unused struct members: don't warn about packed structs (#3088)

lib/checkunusedvar.cpp

@@ -1240,6 +1240,10 @@ void CheckUnusedVar::checkStructMemberUsage()
         if (scope->classStart->fileIndex() != 0 || scope->className.empty())
             continue;
 
+        // Packed struct => possibly used by lowlevel code. Struct members might be required by hardware.
+        if (scope->classEnd->isAttributePacked())
+            continue;
+
         // Bail out if struct/union contains any functions
         if (!scope->functionList.empty())
             continue;

lib/token.h

@@ -386,6 +386,12 @@ public:
     void isAttributeNothrow(bool value) {
         setFlag(fIsAttributeNothrow, value);
     }
+    bool isAttributePacked() const {
+        return getFlag(fIsAttributePacked);
+    }
+    void isAttributePacked(bool value) {
+        setFlag(fIsAttributePacked, value);
+    }
     bool isOperatorKeyword() const {
         return getFlag(fIsOperatorKeyword);
     }
@@ -838,9 +844,10 @@ private:
         fIsAttributeNoreturn    = (1 << 12), // __attribute__((noreturn)), __declspec(noreturn)
         fIsAttributeNothrow     = (1 << 13), // __attribute__((nothrow)), __declspec(nothrow)
         fIsAttributeUsed        = (1 << 14), // __attribute__((used))
-        fIsOperatorKeyword      = (1 << 15), // operator=, etc
-        fIsComplex              = (1 << 16), // complex/_Complex type
-        fIsEnumType             = (1 << 17)  // enumeration type
+        fIsAttributePacked      = (1 << 15), // __attribute__((packed))
+        fIsOperatorKeyword      = (1 << 16), // operator=, etc
+        fIsComplex              = (1 << 17), // complex/_Complex type
+        fIsEnumType             = (1 << 18)  // enumeration type
     };
 
     unsigned int _flags;

lib/tokenize.cpp

@@ -8585,6 +8585,10 @@ void Tokenizer::simplifyAttribute()
                 }
             }
 
+            else if (Token::simpleMatch(tok->previous(), "} __attribute__ ( ( packed )")) {
+                tok->previous()->isAttributePacked(true);
+            }
+
             Token::eraseTokens(tok, tok->next()->link()->next());
             tok->deleteThis();
         }

test/testunusedvar.cpp

@@ -48,6 +48,7 @@ private:
         TEST_CASE(structmember10);
         TEST_CASE(structmember11); // #4168 - initialization with {} / passed by address to unknown function
         TEST_CASE(structmember12); // #7179 - FP unused structmember
+        TEST_CASE(structmember13); // #3088 - __attribute__((packed))
         TEST_CASE(structmember_sizeof);
 
         TEST_CASE(localvar1);
@@ -422,6 +423,13 @@ private:
         ASSERT_EQUALS("", errout.str());
     }
 
+    void structmember13() { // #3088 - struct members required by hardware
+        checkStructMemberUsage("struct S {\n"
+                               "  int x;\n"
+                               "} __attribute__((packed));");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void structmember_extern() {
         // extern struct => no false positive
         checkStructMemberUsage("extern struct AB\n"