libcpp: Fix up ##__VA_OPT__ handling [PR89971]

In the following testcase we incorrectly error about pasting / token
with padding token (which is a result of __VA_OPT__); instead we should
like e.g. for ##arg where arg is empty macro argument clear PASTE_LEFT
flag of the previous token if __VA_OPT__ doesn't add any real tokens
(which can happen either because the macro doesn't have any tokens
passed to ... (i.e. __VA_ARGS__ expands to empty) or when __VA_OPT__
doesn't have any tokens in between ()s).

2021-12-30  Jakub Jelinek  <jakub@redhat.com>

	PR preprocessor/89971
libcpp/
	* macro.c (replace_args): For ##__VA_OPT__, if __VA_OPT__ expands
	to no tokens at all, drop PASTE_LEFT flag from the previous token.
gcc/testsuite/
	* c-c++-common/cpp/va-opt-9.c: New test.

(cherry picked from commit 5545d1edcbdb1701443f94dde7ec97c5ce3e1a6c)

diff --git a/gcc/testsuite/c-c++-common/cpp/va-opt-9.c b/gcc/testsuite/c-c++-common/cpp/va-opt-9.c
new file mode 100644 (file)
index 0000000..5f73ad0
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/cpp/va-opt-9.c
@@ -0,0 +1,20 @@
+/* PR preprocessor/89971 */
+/* { dg-do compile } */
+/* { dg-options "-std=gnu99" { target c } } */
+/* { dg-options "-std=c++20" { target c++ } } */
+
+int a, c;
+#define m1(...) a /##__VA_OPT__(b) c
+#define m2(...) a /##__VA_OPT__() c
+#define m3(...) a##__VA_OPT__()##b = 1
+#define m4(...) a##__VA_OPT__(b c d)##e = 2
+
+int
+foo (void)
+{
+  int d = m1();
+  int e = m2(1);
+  int m3(1 2 3);
+  int m4();
+  return d + e + ab + ae;
+}

diff --git a/libcpp/macro.c b/libcpp/macro.c
index 817c42dbf15bba783e8e41cf8539b6ee8d6048e8..0aa2de8274f4d06ca0d9750a0b43f88480987ce4 100644 (file)
--- a/libcpp/macro.c
+++ b/libcpp/macro.c
@@ -2023,6 +2023,11 @@ replace_args (cpp_reader *pfile, cpp_hashnode *node, cpp_macro *macro,
                  paste_flag = tokens_buff_last_token_ptr (buff);
                }
 
+             if (start && paste_flag == start && (*start)->flags & PASTE_LEFT)
+               /* If __VA_OPT__ expands to nothing (either because __VA_ARGS__
+                  is empty or because it is __VA_OPT__() ), drop PASTE_LEFT
+                  flag from previous token.  */
+               copy_paste_flag (pfile, start, &pfile->avoid_paste);
              if (src->flags & PASTE_LEFT)
                {
                  /* With a non-empty __VA_OPT__ on the LHS of ##, the last