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gccrs: implement unused variable checker on HIR.
This change moves the unused variable checker from the type resolver to HIR. We can now use the HIR Default Visitor, and it will be much more easier to implement other unused lints with this change. gcc/rust/ChangeLog: * Make-lang.in: Add new files rules in Makefile. * lang.opt: Add new flag. * rust-session-manager.cc (Session::compile_crate): Execute new variable checker. * checks/lints/unused-var/rust-unused-var-checker.cc (UnusedVarChecker): Implement unused variable checker. * checks/lints/unused-var/rust-unused-var-checker.h (UnusedVarChecker): Implement unused variable checker. * checks/lints/unused-var/rust-unused-var-collector.cc (UnusedVarCollector): Implement unused variable collector. * checks/lints/unused-var/rust-unused-var-collector.h (UnusedVarCollector): Implement unused variable collector. * checks/lints/unused-var/rust-unused-var-context.cc (UnusedVarContext): Implement unused variable context. * checks/lints/unused-var/rust-unused-var-context.h (UnusedVarContext): Implement unused variable context. gcc/testsuite/ChangeLog: * rust/compile/static_item_0.rs: New test. * rust/compile/template_function_0.rs: New test. Signed-off-by: Lucas Ly Ba <lucas.ly-ba@outlook.com>
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‎gcc/rust/Make-lang.in‎

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@@ -200,6 +200,9 @@ GRS_OBJS = \
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rust/rust-const-checker.o \
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rust/rust-lint-marklive.o \
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rust/rust-lint-unused-var.o \
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rust/rust-unused-var-checker.o \
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rust/rust-unused-var-collector.o \
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rust/rust-unused-var-context.o \
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rust/rust-readonly-check.o \
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rust/rust-hir-type-check-path.o \
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rust/rust-unsafe-checker.o \
@@ -432,6 +435,7 @@ RUST_INCLUDES = -I $(srcdir)/rust \
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-I $(srcdir)/rust/typecheck \
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-I $(srcdir)/rust/checks/lints \
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-I $(srcdir)/rust/checks/errors \
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-I $(srcdir)/rust/checks/lints/unused-var \
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-I $(srcdir)/rust/checks/errors/privacy \
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-I $(srcdir)/rust/checks/errors/borrowck \
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-I $(srcdir)/rust/checks/errors/feature \
@@ -502,6 +506,11 @@ rust/%.o: rust/checks/lints/%.cc
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$(COMPILE) $(RUST_CXXFLAGS) $(RUST_INCLUDES) $<
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$(POSTCOMPILE)
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# build unused variable checking pass files in rust folder
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rust/%.o: rust/checks/lints/unused-var/%.cc
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$(COMPILE) $(RUST_CXXFLAGS) $(RUST_INCLUDES) $<
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$(POSTCOMPILE)
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# build rust/checks/errors files in rust folder
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rust/%.o: rust/checks/errors/%.cc
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$(COMPILE) $(RUST_CXXFLAGS) $(RUST_INCLUDES) $<

‎gcc/rust/checks/lints/unused-var/rust-unused-var-checker.cc‎

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// Copyright (C) 2025 Free Software Foundation, Inc.
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// This file is part of GCC.
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// GCC is free software; you can redistribute it and/or modify it under
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// the terms of the GNU General Public License as published by the Free
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// Software Foundation; either version 3, or (at your option) any later
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// version.
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// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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// WARRANTY; without even the implied warranty of MERCHANTABILITY or
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// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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// for more details.
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// You should have received a copy of the GNU General Public License
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// along with GCC; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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#include "rust-unused-var-checker.h"
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#include "rust-hir-item.h"
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#include "options.h"
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namespace Rust {
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namespace Analysis {
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UnusedVarChecker::UnusedVarChecker ()
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: nr_context (
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Resolver2_0::ImmutableNameResolutionContext::get ().resolver ()),
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mappings (Analysis::Mappings::get ()),
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unused_var_context (std::make_unique<UnusedVarContext> ())
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{}
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void
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UnusedVarChecker::go (HIR::Crate &crate)
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{
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UnusedVarCollector collector (*unused_var_context);
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collector.go (crate);
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for (auto &item : crate.get_items ())
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item->accept_vis (*this);
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}
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void
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UnusedVarChecker::visit (HIR::ConstantItem &item)
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{
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std::string var_name = item.get_identifier ().as_string ();
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bool starts_with_under_score = var_name.compare (0, 1, "_") == 0;
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auto id = item.get_mappings ().get_hirid ();
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if (!unused_var_context->is_variable_used (id) && !starts_with_under_score)
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rust_warning_at (item.get_locus (), OPT_Wunused_variable,
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"unused name '%s'",
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item.get_identifier ().as_string ().c_str ());
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}
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void
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UnusedVarChecker::visit (HIR::StaticItem &item)
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{
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std::string var_name = item.get_identifier ().as_string ();
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bool starts_with_under_score = var_name.compare (0, 1, "_") == 0;
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auto id = item.get_mappings ().get_hirid ();
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if (!unused_var_context->is_variable_used (id) && !starts_with_under_score)
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rust_warning_at (item.get_locus (), OPT_Wunused_variable,
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"unused name '%s'",
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item.get_identifier ().as_string ().c_str ());
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}
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void
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UnusedVarChecker::visit (HIR::TraitItemFunc &item)
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{
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// TODO: check trait item functions if they are not derived.
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}
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void
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UnusedVarChecker::visit (HIR::IdentifierPattern &pattern)
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{
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std::string var_name = pattern.get_identifier ().as_string ();
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bool starts_with_under_score = var_name.compare (0, 1, "_") == 0;
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auto id = pattern.get_mappings ().get_hirid ();
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if (!unused_var_context->is_variable_used (id) && var_name != "self"
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&& !starts_with_under_score)
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rust_warning_at (pattern.get_locus (), OPT_Wunused_variable,
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"unused name '%s'",
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pattern.get_identifier ().as_string ().c_str ());
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}
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} // namespace Analysis
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} // namespace Rust

‎gcc/rust/checks/lints/unused-var/rust-unused-var-checker.h‎

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// Copyright (C) 2025 Free Software Foundation, Inc.
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// This file is part of GCC.
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// GCC is free software; you can redistribute it and/or modify it under
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// the terms of the GNU General Public License as published by the Free
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// Software Foundation; either version 3, or (at your option) any later
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// version.
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// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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// WARRANTY; without even the implied warranty of MERCHANTABILITY or
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// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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// for more details.
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// You should have received a copy of the GNU General Public License
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// along with GCC; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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#include "rust-hir-item.h"
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#include "rust-hir-pattern.h"
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#include "rust-hir-visitor.h"
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#include "rust-immutable-name-resolution-context.h"
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#include "rust-unused-var-collector.h"
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namespace Rust {
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namespace Analysis {
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class UnusedVarChecker : public HIR::DefaultHIRVisitor
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{
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public:
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UnusedVarChecker ();
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void go (HIR::Crate &crate);
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private:
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const Resolver2_0::NameResolutionContext &nr_context;
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Analysis::Mappings &mappings;
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std::unique_ptr<UnusedVarContext> unused_var_context;
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using HIR::DefaultHIRVisitor::visit;
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virtual void visit (HIR::TraitItemFunc &decl) override;
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virtual void visit (HIR::ConstantItem &item) override;
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virtual void visit (HIR::StaticItem &item) override;
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virtual void visit (HIR::IdentifierPattern &identifier) override;
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};
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} // namespace Analysis
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} // namespace Rust

‎gcc/rust/checks/lints/unused-var/rust-unused-var-collector.cc‎

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// Copyright (C) 2025 Free Software Foundation, Inc.
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// This file is part of GCC.
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// GCC is free software; you can redistribute it and/or modify it under
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// the terms of the GNU General Public License as published by the Free
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// Software Foundation; either version 3, or (at your option) any later
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// version.
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// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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// WARRANTY; without even the implied warranty of MERCHANTABILITY or
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// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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// for more details.
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// You should have received a copy of the GNU General Public License
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// along with GCC; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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#include "rust-unused-var-collector.h"
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#include "rust-hir-full-decls.h"
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#include "rust-hir-item.h"
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#include "rust-hir-path.h"
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#include "rust-hir-pattern.h"
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#include "rust-immutable-name-resolution-context.h"
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namespace Rust {
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namespace Analysis {
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UnusedVarCollector::UnusedVarCollector (UnusedVarContext &context)
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: nr_context (
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Resolver2_0::ImmutableNameResolutionContext::get ().resolver ()),
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mappings (Analysis::Mappings::get ()), unused_var_context (context)
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{}
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void
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UnusedVarCollector::go (HIR::Crate &crate)
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{
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for (auto &item : crate.get_items ())
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item->accept_vis (*this);
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}
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void
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UnusedVarCollector::visit (HIR::ConstantItem &item)
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{
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unused_var_context.add_variable (item.get_mappings ().get_hirid ());
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walk (item);
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}
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void
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UnusedVarCollector::visit (HIR::StaticItem &item)
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{
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unused_var_context.add_variable (item.get_mappings ().get_hirid ());
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walk (item);
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}
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void
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UnusedVarCollector::visit (HIR::IdentifierPattern &pattern)
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{
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auto id = pattern.get_mappings ().get_hirid ();
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unused_var_context.add_variable (id);
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}
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void
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UnusedVarCollector::visit (HIR::PathInExpression &expr)
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{
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mark_path_used (expr);
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}
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void
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UnusedVarCollector::visit (HIR::QualifiedPathInExpression &expr)
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{
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mark_path_used (expr);
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}
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void
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UnusedVarCollector::visit (HIR::StructExprFieldIdentifier &ident)
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{
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mark_path_used (ident);
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}
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} // namespace Analysis
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} // namespace Rust

‎gcc/rust/checks/lints/unused-var/rust-unused-var-collector.h‎

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// Copyright (C) 2025 Free Software Foundation, Inc.
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// This file is part of GCC.
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// GCC is free software; you can redistribute it and/or modify it under
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// the terms of the GNU General Public License as published by the Free
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// Software Foundation; either version 3, or (at your option) any later
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// version.
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// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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// WARRANTY; without even the implied warranty of MERCHANTABILITY or
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// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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// for more details.
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// You should have received a copy of the GNU General Public License
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// along with GCC; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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#include "rust-hir-expr.h"
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#include "rust-hir-item.h"
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#include "rust-hir-path.h"
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#include "rust-hir-pattern.h"
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#include "rust-hir-visitor.h"
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#include "rust-mapping-common.h"
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#include "rust-name-resolution-context.h"
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#include "rust-unused-var-context.h"
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#include "rust-name-resolver.h"
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namespace Rust {
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namespace Analysis {
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class UnusedVarCollector : public HIR::DefaultHIRVisitor
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{
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public:
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UnusedVarCollector (UnusedVarContext &context);
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void go (HIR::Crate &crate);
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private:
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const Resolver2_0::NameResolutionContext &nr_context;
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Analysis::Mappings &mappings;
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UnusedVarContext &unused_var_context;
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using HIR::DefaultHIRVisitor::visit;
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virtual void visit (HIR::PathInExpression &expr) override;
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virtual void visit (HIR::StructExprFieldIdentifier &ident) override;
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virtual void visit (HIR::ConstantItem &item) override;
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virtual void visit (HIR::StaticItem &item) override;
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virtual void visit (HIR::IdentifierPattern &pattern) override;
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virtual void visit (HIR::QualifiedPathInExpression &expr) override;
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template <typename T> void mark_path_used (T &path_expr)
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{
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NodeId ast_node_id = path_expr.get_mappings ().get_nodeid ();
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NodeId def_id = nr_context.lookup (ast_node_id).value ();
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HirId hir_id = mappings.lookup_node_to_hir (def_id).value ();
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unused_var_context.mark_used (hir_id);
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}
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};
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} // namespace Analysis
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} // namespace Rust

‎gcc/rust/checks/lints/unused-var/rust-unused-var-context.cc‎

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// Copyright (C) 2025 Free Software Foundation, Inc.
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// This file is part of GCC.
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// GCC is free software; you can redistribute it and/or modify it under
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// the terms of the GNU General Public License as published by the Free
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// Software Foundation; either version 3, or (at your option) any later
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// version.
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// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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// WARRANTY; without even the implied warranty of MERCHANTABILITY or
12+
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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// for more details.
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// You should have received a copy of the GNU General Public License
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// along with GCC; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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#include "rust-unused-var-context.h"
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namespace Rust {
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namespace Analysis {
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void
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UnusedVarContext::add_variable (HirId id)
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{
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if (is_used.find (id) == is_used.end ())
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is_used.insert ({id, false});
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}
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void
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UnusedVarContext::mark_used (HirId id)
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{
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is_used[id] = true;
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}
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bool
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UnusedVarContext::is_variable_used (HirId id) const
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{
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auto it = is_used.find (id);
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return it != is_used.end () && it->second;
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}
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std::string
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UnusedVarContext::as_string () const
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{
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std::stringstream ss;
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ss << "UnusedVarContext: ";
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for (const auto &pair : is_used)
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{
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ss << "HirId: " << pair.first << " Used: " << (pair.second ? "Yes" : "No")
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<< "\n";
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}
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return ss.str ();
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}
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} // namespace Analysis
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} // namespace Rust

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