Fix #10684 FP unusedStructMember with static object (#3681)

Author: chrchr-github

lib/checkunusedvar.cpp

@@ -1426,6 +1426,19 @@ void CheckUnusedVar::checkStructMemberUsage()
                 bailout = true;
                 break;
             }
+            if (var && (var->typeStartToken()->str() == scope.className || var->typeEndToken()->str() == scope.className)) {
+                const std::string addressPattern("!!" + scope.className + " & " + var->name()); // cast from struct
+                const Token* addrTok = scope.bodyEnd;
+                do {
+                    addrTok = Token::findmatch(addrTok, addressPattern.c_str());
+                    if ((addrTok && addrTok->str() == ")" && addrTok->link()->isCast()) || isCPPCast(addrTok)) {
+                        bailout = true;
+                        break;
+                    }
+                    if (addrTok)
+                        addrTok = addrTok->next();
+                } while (addrTok);
+            }
         }
         if (bailout)
             continue;

test/testunusedvar.cpp

@@ -66,6 +66,7 @@ class TestUnusedVar : public TestFixture {
         TEST_CASE(structmember_sizeof);
         TEST_CASE(structmember16); // #10485
         TEST_CASE(structmember17); // #10591
+        TEST_CASE(structmember18); // #10684
 
         TEST_CASE(localvar1);
         TEST_CASE(localvar2);
@@ -1607,6 +1608,24 @@ class TestUnusedVar : public TestFixture {
         TODO_ASSERT_EQUALS("", "[test.cpp:1]: (style) struct member 'T::i' is never used.\n", errout.str()); // due to removeMacroInClassDef()
     }
 
+    void structmember18() { // #10684
+        checkStructMemberUsage("struct S { uint8_t padding[500]; };\n"
+                               "static S s = { 0 };\n"
+                               "uint8_t f() {\n"
+                               "    uint8_t* p = (uint8_t*)&s;\n"
+                               "    return p[10];\n"
+                               "};\n");
+        ASSERT_EQUALS("", errout.str());
+
+        checkStructMemberUsage("struct S { uint8_t padding[500]; };\n"
+                               "uint8_t f(const S& s) {\n"
+                               "    std::cout << &s;\n"
+                               "    auto p = reinterpret_cast<const uint8_t*>(&s);\n"
+                               "    return p[10];\n"
+                               "};\n");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void functionVariableUsage_(const char* file, int line, const char code[], const char filename[] = "test.cpp") {
         // Clear the error buffer..
         errout.str("");