Rollup merge of #21468 - sanxiyn:dead-variant, r=
This implements a wish suggested in #17410, detecting enum variants that are never constructed, even in the presence of `#[derive(Clone)]`. The implementation is general and not specific to `#[derive(Clone)]`. r? @jakub-
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commit
0d37323fd3
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@ -47,6 +47,7 @@ struct MarkSymbolVisitor<'a, 'tcx: 'a> {
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struct_has_extern_repr: bool,
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ignore_non_const_paths: bool,
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inherited_pub_visibility: bool,
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ignore_variant_stack: Vec<ast::NodeId>,
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}
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impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
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@ -59,6 +60,7 @@ impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
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struct_has_extern_repr: false,
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ignore_non_const_paths: false,
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inherited_pub_visibility: false,
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ignore_variant_stack: vec![],
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}
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}
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@ -79,7 +81,9 @@ impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
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def::DefPrimTy(_) => (),
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def::DefVariant(enum_id, variant_id, _) => {
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self.check_def_id(enum_id);
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self.check_def_id(variant_id);
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if !self.ignore_variant_stack.contains(&variant_id.node) {
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self.check_def_id(variant_id);
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}
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}
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_ => {
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self.check_def_id(def.def_id());
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@ -278,6 +282,23 @@ impl<'a, 'tcx, 'v> Visitor<'v> for MarkSymbolVisitor<'a, 'tcx> {
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visit::walk_expr(self, expr);
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}
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fn visit_arm(&mut self, arm: &ast::Arm) {
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if arm.pats.len() == 1 {
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let pat = &*arm.pats[0];
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let variants = pat_util::necessary_variants(&self.tcx.def_map, pat);
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// Inside the body, ignore constructions of variants
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// necessary for the pattern to match. Those construction sites
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// can't be reached unless the variant is constructed elsewhere.
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let len = self.ignore_variant_stack.len();
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self.ignore_variant_stack.push_all(&*variants);
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visit::walk_arm(self, arm);
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self.ignore_variant_stack.truncate(len);
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} else {
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visit::walk_arm(self, arm);
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}
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}
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fn visit_pat(&mut self, pat: &ast::Pat) {
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let def_map = &self.tcx.def_map;
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match pat.node {
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@ -397,6 +418,11 @@ fn create_and_seed_worklist(tcx: &ty::ctxt,
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worklist.push(*id);
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}
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for id in reachable_symbols {
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// Reachable variants can be dead, because we warn about
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// variants never constructed, not variants never used.
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if let Some(ast_map::NodeVariant(..)) = tcx.map.find(*id) {
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continue;
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}
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worklist.push(*id);
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}
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@ -155,3 +155,27 @@ pub fn def_to_path(tcx: &ty::ctxt, id: ast::DefId) -> ast::Path {
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span: DUMMY_SP,
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})
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}
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/// Return variants that are necessary to exist for the pattern to match.
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pub fn necessary_variants(dm: &DefMap, pat: &ast::Pat) -> Vec<ast::NodeId> {
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let mut variants = vec![];
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walk_pat(pat, |p| {
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match p.node {
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ast::PatEnum(_, _) |
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ast::PatIdent(_, _, None) |
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ast::PatStruct(..) => {
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match dm.borrow().get(&p.id) {
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Some(&DefVariant(_, id, _)) => {
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variants.push(id.node);
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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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true
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});
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variants.sort();
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variants.dedup();
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variants
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}
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@ -121,6 +121,7 @@ impl fmt::Display for TestName {
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#[derive(Clone, Copy)]
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enum NamePadding {
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PadNone,
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#[allow(dead_code)]
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PadOnLeft,
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PadOnRight,
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}
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@ -0,0 +1,42 @@
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// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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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(dead_code)]
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#[derive(Copy)]
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enum Enum {
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Variant1, //~ ERROR: variant is never used
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Variant2,
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Variant3,
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}
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fn copy(e: Enum) -> Enum {
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use Enum::*;
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match e {
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Variant1 => Variant1,
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Variant2 => Variant2,
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Variant3 => Variant3,
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}
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}
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fn max(e: Enum) -> Enum {
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use Enum::*;
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match e {
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Variant1 => Variant3,
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Variant2 => Variant3,
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Variant3 => Variant3,
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}
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}
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fn main() {
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let e = Enum::Variant2;
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copy(e);
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max(e);
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}
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