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]
35 fn name(&self) -> &'static str {
40 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MemDiscriminant {
41 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
43 if let ExprKind::Call(ref func, ref func_args) = expr.node;
44 // is `mem::discriminant`
45 if let ExprKind::Path(ref func_qpath) = func.node;
46 if let Some(def_id) = opt_def_id(cx.tables.qpath_def(func_qpath, func.hir_id));
47 if match_def_path(cx.tcx, def_id, &paths::MEM_DISCRIMINANT);
49 let ty_param = cx.tables.node_substs(func.hir_id).type_at(0);
50 if !ty_param.is_enum();
55 MEM_DISCRIMINANT_NON_ENUM,
57 &format!("calling `mem::discriminant` on non-enum type `{}`", ty_param),
59 // if this is a reference to an enum, suggest dereferencing
60 let (base_ty, ptr_depth) = walk_ptrs_ty_depth(ty_param);
61 if ptr_depth >= 1 && base_ty.is_enum() {
62 let param = &func_args[0];
64 // cancel out '&'s first
65 let mut derefs_needed = ptr_depth;
66 let mut cur_expr = param;
67 while derefs_needed > 0 {
68 if let ExprKind::AddrOf(_, ref inner_expr) = cur_expr.node {
70 cur_expr = inner_expr;
76 let derefs: String = iter::repeat('*').take(derefs_needed).collect();
77 db.span_suggestion_with_applicability(
80 format!("{}{}", derefs, snippet(cx, cur_expr.span, "<param>")),
81 Applicability::MachineApplicable,