gccrs: add unused parens lint

gcc/rust/ChangeLog:

	* checks/lints/unused/rust-unused-checker.cc (UnusedChecker::visit):
	Visit GroupExpr and add unused parens warning if not necessary.
	* checks/lints/unused/rust-unused-checker.h:
	New.
	* checks/lints/unused/rust-unused-collector.cc (UnusedCollector::visit):
	Check if a grouped expr in arithmetical or boolean expr is used.
	* checks/lints/unused/rust-unused-collector.h:
	New.
	* checks/lints/unused/rust-unused-context.cc (UnusedContext::add_group):
	Method helper.
	(UnusedContext::is_group_used):
	Likewise.
	* checks/lints/unused/rust-unused-context.h:
	Likewise.

gcc/testsuite/ChangeLog:

	* rust/compile/unused-parens_0.rs: New test.

Signed-off-by: Lucas Ly Ba <[email protected]>

Author: lucasly-ba

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

@@ -134,6 +134,14 @@ UnusedChecker::visit_loop_label (HIR::LoopLabel &label)
     rust_warning_at (lifetime.get_locus (), OPT_Wunused_variable,
 		     "unused label %qs", lifetime.to_string ().c_str ());
 }
+void
+UnusedChecker::visit (HIR::GroupedExpr &expr)
+{
+  auto id = expr.get_mappings ().get_hirid ();
+  if (!unused_context.is_group_used (id))
+    rust_warning_at (expr.get_locus (), OPT_Wunused_variable,
+		     "unnecessary parentheses");
+}
 
 } // namespace Analysis
 } // namespace Rust

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

@@ -45,6 +45,7 @@ class UnusedChecker : public HIR::DefaultHIRVisitor
   virtual void visit (HIR::StructPatternFieldIdent &identifier) override;
   virtual void visit (HIR::EmptyStmt &stmt) override;
   virtual void visit_loop_label (HIR::LoopLabel &label) override;
+  virtual void visit (HIR::GroupedExpr &expr) override;
 };
 } // namespace Analysis
 } // namespace Rust

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

@@ -106,5 +106,25 @@ UnusedCollector::visit (HIR::ContinueExpr &expr)
   walk (expr);
 }
 
+void
+UnusedCollector::visit (HIR::LazyBooleanExpr &expr)
+{
+  if (expr.get_lhs ().get_expression_type () == HIR::Expr::ExprType::Grouped)
+    mark_group_used (expr.get_lhs ());
+  if (expr.get_rhs ().get_expression_type () == HIR::Expr::ExprType::Grouped)
+    mark_group_used (expr.get_rhs ());
+  walk (expr);
+}
+
+void
+UnusedCollector::visit (HIR::ArithmeticOrLogicalExpr &expr)
+{
+  if (expr.get_lhs ().get_expression_type () == HIR::Expr::ExprType::Grouped)
+    mark_group_used (expr.get_lhs ());
+  if (expr.get_rhs ().get_expression_type () == HIR::Expr::ExprType::Grouped)
+    mark_group_used (expr.get_rhs ());
+  walk (expr);
+}
+
 } // namespace Analysis
 } // namespace Rust

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

@@ -55,6 +55,10 @@ class UnusedCollector : public HIR::DefaultHIRVisitor
   virtual void visit (HIR::BreakExpr &expr) override;
   virtual void visit (HIR::ContinueExpr &expr) override;
 
+  // Unused parens
+  virtual void visit (HIR::ArithmeticOrLogicalExpr &expr) override;
+  virtual void visit (HIR::LazyBooleanExpr &expr) override;
+
   template <typename T> HirId get_def_id (T &path_expr)
   {
     NodeId ast_node_id = path_expr.get_mappings ().get_nodeid ();
@@ -75,6 +79,11 @@ class UnusedCollector : public HIR::DefaultHIRVisitor
     auto def_id = get_def_id (path_expr);
     unused_context.add_label (def_id);
   }
+
+  template <typename T> void mark_group_used (T &path_expr)
+  {
+    unused_context.add_group (path_expr.get_mappings ().get_hirid ());
+  }
 };
 } // namespace Analysis
 } // namespace Rust

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

@@ -86,6 +86,19 @@ UnusedContext::is_label_used (HirId id) const
   return used_labels.find (id) != used_labels.end ();
 }
 
+void
+UnusedContext::add_group (HirId id)
+
+{
+  used_groups.emplace (id);
+}
+
+bool
+UnusedContext::is_group_used (HirId id) const
+{
+  return used_groups.find (id) != used_groups.end ();
+}
+
 std::string
 UnusedContext::as_string () const
 {

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

@@ -42,13 +42,18 @@ class UnusedContext
   void add_label (HirId id);
   bool is_label_used (HirId id) const;
 
+  // Unused grup
+  void add_group (HirId id);
+  bool is_group_used (HirId id) const;
+
   std::string as_string () const;
 
 private:
   std::unordered_set<HirId> used_vars;
   std::unordered_set<HirId> mutable_vars;
   std::map<HirId, std::vector<HirId>> assigned_vars;
   std::unordered_set<HirId> used_labels;
+  std::unordered_set<HirId> used_groups;
 };
 
 } // namespace Analysis

gcc/testsuite/rust/compile/unused-parens_0.rs

@@ -0,0 +1,10 @@
+// { dg-additional-options "-frust-unused-check-2.0" }
+pub fn a() {
+    let _a = (true) && (false);
+    let _b = (((2) + 1));
+// { dg-warning "unnecessary parentheses" "" { target *-*-* } .-1 }
+    let _c = ((((1))));
+// { dg-warning "unnecessary parentheses" "" { target *-*-* } .-1 }
+    let _d = (3 << 2) + 1;
+}
+