awk: fix subst code to handle "start of word" pattern correctly (needs REG_STARTEND)

function                                             old     new   delta
awk_sub                                              637     714     +77

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

2 files changed, 51 insertions, 26 deletions

diff --git a/editors/awk.c b/editors/awk.c
index df9b7fdc9..171f0a7ea 100644
--- a/editors/awk.c
+++ b/editors/awk.c
@@ -2504,17 +2504,46 @@ static int awk_sub(node *rn, const char *repl, int nm, var *src, var *dest /*,in
         regex_t sreg, *regex;
         /* True only if called to implement gensub(): */
         int subexp = (src != dest);
-
+#if defined(REG_STARTEND)
+        const char *src_string;
+        size_t src_strlen;
+        regexec_flags = REG_STARTEND;
+#else
+        regexec_flags = 0;
+#endif
         resbuf = NULL;
         residx = 0;
         match_no = 0;
-        regexec_flags = 0;
         regex = as_regex(rn, &sreg);
         sp = getvar_s(src ? src : intvar[F0]);
+#if defined(REG_STARTEND)
+        src_string = sp;
+        src_strlen = strlen(src_string);
+#endif
         replen = strlen(repl);
-        while (regexec(regex, sp, 10, pmatch, regexec_flags) == 0) {
-                int so = pmatch[0].rm_so;
-                int eo = pmatch[0].rm_eo;
+        for (;;) {
+                int so, eo;
+
+#if defined(REG_STARTEND)
+// REG_STARTEND: "This flag is a BSD extension, not present in POSIX"
+                size_t start_ofs = sp - src_string;
+                pmatch[0].rm_so = start_ofs;
+                pmatch[0].rm_eo = src_strlen;
+                if (regexec(regex, src_string, 10, pmatch, regexec_flags) != 0)
+                        break;
+                eo = pmatch[0].rm_eo - start_ofs;
+                so = pmatch[0].rm_so - start_ofs;
+#else
+// BUG:
+// gsub(/\<b*/,"") on "abc" matches empty string at "a...",
+// advances sp one char (see "Empty match" comment later) to "bc"
+// ... and erroneously matches "b" even though it is NOT at the word start.
+                enum { start_ofs = 0 };
+                if (regexec(regex, sp, 10, pmatch, regexec_flags) != 0)
+                        break;
+                so = pmatch[0].rm_so;
+                eo = pmatch[0].rm_eo;
+#endif
 
                 //bb_error_msg("match %u: [%u,%u] '%s'%p", match_no+1, so, eo, sp,sp);
                 resbuf = qrealloc(resbuf, residx + eo + replen, &resbufsize);
@@ -2543,7 +2572,7 @@ static int awk_sub(node *rn, const char *repl, int nm, var *src, var *dest /*,in
                                         }
                                         n = pmatch[j].rm_eo - pmatch[j].rm_so;
                                         resbuf = qrealloc(resbuf, residx + replen + n, &resbufsize);
-                                        memcpy(resbuf + residx, sp + pmatch[j].rm_so, n);
+                                        memcpy(resbuf + residx, sp + pmatch[j].rm_so - start_ofs, n);
                                         residx += n;
                                 } else
                                         resbuf[residx++] = c;
@@ -2557,12 +2586,6 @@ static int awk_sub(node *rn, const char *repl, int nm, var *src, var *dest /*,in
                 if (eo == so) {
                         /* Empty match (e.g. "b*" will match anywhere).
                          * Advance by one char. */
-//BUG (bug 1333):
-//gsub(/\<b*/,"") on "abc" will reach this point, advance to "bc"
-//... and will erroneously match "b" even though it is NOT at the word start.
-//we need REG_NOTBOW but it does not exist...
-//TODO: if EXTRA_COMPAT=y, use GNU matching and re_search,
-//it should be able to do it correctly.
                         /* Subtle: this is safe only because
                          * qrealloc allocated at least one extra byte */
                         resbuf[residx] = *sp;
@@ -2571,7 +2594,7 @@ static int awk_sub(node *rn, const char *repl, int nm, var *src, var *dest /*,in
                         sp++;
                         residx++;
                 }
-                regexec_flags = REG_NOTBOL;
+                regexec_flags |= REG_NOTBOL;
         }
 
         resbuf = qrealloc(resbuf, residx + strlen(sp), &resbufsize);
diff --git a/testsuite/awk.tests b/testsuite/awk.tests
index c61d32947..5a792c241 100755
--- a/testsuite/awk.tests
+++ b/testsuite/awk.tests
@@ -557,14 +557,12 @@ testing 'awk gensub backslashes \' \
         'awk '$sq'BEGIN { s="\\"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
         's=\\
 \\|\\
-' \
-        '' ''
+' '' ''
 testing 'awk gensub backslashes \\' \
         'awk '$sq'BEGIN { s="\\\\"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
         's=\\\\
 \\|\\
-' \
-        '' ''
+' '' ''
 # gawk 5.1.1 handles trailing unpaired \ inconsistently.
 # If replace string is single \, it is used verbatim,
 # but if it is \\\ (three slashes), gawk uses "\<NUL>" (!!!), not "\\" as you would expect.
@@ -572,31 +570,35 @@ testing 'awk gensub backslashes \\\' \
         'awk '$sq'BEGIN { s="\\\\\\"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
         's=\\\\\\
 \\\\|\\\\
-' \
-        '' ''
+' '' ''
 testing 'awk gensub backslashes \\\\' \
         'awk '$sq'BEGIN { s="\\\\\\\\"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
         's=\\\\\\\\
 \\\\|\\\\
-' \
-        '' ''
+' '' ''
 testing 'awk gensub backslashes \&' \
         'awk '$sq'BEGIN { s="\\&"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
         's=\\&
 &|&
-' \
-        '' ''
+' '' ''
 testing 'awk gensub backslashes \0' \
         'awk '$sq'BEGIN { s="\\0"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
         's=\\0
 a|a
-' \
-        '' ''
+' '' ''
 testing 'awk gensub backslashes \\0' \
         'awk '$sq'BEGIN { s="\\\\0"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
         's=\\\\0
 \\0|\\0
-' \
+' '' ''
+
+# The "b" in "abc" should not match <b* pattern.
+# Currently we use REG_STARTEND ("This flag is a BSD extension, not present in POSIX")
+# to implement the code to handle this correctly, but if your libc has no REG_STARTEND,
+# the alternative code mishandles this case.
+testing 'awk gsub erroneous word start match' \
+        "awk 'BEGIN { a=\"abc\"; gsub(/\<b*/,\"\",a); print a }'" \
+        'abc\n' \
         '' ''
 
 exit $FAILCOUNT