src/tools/clippy/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, is_else_clause_of_if_let_else, 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, MatchSource, 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(
  55             scrutinee,
  56             [arm1 @ Arm { guard: None, .. }, arm2 @ Arm { guard: None, .. }],
  57             match_kind,
  58         ) = expr.kind
  59         {
  60             let (scrutinee_ty, ty_ref_count, ty_mutability) =
  61                 peel_mid_ty_refs_is_mutable(cx.typeck_results().expr_ty(scrutinee));
  62             if !(is_type_diagnostic_item(cx, scrutinee_ty, sym::option_type)
  63                 && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::option_type))
  64             {
  65                 return;
  66             }
  67
  68             let expr_ctxt = expr.span.ctxt();
  69             let (some_expr, some_pat, pat_ref_count, is_wild_none) = match (
  70                 try_parse_pattern(cx, arm1.pat, expr_ctxt),
  71                 try_parse_pattern(cx, arm2.pat, expr_ctxt),
  72             ) {
  73                 (Some(OptionPat::Wild), Some(OptionPat::Some { pattern, ref_count }))
  74                     if is_none_expr(cx, arm1.body) =>
  75                 {
  76                     (arm2.body, pattern, ref_count, true)
  77                 },
  78                 (Some(OptionPat::None), Some(OptionPat::Some { pattern, ref_count }))
  79                     if is_none_expr(cx, arm1.body) =>
  80                 {
  81                     (arm2.body, pattern, ref_count, false)
  82                 },
  83                 (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::Wild))
  84                     if is_none_expr(cx, arm2.body) =>
  85                 {
  86                     (arm1.body, pattern, ref_count, true)
  87                 },
  88                 (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::None))
  89                     if is_none_expr(cx, arm2.body) =>
  90                 {
  91                     (arm1.body, pattern, ref_count, false)
  92                 },
  93                 _ => return,
  94             };
  95
  96             // Top level or patterns aren't allowed in closures.
  97             if matches!(some_pat.kind, PatKind::Or(_)) {
  98                 return;
  99             }
 100
 101             let some_expr = match get_some_expr(cx, some_expr, expr_ctxt) {
 102                 Some(expr) => expr,
 103                 None => return,
 104             };
 105
 106             if cx.typeck_results().expr_ty(some_expr) == cx.tcx.types.unit
 107                 && !is_allowed(cx, OPTION_MAP_UNIT_FN, expr.hir_id)
 108             {
 109                 return;
 110             }
 111
 112             if !can_move_expr_to_closure(cx, some_expr) {
 113                 return;
 114             }
 115
 116             // Determine which binding mode to use.
 117             let explicit_ref = some_pat.contains_explicit_ref_binding();
 118             let binding_ref = explicit_ref.or_else(|| (ty_ref_count != pat_ref_count).then(|| ty_mutability));
 119
 120             let as_ref_str = match binding_ref {
 121                 Some(Mutability::Mut) => ".as_mut()",
 122                 Some(Mutability::Not) => ".as_ref()",
 123                 None => "",
 124             };
 125
 126             let mut app = Applicability::MachineApplicable;
 127
 128             // Remove address-of expressions from the scrutinee. Either `as_ref` will be called, or
 129             // it's being passed by value.
 130             let scrutinee = peel_hir_expr_refs(scrutinee).0;
 131             let (scrutinee_str, _) = snippet_with_context(cx, scrutinee.span, expr_ctxt, "..", &mut app);
 132             let scrutinee_str =
 133                 if scrutinee.span.ctxt() == expr.span.ctxt() && scrutinee.precedence().order() < PREC_POSTFIX {
 134                     format!("({})", scrutinee_str)
 135                 } else {
 136                     scrutinee_str.into()
 137                 };
 138
 139             let body_str = if let PatKind::Binding(annotation, _, some_binding, None) = some_pat.kind {
 140                 match can_pass_as_func(cx, some_binding, some_expr) {
 141                     Some(func) if func.span.ctxt() == some_expr.span.ctxt() => {
 142                         snippet_with_applicability(cx, func.span, "..", &mut app).into_owned()
 143                     },
 144                     _ => {
 145                         if match_var(some_expr, some_binding.name)
 146                             && !is_allowed(cx, MATCH_AS_REF, expr.hir_id)
 147                             && binding_ref.is_some()
 148                         {
 149                             return;
 150                         }
 151
 152                         // `ref` and `ref mut` annotations were handled earlier.
 153                         let annotation = if matches!(annotation, BindingAnnotation::Mutable) {
 154                             "mut "
 155                         } else {
 156                             ""
 157                         };
 158                         format!(
 159                             "|{}{}| {}",
 160                             annotation,
 161                             some_binding,
 162                             snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 163                         )
 164                     },
 165                 }
 166             } else if !is_wild_none && explicit_ref.is_none() {
 167                 // TODO: handle explicit reference annotations.
 168                 format!(
 169                     "|{}| {}",
 170                     snippet_with_context(cx, some_pat.span, expr_ctxt, "..", &mut app).0,
 171                     snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 172                 )
 173             } else {
 174                 // Refutable bindings and mixed reference annotations can't be handled by `map`.
 175                 return;
 176             };
 177
 178             span_lint_and_sugg(
 179                 cx,
 180                 MANUAL_MAP,
 181                 expr.span,
 182                 "manual implementation of `Option::map`",
 183                 "try this",
 184                 if matches!(match_kind, MatchSource::IfLetDesugar { .. }) && is_else_clause_of_if_let_else(cx.tcx, expr)
 185                 {
 186                     format!("{{ {}{}.map({}) }}", scrutinee_str, as_ref_str, body_str)
 187                 } else {
 188                     format!("{}{}.map({})", scrutinee_str, as_ref_str, body_str)
 189                 },
 190                 app,
 191             );
 192         }
 193     }
 194 }
 195
 196 // Checks if the expression can be moved into a closure as is.
 197 fn can_move_expr_to_closure(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
 198     struct V<'cx, 'tcx> {
 199         cx: &'cx LateContext<'tcx>,
 200         make_closure: bool,
 201     }
 202     impl Visitor<'tcx> for V<'_, 'tcx> {
 203         type Map = ErasedMap<'tcx>;
 204         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 205             NestedVisitorMap::None
 206         }
 207
 208         fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
 209             match e.kind {
 210                 ExprKind::Break(..)
 211                 | ExprKind::Continue(_)
 212                 | ExprKind::Ret(_)
 213                 | ExprKind::Yield(..)
 214                 | ExprKind::InlineAsm(_)
 215                 | ExprKind::LlvmInlineAsm(_) => {
 216                     self.make_closure = false;
 217                 },
 218                 // Accessing a field of a local value can only be done if the type isn't
 219                 // partially moved.
 220                 ExprKind::Field(base_expr, _)
 221                     if matches!(
 222                         base_expr.kind,
 223                         ExprKind::Path(QPath::Resolved(_, Path { res: Res::Local(_), .. }))
 224                     ) && can_partially_move_ty(self.cx, self.cx.typeck_results().expr_ty(base_expr)) =>
 225                 {
 226                     // TODO: check if the local has been partially moved. Assume it has for now.
 227                     self.make_closure = false;
 228                     return;
 229                 }
 230                 _ => (),
 231             };
 232             walk_expr(self, e);
 233         }
 234     }
 235
 236     let mut v = V { cx, make_closure: true };
 237     v.visit_expr(expr);
 238     v.make_closure
 239 }
 240
 241 // Checks whether the expression could be passed as a function, or whether a closure is needed.
 242 // Returns the function to be passed to `map` if it exists.
 243 fn can_pass_as_func(cx: &LateContext<'tcx>, binding: Ident, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
 244     match expr.kind {
 245         ExprKind::Call(func, [arg])
 246             if match_var(arg, binding.name) && cx.typeck_results().expr_adjustments(arg).is_empty() =>
 247         {
 248             Some(func)
 249         },
 250         _ => None,
 251     }
 252 }
 253
 254 enum OptionPat<'a> {
 255     Wild,
 256     None,
 257     Some {
 258         // The pattern contained in the `Some` tuple.
 259         pattern: &'a Pat<'a>,
 260         // The number of references before the `Some` tuple.
 261         // e.g. `&&Some(_)` has a ref count of 2.
 262         ref_count: usize,
 263     },
 264 }
 265
 266 // Try to parse into a recognized `Option` pattern.
 267 // i.e. `_`, `None`, `Some(..)`, or a reference to any of those.
 268 fn try_parse_pattern(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 269     fn f(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ref_count: usize, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 270         match pat.kind {
 271             PatKind::Wild => Some(OptionPat::Wild),
 272             PatKind::Ref(pat, _) => f(cx, pat, ref_count + 1, ctxt),
 273             PatKind::Path(QPath::Resolved(None, path))
 274                 if path
 275                     .res
 276                     .opt_def_id()
 277                     .map_or(false, |id| match_def_path(cx, id, &paths::OPTION_NONE)) =>
 278             {
 279                 Some(OptionPat::None)
 280             },
 281             PatKind::TupleStruct(QPath::Resolved(None, path), [pattern], _)
 282                 if path
 283                     .res
 284                     .opt_def_id()
 285                     .map_or(false, |id| match_def_path(cx, id, &paths::OPTION_SOME))
 286                     && pat.span.ctxt() == ctxt =>
 287             {
 288                 Some(OptionPat::Some { pattern, ref_count })
 289             },
 290             _ => None,
 291         }
 292     }
 293     f(cx, pat, 0, ctxt)
 294 }
 295
 296 // Checks for an expression wrapped by the `Some` constructor. Returns the contained expression.
 297 fn get_some_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, ctxt: SyntaxContext) -> Option<&'tcx Expr<'tcx>> {
 298     // TODO: Allow more complex expressions.
 299     match expr.kind {
 300         ExprKind::Call(
 301             Expr {
 302                 kind: ExprKind::Path(QPath::Resolved(None, path)),
 303                 ..
 304             },
 305             [arg],
 306         ) if ctxt == expr.span.ctxt() => {
 307             if match_def_path(cx, path.res.opt_def_id()?, &paths::OPTION_SOME) {
 308                 Some(arg)
 309             } else {
 310                 None
 311             }
 312         },
 313         ExprKind::Block(
 314             Block {
 315                 stmts: [],
 316                 expr: Some(expr),
 317                 ..
 318             },
 319             _,
 320         ) => get_some_expr(cx, expr, ctxt),
 321         _ => None,
 322     }
 323 }
 324
 325 // Checks for the `None` value.
 326 fn is_none_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
 327     match expr.kind {
 328         ExprKind::Path(QPath::Resolved(None, path)) => path
 329             .res
 330             .opt_def_id()
 331             .map_or(false, |id| match_def_path(cx, id, &paths::OPTION_NONE)),
 332         ExprKind::Block(
 333             Block {
 334                 stmts: [],
 335                 expr: Some(expr),
 336                 ..
 337             },
 338             _,
 339         ) => is_none_expr(cx, expr),
 340         _ => false,
 341     }
 342 }