gccrs: add unused-assignments lint

gcc/rust/ChangeLog:

	* checks/lints/unused-var/rust-unused-var-checker.cc (UnusedVarChecker::UnusedVarChecker):
	(UnusedVarChecker::visit): Make warning for unused assignments.
	* checks/lints/unused-var/rust-unused-var-checker.h: Same.
	* checks/lints/unused-var/rust-unused-var-collector.cc (UnusedVarCollector::UnusedVarCollector):
	(UnusedVarCollector::visit): Handle assign via visitor.
	* checks/lints/unused-var/rust-unused-var-collector.h: Same.
	* checks/lints/unused-var/rust-unused-var-context.cc (UnusedVarContext::add_assign):
	(UnusedVarContext::remove_assign): add method for the lint.
	(UnusedVarContext::is_variable_assigned): Same.
	* checks/lints/unused-var/rust-unused-var-context.h: Add method to get the hir_def_id of an expr.
	* hir/tree/rust-hir-visitor.cc (DefaultHIRVisitor::walk_right): add walk_right for assign default visitor.
	* hir/tree/rust-hir-visitor.h: Same.

Signed-off-by: Lucas Ly Ba <lucas.ly-ba@outlook.com>

Author: lucasly-ba

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

@@ -17,6 +17,7 @@
 // <http://www.gnu.org/licenses/>.
 
 #include "rust-unused-var-checker.h"
+#include "rust-hir-expr.h"
 #include "rust-hir-item.h"
 
 #include "options.h"
@@ -25,7 +26,7 @@ namespace Rust {
 namespace Analysis {
 UnusedVarChecker::UnusedVarChecker ()
   : nr_context (
-    Resolver2_0::ImmutableNameResolutionContext::get ().resolver ()),
+      Resolver2_0::ImmutableNameResolutionContext::get ().resolver ()),
     mappings (Analysis::Mappings::get ()),
     unused_var_context (std::make_unique<UnusedVarContext> ())
 {}
@@ -78,5 +79,22 @@ UnusedVarChecker::visit (HIR::IdentifierPattern &pattern)
 		     "unused name '%s'",
 		     pattern.get_identifier ().as_string ().c_str ());
 }
+void
+
+UnusedVarChecker::visit (HIR::AssignmentExpr &expr)
+
+{
+  const auto &lhs = expr.get_lhs ();
+  std::string var_name = lhs.as_string ();
+  bool starts_with_under_score = var_name.compare (0, 1, "_") == 0;
+  NodeId ast_node_id = lhs.get_mappings ().get_nodeid ();
+  NodeId def_id = nr_context.lookup (ast_node_id).value ();
+  HirId id = mappings.lookup_node_to_hir (def_id).value ();
+  if (unused_var_context->is_variable_assigned (
+	id, lhs.get_mappings ().get_hirid ())
+      && !starts_with_under_score)
+    rust_warning_at (lhs.get_locus (), OPT_Wunused_variable,
+		     "unused assignment '%s'", var_name.c_str ());
+}
 } // namespace Analysis
-} // namespace Rust
+} // namespace Rust

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

@@ -16,6 +16,7 @@
 // along with GCC; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
+#include "rust-hir-expr.h"
 #include "rust-hir-item.h"
 #include "rust-hir-pattern.h"
 #include "rust-hir-visitor.h"
@@ -40,6 +41,7 @@ class UnusedVarChecker : public HIR::DefaultHIRVisitor
   virtual void visit (HIR::ConstantItem &item) override;
   virtual void visit (HIR::StaticItem &item) override;
   virtual void visit (HIR::IdentifierPattern &identifier) override;
+  virtual void visit (HIR::AssignmentExpr &identifier) override;
 };
 } // namespace Analysis
-} // namespace Rust
+} // namespace Rust

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

@@ -17,17 +17,19 @@
 // <http://www.gnu.org/licenses/>.
 
 #include "rust-unused-var-collector.h"
+#include "rust-hir-expr.h"
 #include "rust-hir-full-decls.h"
 #include "rust-hir-item.h"
 #include "rust-hir-path.h"
 #include "rust-hir-pattern.h"
 #include "rust-immutable-name-resolution-context.h"
+#include "tree-check.h"
 
 namespace Rust {
 namespace Analysis {
 UnusedVarCollector::UnusedVarCollector (UnusedVarContext &context)
   : nr_context (
-    Resolver2_0::ImmutableNameResolutionContext::get ().resolver ()),
+      Resolver2_0::ImmutableNameResolutionContext::get ().resolver ()),
     mappings (Analysis::Mappings::get ()), unused_var_context (context)
 {}
 void
@@ -54,8 +56,7 @@ UnusedVarCollector::visit (HIR::StaticItem &item)
 void
 UnusedVarCollector::visit (HIR::IdentifierPattern &pattern)
 {
-  auto id = pattern.get_mappings ().get_hirid ();
-  unused_var_context.add_variable (id);
+  unused_var_context.add_variable (pattern.get_mappings ().get_hirid ());
 }
 
 void
@@ -75,5 +76,14 @@ UnusedVarCollector::visit (HIR::StructExprFieldIdentifier &ident)
 {
   mark_path_used (ident);
 }
+void
+UnusedVarCollector::visit (HIR::AssignmentExpr &expr)
+{
+  auto def_id = get_def_id (expr);
+  HirId id = expr.get_lhs ().get_mappings ().get_hirid ();
+  unused_var_context.add_assign (def_id, id);
+  walk_right (expr);
+}
+
 } // namespace Analysis
 } // namespace Rust

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

@@ -46,14 +46,22 @@ class UnusedVarCollector : public HIR::DefaultHIRVisitor
   virtual void visit (HIR::StaticItem &item) override;
   virtual void visit (HIR::IdentifierPattern &pattern) override;
   virtual void visit (HIR::QualifiedPathInExpression &expr) override;
+  virtual void visit (HIR::AssignmentExpr &expr) override;
 
-  template <typename T> void mark_path_used (T &path_expr)
+  template <typename T> HirId get_def_id (T &path_expr)
   {
     NodeId ast_node_id = path_expr.get_mappings ().get_nodeid ();
-    NodeId def_id = nr_context.lookup (ast_node_id).value ();
-    HirId hir_id = mappings.lookup_node_to_hir (def_id).value ();
-    unused_var_context.mark_used (hir_id);
+    NodeId id = nr_context.lookup (ast_node_id).value ();
+    HirId def_id = mappings.lookup_node_to_hir (id).value ();
+    return def_id;
+  }
+
+  template <typename T> void mark_path_used (T &path_expr)
+  {
+    auto def_id = get_def_id (path_expr);
+    unused_var_context.mark_used (def_id);
+    unused_var_context.remove_assign (def_id);
   }
 };
 } // namespace Analysis
-} // namespace Rust
+} // namespace Rust

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

@@ -41,6 +41,26 @@ UnusedVarContext::is_variable_used (HirId id) const
   return it != is_used.end () && it->second;
 }
 
+void
+UnusedVarContext::add_assign (HirId id_def, HirId id)
+{
+  assigned_vars[id_def].push_back (id);
+}
+
+void
+UnusedVarContext::remove_assign (HirId id_def)
+{
+  if (assigned_vars.find (id_def) != assigned_vars.end ())
+    assigned_vars[id_def].pop_back ();
+}
+bool
+UnusedVarContext::is_variable_assigned (HirId id_def, HirId id)
+{
+  auto assigned_vec = assigned_vars[id_def];
+  return std::find (assigned_vec.begin (), assigned_vec.end (), id)
+	 != assigned_vec.end ();
+}
+
 std::string
 UnusedVarContext::as_string () const
 {

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

@@ -25,13 +25,17 @@ class UnusedVarContext
 public:
   void add_variable (HirId id);
   void mark_used (HirId id);
-
   bool is_variable_used (HirId id) const;
 
+  void add_assign (HirId id_def, HirId id);
+  void remove_assign (HirId id_def);
+  bool is_variable_assigned (HirId id_def, HirId id);
+
   std::string as_string () const;
 
 private:
   std::map<HirId, bool> is_used;
+  std::map<HirId, std::vector<HirId>> assigned_vars;
 };
 } // namespace Analysis
 } // namespace Rust

gcc/rust/hir/tree/rust-hir-visitor.cc

@@ -197,6 +197,13 @@ DefaultHIRVisitor::walk (AssignmentExpr &expr)
   expr.get_rhs ().accept_vis (*this);
 }
 
+void
+DefaultHIRVisitor::walk_right (AssignmentExpr &expr)
+{
+  visit_outer_attrs (expr);
+  expr.get_rhs ().accept_vis (*this);
+}
+
 void
 DefaultHIRVisitor::walk (CompoundAssignmentExpr &expr)
 {

gcc/rust/hir/tree/rust-hir-visitor.h

@@ -356,6 +356,7 @@ class DefaultHIRVisitor : public HIRFullVisitor
   virtual void walk (LazyBooleanExpr &) final;
   virtual void walk (TypeCastExpr &) final;
   virtual void walk (AssignmentExpr &) final;
+  virtual void walk_right (AssignmentExpr &) final;
   virtual void walk (CompoundAssignmentExpr &) final;
   virtual void walk (GroupedExpr &) final;