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::higher::IfLetOrMatch;
   4 use clippy_utils::source::{snippet_with_applicability, snippet_with_context};
   5 use clippy_utils::ty::{is_type_diagnostic_item, peel_mid_ty_refs_is_mutable, type_is_unsafe_function};
   6 use clippy_utils::{
   7     can_move_expr_to_closure, in_constant, is_else_clause, is_lang_ctor, is_lint_allowed, path_to_local_id,
   8     peel_hir_expr_refs, peel_hir_expr_while, CaptureKind,
   9 };
  10 use rustc_ast::util::parser::PREC_POSTFIX;
  11 use rustc_errors::Applicability;
  12 use rustc_hir::LangItem::{OptionNone, OptionSome};
  13 use rustc_hir::{
  14     def::Res, Arm, BindingAnnotation, Block, BlockCheckMode, Expr, ExprKind, HirId, Mutability, Pat, PatKind, Path,
  15     QPath, UnsafeSource,
  16 };
  17 use rustc_lint::{LateContext, LateLintPass, LintContext};
  18 use rustc_middle::lint::in_external_macro;
  19 use rustc_session::{declare_lint_pass, declare_tool_lint};
  20 use rustc_span::{sym, SyntaxContext};
  21
  22 declare_clippy_lint! {
  23     /// ### What it does
  24     /// Checks for usages of `match` which could be implemented using `map`
  25     ///
  26     /// ### Why is this bad?
  27     /// Using the `map` method is clearer and more concise.
  28     ///
  29     /// ### Example
  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     #[clippy::version = "1.52.0"]
  41     pub MANUAL_MAP,
  42     style,
  43     "reimplementation of `map`"
  44 }
  45
  46 declare_lint_pass!(ManualMap => [MANUAL_MAP]);
  47
  48 impl LateLintPass<'_> for ManualMap {
  49     #[allow(clippy::too_many_lines)]
  50     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  51         let (scrutinee, then_pat, then_body, else_pat, else_body) = match IfLetOrMatch::parse(cx, expr) {
  52             Some(IfLetOrMatch::IfLet(scrutinee, pat, body, Some(r#else))) => (scrutinee, pat, body, None, r#else),
  53             Some(IfLetOrMatch::Match(
  54                 scrutinee,
  55                 [arm1 @ Arm { guard: None, .. }, arm2 @ Arm { guard: None, .. }],
  56                 _,
  57             )) => (scrutinee, arm1.pat, arm1.body, Some(arm2.pat), arm2.body),
  58             _ => return,
  59         };
  60         if in_external_macro(cx.sess(), expr.span) || in_constant(cx, expr.hir_id) {
  61             return;
  62         }
  63
  64         let (scrutinee_ty, ty_ref_count, ty_mutability) =
  65             peel_mid_ty_refs_is_mutable(cx.typeck_results().expr_ty(scrutinee));
  66         if !(is_type_diagnostic_item(cx, scrutinee_ty, sym::Option)
  67             && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::Option))
  68         {
  69             return;
  70         }
  71
  72         let expr_ctxt = expr.span.ctxt();
  73         let (some_expr, some_pat, pat_ref_count, is_wild_none) = match (
  74             try_parse_pattern(cx, then_pat, expr_ctxt),
  75             else_pat.map_or(Some(OptionPat::Wild), |p| try_parse_pattern(cx, p, expr_ctxt)),
  76         ) {
  77             (Some(OptionPat::Wild), Some(OptionPat::Some { pattern, ref_count })) if is_none_expr(cx, then_body) => {
  78                 (else_body, pattern, ref_count, true)
  79             },
  80             (Some(OptionPat::None), Some(OptionPat::Some { pattern, ref_count })) if is_none_expr(cx, then_body) => {
  81                 (else_body, pattern, ref_count, false)
  82             },
  83             (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::Wild)) if is_none_expr(cx, else_body) => {
  84                 (then_body, pattern, ref_count, true)
  85             },
  86             (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::None)) if is_none_expr(cx, else_body) => {
  87                 (then_body, pattern, ref_count, false)
  88             },
  89             _ => return,
  90         };
  91
  92         // Top level or patterns aren't allowed in closures.
  93         if matches!(some_pat.kind, PatKind::Or(_)) {
  94             return;
  95         }
  96
  97         let some_expr = match get_some_expr(cx, some_expr, false, expr_ctxt) {
  98             Some(expr) => expr,
  99             None => return,
 100         };
 101
 102         // These two lints will go back and forth with each other.
 103         if cx.typeck_results().expr_ty(some_expr.expr) == cx.tcx.types.unit
 104             && !is_lint_allowed(cx, OPTION_MAP_UNIT_FN, expr.hir_id)
 105         {
 106             return;
 107         }
 108
 109         // `map` won't perform any adjustments.
 110         if !cx.typeck_results().expr_adjustments(some_expr.expr).is_empty() {
 111             return;
 112         }
 113
 114         // Determine which binding mode to use.
 115         let explicit_ref = some_pat.contains_explicit_ref_binding();
 116         let binding_ref = explicit_ref.or_else(|| (ty_ref_count != pat_ref_count).then(|| ty_mutability));
 117
 118         let as_ref_str = match binding_ref {
 119             Some(Mutability::Mut) => ".as_mut()",
 120             Some(Mutability::Not) => ".as_ref()",
 121             None => "",
 122         };
 123
 124         match can_move_expr_to_closure(cx, some_expr.expr) {
 125             Some(captures) => {
 126                 // Check if captures the closure will need conflict with borrows made in the scrutinee.
 127                 // TODO: check all the references made in the scrutinee expression. This will require interacting
 128                 // with the borrow checker. Currently only `<local>[.<field>]*` is checked for.
 129                 if let Some(binding_ref_mutability) = binding_ref {
 130                     let e = peel_hir_expr_while(scrutinee, |e| match e.kind {
 131                         ExprKind::Field(e, _) | ExprKind::AddrOf(_, _, e) => Some(e),
 132                         _ => None,
 133                     });
 134                     if let ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(l), .. })) = e.kind {
 135                         match captures.get(l) {
 136                             Some(CaptureKind::Value | CaptureKind::Ref(Mutability::Mut)) => return,
 137                             Some(CaptureKind::Ref(Mutability::Not)) if binding_ref_mutability == Mutability::Mut => {
 138                                 return;
 139                             },
 140                             Some(CaptureKind::Ref(Mutability::Not)) | None => (),
 141                         }
 142                     }
 143                 }
 144             },
 145             None => return,
 146         };
 147
 148         let mut app = Applicability::MachineApplicable;
 149
 150         // Remove address-of expressions from the scrutinee. Either `as_ref` will be called, or
 151         // it's being passed by value.
 152         let scrutinee = peel_hir_expr_refs(scrutinee).0;
 153         let (scrutinee_str, _) = snippet_with_context(cx, scrutinee.span, expr_ctxt, "..", &mut app);
 154         let scrutinee_str =
 155             if scrutinee.span.ctxt() == expr.span.ctxt() && scrutinee.precedence().order() < PREC_POSTFIX {
 156                 format!("({})", scrutinee_str)
 157             } else {
 158                 scrutinee_str.into()
 159             };
 160
 161         let body_str = if let PatKind::Binding(annotation, id, some_binding, None) = some_pat.kind {
 162             if_chain! {
 163                 if !some_expr.needs_unsafe_block;
 164                 if let Some(func) = can_pass_as_func(cx, id, some_expr.expr);
 165                 if func.span.ctxt() == some_expr.expr.span.ctxt();
 166                 then {
 167                     snippet_with_applicability(cx, func.span, "..", &mut app).into_owned()
 168                 } else {
 169                     if path_to_local_id(some_expr.expr, id)
 170                         && !is_lint_allowed(cx, MATCH_AS_REF, expr.hir_id)
 171                         && binding_ref.is_some()
 172                     {
 173                         return;
 174                     }
 175
 176                     // `ref` and `ref mut` annotations were handled earlier.
 177                     let annotation = if matches!(annotation, BindingAnnotation::Mutable) {
 178                         "mut "
 179                     } else {
 180                         ""
 181                     };
 182                     let expr_snip = snippet_with_context(cx, some_expr.expr.span, expr_ctxt, "..", &mut app).0;
 183                     if some_expr.needs_unsafe_block {
 184                         format!("|{}{}| unsafe {{ {} }}", annotation, some_binding, expr_snip)
 185                     } else {
 186                         format!("|{}{}| {}", annotation, some_binding, expr_snip)
 187                     }
 188                 }
 189             }
 190         } else if !is_wild_none && explicit_ref.is_none() {
 191             // TODO: handle explicit reference annotations.
 192             let pat_snip = snippet_with_context(cx, some_pat.span, expr_ctxt, "..", &mut app).0;
 193             let expr_snip = snippet_with_context(cx, some_expr.expr.span, expr_ctxt, "..", &mut app).0;
 194             if some_expr.needs_unsafe_block {
 195                 format!("|{}| unsafe {{ {} }}", pat_snip, expr_snip)
 196             } else {
 197                 format!("|{}| {}", pat_snip, expr_snip)
 198             }
 199         } else {
 200             // Refutable bindings and mixed reference annotations can't be handled by `map`.
 201             return;
 202         };
 203
 204         span_lint_and_sugg(
 205             cx,
 206             MANUAL_MAP,
 207             expr.span,
 208             "manual implementation of `Option::map`",
 209             "try this",
 210             if else_pat.is_none() && is_else_clause(cx.tcx, expr) {
 211                 format!("{{ {}{}.map({}) }}", scrutinee_str, as_ref_str, body_str)
 212             } else {
 213                 format!("{}{}.map({})", scrutinee_str, as_ref_str, body_str)
 214             },
 215             app,
 216         );
 217     }
 218 }
 219
 220 // Checks whether the expression could be passed as a function, or whether a closure is needed.
 221 // Returns the function to be passed to `map` if it exists.
 222 fn can_pass_as_func(cx: &LateContext<'tcx>, binding: HirId, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
 223     match expr.kind {
 224         ExprKind::Call(func, [arg])
 225             if path_to_local_id(arg, binding)
 226                 && cx.typeck_results().expr_adjustments(arg).is_empty()
 227                 && !type_is_unsafe_function(cx, cx.typeck_results().expr_ty(func).peel_refs()) =>
 228         {
 229             Some(func)
 230         },
 231         _ => None,
 232     }
 233 }
 234
 235 enum OptionPat<'a> {
 236     Wild,
 237     None,
 238     Some {
 239         // The pattern contained in the `Some` tuple.
 240         pattern: &'a Pat<'a>,
 241         // The number of references before the `Some` tuple.
 242         // e.g. `&&Some(_)` has a ref count of 2.
 243         ref_count: usize,
 244     },
 245 }
 246
 247 struct SomeExpr<'tcx> {
 248     expr: &'tcx Expr<'tcx>,
 249     needs_unsafe_block: bool,
 250 }
 251
 252 // Try to parse into a recognized `Option` pattern.
 253 // i.e. `_`, `None`, `Some(..)`, or a reference to any of those.
 254 fn try_parse_pattern(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 255     fn f(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ref_count: usize, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 256         match pat.kind {
 257             PatKind::Wild => Some(OptionPat::Wild),
 258             PatKind::Ref(pat, _) => f(cx, pat, ref_count + 1, ctxt),
 259             PatKind::Path(ref qpath) if is_lang_ctor(cx, qpath, OptionNone) => Some(OptionPat::None),
 260             PatKind::TupleStruct(ref qpath, [pattern], _)
 261                 if is_lang_ctor(cx, qpath, OptionSome) && pat.span.ctxt() == ctxt =>
 262             {
 263                 Some(OptionPat::Some { pattern, ref_count })
 264             },
 265             _ => None,
 266         }
 267     }
 268     f(cx, pat, 0, ctxt)
 269 }
 270
 271 // Checks for an expression wrapped by the `Some` constructor. Returns the contained expression.
 272 fn get_some_expr(
 273     cx: &LateContext<'tcx>,
 274     expr: &'tcx Expr<'_>,
 275     needs_unsafe_block: bool,
 276     ctxt: SyntaxContext,
 277 ) -> Option<SomeExpr<'tcx>> {
 278     // TODO: Allow more complex expressions.
 279     match expr.kind {
 280         ExprKind::Call(
 281             Expr {
 282                 kind: ExprKind::Path(ref qpath),
 283                 ..
 284             },
 285             [arg],
 286         ) if ctxt == expr.span.ctxt() && is_lang_ctor(cx, qpath, OptionSome) => Some(SomeExpr {
 287             expr: arg,
 288             needs_unsafe_block,
 289         }),
 290         ExprKind::Block(
 291             Block {
 292                 stmts: [],
 293                 expr: Some(expr),
 294                 rules,
 295                 ..
 296             },
 297             _,
 298         ) => get_some_expr(
 299             cx,
 300             expr,
 301             needs_unsafe_block || *rules == BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided),
 302             ctxt,
 303         ),
 304         _ => None,
 305     }
 306 }
 307
 308 // Checks for the `None` value.
 309 fn is_none_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
 310     match expr.kind {
 311         ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
 312         ExprKind::Block(
 313             Block {
 314                 stmts: [],
 315                 expr: Some(expr),
 316                 ..
 317             },
 318             _,
 319         ) => is_none_expr(cx, expr),
 320         _ => false,
 321     }
 322 }