1 use crate::utils::{match_def_path, opt_def_id, paths, snippet, span_lint_and_then, walk_ptrs_ty_depth};
2 use if_chain::if_chain;
3 use rustc::hir::{Expr, ExprKind};
4 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
5 use rustc::{declare_tool_lint, lint_array};
6 use rustc_errors::Applicability;
10 /// **What it does:** Checks for calls of `mem::discriminant()` on a non-enum type.
12 /// **Why is this bad?** The value of `mem::discriminant()` on non-enum types
15 /// **Known problems:** None.
19 /// mem::discriminant(&"hello");
20 /// mem::discriminant(&&Some(2));
22 declare_clippy_lint! {
23 pub MEM_DISCRIMINANT_NON_ENUM,
25 "calling mem::descriminant on non-enum type"
28 pub struct MemDiscriminant;
30 impl LintPass for MemDiscriminant {
31 fn get_lints(&self) -> LintArray {
32 lint_array![MEM_DISCRIMINANT_NON_ENUM]
36 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MemDiscriminant {
37 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
39 if let ExprKind::Call(ref func, ref func_args) = expr.node;
40 // is `mem::discriminant`
41 if let ExprKind::Path(ref func_qpath) = func.node;
42 if let Some(def_id) = opt_def_id(cx.tables.qpath_def(func_qpath, func.hir_id));
43 if match_def_path(cx.tcx, def_id, &paths::MEM_DISCRIMINANT);
45 let ty_param = cx.tables.node_substs(func.hir_id).type_at(0);
46 if !ty_param.is_enum();
51 MEM_DISCRIMINANT_NON_ENUM,
53 &format!("calling `mem::discriminant` on non-enum type `{}`", ty_param),
55 // if this is a reference to an enum, suggest dereferencing
56 let (base_ty, ptr_depth) = walk_ptrs_ty_depth(ty_param);
57 if ptr_depth >= 1 && base_ty.is_enum() {
58 let param = &func_args[0];
60 // cancel out '&'s first
61 let mut derefs_needed = ptr_depth;
62 let mut cur_expr = param;
63 while derefs_needed > 0 {
64 if let ExprKind::AddrOf(_, ref inner_expr) = cur_expr.node {
66 cur_expr = inner_expr;
72 let derefs: String = iter::repeat('*').take(derefs_needed).collect();
73 db.span_suggestion_with_applicability(
76 format!("{}{}", derefs, snippet(cx, cur_expr.span, "<param>")),
77 Applicability::MachineApplicable,