Fix #12178 extern "C++" scope generates valueflow (#5654)

Author: chrchr-github

lib/tokenize.cpp

@@ -3592,17 +3592,18 @@ void Tokenizer::simplifyExternC()
 
     // Add attributes to all tokens within `extern "C"` inlines and blocks, and remove the `extern "C"` tokens.
     for (Token *tok = list.front(); tok; tok = tok->next()) {
-        if (Token::simpleMatch(tok, "extern \"C\"")) {
+        if (Token::Match(tok, "extern \"C\"|\"C++\"")) {
             Token *tok2 = tok->next();
+            const bool isExtC = tok->next()->str().size() == 3;
             if (tok->strAt(2) == "{") {
                 tok2 = tok2->next(); // skip {
                 while ((tok2 = tok2->next()) && tok2 != tok->linkAt(2))
-                    tok2->isExternC(true);
+                    tok2->isExternC(isExtC);
                 tok->linkAt(2)->deleteThis(); // }
                 tok->deleteNext(2); // "C" {
             } else {
                 while ((tok2 = tok2->next()) && !Token::Match(tok2, "[;{]"))
-                    tok2->isExternC(true);
+                    tok2->isExternC(isExtC);
                 tok->deleteNext(); // "C"
             }
             tok->deleteThis(); // extern

test/testsimplifytemplate.cpp

@@ -4163,7 +4163,8 @@ class TestSimplifyTemplate : public TestFixture {
 
     void template163() { // #9685 syntax error
         const char code[] = "extern \"C++\" template < typename T > T * test ( ) { return nullptr ; }";
-        ASSERT_EQUALS(code, tok(code));
+        const char expected[] = "template < typename T > T * test ( ) { return nullptr ; }";
+        ASSERT_EQUALS(expected, tok(code));
     }
 
     void template164() {  // #9394

test/testtokenize.cpp

@@ -1548,8 +1548,47 @@ class TestTokenizer : public TestFixture {
 
 
     void simplifyExternC() {
-        ASSERT_EQUALS("int foo ( ) ;", tokenizeAndStringify("extern \"C\" int foo();"));
-        ASSERT_EQUALS("int foo ( ) ;", tokenizeAndStringify("extern \"C\" { int foo(); }"));
+        const char expected[] = "int foo ( ) ;";
+        {
+            const char code[] = "extern \"C\" int foo();";
+            // tokenize..
+            Tokenizer tokenizer(&settings0, this);
+            std::istringstream istr(code);
+            ASSERT(tokenizer.tokenize(istr, "test.cpp"));
+            // Expected result..
+            ASSERT_EQUALS(expected, tokenizer.tokens()->stringifyList(nullptr, false));
+            ASSERT(tokenizer.tokens()->next()->isExternC());
+        }
+        {
+            const char code[] = "extern \"C\" { int foo(); }";
+            // tokenize..
+            Tokenizer tokenizer(&settings0, this);
+            std::istringstream istr(code);
+            ASSERT(tokenizer.tokenize(istr, "test.cpp"));
+            // Expected result..
+            ASSERT_EQUALS(expected, tokenizer.tokens()->stringifyList(nullptr, false));
+            ASSERT(tokenizer.tokens()->next()->isExternC());
+        }
+        {
+            const char code[] = "extern \"C++\" int foo();";
+            // tokenize..
+            Tokenizer tokenizer(&settings0, this);
+            std::istringstream istr(code);
+            ASSERT(tokenizer.tokenize(istr, "test.cpp"));
+            // Expected result..
+            ASSERT_EQUALS(expected, tokenizer.tokens()->stringifyList(nullptr, false));
+            ASSERT(!tokenizer.tokens()->next()->isExternC());
+        }
+        {
+            const char code[] = "extern \"C++\" { int foo(); }";
+            // tokenize..
+            Tokenizer tokenizer(&settings0, this);
+            std::istringstream istr(code);
+            ASSERT(tokenizer.tokenize(istr, "test.cpp"));
+            // Expected result..
+            ASSERT_EQUALS(expected, tokenizer.tokens()->stringifyList(nullptr, false));
+            ASSERT(!tokenizer.tokens()->next()->isExternC());
+        }
     }
 
     void simplifyFunctionParameters() {