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Merge #3346
3346: Add lint for calling `mem::discriminant` on a non-enum type r=flip1995 a=HMPerson1 Also, if the type is a reference to an enum, we suggest removing `&`s and/or dereferencing. Fixes #3342 Co-authored-by: HMPerson1 <hmperson1@gmail.com> Co-authored-by: Philipp Krones <hello@philkrones.com>
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‎CHANGELOG.md‎

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@@ -744,6 +744,7 @@ All notable changes to this project will be documented in this file.
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[`match_same_arms`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#match_same_arms
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[`match_wild_err_arm`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#match_wild_err_arm
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[`maybe_infinite_iter`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#maybe_infinite_iter
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[`mem_discriminant_non_enum`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#mem_discriminant_non_enum
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[`mem_forget`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#mem_forget
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[`mem_replace_option_with_none`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#mem_replace_option_with_none
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[`min_max`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#min_max

‎README.md‎

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@@ -9,7 +9,7 @@ We are currently in the process of discussing Clippy 1.0 via the RFC process in
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A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
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[There are 281 lints included in this crate!](https://rust-lang-nursery.github.io/rust-clippy/master/index.html)
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[There are 282 lints included in this crate!](https://rust-lang-nursery.github.io/rust-clippy/master/index.html)
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We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
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‎clippy_lints/src/lib.rs‎

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@@ -144,6 +144,7 @@ pub mod loops;
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pub mod map_clone;
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pub mod map_unit_fn;
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pub mod matches;
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pub mod mem_discriminant;
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pub mod mem_forget;
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pub mod mem_replace;
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pub mod methods;
@@ -398,6 +399,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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reg.register_early_lint_pass(box doc::Doc::new(conf.doc_valid_idents.clone()));
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reg.register_late_lint_pass(box neg_multiply::NegMultiply);
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reg.register_early_lint_pass(box unsafe_removed_from_name::UnsafeNameRemoval);
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reg.register_late_lint_pass(box mem_discriminant::MemDiscriminant);
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reg.register_late_lint_pass(box mem_forget::MemForget);
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reg.register_late_lint_pass(box mem_replace::MemReplace);
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reg.register_late_lint_pass(box arithmetic::Arithmetic::default());
@@ -612,6 +614,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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matches::MATCH_REF_PATS,
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matches::MATCH_WILD_ERR_ARM,
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matches::SINGLE_MATCH,
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mem_discriminant::MEM_DISCRIMINANT_NON_ENUM,
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mem_replace::MEM_REPLACE_OPTION_WITH_NONE,
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methods::CHARS_LAST_CMP,
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methods::CHARS_NEXT_CMP,
@@ -924,6 +927,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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loops::NEVER_LOOP,
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loops::REVERSE_RANGE_LOOP,
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loops::WHILE_IMMUTABLE_CONDITION,
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mem_discriminant::MEM_DISCRIMINANT_NON_ENUM,
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methods::CLONE_DOUBLE_REF,
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methods::TEMPORARY_CSTRING_AS_PTR,
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minmax::MIN_MAX,

‎clippy_lints/src/mem_discriminant.rs‎

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// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use crate::rustc::hir::{Expr, ExprKind};
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use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use crate::rustc::{declare_tool_lint, lint_array};
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use crate::rustc_errors::Applicability;
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use crate::utils::{match_def_path, opt_def_id, paths, snippet, span_lint_and_then, walk_ptrs_ty_depth};
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use if_chain::if_chain;
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use std::iter;
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/// **What it does:** Checks for calls of `mem::discriminant()` on a non-enum type.
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///
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/// **Why is this bad?** The value of `mem::discriminant()` on non-enum types
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/// is unspecified.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// mem::discriminant(&"hello");
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/// mem::discriminant(&&Some(2));
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/// ```
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declare_clippy_lint! {
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pub MEM_DISCRIMINANT_NON_ENUM,
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correctness,
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"calling mem::descriminant on non-enum type"
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}
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pub struct MemDiscriminant;
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impl LintPass for MemDiscriminant {
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fn get_lints(&self) -> LintArray {
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lint_array![MEM_DISCRIMINANT_NON_ENUM]
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MemDiscriminant {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if_chain! {
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if let ExprKind::Call(ref func, ref func_args) = expr.node;
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// is `mem::discriminant`
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if let ExprKind::Path(ref func_qpath) = func.node;
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if let Some(def_id) = opt_def_id(cx.tables.qpath_def(func_qpath, func.hir_id));
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if match_def_path(cx.tcx, def_id, &paths::MEM_DISCRIMINANT);
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// type is non-enum
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let ty_param = cx.tables.node_substs(func.hir_id).type_at(0);
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if !ty_param.is_enum();
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then {
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span_lint_and_then(
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cx,
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MEM_DISCRIMINANT_NON_ENUM,
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expr.span,
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&format!("calling `mem::discriminant` on non-enum type `{}`", ty_param),
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|db| {
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// if this is a reference to an enum, suggest dereferencing
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let (base_ty, ptr_depth) = walk_ptrs_ty_depth(ty_param);
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if ptr_depth >= 1 && base_ty.is_enum() {
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let param = &func_args[0];
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// cancel out '&'s first
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let mut derefs_needed = ptr_depth;
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let mut cur_expr = param;
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while derefs_needed > 0 {
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if let ExprKind::AddrOf(_, ref inner_expr) = cur_expr.node {
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derefs_needed -= 1;
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cur_expr = inner_expr;
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} else {
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break;
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}
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}
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let derefs: String = iter::repeat('*').take(derefs_needed).collect();
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db.span_suggestion_with_applicability(
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param.span,
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"try dereferencing",
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format!("{}{}", derefs, snippet(cx, cur_expr.span, "<param>")),
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Applicability::MachineApplicable,
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);
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}
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},
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)
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}
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}
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}
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}

‎clippy_lints/src/utils/paths.rs‎

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@@ -55,6 +55,7 @@ pub const LATE_CONTEXT: [&str; 4] = ["rustc", "lint", "context", "LateContext"];
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pub const LINKED_LIST: [&str; 4] = ["alloc", "collections", "linked_list", "LinkedList"];
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pub const LINT: [&str; 3] = ["rustc", "lint", "Lint"];
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pub const LINT_ARRAY: [&str; 3] = ["rustc", "lint", "LintArray"];
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pub const MEM_DISCRIMINANT: [&str; 3] = ["core", "mem", "discriminant"];
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pub const MEM_FORGET: [&str; 3] = ["core", "mem", "forget"];
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pub const MEM_REPLACE: [&str; 3] = ["core", "mem", "replace"];
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pub const MEM_UNINIT: [&str; 3] = ["core", "mem", "uninitialized"];

‎tests/ui/mem_discriminant.rs‎

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// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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#![deny(clippy::mem_discriminant_non_enum)]
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use std::mem;
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enum Foo {
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One(usize),
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Two(u8),
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}
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struct A(Foo);
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fn main() {
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// bad
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mem::discriminant(&"hello");
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mem::discriminant(&&Some(2));
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mem::discriminant(&&None::<u8>);
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mem::discriminant(&&Foo::One(5));
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mem::discriminant(&&Foo::Two(5));
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mem::discriminant(&A(Foo::One(0)));
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let ro = &Some(3);
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let rro = &ro;
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mem::discriminant(&ro);
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mem::discriminant(rro);
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mem::discriminant(&rro);
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macro_rules! mem_discriminant_but_in_a_macro {
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($param:expr) => (mem::discriminant($param))
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}
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mem_discriminant_but_in_a_macro!(&rro);
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let rrrrro = &&&rro;
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mem::discriminant(&rrrrro);
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mem::discriminant(*rrrrro);
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// ok
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mem::discriminant(&Some(2));
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mem::discriminant(&None::<u8>);
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mem::discriminant(&Foo::One(5));
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mem::discriminant(&Foo::Two(5));
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mem::discriminant(ro);
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mem::discriminant(*rro);
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mem::discriminant(****rrrrro);
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}

‎tests/ui/mem_discriminant.stderr‎

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error: calling `mem::discriminant` on non-enum type `&str`
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--> $DIR/mem_discriminant.rs:24:5
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|
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24 | mem::discriminant(&"hello");
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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note: lint level defined here
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--> $DIR/mem_discriminant.rs:11:9
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|
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11 | #![deny(clippy::mem_discriminant_non_enum)]
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: calling `mem::discriminant` on non-enum type `&std::option::Option<i32>`
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--> $DIR/mem_discriminant.rs:25:5
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|
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25 | mem::discriminant(&&Some(2));
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| ^^^^^^^^^^^^^^^^^^---------^
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| |
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| help: try dereferencing: `&Some(2)`
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error: calling `mem::discriminant` on non-enum type `&std::option::Option<u8>`
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--> $DIR/mem_discriminant.rs:26:5
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|
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26 | mem::discriminant(&&None::<u8>);
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| ^^^^^^^^^^^^^^^^^^------------^
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| |
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| help: try dereferencing: `&None::<u8>`
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error: calling `mem::discriminant` on non-enum type `&Foo`
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--> $DIR/mem_discriminant.rs:27:5
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|
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27 | mem::discriminant(&&Foo::One(5));
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| ^^^^^^^^^^^^^^^^^^-------------^
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| |
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| help: try dereferencing: `&Foo::One(5)`
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error: calling `mem::discriminant` on non-enum type `&Foo`
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--> $DIR/mem_discriminant.rs:28:5
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|
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28 | mem::discriminant(&&Foo::Two(5));
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| ^^^^^^^^^^^^^^^^^^-------------^
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| |
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| help: try dereferencing: `&Foo::Two(5)`
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error: calling `mem::discriminant` on non-enum type `A`
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--> $DIR/mem_discriminant.rs:29:5
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|
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29 | mem::discriminant(&A(Foo::One(0)));
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: calling `mem::discriminant` on non-enum type `&std::option::Option<i32>`
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--> $DIR/mem_discriminant.rs:33:5
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|
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33 | mem::discriminant(&ro);
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| ^^^^^^^^^^^^^^^^^^---^
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| |
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| help: try dereferencing: `ro`
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error: calling `mem::discriminant` on non-enum type `&std::option::Option<i32>`
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--> $DIR/mem_discriminant.rs:34:5
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|
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34 | mem::discriminant(rro);
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| ^^^^^^^^^^^^^^^^^^---^
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| |
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| help: try dereferencing: `*rro`
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error: calling `mem::discriminant` on non-enum type `&&std::option::Option<i32>`
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--> $DIR/mem_discriminant.rs:35:5
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|
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35 | mem::discriminant(&rro);
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| ^^^^^^^^^^^^^^^^^^----^
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| |
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| help: try dereferencing: `*rro`
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error: calling `mem::discriminant` on non-enum type `&&std::option::Option<i32>`
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--> $DIR/mem_discriminant.rs:38:27
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|
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38 | ($param:expr) => (mem::discriminant($param))
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| ^^^^^^^^^^^^^^^^^^^^^^^^^
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...
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41 | mem_discriminant_but_in_a_macro!(&rro);
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| ---------------------------------------
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| | |
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| | help: try dereferencing: `*rro`
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| in this macro invocation
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error: calling `mem::discriminant` on non-enum type `&&&&&std::option::Option<i32>`
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--> $DIR/mem_discriminant.rs:44:5
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|
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44 | mem::discriminant(&rrrrro);
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| ^^^^^^^^^^^^^^^^^^-------^
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| |
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| help: try dereferencing: `****rrrrro`
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error: calling `mem::discriminant` on non-enum type `&&&std::option::Option<i32>`
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--> $DIR/mem_discriminant.rs:45:5
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|
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45 | mem::discriminant(*rrrrro);
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| ^^^^^^^^^^^^^^^^^^-------^
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| |
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| help: try dereferencing: `****rrrrro`
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error: aborting due to 12 previous errors
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