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::{is_type_diagnostic_item, peel_mid_ty_refs_is_mutable};
   5 use clippy_utils::{
   6     can_move_expr_to_closure, in_constant, is_allowed, is_else_clause, is_lang_ctor, match_var, peel_hir_expr_refs,
   7 };
   8 use rustc_ast::util::parser::PREC_POSTFIX;
   9 use rustc_errors::Applicability;
  10 use rustc_hir::LangItem::{OptionNone, OptionSome};
  11 use rustc_hir::{Arm, BindingAnnotation, Block, Expr, ExprKind, MatchSource, Mutability, Pat, PatKind};
  12 use rustc_lint::{LateContext, LateLintPass, LintContext};
  13 use rustc_middle::lint::in_external_macro;
  14 use rustc_session::{declare_lint_pass, declare_tool_lint};
  15 use rustc_span::{
  16     symbol::{sym, Ident},
  17     SyntaxContext,
  18 };
  19
  20 declare_clippy_lint! {
  21     /// **What it does:** Checks for usages of `match` which could be implemented using `map`
  22     ///
  23     /// **Why is this bad?** Using the `map` method is clearer and more concise.
  24     ///
  25     /// **Known problems:** None.
  26     ///
  27     /// **Example:**
  28     ///
  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         if let ExprKind::Match(
  50             scrutinee,
  51             [arm1 @ Arm { guard: None, .. }, arm2 @ Arm { guard: None, .. }],
  52             match_kind,
  53         ) = expr.kind
  54         {
  55             if in_external_macro(cx.sess(), expr.span) || in_constant(cx, expr.hir_id) {
  56                 return;
  57             }
  58
  59             let (scrutinee_ty, ty_ref_count, ty_mutability) =
  60                 peel_mid_ty_refs_is_mutable(cx.typeck_results().expr_ty(scrutinee));
  61             if !(is_type_diagnostic_item(cx, scrutinee_ty, sym::option_type)
  62                 && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::option_type))
  63             {
  64                 return;
  65             }
  66
  67             let expr_ctxt = expr.span.ctxt();
  68             let (some_expr, some_pat, pat_ref_count, is_wild_none) = match (
  69                 try_parse_pattern(cx, arm1.pat, expr_ctxt),
  70                 try_parse_pattern(cx, arm2.pat, expr_ctxt),
  71             ) {
  72                 (Some(OptionPat::Wild), Some(OptionPat::Some { pattern, ref_count }))
  73                     if is_none_expr(cx, arm1.body) =>
  74                 {
  75                     (arm2.body, pattern, ref_count, true)
  76                 },
  77                 (Some(OptionPat::None), Some(OptionPat::Some { pattern, ref_count }))
  78                     if is_none_expr(cx, arm1.body) =>
  79                 {
  80                     (arm2.body, pattern, ref_count, false)
  81                 },
  82                 (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::Wild))
  83                     if is_none_expr(cx, arm2.body) =>
  84                 {
  85                     (arm1.body, pattern, ref_count, true)
  86                 },
  87                 (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::None))
  88                     if is_none_expr(cx, arm2.body) =>
  89                 {
  90                     (arm1.body, pattern, ref_count, false)
  91                 },
  92                 _ => return,
  93             };
  94
  95             // Top level or patterns aren't allowed in closures.
  96             if matches!(some_pat.kind, PatKind::Or(_)) {
  97                 return;
  98             }
  99
 100             let some_expr = match get_some_expr(cx, some_expr, expr_ctxt) {
 101                 Some(expr) => expr,
 102                 None => return,
 103             };
 104
 105             if cx.typeck_results().expr_ty(some_expr) == cx.tcx.types.unit
 106                 && !is_allowed(cx, OPTION_MAP_UNIT_FN, expr.hir_id)
 107             {
 108                 return;
 109             }
 110
 111             if !can_move_expr_to_closure(cx, some_expr) {
 112                 return;
 113             }
 114
 115             // Determine which binding mode to use.
 116             let explicit_ref = some_pat.contains_explicit_ref_binding();
 117             let binding_ref = explicit_ref.or_else(|| (ty_ref_count != pat_ref_count).then(|| ty_mutability));
 118
 119             let as_ref_str = match binding_ref {
 120                 Some(Mutability::Mut) => ".as_mut()",
 121                 Some(Mutability::Not) => ".as_ref()",
 122                 None => "",
 123             };
 124
 125             let mut app = Applicability::MachineApplicable;
 126
 127             // Remove address-of expressions from the scrutinee. Either `as_ref` will be called, or
 128             // it's being passed by value.
 129             let scrutinee = peel_hir_expr_refs(scrutinee).0;
 130             let (scrutinee_str, _) = snippet_with_context(cx, scrutinee.span, expr_ctxt, "..", &mut app);
 131             let scrutinee_str =
 132                 if scrutinee.span.ctxt() == expr.span.ctxt() && scrutinee.precedence().order() < PREC_POSTFIX {
 133                     format!("({})", scrutinee_str)
 134                 } else {
 135                     scrutinee_str.into()
 136                 };
 137
 138             let body_str = if let PatKind::Binding(annotation, _, some_binding, None) = some_pat.kind {
 139                 match can_pass_as_func(cx, some_binding, some_expr) {
 140                     Some(func) if func.span.ctxt() == some_expr.span.ctxt() => {
 141                         snippet_with_applicability(cx, func.span, "..", &mut app).into_owned()
 142                     },
 143                     _ => {
 144                         if match_var(some_expr, some_binding.name)
 145                             && !is_allowed(cx, MATCH_AS_REF, expr.hir_id)
 146                             && binding_ref.is_some()
 147                         {
 148                             return;
 149                         }
 150
 151                         // `ref` and `ref mut` annotations were handled earlier.
 152                         let annotation = if matches!(annotation, BindingAnnotation::Mutable) {
 153                             "mut "
 154                         } else {
 155                             ""
 156                         };
 157                         format!(
 158                             "|{}{}| {}",
 159                             annotation,
 160                             some_binding,
 161                             snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 162                         )
 163                     },
 164                 }
 165             } else if !is_wild_none && explicit_ref.is_none() {
 166                 // TODO: handle explicit reference annotations.
 167                 format!(
 168                     "|{}| {}",
 169                     snippet_with_context(cx, some_pat.span, expr_ctxt, "..", &mut app).0,
 170                     snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 171                 )
 172             } else {
 173                 // Refutable bindings and mixed reference annotations can't be handled by `map`.
 174                 return;
 175             };
 176
 177             span_lint_and_sugg(
 178                 cx,
 179                 MANUAL_MAP,
 180                 expr.span,
 181                 "manual implementation of `Option::map`",
 182                 "try this",
 183                 if matches!(match_kind, MatchSource::IfLetDesugar { .. }) && is_else_clause(cx.tcx, expr) {
 184                     format!("{{ {}{}.map({}) }}", scrutinee_str, as_ref_str, body_str)
 185                 } else {
 186                     format!("{}{}.map({})", scrutinee_str, as_ref_str, body_str)
 187                 },
 188                 app,
 189             );
 190         }
 191     }
 192 }
 193
 194 // Checks whether the expression could be passed as a function, or whether a closure is needed.
 195 // Returns the function to be passed to `map` if it exists.
 196 fn can_pass_as_func(cx: &LateContext<'tcx>, binding: Ident, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
 197     match expr.kind {
 198         ExprKind::Call(func, [arg])
 199             if match_var(arg, binding.name) && cx.typeck_results().expr_adjustments(arg).is_empty() =>
 200         {
 201             Some(func)
 202         },
 203         _ => None,
 204     }
 205 }
 206
 207 enum OptionPat<'a> {
 208     Wild,
 209     None,
 210     Some {
 211         // The pattern contained in the `Some` tuple.
 212         pattern: &'a Pat<'a>,
 213         // The number of references before the `Some` tuple.
 214         // e.g. `&&Some(_)` has a ref count of 2.
 215         ref_count: usize,
 216     },
 217 }
 218
 219 // Try to parse into a recognized `Option` pattern.
 220 // i.e. `_`, `None`, `Some(..)`, or a reference to any of those.
 221 fn try_parse_pattern(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 222     fn f(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ref_count: usize, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 223         match pat.kind {
 224             PatKind::Wild => Some(OptionPat::Wild),
 225             PatKind::Ref(pat, _) => f(cx, pat, ref_count + 1, ctxt),
 226             PatKind::Path(ref qpath) if is_lang_ctor(cx, qpath, OptionNone) => Some(OptionPat::None),
 227             PatKind::TupleStruct(ref qpath, [pattern], _)
 228                 if is_lang_ctor(cx, qpath, OptionSome) && pat.span.ctxt() == ctxt =>
 229             {
 230                 Some(OptionPat::Some { pattern, ref_count })
 231             },
 232             _ => None,
 233         }
 234     }
 235     f(cx, pat, 0, ctxt)
 236 }
 237
 238 // Checks for an expression wrapped by the `Some` constructor. Returns the contained expression.
 239 fn get_some_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, ctxt: SyntaxContext) -> Option<&'tcx Expr<'tcx>> {
 240     // TODO: Allow more complex expressions.
 241     match expr.kind {
 242         ExprKind::Call(
 243             Expr {
 244                 kind: ExprKind::Path(ref qpath),
 245                 ..
 246             },
 247             [arg],
 248         ) if ctxt == expr.span.ctxt() && is_lang_ctor(cx, qpath, OptionSome) => Some(arg),
 249         ExprKind::Block(
 250             Block {
 251                 stmts: [],
 252                 expr: Some(expr),
 253                 ..
 254             },
 255             _,
 256         ) => get_some_expr(cx, expr, ctxt),
 257         _ => None,
 258     }
 259 }
 260
 261 // Checks for the `None` value.
 262 fn is_none_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
 263     match expr.kind {
 264         ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
 265         ExprKind::Block(
 266             Block {
 267                 stmts: [],
 268                 expr: Some(expr),
 269                 ..
 270             },
 271             _,
 272         ) => is_none_expr(cx, expr),
 273         _ => false,
 274     }
 275 }