CPreProcessor,C: skip #ifdef __cplusplus ~ #endif branch

Close #2647.

C parser doesn't work when C++ code "extern "C" {" and "}" is given.

    $ cat /tmp/extern-c.c
    extern "C" {
    #ifdef X
      void f() {}
    #else
      void g() {}
    #endif
    }
    $ u-ctags --output-format=xref --kinds-c=+plz --fields=+nie -o - /tmp/extern-c.c
    f                function      3 /tmp/extern-c.c  void f() {}

    $ cat /tmp/none-extern-c.c
    #ifdef X
      void f() {}
    #else
      void g() {}
    #endif
    $ u-ctags --output-format=xref --kinds-c=+plz --fields=+nie -o - /tmp/none-extern-c.c
    f                function      2 /tmp/none-extern-c.c void f() {}
    g                function      4 /tmp/none-extern-c.c void g() {}

The function g() is missed if the code is surrounded by extern "C" { and }.

This change uses a heuristic rule to skip the code in the C parser.

In most of cases, the code is in #ifdef __cplusplus ~ #endif branch.
So when the CPreProcessor parser detects #ifdef __cplusplus ~ #endif,
with this change, the CPreProcessor parser doesn't pass the code inside __cplusplus branch
to its client parser that requests to the CPreProcessor parser to do so.

C parser requests it. C++ parser doesn't.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>

parsers/asm.c

@@ -323,6 +323,7 @@ static void findAsmTags (void)
 		.headerKindIndex = KIND_GHOST_INDEX,
 		.headerSystemRoleIndex = 0,
 		.headerLocalRoleIndex = 0,
+		.skip__cplusplus_branch = false,
 	};
 	cppInit (&initData);
 

parsers/c.c

@@ -3508,6 +3508,7 @@ static rescanReason findCTags (const unsigned int passCount)
 		.headerKindIndex = kind_for_header,
 		.headerSystemRoleIndex = role_for_header_system,
 		.headerLocalRoleIndex = role_for_header_local,
+		.skip__cplusplus_branch = !isInputLanguage (Lang_cpp),
 	};
 	cppInit (&initData);
 

parsers/cpreprocessor.c

@@ -99,6 +99,8 @@ typedef struct sCppState {
 
 	int macrodefFieldIndex;
 
+	bool skip__cplusplus_branch;
+
 	struct sDirective {
 		enum eState state;       /* current directive being processed */
 		bool	accept;          /* is a directive syntactically permitted? */
@@ -317,6 +319,8 @@ static void cppInitCommon(langType clientLang, const struct cppInitData *initDat
 		Cpp.headerLocalRoleIndex = CPREPRO_HEADER_KIND_LOCAL_ROLE;
 	}
 
+	Cpp.skip__cplusplus_branch = initData->skip__cplusplus_branch;
+
 	Cpp.directive.state     = DRCTV_NONE;
 	Cpp.directive.accept    = true;
 	Cpp.directive.nestLevel = 0;
@@ -931,10 +935,32 @@ static void directivePragma (int c)
 	Cpp.directive.state = DRCTV_NONE;
 }
 
+static bool isDefCondition (const int c, const char *condition)
+{
+	if (*condition == '\0')
+		return true;
+	else if (c == EOF)
+		return false;
+
+	if (*condition != '\0' && c == condition[0])
+	{
+		const int next = cppGetcFromUngetBufferOrFile ();
+		return isDefCondition (next, condition + 1);
+	}
+
+	return false;
+}
+
 static bool directiveIf (const int c)
 {
 	DebugStatement ( const bool ignore0 = isIgnore (); )
-	const bool ignore = pushConditional ((bool) (c != '0'));
+	bool firstBranchChosen = true;
+
+	if (c == '0'
+		|| (Cpp.skip__cplusplus_branch && isDefCondition (c, "__cplusplus")))
+		firstBranchChosen = false;
+
+	const bool ignore = pushConditional (firstBranchChosen);
 
 	Cpp.directive.state = DRCTV_NONE;
 	DebugStatement ( debugCppNest (true, Cpp.directive.nestLevel);
@@ -1624,6 +1650,7 @@ static void findCppTags (void)
 		.headerKindIndex = KIND_GHOST_INDEX,
 		.headerSystemRoleIndex = 0,
 		.headerLocalRoleIndex = 0,
+		.skip__cplusplus_branch = false,
 	};
 
 	cppInitCommon (Cpp.lang, &initData);

parsers/cpreprocessor.h

@@ -91,6 +91,8 @@ struct cppInitData {
 	int headerKindIndex;
 	int headerSystemRoleIndex;
 	int headerLocalRoleIndex;
+
+	bool skip__cplusplus_branch; /* #ifdef __cplusplus ... #endif */
 };
 
 extern void cppInit (const struct cppInitData *initData);

parsers/cxx/cxx_parser.c

@@ -1821,7 +1821,8 @@ bool cxxParserParseIfForWhileSwitchCatchParenthesis(void)
 	return true;
 }
 
-static rescanReason cxxParserMain(const unsigned int passCount)
+static rescanReason cxxParserMain(const unsigned int passCount,
+								  bool cppSkip__cpluscplus_branch)
 {
 	cxxScopeClear();
 	cxxTokenAPINewFile();
@@ -1848,6 +1849,7 @@ static rescanReason cxxParserMain(const unsigned int passCount)
 		.headerKindIndex = kind_for_header,
 		.headerSystemRoleIndex = role_for_header_system,
 		.headerLocalRoleIndex = role_for_header_local,
+		.skip__cplusplus_branch = cppSkip__cpluscplus_branch,
 	};
 
 	cppInit(&initData);
@@ -1885,7 +1887,7 @@ rescanReason cxxCParserMain(const unsigned int passCount)
 	g_cxx.bConfirmedCPPLanguage = false;
 	cxxKeywordEnablePublicProtectedPrivate(false);
 
-	rescanReason r = cxxParserMain(passCount);
+	rescanReason r = cxxParserMain(passCount, true);
 	CXX_DEBUG_LEAVE();
 	return r;
 }
@@ -1899,7 +1901,7 @@ rescanReason cxxCUDAParserMain(const unsigned int passCount)
 	g_cxx.bConfirmedCPPLanguage = false;
 	cxxKeywordEnablePublicProtectedPrivate(false);
 
-	rescanReason r = cxxParserMain(passCount);
+	rescanReason r = cxxParserMain(passCount, true);
 	CXX_DEBUG_LEAVE();
 	return r;
 }
@@ -1915,7 +1917,7 @@ rescanReason cxxCppParserMain(const unsigned int passCount)
 	g_cxx.bConfirmedCPPLanguage = !isInputHeaderFile();
 	cxxKeywordEnablePublicProtectedPrivate(g_cxx.bConfirmedCPPLanguage);
 
-	rescanReason r = cxxParserMain(passCount);
+	rescanReason r = cxxParserMain(passCount, false);
 	CXX_DEBUG_LEAVE();
 	return r;
 }

parsers/dts.c

@@ -50,6 +50,7 @@ static void runCppGetc (void)
 		.headerKindIndex = KIND_GHOST_INDEX,
 		.headerSystemRoleIndex = 0,
 		.headerLocalRoleIndex = 0,
+		.skip__cplusplus_branch = false,
 	};
 	cppInit (&initData);
 

parsers/ldscript.c

@@ -708,6 +708,7 @@ static void findLdScriptTags (void)
 		.headerKindIndex = KIND_GHOST_INDEX,
 		.headerSystemRoleIndex = 0,
 		.headerLocalRoleIndex = 0,
+		.skip__cplusplus_branch = false,
 	};
 	cppInit (&initData);
 

parsers/protobuf.c

@@ -666,6 +666,7 @@ static void findProtobufTags (void)
 		.headerKindIndex = KIND_GHOST_INDEX,
 		.headerSystemRoleIndex = 0,
 		.headerLocalRoleIndex = 0,
+		.skip__cplusplus_branch = false,
 	};
 	cppInit (&initData);
 	token.value = vStringNew ();