) {
 110                 return;
 111             }
 112
 113             // Determine which binding mode to use.
 114             let explicit_ref = some_pat.contains_explicit_ref_binding();
 115             let binding_ref = explicit_ref.or_else(|| (ty_ref_count != pat_ref_count).then(|| ty_mutability));
 116
 117             let as_ref_str = match binding_ref {
 118                 Some(Mutability::Mut) => ".as_mut()",
 119                 Some(Mutability::Not) => ".as_ref()",
 120                 None => "",
 121             };
 122
 123             let mut app = Applicability::MachineApplicable;
 124
 125             // Remove address-of expressions from the scrutinee. Either `as_ref` will be called, or
 126             // it's being passed by value.
 127             let scrutinee = peel_hir_expr_refs(scrutinee).0;
 128             let (scrutinee_str, _) = snippet_with_context(cx, scrutinee.span, expr_ctxt, "..", &mut app);
 129             let scrutinee_str =
 130                 if scrutinee.span.ctxt() == expr.span.ctxt() && scrutinee.precedence().order() < PREC_POSTFIX {
 131                     format!("({})", scrutinee_str)
 132                 } else {
 133                     scrutinee_str.into()
 134                 };
 135
 136             let body_str = if let PatKind::Binding(annotation, _, some_binding, None) = some_pat.kind {
 137                 match can_pass_as_func(cx, some_binding, some_expr) {
 138                     Some(func) if func.span.ctxt() == some_expr.span.ctxt() => {
 139                         snippet_with_applicability(cx, func.span, "..", &mut app).into_owned()
 140                     },
 141                     _ => {
 142                         if match_var(some_expr, some_binding.name)
 143                             && !is_allowed(cx, MATCH_AS_REF, expr.hir_id)
 144                             && binding_ref.is_some()
 145                         {
 146                             return;
 147                         }
 148
 149                         // `ref` and `ref mut` annotations were handled earlier.
 150                         let annotation = if matches!(annotation, BindingAnnotation::Mutable) {
 151                             "mut "
 152                         } else {
 153                             ""
 154                         };
 155                         format!(
 156                             "|{}{}| {}",
 157                             annotation,
 158                             some_binding,
 159                             snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 160                         )
 161                     },
 162                 }
 163             } else if !is_wild_none && explicit_ref.is_none() {
 164                 // TODO: handle explicit reference annotations.
 165                 format!(
 166                     "|{}| {}",
 167                     snippet_with_context(cx, some_pat.span, expr_ctxt, "..", &mut app).0,
 168                     snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 169                 )
 170             } else {
 171                 // Refutable bindings and mixed reference annotations can't be handled by `map`.
 172                 return;
 173             };
 174
 175             span_lint_and_sugg(
 176                 cx,
 177                 MANUAL_MAP,
 178                 expr.span,
 179                 "manual implementation of `Option::map`",
 180                 "try this",
 181                 format!("{}{}.map({})", scrutinee_str, as_ref_str, body_str),
 182                 app,
 183             );
 184         }
 185     }
 186 }
 187
 188 // Checks if the expression can be moved into a closure as is.
 189 fn can_move_expr_to_closure(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
 190     struct V<'cx, 'tcx> {
 191         cx: &'cx LateContext<'tcx>,
 192         make_closure: bool,
 193     }
 194     impl Visitor<'tcx> for V<'_, 'tcx> {
 195         type Map = ErasedMap<'tcx>;
 196         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 197             NestedVisitorMap::None
 198         }
 199
 200         fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
 201             match e.kind {
 202                 ExprKind::Break(..)
 203                 | ExprKind::Continue(_)
 204                 | ExprKind::Ret(_)
 205                 | ExprKind::Yield(..)
 206                 | ExprKind::InlineAsm(_)
 207                 | ExprKind::LlvmInlineAsm(_) => {
 208                     self.make_closure = false;
 209                 },
 210                 // Accessing a field of a local value can only be done if the type isn't
 211                 // partially moved.
 212                 ExprKind::Field(base_expr, _)
 213                     if matches!(
 214                         base_expr.kind,
 215                         ExprKind::Path(QPath::Resolved(_, Path { res: Res::Local(_), .. }))
 216                     ) && can_partially_move_ty(self.cx, self.cx.typeck_results().expr_ty(base_expr)) =>
 217                 {
 218                     // TODO: check if the local has been partially moved. Assume it has for now.
 219                     self.make_closure = false;
 220                     return;
 221                 }
 222                 _ => (),
 223             };
 224             walk_expr(self, e);
 225         }
 226     }
 227
 228     let mut v = V { cx, make_closure: true };
 229     v.visit_expr(expr);
 230     v.make_closure
 231 }
 232
 233 // Checks whether the expression could be passed as a function, or whether a closure is needed.
 234 // Returns the function to be passed to `map` if it exists.
 235 fn can_pass_as_func(cx: &LateContext<'tcx>, binding: Ident, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
 236     match expr.kind {
 237         ExprKind::Call(func, [arg])
 238             if match_var(arg, binding.name) && cx.typeck_results().expr_adjustments(arg).is_empty() =>
 239         {
 240             Some(func)
 241         },
 242         _ => None,
 243     }
 244 }
 245
 246 enum OptionPat<'a> {
 247     Wild,
 248     None,
 249     Some {
 250         // The pattern contained in the `Some` tuple.
 251         pattern: &'a Pat<'a>,
 252         // The number of references before the `Some` tuple.
 253         // e.g. `&&Some(_)` has a ref count of 2.
 254         ref_count: usize,
 255     },
 256 }
 257
 258 // Try to parse into a recognized `Option` pattern.
 259 // i.e. `_`, `None`, `Some(..)`, or a reference to any of those.
 260 fn try_parse_pattern(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 261     fn f(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ref_count: usize, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 262         match pat.kind {
 263             PatKind::Wild => Some(OptionPat::Wild),
 264             PatKind::Ref(pat, _) => f(cx, pat, ref_count + 1, ctxt),
 265             PatKind::Path(QPath::Resolved(None, path))
 266                 if path
 267                     .res
 268                     .opt_def_id()
 269                     .map_or(false, |id| match_def_path(cx, id, &paths::OPTION_NONE)) =>
 270             {
 271                 Some(OptionPat::None)
 272             },
 273             PatKind::TupleStruct(QPath::Resolved(None, path), [pattern], _)
 274                 if path
 275                     .res
 276                     .opt_def_id()
 277                     .map_or(false, |id| match_def_path(cx, id, &paths::OPTION_SOME))
 278                     && pat.span.ctxt() == ctxt =>
 279             {
 280                 Some(OptionPat::Some { pattern, ref_count })
 281             },
 282             _ => None,
 283         }
 284     }
 285     f(cx, pat, 0, ctxt)
 286 }
 287
 288 // Checks for an expression wrapped by the `Some` constructor. Returns the contained expression.
 289 fn get_some_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, ctxt: SyntaxContext) -> Option<&'tcx Expr<'tcx>> {
 290     // TODO: Allow more complex expressions.
 291     match expr.kind {
 292         ExprKind::Call(
 293             Expr {
 294                 kind: ExprKind::Path(QPath::Resolved(None, path)),
 295                 ..
 296             },
 297             [arg],
 298         ) if ctxt == expr.span.ctxt() => {
 299             if match_def_path(cx, path.res.opt_def_id()?, &paths::OPTION_SOME) {
 300                 Some(arg)
 301             } else {
 302                 None
 303             }
 304         },
 305         ExprKind::Block(
 306             Block {
 307                 stmts: [],
 308                 expr: Some(expr),
 309                 ..
 310             },
 311             _,
 312         ) => get_some_expr(cx, expr, ctxt),
 313         _ => None,
 314     }
 315 }
 316
 317 // Checks for the `None` value.
 318 fn is_none_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
 319     match expr.kind {
 320         ExprKind::Path(QPath::Resolved(None, path)) => path
 321             .res
 322             .opt_def_id()
 323             .map_or(false, |id| match_def_path(cx, id, &paths::OPTION_NONE)),
 324         ExprKind::Block(
 325             Block {
 326                 stmts: [],
 327                 expr: Some(expr),
 328                 ..
 329             },
 330             _,
 331         ) => is_none_expr(cx, expr),
 332         _ => false,
 333     }
 334 }