sizeofCalculation: skip if void-casted inside a macro (#6888)

lib/checksizeof.cpp

@@ -250,6 +250,17 @@ void CheckSizeof::sizeofCalculation()
 
     for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next()) {
         if (Token::simpleMatch(tok, "sizeof (")) {
+
+            // ignore if the `sizeof` result is cast to void inside a macro, i.e. the calculation is
+            // expected to be parsed but skipped, such as in a disabled custom ASSERT() macro
+            if (tok->isExpandedMacro() && tok->previous()) {
+                const Token *cast_end = (tok->previous()->str() == "(") ? tok->previous() : tok;
+                if (Token::simpleMatch(cast_end->tokAt(-3), "( void )") ||
+                    Token::simpleMatch(cast_end->tokAt(-1), "static_cast<void>")) {
+                    continue;
+                }
+            }
+
             const Token *argument = tok->next()->astOperand2();
             if (argument && argument->isCalculation() && (!argument->isExpandedMacro() || printInconclusive))
                 sizeofCalculationError(argument, argument->isExpandedMacro());

test/testsizeof.cpp

@@ -108,6 +108,25 @@ private:
 
         check("sizeof(--foo)");
         ASSERT_EQUALS("[test.cpp:1]: (warning) Found calculation inside sizeof().\n", errout.str());
+
+        // #6888
+        check("int f(int i) {\n"
+              "  $($void$)$sizeof$($i $!= $2$);\n" // '$' sets Token::isExpandedMacro() to true
+              "  $($void$)$($($($($sizeof$($i $!= $2$)$)$)$)$);\n"
+              "  $static_cast<void>$($sizeof($i $!= $2$)$);\n"
+              "  $static_cast<void>$($($($($($sizeof$($i $!= $2$)$)$)$)$)$);\n"
+              "  return i + foo(1);\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        check("int f(int i) {\n"
+              "  $sizeof$($i $!= $2$);\n"
+              "  $($($sizeof($i $!= 2$)$)$);\n"
+              "  return i + foo(1);\n"
+              "}");
+        ASSERT_EQUALS("[test.cpp:2]: (warning, inconclusive) Found calculation inside sizeof().\n"
+                      "[test.cpp:3]: (warning, inconclusive) Found calculation inside sizeof().\n", errout.str());
+
     }
 
     void sizeofForArrayParameter() {