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_else_clause, is_lang_ctor, is_lint_allowed, path_to_local_id,
   7     peel_hir_expr_refs,
   8 };
   9 use rustc_ast::util::parser::PREC_POSTFIX;
  10 use rustc_errors::Applicability;
  11 use rustc_hir::LangItem::{OptionNone, OptionSome};
  12 use rustc_hir::{Arm, BindingAnnotation, Block, Expr, ExprKind, HirId, MatchSource, Mutability, Pat, PatKind};
  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::{sym, SyntaxContext};
  17
  18 declare_clippy_lint! {
  19     /// **What it does:** Checks for usages of `match` which could be implemented using `map`
  20     ///
  21     /// **Why is this bad?** Using the `map` method is clearer and more concise.
  22     ///
  23     /// **Known problems:** None.
  24     ///
  25     /// **Example:**
  26     ///
  27     /// ```rust
  28     /// match Some(0) {
  29     ///     Some(x) => Some(x + 1),
  30     ///     None => None,
  31     /// };
  32     /// ```
  33     /// Use instead:
  34     /// ```rust
  35     /// Some(0).map(|x| x + 1);
  36     /// ```
  37     pub MANUAL_MAP,
  38     style,
  39     "reimplementation of `map`"
  40 }
  41
  42 declare_lint_pass!(ManualMap => [MANUAL_MAP]);
  43
  44 impl LateLintPass<'_> for ManualMap {
  45     #[allow(clippy::too_many_lines)]
  46     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  47         if let ExprKind::Match(
  48             scrutinee,
  49             [arm1 @ Arm { guard: None, .. }, arm2 @ Arm { guard: None, .. }],
  50             match_kind,
  51         ) = expr.kind
  52         {
  53             if in_external_macro(cx.sess(), expr.span) || in_constant(cx, expr.hir_id) {
  54                 return;
  55             }
  56
  57             let (scrutinee_ty, ty_ref_count, ty_mutability) =
  58                 peel_mid_ty_refs_is_mutable(cx.typeck_results().expr_ty(scrutinee));
  59             if !(is_type_diagnostic_item(cx, scrutinee_ty, sym::option_type)
  60                 && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::option_type))
  61             {
  62                 return;
  63             }
  64
  65             let expr_ctxt = expr.span.ctxt();
  66             let (some_expr, some_pat, pat_ref_count, is_wild_none) = match (
  67                 try_parse_pattern(cx, arm1.pat, expr_ctxt),
  68                 try_parse_pattern(cx, arm2.pat, expr_ctxt),
  69             ) {
  70                 (Some(OptionPat::Wild), Some(OptionPat::Some { pattern, ref_count }))
  71                     if is_none_expr(cx, arm1.body) =>
  72                 {
  73                     (arm2.body, pattern, ref_count, true)
  74                 },
  75                 (Some(OptionPat::None), Some(OptionPat::Some { pattern, ref_count }))
  76                     if is_none_expr(cx, arm1.body) =>
  77                 {
  78                     (arm2.body, pattern, ref_count, false)
  79                 },
  80                 (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::Wild))
  81                     if is_none_expr(cx, arm2.body) =>
  82                 {
  83                     (arm1.body, pattern, ref_count, true)
  84                 },
  85                 (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::None))
  86                     if is_none_expr(cx, arm2.body) =>
  87                 {
  88                     (arm1.body, pattern, ref_count, false)
  89                 },
  90                 _ => return,
  91             };
  92
  93             // Top level or patterns aren't allowed in closures.
  94             if matches!(some_pat.kind, PatKind::Or(_)) {
  95                 return;
  96             }
  97
  98             let some_expr = match get_some_expr(cx, some_expr, expr_ctxt) {
  99                 Some(expr) => expr,
 100                 None => return,
 101             };
 102
 103             // These two lints will go back and forth with each other.
 104             if cx.typeck_results().expr_ty(some_expr) == cx.tcx.types.unit
 105                 && !is_lint_allowed(cx, OPTION_MAP_UNIT_FN, expr.hir_id)
 106             {
 107                 return;
 108             }
 109
 110             // `map` won't perform any adjustments.
 111             if !cx.typeck_results().expr_adjustments(some_expr).is_empty() {
 112                 return;
 113             }
 114
 115             if !can_move_expr_to_closure(cx, some_expr) {
 116                 return;
 117             }
 118
 119             // Determine which binding mode to use.
 120             let explicit_ref = some_pat.contains_explicit_ref_binding();
 121             let binding_ref = explicit_ref.or_else(|| (ty_ref_count != pat_ref_count).then(|| ty_mutability));
 122
 123             let as_ref_str = match binding_ref {
 124                 Some(Mutability::Mut) => ".as_mut()",
 125                 Some(Mutability::Not) => ".as_ref()",
 126                 None => "",
 127             };
 128
 129             let mut app = Applicability::MachineApplicable;
 130
 131             // Remove address-of expressions from the scrutinee. Either `as_ref` will be called, or
 132             // it's being passed by value.
 133             let scrutinee = peel_hir_expr_refs(scrutinee).0;
 134             let (scrutinee_str, _) = snippet_with_context(cx, scrutinee.span, expr_ctxt, "..", &mut app);
 135             let scrutinee_str =
 136                 if scrutinee.span.ctxt() == expr.span.ctxt() && scrutinee.precedence().order() < PREC_POSTFIX {
 137                     format!("({})", scrutinee_str)
 138                 } else {
 139                     scrutinee_str.into()
 140                 };
 141
 142             let body_str = if let PatKind::Binding(annotation, id, some_binding, None) = some_pat.kind {
 143                 match can_pass_as_func(cx, id, some_expr) {
 144                     Some(func) if func.span.ctxt() == some_expr.span.ctxt() => {
 145                         snippet_with_applicability(cx, func.span, "..", &mut app).into_owned()
 146                     },
 147                     _ => {
 148                         if path_to_local_id(some_expr, id)
 149                             && !is_lint_allowed(cx, MATCH_AS_REF, expr.hir_id)
 150                             && binding_ref.is_some()
 151                         {
 152                             return;
 153                         }
 154
 155                         // `ref` and `ref mut` annotations were handled earlier.
 156                         let annotation = if matches!(annotation, BindingAnnotation::Mutable) {
 157                             "mut "
 158                         } else {
 159                             ""
 160                         };
 161                         format!(
 162                             "|{}{}| {}",
 163                             annotation,
 164                             some_binding,
 165                             snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 166                         )
 167                     },
 168                 }
 169             } else if !is_wild_none && explicit_ref.is_none() {
 170                 // TODO: handle explicit reference annotations.
 171                 format!(
 172                     "|{}| {}",
 173                     snippet_with_context(cx, some_pat.span, expr_ctxt, "..", &mut app).0,
 174                     snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 175                 )
 176             } else {
 177                 // Refutable bindings and mixed reference annotations can't be handled by `map`.
 178                 return;
 179             };
 180
 181             span_lint_and_sugg(
 182                 cx,
 183                 MANUAL_MAP,
 184                 expr.span,
 185                 "manual implementation of `Option::map`",
 186                 "try this",
 187                 if matches!(match_kind, MatchSource::IfLetDesugar { .. }) && is_else_clause(cx.tcx, expr) {
 188                     format!("{{ {}{}.map({}) }}", scrutinee_str, as_ref_str, body_str)
 189                 } else {
 190                     format!("{}{}.map({})", scrutinee_str, as_ref_str, body_str)
 191                 },
 192                 app,
 193             );
 194         }
 195     }
 196 }
 197
 198 // Checks whether the expression could be passed as a function, or whether a closure is needed.
 199 // Returns the function to be passed to `map` if it exists.
 200 fn can_pass_as_func(cx: &LateContext<'tcx>, binding: HirId, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
 201     match expr.kind {
 202         ExprKind::Call(func, [arg])
 203             if path_to_local_id(arg, binding) && cx.typeck_results().expr_adjustments(arg).is_empty() =>
 204         {
 205             Some(func)
 206         },
 207         _ => None,
 208     }
 209 }
 210
 211 enum OptionPat<'a> {
 212     Wild,
 213     None,
 214     Some {
 215         // The pattern contained in the `Some` tuple.
 216         pattern: &'a Pat<'a>,
 217         // The number of references before the `Some` tuple.
 218         // e.g. `&&Some(_)` has a ref count of 2.
 219         ref_count: usize,
 220     },
 221 }
 222
 223 // Try to parse into a recognized `Option` pattern.
 224 // i.e. `_`, `None`, `Some(..)`, or a reference to any of those.
 225 fn try_parse_pattern(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 226     fn f(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ref_count: usize, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 227         match pat.kind {
 228             PatKind::Wild => Some(OptionPat::Wild),
 229             PatKind::Ref(pat, _) => f(cx, pat, ref_count + 1, ctxt),
 230             PatKind::Path(ref qpath) if is_lang_ctor(cx, qpath, OptionNone) => Some(OptionPat::None),
 231             PatKind::TupleStruct(ref qpath, [pattern], _)
 232                 if is_lang_ctor(cx, qpath, OptionSome) && pat.span.ctxt() == ctxt =>
 233             {
 234                 Some(OptionPat::Some { pattern, ref_count })
 235             },
 236             _ => None,
 237         }
 238     }
 239     f(cx, pat, 0, ctxt)
 240 }
 241
 242 // Checks for an expression wrapped by the `Some` constructor. Returns the contained expression.
 243 fn get_some_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, ctxt: SyntaxContext) -> Option<&'tcx Expr<'tcx>> {
 244     // TODO: Allow more complex expressions.
 245     match expr.kind {
 246         ExprKind::Call(
 247             Expr {
 248                 kind: ExprKind::Path(ref qpath),
 249                 ..
 250             },
 251             [arg],
 252         ) if ctxt == expr.span.ctxt() && is_lang_ctor(cx, qpath, OptionSome) => Some(arg),
 253         ExprKind::Block(
 254             Block {
 255                 stmts: [],
 256                 expr: Some(expr),
 257                 ..
 258             },
 259             _,
 260         ) => get_some_expr(cx, expr, ctxt),
 261         _ => None,
 262     }
 263 }
 264
 265 // Checks for the `None` value.
 266 fn is_none_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
 267     match expr.kind {
 268         ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
 269         ExprKind::Block(
 270             Block {
 271                 stmts: [],
 272                 expr: Some(expr),
 273                 ..
 274             },
 275             _,
 276         ) => is_none_expr(cx, expr),
 277         _ => false,
 278     }
 279 }