Fix #12176 false positive: unassignedVariable (#5656)

Author: chrchr-github

lib/checkunusedvar.cpp

@@ -1356,7 +1356,8 @@ void CheckUnusedVar::checkFunctionVariableUsage()
                 unassignedVariableError(usage._var->nameToken(), varname);
             }
             // variable has been read but not written
-            else if (!usage._write && !usage._allocateMemory && var && !var->isStlType() && !isEmptyType(var->type()))
+            else if (!usage._write && !usage._allocateMemory && var && !var->isStlType() && !isEmptyType(var->type()) &&
+                     !(var->type() && var->type()->needInitialization == Type::NeedInitialization::False))
                 unassignedVariableError(usage._var->nameToken(), varname);
             else if (!usage._var->isMaybeUnused() && !usage._modified && !usage._read && var) {
                 const Token* vnt = var->nameToken();

test/testunusedvar.cpp

@@ -140,6 +140,7 @@ class TestUnusedVar : public TestFixture {
         TEST_CASE(localvar67); // #9946
         TEST_CASE(localvar68);
         TEST_CASE(localvar69);
+        TEST_CASE(localvar70);
         TEST_CASE(localvarloops); // loops
         TEST_CASE(localvaralias1);
         TEST_CASE(localvaralias2); // ticket #1637
@@ -3827,6 +3828,15 @@ class TestUnusedVar : public TestFixture {
         ASSERT_EQUALS("", errout.str());
     }
 
+    void localvar70() {
+        functionVariableUsage("struct S { int i = 0; };\n" // #12176
+                              "void f(S s) {\n"
+                              "    S s1;\n"
+                              "    if (s == s1) {}\n"
+                              "}\n");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void localvarloops() {
         // loops
         functionVariableUsage("void fun(int c) {\n"