loplugin:unusedfields, fix var taking ref

Change-Id: I0ea1f0c7488c140fca9f64de326c6ac588ece925

compilerplugins/clang/test/unusedfields.cxx

@@ -116,16 +116,19 @@ struct ReadOnlyAnalysis
 // expected-error@-2 {{read m_f3 [loplugin:unusedfields]}}
 // expected-error@-3 {{read m_f4 [loplugin:unusedfields]}}
 // expected-error@-4 {{read m_f5 [loplugin:unusedfields]}}
-// expected-error@-5 {{write m_f2 [loplugin:unusedfields]}}
-// expected-error@-6 {{write m_f3 [loplugin:unusedfields]}}
-// expected-error@-7 {{write m_f4 [loplugin:unusedfields]}}
-// expected-error@-8 {{write m_f5 [loplugin:unusedfields]}}
+// expected-error@-5 {{read m_f6 [loplugin:unusedfields]}}
+// expected-error@-6 {{write m_f2 [loplugin:unusedfields]}}
+// expected-error@-7 {{write m_f3 [loplugin:unusedfields]}}
+// expected-error@-8 {{write m_f4 [loplugin:unusedfields]}}
+// expected-error@-9 {{write m_f5 [loplugin:unusedfields]}}
+// expected-error@-10 {{write m_f6 [loplugin:unusedfields]}}
 {
     int m_f1;
     int m_f2;
     int m_f3;
     std::vector<int> m_f4;
     int m_f5;
+    int m_f6;
 
     // check that we dont see a write of m_f1
     ReadOnlyAnalysis() : m_f1(0) {}
@@ -141,6 +144,13 @@ struct ReadOnlyAnalysis
 
     // check that we see a write when we pass by non-const ref
     void method5() { ReadOnly1 a(m_f5); }
+
+    // check that we see a write when we pass by non-const ref
+    void method6()
+    {
+        int& r = m_f6;
+        r = 1;
+    }
 };
 
 struct ReadOnlyAnalysis2

compilerplugins/clang/unusedfields.cxx

@@ -611,6 +611,19 @@ void UnusedFields::checkReadOnly(const FieldDecl* fieldDecl, const Expr* memberE
     {
         if (!parent)
         {
+            // check if we have an expression like
+            //    int& r = m_field;
+            auto parentsRange = compiler.getASTContext().getParents(*child);
+            if (parentsRange.begin() != parentsRange.end())
+            {
+                auto varDecl = dyn_cast_or_null<VarDecl>(parentsRange.begin()->get<Decl>());
+                // The isImplicit() call is to avoid triggering when we see the vardecl which is part of a for-range statement,
+                // which is of type 'T&&' and also an l-value-ref ?
+                if (varDecl && !varDecl->isImplicit() && loplugin::TypeCheck(varDecl->getType()).LvalueReference().NonConst())
+                {
+                    bPotentiallyWrittenTo = true;
+                }
+            }
             break;
         }
         if (isa<CXXReinterpretCastExpr>(parent))

solenv/CompilerTest_compilerplugins_clang.mk

@@ -38,13 +38,11 @@ $(eval $(call gb_CompilerTest_add_exception_objects,compilerplugins_clang, \
     compilerplugins/clang/test/unnecessaryoverride-dtor \
     compilerplugins/clang/test/unnecessaryparen \
     compilerplugins/clang/test/unoany \
+    compilerplugins/clang/test/unusedfields \
     compilerplugins/clang/test/useuniqueptr \
     compilerplugins/clang/test/vclwidgets \
 ))
 
-# FIXME Fails with clang-3.8.
-#    compilerplugins/clang/test/unusedfields \
-
 $(eval $(call gb_CompilerTest_use_externals,compilerplugins_clang, \
     boost_headers \
     cppunit \