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};
   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, Expr, ExprKind, HirId, Mutability, Pat, PatKind, Path, QPath,
  15 };
  16 use rustc_lint::{LateContext, LateLintPass, LintContext};
  17 use rustc_middle::lint::in_external_macro;
  18 use rustc_session::{declare_lint_pass, declare_tool_lint};
  19 use rustc_span::{sym, SyntaxContext};
  20
  21 declare_clippy_lint! {
  22     /// ### What it does
  23     /// Checks for usages of `match` which could be implemented using `map`
  24     ///
  25     /// ### Why is this bad?
  26     /// Using the `map` method is clearer and more concise.
  27     ///
  28     /// ### Example
  29     /// ```rust
  30     /// match Some(0) {
  31     ///     Some(x) => Some(x + 1),
  32     ///     None => None,
  33     /// };
  34     /// ```
  35     /// Use instead:
  36     /// ```rust
  37     /// Some(0).map(|x| x + 1);
  38     /// ```
  39     pub MANUAL_MAP,
  40     style,
  41     "reimplementation of `map`"
  42 }
  43
  44 declare_lint_pass!(ManualMap => [MANUAL_MAP]);
  45
  46 impl LateLintPass<'_> for ManualMap {
  47     #[allow(clippy::too_many_lines)]
  48     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  49         let (scrutinee, then_pat, then_body, else_pat, else_body) = match IfLetOrMatch::parse(cx, expr) {
  50             Some(IfLetOrMatch::IfLet(scrutinee, pat, body, Some(r#else))) => (scrutinee, pat, body, None, r#else),
  51             Some(IfLetOrMatch::Match(
  52                 scrutinee,
  53                 [arm1 @ Arm { guard: None, .. }, arm2 @ Arm { guard: None, .. }],
  54                 _,
  55             )) => (scrutinee, arm1.pat, arm1.body, Some(arm2.pat), arm2.body),
  56             _ => return,
  57         };
  58         if in_external_macro(cx.sess(), expr.span) || in_constant(cx, expr.hir_id) {
  59             return;
  60         }
  61
  62         let (scrutinee_ty, ty_ref_count, ty_mutability) =
  63             peel_mid_ty_refs_is_mutable(cx.typeck_results().expr_ty(scrutinee));
  64         if !(is_type_diagnostic_item(cx, scrutinee_ty, sym::Option)
  65             && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::Option))
  66         {
  67             return;
  68         }
  69
  70         let expr_ctxt = expr.span.ctxt();
  71         let (some_expr, some_pat, pat_ref_count, is_wild_none) = match (
  72             try_parse_pattern(cx, then_pat, expr_ctxt),
  73             else_pat.map_or(Some(OptionPat::Wild), |p| try_parse_pattern(cx, p, expr_ctxt)),
  74         ) {
  75             (Some(OptionPat::Wild), Some(OptionPat::Some { pattern, ref_count })) if is_none_expr(cx, then_body) => {
  76                 (else_body, pattern, ref_count, true)
  77             },
  78             (Some(OptionPat::None), Some(OptionPat::Some { pattern, ref_count })) if is_none_expr(cx, then_body) => {
  79                 (else_body, pattern, ref_count, false)
  80             },
  81             (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::Wild)) if is_none_expr(cx, else_body) => {
  82                 (then_body, pattern, ref_count, true)
  83             },
  84             (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::None)) if is_none_expr(cx, else_body) => {
  85                 (then_body, pattern, ref_count, false)
  86             },
  87             _ => return,
  88         };
  89
  90         // Top level or patterns aren't allowed in closures.
  91         if matches!(some_pat.kind, PatKind::Or(_)) {
  92             return;
  93         }
  94
  95         let some_expr = match get_some_expr(cx, some_expr, expr_ctxt) {
  96             Some(expr) => expr,
  97             None => return,
  98         };
  99
 100         // These two lints will go back and forth with each other.
 101         if cx.typeck_results().expr_ty(some_expr) == cx.tcx.types.unit
 102             && !is_lint_allowed(cx, OPTION_MAP_UNIT_FN, expr.hir_id)
 103         {
 104             return;
 105         }
 106
 107         // `map` won't perform any adjustments.
 108         if !cx.typeck_results().expr_adjustments(some_expr).is_empty() {
 109             return;
 110         }
 111
 112         // Determine which binding mode to use.
 113         let explicit_ref = some_pat.contains_explicit_ref_binding();
 114         let binding_ref = explicit_ref.or_else(|| (ty_ref_count != pat_ref_count).then(|| ty_mutability));
 115
 116         let as_ref_str = match binding_ref {
 117             Some(Mutability::Mut) => ".as_mut()",
 118             Some(Mutability::Not) => ".as_ref()",
 119             None => "",
 120         };
 121
 122         match can_move_expr_to_closure(cx, some_expr) {
 123             Some(captures) => {
 124                 // Check if captures the closure will need conflict with borrows made in the scrutinee.
 125                 // TODO: check all the references made in the scrutinee expression. This will require interacting
 126                 // with the borrow checker. Currently only `<local>[.<field>]*` is checked for.
 127                 if let Some(binding_ref_mutability) = binding_ref {
 128                     let e = peel_hir_expr_while(scrutinee, |e| match e.kind {
 129                         ExprKind::Field(e, _) | ExprKind::AddrOf(_, _, e) => Some(e),
 130                         _ => None,
 131                     });
 132                     if let ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(l), .. })) = e.kind {
 133                         match captures.get(l) {
 134                             Some(CaptureKind::Value | CaptureKind::Ref(Mutability::Mut)) => return,
 135                             Some(CaptureKind::Ref(Mutability::Not)) if binding_ref_mutability == Mutability::Mut => {
 136                                 return;
 137                             },
 138                             Some(CaptureKind::Ref(Mutability::Not)) | None => (),
 139                         }
 140                     }
 141                 }
 142             },
 143             None => return,
 144         };
 145
 146         let mut app = Applicability::MachineApplicable;
 147
 148         // Remove address-of expressions from the scrutinee. Either `as_ref` will be called, or
 149         // it's being passed by value.
 150         let scrutinee = peel_hir_expr_refs(scrutinee).0;
 151         let (scrutinee_str, _) = snippet_with_context(cx, scrutinee.span, expr_ctxt, "..", &mut app);
 152         let scrutinee_str =
 153             if scrutinee.span.ctxt() == expr.span.ctxt() && scrutinee.precedence().order() < PREC_POSTFIX {
 154                 format!("({})", scrutinee_str)
 155             } else {
 156                 scrutinee_str.into()
 157             };
 158
 159         let body_str = if let PatKind::Binding(annotation, id, some_binding, None) = some_pat.kind {
 160             match can_pass_as_func(cx, id, some_expr) {
 161                 Some(func) if func.span.ctxt() == some_expr.span.ctxt() => {
 162                     snippet_with_applicability(cx, func.span, "..", &mut app).into_owned()
 163                 },
 164                 _ => {
 165                     if path_to_local_id(some_expr, id)
 166                         && !is_lint_allowed(cx, MATCH_AS_REF, expr.hir_id)
 167                         && binding_ref.is_some()
 168                     {
 169                         return;
 170                     }
 171
 172                     // `ref` and `ref mut` annotations were handled earlier.
 173                     let annotation = if matches!(annotation, BindingAnnotation::Mutable) {
 174                         "mut "
 175                     } else {
 176                         ""
 177                     };
 178                     format!(
 179                         "|{}{}| {}",
 180                         annotation,
 181                         some_binding,
 182                         snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 183                     )
 184                 },
 185             }
 186         } else if !is_wild_none && explicit_ref.is_none() {
 187             // TODO: handle explicit reference annotations.
 188             format!(
 189                 "|{}| {}",
 190                 snippet_with_context(cx, some_pat.span, expr_ctxt, "..", &mut app).0,
 191                 snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 192             )
 193         } else {
 194             // Refutable bindings and mixed reference annotations can't be handled by `map`.
 195             return;
 196         };
 197
 198         span_lint_and_sugg(
 199             cx,
 200             MANUAL_MAP,
 201             expr.span,
 202             "manual implementation of `Option::map`",
 203             "try this",
 204             if else_pat.is_none() && is_else_clause(cx.tcx, expr) {
 205                 format!("{{ {}{}.map({}) }}", scrutinee_str, as_ref_str, body_str)
 206             } else {
 207                 format!("{}{}.map({})", scrutinee_str, as_ref_str, body_str)
 208             },
 209             app,
 210         );
 211     }
 212 }
 213
 214 // Checks whether the expression could be passed as a function, or whether a closure is needed.
 215 // Returns the function to be passed to `map` if it exists.
 216 fn can_pass_as_func(cx: &LateContext<'tcx>, binding: HirId, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
 217     match expr.kind {
 218         ExprKind::Call(func, [arg])
 219             if path_to_local_id(arg, binding) && cx.typeck_results().expr_adjustments(arg).is_empty() =>
 220         {
 221             Some(func)
 222         },
 223         _ => None,
 224     }
 225 }
 226
 227 enum OptionPat<'a> {
 228     Wild,
 229     None,
 230     Some {
 231         // The pattern contained in the `Some` tuple.
 232         pattern: &'a Pat<'a>,
 233         // The number of references before the `Some` tuple.
 234         // e.g. `&&Some(_)` has a ref count of 2.
 235         ref_count: usize,
 236     },
 237 }
 238
 239 // Try to parse into a recognized `Option` pattern.
 240 // i.e. `_`, `None`, `Some(..)`, or a reference to any of those.
 241 fn try_parse_pattern(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 242     fn f(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ref_count: usize, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 243         match pat.kind {
 244             PatKind::Wild => Some(OptionPat::Wild),
 245             PatKind::Ref(pat, _) => f(cx, pat, ref_count + 1, ctxt),
 246             PatKind::Path(ref qpath) if is_lang_ctor(cx, qpath, OptionNone) => Some(OptionPat::None),
 247             PatKind::TupleStruct(ref qpath, [pattern], _)
 248                 if is_lang_ctor(cx, qpath, OptionSome) && pat.span.ctxt() == ctxt =>
 249             {
 250                 Some(OptionPat::Some { pattern, ref_count })
 251             },
 252             _ => None,
 253         }
 254     }
 255     f(cx, pat, 0, ctxt)
 256 }
 257
 258 // Checks for an expression wrapped by the `Some` constructor. Returns the contained expression.
 259 fn get_some_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, ctxt: SyntaxContext) -> Option<&'tcx Expr<'tcx>> {
 260     // TODO: Allow more complex expressions.
 261     match expr.kind {
 262         ExprKind::Call(
 263             Expr {
 264                 kind: ExprKind::Path(ref qpath),
 265                 ..
 266             },
 267             [arg],
 268         ) if ctxt == expr.span.ctxt() && is_lang_ctor(cx, qpath, OptionSome) => Some(arg),
 269         ExprKind::Block(
 270             Block {
 271                 stmts: [],
 272                 expr: Some(expr),
 273                 ..
 274             },
 275             _,
 276         ) => get_some_expr(cx, expr, ctxt),
 277         _ => None,
 278     }
 279 }
 280
 281 // Checks for the `None` value.
 282 fn is_none_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
 283     match expr.kind {
 284         ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
 285         ExprKind::Block(
 286             Block {
 287                 stmts: [],
 288                 expr: Some(expr),
 289                 ..
 290             },
 291             _,
 292         ) => is_none_expr(cx, expr),
 293         _ => false,
 294     }
 295 }