awk: FS regex matches only non-empty separators (gawk compat)

function                                             old     new   delta
awk_split                                            484     553     +69

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 32 insertions, 8 deletions

diff --git a/editors/awk.c b/editors/awk.c
index d56d6330d..2c15f9e4e 100644
--- a/editors/awk.c
+++ b/editors/awk.c
@@ -1763,6 +1763,29 @@ static void fsrealloc(int size)
         nfields = size;
 }
 
+static int regexec1_nonempty(const regex_t *preg, const char *s, regmatch_t pmatch[])
+{
+        int r = regexec(preg, s, 1, pmatch, 0);
+        if (r == 0 && pmatch[0].rm_eo == 0) {
+                /* For example, happens when FS can match
+                 * an empty string (awk -F ' *'). Logically,
+                 * this should split into one-char fields.
+                 * However, gawk 5.0.1 searches for first
+                 * _non-empty_ separator string match:
+                 */
+                size_t ofs = 0;
+                do {
+                        ofs++;
+                        if (!s[ofs])
+                                return REG_NOMATCH;
+                        regexec(preg, s + ofs, 1, pmatch, 0);
+                } while (pmatch[0].rm_eo == 0);
+                pmatch[0].rm_so += ofs;
+                pmatch[0].rm_eo += ofs;
+        }
+        return r;
+}
+
 static int awk_split(const char *s, node *spl, char **slist)
 {
         int n;
@@ -1788,17 +1811,11 @@ static int awk_split(const char *s, node *spl, char **slist)
                         regmatch_t pmatch[2]; // TODO: why [2]? [1] is enough...
 
                         l = strcspn(s, c+2); /* len till next NUL or \n */
-                        if (regexec(icase ? spl->r.ire : spl->l.re, s, 1, pmatch, 0) == 0
+                        if (regexec1_nonempty(icase ? spl->r.ire : spl->l.re, s, pmatch) == 0
                          && pmatch[0].rm_so <= l
                         ) {
+                                /* if (pmatch[0].rm_eo == 0) ... - impossible */
                                 l = pmatch[0].rm_so;
-                                if (pmatch[0].rm_eo == 0) {
-                                        /* For example, happens when FS can match
-                                         * an empthy string (awk -F ' *')
-                                         */
-                                        l++;
-                                        pmatch[0].rm_eo++;
-                                }
                                 n++; /* we saw yet another delimiter */
                         } else {
                                 pmatch[0].rm_eo = l;
diff --git a/testsuite/awk.tests b/testsuite/awk.tests
index 87f6b5007..06a531d96 100755
--- a/testsuite/awk.tests
+++ b/testsuite/awk.tests
@@ -398,5 +398,12 @@ testing 'awk do not allow "str"++' \
         '' \
         'anything'
 
+#gawk compat: FS regex matches only non-empty separators:
+#with -*, the splitting is NOT f o o b a r, but foo bar:
+testing 'awk FS regex which can match empty string' \
+        "awk -F '-*' '{print \$1 \"-\" \$2 \"=\" \$3 \"*\" \$4}'" \
+        "foo-bar=*\n" \
+        '' \
+        'foo--bar'
 
 exit $FAILCOUNT