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Fix: simplecpp ## fails to expand function-like macro when '(' is not adjacent #655

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paulafy6 wants to merge 2 commits into cppcheck-opensource:master

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from paulafy6:fix-preprocessor-concat

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Fix: simplecpp ## fails to expand function-like macro when '(' is not adjacent #655

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a328c4d

Fix: simplecpp ## fails to expand function-like macro when '(' is not…

paulafy6 Aug 18, 2026

a2f6f52

test: add regression test for ## PAR-style indirection (hashhash_func…

paulafy6 Aug 18, 2026

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57 changes: 51 additions & 6 deletions 57 simplecpp.cpp

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -2453,16 +2453,61 @@ namespace simplecpp {
		output.deleteToken(A);
		TokenList tokens(files);
		tokens.push_back(new Token(strAB, tok->location));
		// for function like macros, push the (...)
		if (tokensB.empty() && sameline(B,B->next) && B->next->op=='(') {
		const MacroMap::const_iterator it = macros.find(strAB);
		if (it != macros.end() && expandedmacros.find(strAB) == expandedmacros.end() && it->second.functionLike()) {
		const Token * const tok2 = appendTokens(tokens, loc, B->next, macros, expandedmacros, parametertokens);
		// If strAB names a function-like macro, locate and append its argument list '(...)'
		// from the remaining replacement tokens, then expand the whole call.
		// 'forwardScan' is true when the argument list was consumed via the forward scan
		// path below (not adjacent), so that expandToken() is called instead of
		// the normal takeTokens() path even when expandResult is false.
		bool forwardScan = false;
		const MacroMap::const_iterator it = macros.find(strAB);
		const bool isFunctionLikeMacro = (it != macros.end() && expandedmacros.find(strAB) == expandedmacros.end() && it->second.functionLike());
		if (tokensB.empty() && isFunctionLikeMacro) {
		// Fast path: '(' is the very next token after B on the same line.
		const Token *lpar = (sameline(B, B->next) && B->next->op == '(') ? B->next : nullptr;
		if (!lpar && !expandResult) {
		// Forward-scan path: '(' is not immediately adjacent to B.
		// This handles PAR-style indirection patterns such as:
		// #define PAR(a, ...) a __VA_ARGS__
		// #define DISPATCH(kind, ...) PAR(PREFIX_ ## kind, (__VA_ARGS__))
		// where the '(' for PREFIX_kind belongs to the __VA_ARGS__ parameter
		// and is separated from B by a comma in the replacement text.
		// Only active in the appendTokens context (expandResult==false) to
		// avoid unintended side-effects inside the main expansion loop.
		for (const Token *scan = nextTok; sameline(B, scan); scan = scan->next) {
		if (scan->op == '(') {
		// Found a literal '(' after skipping separators.
		lpar = scan;
		forwardScan = true;
		break;
		}
		if (scan->op == ',') {
		// Argument separator — skip and keep scanning.
		continue;
		}
		if (scan->name) {
		// Named token: expand it and check whether it starts with '(...)'
		// (covers the case where __VA_ARGS__ expands to a parenthesised list).
		TokenList expanded(files);
		if (expandArg(expanded, scan, loc, macros, expandedmacros, parametertokens) &&
		expanded.cfront() && expanded.cfront()->op == '(') {
		for (Token *t = expanded.front(); t; t = t->next)
		t->location = loc;
		tokens.takeTokens(expanded);
		nextTok = scan->next;
		forwardScan = true;
		}
		break; // stop at any name token, whether consumed or not
		}
		break; // any other operator — stop scan
		}
		}
		if (lpar) {
		const Token * const tok2 = appendTokens(tokens, loc, lpar, macros, expandedmacros, parametertokens);
		if (tok2)
		nextTok = tok2->next;
		}
		}
		if (expandResult)
		if (expandResult \|\| forwardScan)
		expandToken(output, loc, tokens.cfront(), macros, expandedmacros, parametertokens);
		else
		output.takeTokens(tokens);
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21 changes: 21 additions & 0 deletions 21 test.cpp

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -2038,6 +2038,26 @@ static void hashhash_universal_character_2()
		ASSERT_EQUALS("file0,1,syntax_error,failed to expand 'A', Invalid ## usage when expanding 'A': Combining '\\U0104' and '0104' yields universal character '\\U01040104'. This is undefined behavior according to C standard chapter 5.1.1.2, paragraph 4.\n", toString(outputList));
		}

		// Regression test: ## result is a function-like macro whose '(' is not adjacent.
		// PAR-style indirection hides '(' behind a comma/parameter in the replacement text.
		// Previously caused [unknownMacro] and aborted TU expansion.
		static void hashhash_funclike_par_indirection()
		{
		// Single dispatch: PREFIX_ ## kind → PREFIX_SCALAR, '(' separated by ','
		ASSERT_EQUALS("\n\n\nint x",
		preprocess("#define PAR(a, ...) a __VA_ARGS__\n"
		"#define PREFIX_SCALAR(T, N) T N\n"
		"#define DISPATCH(kind, ...) PAR(PREFIX_ ## kind, (__VA_ARGS__))\n"
		"DISPATCH(SCALAR, int, x)\n"));

		// Chained: two DISPATCH calls with different PREFIX_ specialisations
		ASSERT_EQUALS("\n\n\n\nint x float arr [ 10 ]",
		preprocess("#define PAR(a, ...) a __VA_ARGS__\n"
		"#define PREFIX_SCALAR(T, N) T N\n"
		"#define PREFIX_ARRAY(T, N, S) T N[S]\n"
		"#define DISPATCH(kind, ...) PAR(PREFIX_ ## kind, (__VA_ARGS__))\n"
		"DISPATCH(SCALAR, int, x) DISPATCH(ARRAY, float, arr, 10)\n"));
		}

		static void has_include_1()
		{
Expand Down Expand Up		@@ -4669,6 +4689,7 @@ static void runTests(int argc, char **argv, Input input)
		// the behavior is undefined."
		TEST_CASE(hashhash_universal_character);
		TEST_CASE(hashhash_universal_character_2);
		TEST_CASE(hashhash_funclike_par_indirection); // PAR-style ## indirection: '(' not adjacent to ## result

		// c++17 __has_include
		TEST_CASE(has_include_1);
Expand Down

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