use crate::utils::{match_def_path, paths, snippet, span_lint_and_then, walk_ptrs_ty_depth}; use if_chain::if_chain; use rustc_errors::Applicability; use rustc_hir::{BorrowKind, Expr, ExprKind}; use rustc_lint::{LateContext, LateLintPass}; use rustc_session::{declare_lint_pass, declare_tool_lint}; use std::iter; declare_clippy_lint! { /// **What it does:** Checks for calls of `mem::discriminant()` on a non-enum type. /// /// **Why is this bad?** The value of `mem::discriminant()` on non-enum types /// is unspecified. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// use std::mem; /// /// mem::discriminant(&"hello"); /// mem::discriminant(&&Some(2)); /// ``` pub MEM_DISCRIMINANT_NON_ENUM, correctness, "calling `mem::descriminant` on non-enum type" } declare_lint_pass!(MemDiscriminant => [MEM_DISCRIMINANT_NON_ENUM]); impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MemDiscriminant { fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) { if_chain! { if let ExprKind::Call(ref func, ref func_args) = expr.kind; // is `mem::discriminant` if let ExprKind::Path(ref func_qpath) = func.kind; if let Some(def_id) = cx.tables.qpath_res(func_qpath, func.hir_id).opt_def_id(); if match_def_path(cx, def_id, &paths::MEM_DISCRIMINANT); // type is non-enum let ty_param = cx.tables.node_substs(func.hir_id).type_at(0); if !ty_param.is_enum(); then { span_lint_and_then( cx, MEM_DISCRIMINANT_NON_ENUM, expr.span, &format!("calling `mem::discriminant` on non-enum type `{}`", ty_param), |db| { // if this is a reference to an enum, suggest dereferencing let (base_ty, ptr_depth) = walk_ptrs_ty_depth(ty_param); if ptr_depth >= 1 && base_ty.is_enum() { let param = &func_args[0]; // cancel out '&'s first let mut derefs_needed = ptr_depth; let mut cur_expr = param; while derefs_needed > 0 { if let ExprKind::AddrOf(BorrowKind::Ref, _, ref inner_expr) = cur_expr.kind { derefs_needed -= 1; cur_expr = inner_expr; } else { break; } } let derefs: String = iter::repeat('*').take(derefs_needed).collect(); db.span_suggestion( param.span, "try dereferencing", format!("{}{}", derefs, snippet(cx, cur_expr.span, "")), Applicability::MachineApplicable, ); } }, ) } } } }