src/tools/clippy/clippy_lints/src/matches/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, type_is_unsafe_function};
   5 use clippy_utils::{
   6     can_move_expr_to_closure, is_else_clause, is_lang_ctor, is_lint_allowed, path_to_local_id, peel_blocks,
   7     peel_hir_expr_refs, peel_hir_expr_while, CaptureKind,
   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::{
  13     def::Res, Arm, BindingAnnotation, Block, BlockCheckMode, Expr, ExprKind, HirId, Mutability, Pat, PatKind, Path,
  14     QPath, UnsafeSource,
  15 };
  16 use rustc_lint::LateContext;
  17 use rustc_span::{sym, SyntaxContext};
  18
  19 use super::MANUAL_MAP;
  20
  21 pub(super) fn check_match<'tcx>(
  22     cx: &LateContext<'tcx>,
  23     expr: &'tcx Expr<'_>,
  24     scrutinee: &'tcx Expr<'_>,
  25     arms: &'tcx [Arm<'_>],
  26 ) {
  27     if let [arm1, arm2] = arms
  28         && arm1.guard.is_none()
  29         && arm2.guard.is_none()
  30     {
  31         check(cx, expr, scrutinee, arm1.pat, arm1.body, Some(arm2.pat), arm2.body);
  32     }
  33 }
  34
  35 pub(super) fn check_if_let<'tcx>(
  36     cx: &LateContext<'tcx>,
  37     expr: &'tcx Expr<'_>,
  38     let_pat: &'tcx Pat<'_>,
  39     let_expr: &'tcx Expr<'_>,
  40     then_expr: &'tcx Expr<'_>,
  41     else_expr: &'tcx Expr<'_>,
  42 ) {
  43     check(cx, expr, let_expr, let_pat, then_expr, None, else_expr);
  44 }
  45
  46 #[expect(clippy::too_many_lines)]
  47 fn check<'tcx>(
  48     cx: &LateContext<'tcx>,
  49     expr: &'tcx Expr<'_>,
  50     scrutinee: &'tcx Expr<'_>,
  51     then_pat: &'tcx Pat<'_>,
  52     then_body: &'tcx Expr<'_>,
  53     else_pat: Option<&'tcx Pat<'_>>,
  54     else_body: &'tcx Expr<'_>,
  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)
  59         && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::Option))
  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, then_pat, expr_ctxt),
  67         else_pat.map_or(Some(OptionPat::Wild), |p| try_parse_pattern(cx, p, expr_ctxt)),
  68     ) {
  69         (Some(OptionPat::Wild), Some(OptionPat::Some { pattern, ref_count })) if is_none_expr(cx, then_body) => {
  70             (else_body, pattern, ref_count, true)
  71         },
  72         (Some(OptionPat::None), Some(OptionPat::Some { pattern, ref_count })) if is_none_expr(cx, then_body) => {
  73             (else_body, pattern, ref_count, false)
  74         },
  75         (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::Wild)) if is_none_expr(cx, else_body) => {
  76             (then_body, pattern, ref_count, true)
  77         },
  78         (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::None)) if is_none_expr(cx, else_body) => {
  79             (then_body, pattern, ref_count, false)
  80         },
  81         _ => return,
  82     };
  83
  84     // Top level or patterns aren't allowed in closures.
  85     if matches!(some_pat.kind, PatKind::Or(_)) {
  86         return;
  87     }
  88
  89     let some_expr = match get_some_expr(cx, some_expr, false, expr_ctxt) {
  90         Some(expr) => expr,
  91         None => return,
  92     };
  93
  94     // These two lints will go back and forth with each other.
  95     if cx.typeck_results().expr_ty(some_expr.expr) == cx.tcx.types.unit
  96         && !is_lint_allowed(cx, OPTION_MAP_UNIT_FN, expr.hir_id)
  97     {
  98         return;
  99     }
 100
 101     // `map` won't perform any adjustments.
 102     if !cx.typeck_results().expr_adjustments(some_expr.expr).is_empty() {
 103         return;
 104     }
 105
 106     // Determine which binding mode to use.
 107     let explicit_ref = some_pat.contains_explicit_ref_binding();
 108     let binding_ref = explicit_ref.or_else(|| (ty_ref_count != pat_ref_count).then(|| ty_mutability));
 109
 110     let as_ref_str = match binding_ref {
 111         Some(Mutability::Mut) => ".as_mut()",
 112         Some(Mutability::Not) => ".as_ref()",
 113         None => "",
 114     };
 115
 116     match can_move_expr_to_closure(cx, some_expr.expr) {
 117         Some(captures) => {
 118             // Check if captures the closure will need conflict with borrows made in the scrutinee.
 119             // TODO: check all the references made in the scrutinee expression. This will require interacting
 120             // with the borrow checker. Currently only `<local>[.<field>]*` is checked for.
 121             if let Some(binding_ref_mutability) = binding_ref {
 122                 let e = peel_hir_expr_while(scrutinee, |e| match e.kind {
 123                     ExprKind::Field(e, _) | ExprKind::AddrOf(_, _, e) => Some(e),
 124                     _ => None,
 125                 });
 126                 if let ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(l), .. })) = e.kind {
 127                     match captures.get(l) {
 128                         Some(CaptureKind::Value | CaptureKind::Ref(Mutability::Mut)) => return,
 129                         Some(CaptureKind::Ref(Mutability::Not)) if binding_ref_mutability == Mutability::Mut => {
 130                             return;
 131                         },
 132                         Some(CaptureKind::Ref(Mutability::Not)) | None => (),
 133                     }
 134                 }
 135             }
 136         },
 137         None => return,
 138     };
 139
 140     let mut app = Applicability::MachineApplicable;
 141
 142     // Remove address-of expressions from the scrutinee. Either `as_ref` will be called, or
 143     // it's being passed by value.
 144     let scrutinee = peel_hir_expr_refs(scrutinee).0;
 145     let (scrutinee_str, _) = snippet_with_context(cx, scrutinee.span, expr_ctxt, "..", &mut app);
 146     let scrutinee_str = if scrutinee.span.ctxt() == expr.span.ctxt() && scrutinee.precedence().order() < PREC_POSTFIX {
 147         format!("({})", scrutinee_str)
 148     } else {
 149         scrutinee_str.into()
 150     };
 151
 152     let body_str = if let PatKind::Binding(annotation, id, some_binding, None) = some_pat.kind {
 153         if_chain! {
 154             if !some_expr.needs_unsafe_block;
 155             if let Some(func) = can_pass_as_func(cx, id, some_expr.expr);
 156             if func.span.ctxt() == some_expr.expr.span.ctxt();
 157             then {
 158                 snippet_with_applicability(cx, func.span, "..", &mut app).into_owned()
 159             } else {
 160                 if path_to_local_id(some_expr.expr, id)
 161                     && !is_lint_allowed(cx, MATCH_AS_REF, expr.hir_id)
 162                     && binding_ref.is_some()
 163                 {
 164                     return;
 165                 }
 166
 167                 // `ref` and `ref mut` annotations were handled earlier.
 168                 let annotation = if matches!(annotation, BindingAnnotation::Mutable) {
 169                     "mut "
 170                 } else {
 171                     ""
 172                 };
 173                 let expr_snip = snippet_with_context(cx, some_expr.expr.span, expr_ctxt, "..", &mut app).0;
 174                 if some_expr.needs_unsafe_block {
 175                     format!("|{}{}| unsafe {{ {} }}", annotation, some_binding, expr_snip)
 176                 } else {
 177                     format!("|{}{}| {}", annotation, some_binding, expr_snip)
 178                 }
 179             }
 180         }
 181     } else if !is_wild_none && explicit_ref.is_none() {
 182         // TODO: handle explicit reference annotations.
 183         let pat_snip = snippet_with_context(cx, some_pat.span, expr_ctxt, "..", &mut app).0;
 184         let expr_snip = snippet_with_context(cx, some_expr.expr.span, expr_ctxt, "..", &mut app).0;
 185         if some_expr.needs_unsafe_block {
 186             format!("|{}| unsafe {{ {} }}", pat_snip, expr_snip)
 187         } else {
 188             format!("|{}| {}", pat_snip, expr_snip)
 189         }
 190     } else {
 191         // Refutable bindings and mixed reference annotations can't be handled by `map`.
 192         return;
 193     };
 194
 195     span_lint_and_sugg(
 196         cx,
 197         MANUAL_MAP,
 198         expr.span,
 199         "manual implementation of `Option::map`",
 200         "try this",
 201         if else_pat.is_none() && is_else_clause(cx.tcx, expr) {
 202             format!("{{ {}{}.map({}) }}", scrutinee_str, as_ref_str, body_str)
 203         } else {
 204             format!("{}{}.map({})", scrutinee_str, as_ref_str, body_str)
 205         },
 206         app,
 207     );
 208 }
 209
 210 // Checks whether the expression could be passed as a function, or whether a closure is needed.
 211 // Returns the function to be passed to `map` if it exists.
 212 fn can_pass_as_func<'tcx>(cx: &LateContext<'tcx>, binding: HirId, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
 213     match expr.kind {
 214         ExprKind::Call(func, [arg])
 215             if path_to_local_id(arg, binding)
 216                 && cx.typeck_results().expr_adjustments(arg).is_empty()
 217                 && !type_is_unsafe_function(cx, cx.typeck_results().expr_ty(func).peel_refs()) =>
 218         {
 219             Some(func)
 220         },
 221         _ => None,
 222     }
 223 }
 224
 225 enum OptionPat<'a> {
 226     Wild,
 227     None,
 228     Some {
 229         // The pattern contained in the `Some` tuple.
 230         pattern: &'a Pat<'a>,
 231         // The number of references before the `Some` tuple.
 232         // e.g. `&&Some(_)` has a ref count of 2.
 233         ref_count: usize,
 234     },
 235 }
 236
 237 struct SomeExpr<'tcx> {
 238     expr: &'tcx Expr<'tcx>,
 239     needs_unsafe_block: bool,
 240 }
 241
 242 // Try to parse into a recognized `Option` pattern.
 243 // i.e. `_`, `None`, `Some(..)`, or a reference to any of those.
 244 fn try_parse_pattern<'tcx>(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ctxt: SyntaxContext) -> Option<OptionPat<'tcx>> {
 245     fn f<'tcx>(
 246         cx: &LateContext<'tcx>,
 247         pat: &'tcx Pat<'_>,
 248         ref_count: usize,
 249         ctxt: SyntaxContext,
 250     ) -> Option<OptionPat<'tcx>> {
 251         match pat.kind {
 252             PatKind::Wild => Some(OptionPat::Wild),
 253             PatKind::Ref(pat, _) => f(cx, pat, ref_count + 1, ctxt),
 254             PatKind::Path(ref qpath) if is_lang_ctor(cx, qpath, OptionNone) => Some(OptionPat::None),
 255             PatKind::TupleStruct(ref qpath, [pattern], _)
 256                 if is_lang_ctor(cx, qpath, OptionSome) && pat.span.ctxt() == ctxt =>
 257             {
 258                 Some(OptionPat::Some { pattern, ref_count })
 259             },
 260             _ => None,
 261         }
 262     }
 263     f(cx, pat, 0, ctxt)
 264 }
 265
 266 // Checks for an expression wrapped by the `Some` constructor. Returns the contained expression.
 267 fn get_some_expr<'tcx>(
 268     cx: &LateContext<'tcx>,
 269     expr: &'tcx Expr<'_>,
 270     needs_unsafe_block: bool,
 271     ctxt: SyntaxContext,
 272 ) -> Option<SomeExpr<'tcx>> {
 273     // TODO: Allow more complex expressions.
 274     match expr.kind {
 275         ExprKind::Call(
 276             Expr {
 277                 kind: ExprKind::Path(ref qpath),
 278                 ..
 279             },
 280             [arg],
 281         ) if ctxt == expr.span.ctxt() && is_lang_ctor(cx, qpath, OptionSome) => Some(SomeExpr {
 282             expr: arg,
 283             needs_unsafe_block,
 284         }),
 285         ExprKind::Block(
 286             Block {
 287                 stmts: [],
 288                 expr: Some(expr),
 289                 rules,
 290                 ..
 291             },
 292             _,
 293         ) => get_some_expr(
 294             cx,
 295             expr,
 296             needs_unsafe_block || *rules == BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided),
 297             ctxt,
 298         ),
 299         _ => None,
 300     }
 301 }
 302
 303 // Checks for the `None` value.
 304 fn is_none_expr(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 305     matches!(peel_blocks(expr).kind, ExprKind::Path(ref qpath) if is_lang_ctor(cx, qpath, OptionNone))
 306 }