scanner: backport isatty hack to Flex 2.5.x.

* parser.l (VER, FLEX_VER): New macros.
(isatty): Define the macro differently for Flex 2.5.36 and
older, to counteract the skeleton's "extern int isatty(int)"
declaration. This involves a dummy global variable.
(no_isatty): New dummy global, only under Flex 2.5.36 and
older.

1 files changed, 18 insertions, 1 deletions

diff --git a/parser.l b/parser.l
index 8bcb53ba..7c8b3842 100644
--- a/parser.l
+++ b/parser.l
@@ -46,11 +46,28 @@
 #include "parser.h"
 #include "txr.h"
 
+#define VER(MAJ, MIN, SUB) ((MAJ) * 100000 + (MIN) * 1000 + SUB)
+
+#define FLEX_VER VER(YY_FLEX_MAJOR_VERSION,     \
+                     YY_FLEX_MINOR_VERSION,     \
+                     YY_FLEX_SUBMINOR_VERSION)
+
 #define YY_NO_UNISTD_H
 
-/* Defeat flex's calls to isatty, which happene even in batch mode */
+/* Defeat flex's calls to isatty, which happens even in batch mode */
+
 #undef isatty
+
+/*
+ * Until 2.5.36, the Flex skeleton contained "extern int isatty(int)",
+ * requiring special handling.
+ */
+#if FLEX_VER <= VER(2, 5, 36)
+#define isatty(x) no_isatty
+int no_isatty = 0;
+#else
 #define isatty(x) 0
+#endif
 
 #define YY_INPUT(buf, result, max_size)                                 \
   do {                                                                  \