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::higher;
   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,
   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::{Arm, BindingAnnotation, Block, Expr, ExprKind, HirId, Mutability, Pat, PatKind};
  14 use rustc_lint::{LateContext, LateLintPass, LintContext};
  15 use rustc_middle::lint::in_external_macro;
  16 use rustc_session::{declare_lint_pass, declare_tool_lint};
  17 use rustc_span::{sym, SyntaxContext};
  18
  19 declare_clippy_lint! {
  20     /// ### What it does
  21     /// Checks for usages of `match` which could be implemented using `map`
  22     ///
  23     /// ### Why is this bad?
  24     /// Using the `map` method is clearer and more concise.
  25     ///
  26     /// ### Example
  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 Some(higher::IfLet {
  48             let_pat,
  49             let_expr,
  50             if_then,
  51             if_else: Some(if_else),
  52         }) = higher::IfLet::hir(cx, expr)
  53         {
  54             manage_lint(cx, expr, (&let_pat.kind, if_then), (&PatKind::Wild, if_else), let_expr);
  55         }
  56
  57         if let ExprKind::Match(scrutinee, [then @ Arm { guard: None, .. }, r#else @ Arm { guard: None, .. }], _) =
  58             expr.kind
  59         {
  60             manage_lint(
  61                 cx,
  62                 expr,
  63                 (&then.pat.kind, then.body),
  64                 (&r#else.pat.kind, r#else.body),
  65                 scrutinee,
  66             );
  67         }
  68     }
  69 }
  70
  71 fn manage_lint<'tcx>(
  72     cx: &LateContext<'tcx>,
  73     expr: &'tcx Expr<'_>,
  74     then: (&'tcx PatKind<'_>, &'tcx Expr<'_>),
  75     r#else: (&'tcx PatKind<'_>, &'tcx Expr<'_>),
  76     scrut: &'tcx Expr<'_>,
  77 ) {
  78     if in_external_macro(cx.sess(), expr.span) || in_constant(cx, expr.hir_id) {
  79         return;
  80     }
  81
  82     let (scrutinee_ty, ty_ref_count, ty_mutability) = peel_mid_ty_refs_is_mutable(cx.typeck_results().expr_ty(scrut));
  83     if !(is_type_diagnostic_item(cx, scrutinee_ty, sym::option_type)
  84         && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::option_type))
  85     {
  86         return;
  87     }
  88
  89     let (then_pat, then_expr) = then;
  90     let (else_pat, else_expr) = r#else;
  91
  92     let expr_ctxt = expr.span.ctxt();
  93     let (some_expr, some_pat, pat_ref_count, is_wild_none) = match (
  94         try_parse_pattern(cx, then_pat, expr_ctxt),
  95         try_parse_pattern(cx, else_pat, expr_ctxt),
  96     ) {
  97         (Some(OptionPat::Wild), Some(OptionPat::Some { pattern, ref_count })) if is_none_expr(cx, then_expr) => {
  98             (else_expr, pattern, ref_count, true)
  99         },
 100         (Some(OptionPat::None), Some(OptionPat::Some { pattern, ref_count })) if is_none_expr(cx, then_expr) => {
 101             (else_expr, pattern, ref_count, false)
 102         },
 103         (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::Wild)) if is_none_expr(cx, else_expr) => {
 104             (then_expr, pattern, ref_count, true)
 105         },
 106         (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::None)) if is_none_expr(cx, else_expr) => {
 107             (then_expr, pattern, ref_count, false)
 108         },
 109         _ => return,
 110     };
 111
 112     // Top level or patterns aren't allowed in closures.
 113     if matches!(some_pat.kind, PatKind::Or(_)) {
 114         return;
 115     }
 116
 117     let some_expr = match get_some_expr(cx, some_expr, expr_ctxt) {
 118         Some(expr) => expr,
 119         None => return,
 120     };
 121
 122     if cx.typeck_results().expr_ty(some_expr) == cx.tcx.types.unit && !is_lint_allowed(cx, OPTION_MAP_UNIT_FN, expr.hir_id) {
 123         return;
 124     }
 125
 126     // `map` won't perform any adjustments.
 127     if !cx.typeck_results().expr_adjustments(some_expr).is_empty() {
 128         return;
 129     }
 130
 131     if !can_move_expr_to_closure(cx, some_expr) {
 132         return;
 133     }
 134
 135     // Determine which binding mode to use.
 136     let explicit_ref = some_pat.contains_explicit_ref_binding();
 137     let binding_ref = explicit_ref.or_else(|| (ty_ref_count != pat_ref_count).then(|| ty_mutability));
 138
 139     let as_ref_str = match binding_ref {
 140         Some(Mutability::Mut) => ".as_mut()",
 141         Some(Mutability::Not) => ".as_ref()",
 142         None => "",
 143     };
 144
 145     let mut app = Applicability::MachineApplicable;
 146
 147     // Remove address-of expressions from the scrutinee. Either `as_ref` will be called, or
 148     // it's being passed by value.
 149     let scrutinee = peel_hir_expr_refs(scrut).0;
 150     let (scrutinee_str, _) = snippet_with_context(cx, scrutinee.span, expr_ctxt, "..", &mut app);
 151     let scrutinee_str = if scrutinee.span.ctxt() == expr.span.ctxt() && scrutinee.precedence().order() < PREC_POSTFIX {
 152         format!("({})", scrutinee_str)
 153     } else {
 154         scrutinee_str.into()
 155     };
 156
 157     let body_str = if let PatKind::Binding(annotation, id, some_binding, None) = some_pat.kind {
 158         match can_pass_as_func(cx, id, some_expr) {
 159             Some(func) if func.span.ctxt() == some_expr.span.ctxt() => {
 160                 snippet_with_applicability(cx, func.span, "..", &mut app).into_owned()
 161             },
 162             _ => {
 163                 if path_to_local_id(some_expr, id)
 164                     && !is_lint_allowed(cx, MATCH_AS_REF, expr.hir_id)
 165                     && binding_ref.is_some()
 166                 {
 167                     return;
 168                 }
 169
 170                 // `ref` and `ref mut` annotations were handled earlier.
 171                 let annotation = if matches!(annotation, BindingAnnotation::Mutable) {
 172                     "mut "
 173                 } else {
 174                     ""
 175                 };
 176                 format!(
 177                     "|{}{}| {}",
 178                     annotation,
 179                     some_binding,
 180                     snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 181                 )
 182             },
 183         }
 184     } else if !is_wild_none && explicit_ref.is_none() {
 185         // TODO: handle explicit reference annotations.
 186         format!(
 187             "|{}| {}",
 188             snippet_with_context(cx, some_pat.span, expr_ctxt, "..", &mut app).0,
 189             snippet_with_context(cx, some_expr.span, expr_ctxt, "..", &mut app).0
 190         )
 191     } else {
 192         // Refutable bindings and mixed reference annotations can't be handled by `map`.
 193         return;
 194     };
 195
 196     span_lint_and_sugg(
 197         cx,
 198         MANUAL_MAP,
 199         expr.span,
 200         "manual implementation of `Option::map`",
 201         "try this",
 202         if is_else_clause(cx.tcx, expr) {
 203             format!("{{ {}{}.map({}) }}", scrutinee_str, as_ref_str, body_str)
 204         } else {
 205             format!("{}{}.map({})", scrutinee_str, as_ref_str, body_str)
 206         },
 207         app,
 208     );
 209 }
 210
 211 // Checks whether the expression could be passed as a function, or whether a closure is needed.
 212 // Returns the function to be passed to `map` if it exists.
 213 fn can_pass_as_func(cx: &LateContext<'tcx>, binding: HirId, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
 214     match expr.kind {
 215         ExprKind::Call(func, [arg])
 216             if path_to_local_id (arg, binding) && cx.typeck_results().expr_adjustments(arg).is_empty() =>
 217         {
 218             Some(func)
 219         },
 220         _ => None,
 221     }
 222 }
 223
 224 enum OptionPat<'a> {
 225     Wild,
 226     None,
 227     Some {
 228         // The pattern contained in the `Some` tuple.
 229         pattern: &'a Pat<'a>,
 230         // The number of references before the `Some` tuple.
 231         // e.g. `&&Some(_)` has a ref count of 2.
 232         ref_count: usize,
 233     },
 234 }
 235
 236 // Try to parse into a recognized `Option` pattern.
 237 // i.e. `_`, `None`, `Some(..)`, or a reference to any of those.
 238 fn try_parse_pattern(
 239     cx: &LateContext<'tcx>,
 240     pat_kind: &'tcx PatKind<'_>,
 241     ctxt: SyntaxContext,
 242 ) -> Option<OptionPat<'tcx>> {
 243     fn f(
 244         cx: &LateContext<'tcx>,
 245         pat_kind: &'tcx PatKind<'_>,
 246         ref_count: usize,
 247         ctxt: SyntaxContext,
 248     ) -> Option<OptionPat<'tcx>> {
 249         match pat_kind {
 250             PatKind::Wild => Some(OptionPat::Wild),
 251             PatKind::Ref(ref_pat, _) => f(cx, &ref_pat.kind, ref_count + 1, ctxt),
 252             PatKind::Path(ref qpath) if is_lang_ctor(cx, qpath, OptionNone) => Some(OptionPat::None),
 253             PatKind::TupleStruct(ref qpath, [pattern], _) if is_lang_ctor(cx, qpath, OptionSome) => {
 254                 Some(OptionPat::Some { pattern, ref_count })
 255             },
 256             _ => None,
 257         }
 258     }
 259     f(cx, pat_kind, 0, ctxt)
 260 }
 261
 262 // Checks for an expression wrapped by the `Some` constructor. Returns the contained expression.
 263 fn get_some_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, ctxt: SyntaxContext) -> Option<&'tcx Expr<'tcx>> {
 264     // TODO: Allow more complex expressions.
 265     match expr.kind {
 266         ExprKind::Call(
 267             Expr {
 268                 kind: ExprKind::Path(ref qpath),
 269                 ..
 270             },
 271             [arg],
 272         ) if ctxt == expr.span.ctxt() && is_lang_ctor(cx, qpath, OptionSome) => Some(arg),
 273         ExprKind::Block(
 274             Block {
 275                 stmts: [],
 276                 expr: Some(expr),
 277                 ..
 278             },
 279             _,
 280         ) => get_some_expr(cx, expr, ctxt),
 281         _ => None,
 282     }
 283 }
 284
 285 // Checks for the `None` value.
 286 fn is_none_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
 287     match expr.kind {
 288         ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
 289         ExprKind::Block(
 290             Block {
 291                 stmts: [],
 292                 expr: Some(expr),
 293                 ..
 294             },
 295             _,
 296         ) => is_none_expr(cx, expr),
 297         _ => false,
 298     }
 299 }