From b23b3d21292a0290971a5d16abb2593659a03b48 Mon Sep 17 00:00:00 2001
From: chrchr-github <christian.riesch@live.com>
Date: Sat, 13 Jul 2024 21:13:54 +0200
Subject: [PATCH] Fix  #12935 FP unassignedVariable with static empty QString
 in function

---
 lib/checkunusedvar.cpp | 14 +++++++++++++-
 test/cfg/qt.cpp        |  6 ++++++
 test/testunusedvar.cpp | 10 ++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/lib/checkunusedvar.cpp b/lib/checkunusedvar.cpp
index d91d80f10d6..ae9e8c8f240 100644
--- a/lib/checkunusedvar.cpp
+++ b/lib/checkunusedvar.cpp
@@ -1149,6 +1149,16 @@ void CheckUnusedVar::checkFunctionVariableUsage_iterateScopes(const Scope* const
     }
 }
 
+static bool isReturnedByRef(const Variable* var, const Function* func)
+{
+    if (!func || !Function::returnsReference(func, true))
+        return false;
+    const std::vector<const Token*> returns = Function::findReturns(func);
+    return std::any_of(returns.begin(), returns.end(), [var](const Token* tok) {
+        return tok->varId() == var->declarationId();
+    });
+}
+
 void CheckUnusedVar::checkFunctionVariableUsage()
 {
     if (!mSettings->severity.isEnabled(Severity::style) && !mSettings->checkLibrary && !mSettings->isPremiumEnabled("unusedVariable"))
@@ -1364,7 +1374,9 @@ void CheckUnusedVar::checkFunctionVariableUsage()
             }
             // variable has been read but not written
             else if (!usage._write && !usage._allocateMemory && var && !var->isStlType() && !isEmptyType(var->type()) &&
-                     !(var->type() && var->type()->needInitialization == Type::NeedInitialization::False))
+                     !(var->type() && var->type()->needInitialization == Type::NeedInitialization::False) &&
+                     !(var->valueType() && var->valueType()->container) &&
+                     !(var->isStatic() && isReturnedByRef(var, scope->function)))
                 unassignedVariableError(usage._var->nameToken(), varname);
             else if (!usage._var->isMaybeUnused() && !usage._modified && !usage._read && var) {
                 const Token* vnt = var->nameToken();
diff --git a/test/cfg/qt.cpp b/test/cfg/qt.cpp
index a78e5d67996..b6d0ba760f9 100644
--- a/test/cfg/qt.cpp
+++ b/test/cfg/qt.cpp
@@ -790,3 +790,9 @@ void constVariablePointer_QVector(QVector<int*>& qv, int* p)
 {
     qv.push_back(p); // #12661
 }
+
+const QString& unassignedVariable_static_QString() // #12935
+{
+    static QString qs;
+    return qs;
+}
diff --git a/test/testunusedvar.cpp b/test/testunusedvar.cpp
index 38cc4e681fe..d8efbd702d4 100644
--- a/test/testunusedvar.cpp
+++ b/test/testunusedvar.cpp
@@ -5887,6 +5887,16 @@ class TestUnusedVar : public TestFixture {
                               "    return k;\n"
                               "}\n");
         ASSERT_EQUALS("", errout_str());
+
+        functionVariableUsage("int& f() {\n" // #12935
+                              "    static int i;\n"
+                              "    return i;\n"
+                              "}\n"
+                              "int* g() {\n"
+                              "    static int j;\n"
+                              "    return &j;\n"
+                              "}\n");
+        ASSERT_EQUALS("", errout_str());
     }
 
     void localvarextern() {