1 use clippy_utils::diagnostics::span_lint_and_then;
2 use clippy_utils::source::snippet;
3 use clippy_utils::ty::walk_ptrs_ty_depth;
4 use clippy_utils::{match_def_path, paths};
5 use if_chain::if_chain;
6 use rustc_errors::Applicability;
7 use rustc_hir::{BorrowKind, Expr, ExprKind};
8 use rustc_lint::{LateContext, LateLintPass};
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
12 declare_clippy_lint! {
13 /// **What it does:** Checks for calls of `mem::discriminant()` on a non-enum type.
15 /// **Why is this bad?** The value of `mem::discriminant()` on non-enum types
18 /// **Known problems:** None.
24 /// mem::discriminant(&"hello");
25 /// mem::discriminant(&&Some(2));
27 pub MEM_DISCRIMINANT_NON_ENUM,
29 "calling `mem::descriminant` on non-enum type"
32 declare_lint_pass!(MemDiscriminant => [MEM_DISCRIMINANT_NON_ENUM]);
34 impl<'tcx> LateLintPass<'tcx> for MemDiscriminant {
35 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
37 if let ExprKind::Call(func, func_args) = expr.kind;
38 // is `mem::discriminant`
39 if let ExprKind::Path(ref func_qpath) = func.kind;
40 if let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id();
41 if match_def_path(cx, def_id, &paths::MEM_DISCRIMINANT);
43 let ty_param = cx.typeck_results().node_substs(func.hir_id).type_at(0);
44 if !ty_param.is_enum();
49 MEM_DISCRIMINANT_NON_ENUM,
51 &format!("calling `mem::discriminant` on non-enum type `{}`", ty_param),
53 // if this is a reference to an enum, suggest dereferencing
54 let (base_ty, ptr_depth) = walk_ptrs_ty_depth(ty_param);
55 if ptr_depth >= 1 && base_ty.is_enum() {
56 let param = &func_args[0];
58 // cancel out '&'s first
59 let mut derefs_needed = ptr_depth;
60 let mut cur_expr = param;
61 while derefs_needed > 0 {
62 if let ExprKind::AddrOf(BorrowKind::Ref, _, inner_expr) = cur_expr.kind {
64 cur_expr = inner_expr;
70 let derefs: String = iter::repeat('*').take(derefs_needed).collect();
74 format!("{}{}", derefs, snippet(cx, cur_expr.span, "<param>")),
75 Applicability::MachineApplicable,