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