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             // These two lints will go back and forth with each other.
 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             // `map` won't perform any adjustments.
 113             if !cx.typeck_results().expr_adjustments(some_expr).is_empty() {
 114                 return;
 115             }
 116
 117             if !can_move_expr_to_closure(cx, some_expr) {
 118                 return;
 119             }
 120
 121             // Determine which binding mode to use.
 122             let explicit_ref = some_pat.contains_explicit_ref_binding();
 123             let binding_ref = explicit_ref.or_else(|| (ty_ref_count != pat_ref_count).then(|| ty_mutability));
 124
 125             let as_ref_str = match binding_ref {
 126                 Some(Mutability::Mut) => ".as_mut()",
 127                 Some(Mutability::Not) => ".as_ref()",
 128                 None => "",
 129             };
 130
 131             let mut app = Applicability::MachineApplicable;
 132
 133             // Remove address-of expressions from the scrutinee. Either `as_ref` will be called, or
 134             // it's being passed by value.
 135             let scrutinee = peel_hir_expr_refs(scrutinee).0;
 136             let (scrutinee_str, _) = snippet_with_context(cx, scrutinee.span, expr_ctxt, "..", &mut app);
 137             let scrutinee_str =
 138                 if scrutinee.span.ctxt() == expr.span.ctxt() && scrutinee.precedence().order() < PREC_POSTFIX {
 139                     format!("({})", scrutinee_str)
 140                 } else {
 141                     scrutinee_str.into()
 142                 };
 143
 144             let body_str = if let PatKind::Binding(annotation, _, some_binding, None) = some_pat.kind {
 145                 match can_pass_as_func(cx, some_binding, some_expr) {
 146                     Some(func) if func.span.ctxt() == some_expr.span.ctxt() => {
 147                         snippet_with_applicability(cx, func.span, "..", &mut app).into_owned()
 148                     },
 149                     _ => {
 150                         if match_var(some_expr, some_binding.name)
 151                             && !is_allowed(cx, MATCH_AS_REF, expr.hir_id)
 152                             && binding_ref.is_some()
 153                         {
 154                             return;
 155                         }
 156
 157                         // `ref` and `ref mut` annotations were handled earlier.
 158                         let annotation = if matches!(annotation, BindingAnnotation::Mutable) {
 159                             "mut "
 160                         } else {
 161                             ""
 162                         };
 163                         format!(
 164                             "|{}{}| {}",
 165                             annotation,
 166                             some_binding,
 167                             snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 168                         )
 169                     },
 170                 }
 171             } else if !is_wild_none && explicit_ref.is_none() {
 172                 // TODO: handle explicit reference annotations.
 173                 format!(
 174                     "|{}| {}",
 175                     snippet_with_context(cx, some_pat.span, expr_ctxt, "..", &mut app).0,
 176                     snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 177                 )
 178             } else {
 179                 // Refutable bindings and mixed reference annotations can't be handled by `map`.
 180                 return;
 181             };
 182
 183             span_lint_and_sugg(
 184                 cx,
 185                 MANUAL_MAP,
 186                 expr.span,
 187                 "manual implementation of `Option::map`",
 188                 "try this",
 189                 if matches!(match_kind, MatchSource::IfLetDesugar { .. }) && is_else_clause(cx.tcx, expr) {
 190                     format!("{{ {}{}.map({}) }}", scrutinee_str, as_ref_str, body_str)
 191                 } else {
 192                     format!("{}{}.map({})", scrutinee_str, as_ref_str, body_str)
 193                 },
 194                 app,
 195             );
 196         }
 197     }
 198 }
 199
 200 // Checks whether the expression could be passed as a function, or whether a closure is needed.
 201 // Returns the function to be passed to `map` if it exists.
 202 fn can_pass_as_func(cx: &LateContext<'tcx>, binding: Ident, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
 203     match expr.kind {
 204         ExprKind::Call(func, [arg])
 205             if match_var(arg, binding.name) && cx.typeck_results().expr_adjustments(arg).is_empty() =>
 206         {
 207             Some(func)
 208         },
 209         _ => None,
 210     }
 211 }
 212
 213 enum OptionPat<'a> {
 214     Wild,
 215     None,
 216     Some {
 217         // The pattern contained in the `Some` tuple.
 218         pattern: &'a Pat<'a>,
 219         // The number of references before the `Some` tuple.
 220         // e.g. `&&Some(_)` has a ref count of 2.
 221         ref_count: usize,
 222     },
 223 }
 224
 225 // Try to parse into a recognized `Option` pattern.
 226 // i.e. `_`, `None`, `Some(..)`, or a reference to any of those.
 227 fn try_parse_pattern(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 228     fn f(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ref_count: usize, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 229         match pat.kind {
 230             PatKind::Wild => Some(OptionPat::Wild),
 231             PatKind::Ref(pat, _) => f(cx, pat, ref_count + 1, ctxt),
 232             PatKind::Path(ref qpath) if is_lang_ctor(cx, qpath, OptionNone) => Some(OptionPat::None),
 233             PatKind::TupleStruct(ref qpath, [pattern], _)
 234                 if is_lang_ctor(cx, qpath, OptionSome) && pat.span.ctxt() == ctxt =>
 235             {
 236                 Some(OptionPat::Some { pattern, ref_count })
 237             },
 238             _ => None,
 239         }
 240     }
 241     f(cx, pat, 0, ctxt)
 242 }
 243
 244 // Checks for an expression wrapped by the `Some` constructor. Returns the contained expression.
 245 fn get_some_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, ctxt: SyntaxContext) -> Option<&'tcx Expr<'tcx>> {
 246     // TODO: Allow more complex expressions.
 247     match expr.kind {
 248         ExprKind::Call(
 249             Expr {
 250                 kind: ExprKind::Path(ref qpath),
 251                 ..
 252             },
 253             [arg],
 254         ) if ctxt == expr.span.ctxt() && is_lang_ctor(cx, qpath, OptionSome) => Some(arg),
 255         ExprKind::Block(
 256             Block {
 257                 stmts: [],
 258                 expr: Some(expr),
 259                 ..
 260             },
 261             _,
 262         ) => get_some_expr(cx, expr, ctxt),
 263         _ => None,
 264     }
 265 }
 266
 267 // Checks for the `None` value.
 268 fn is_none_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
 269     match expr.kind {
 270         ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
 271         ExprKind::Block(
 272             Block {
 273                 stmts: [],
 274                 expr: Some(expr),
 275                 ..
 276             },
 277             _,
 278         ) => is_none_expr(cx, expr),
 279         _ => false,
 280     }
 281 }