core: fix string evaluation with regex replacement when the string is empty

ChangeLog.adoc

@@ -25,6 +25,7 @@ New features::
 
 Bug fixes::
 
+  * core: fix string evaluation with regex replacement when the string is empty
   * core: fix check of tags in lines (command /filter and hook_print)
   * core: fix clear of completion item in case of partial completion (issue #1162)
   * core: send signal "key_pressed" for mouse code only if the string is UTF-8 valid (issue #1220)

src/core/wee-eval.c

@@ -1100,6 +1100,7 @@ eval_replace_regex (const char *string, regex_t *regex, const char *replace,
 {
     char *result, *result2, *str_replace;
     int length, length_replace, start_offset, i, rc, end;
+    int empty_replace_allowed;
     struct t_eval_regex eval_regex;
 
     if (!string || !regex || !replace)
@@ -1114,7 +1115,11 @@ eval_replace_regex (const char *string, regex_t *regex, const char *replace,
     eval_context->regex = &eval_regex;
 
     start_offset = 0;
-    while (result && result[start_offset])
+
+    /* we allow one empty replace if input string is empty */
+    empty_replace_allowed = (result[0]) ? 0 : 1;
+
+    while (result)
     {
         for (i = 0; i < 100; i++)
         {
@@ -1122,16 +1127,20 @@ eval_replace_regex (const char *string, regex_t *regex, const char *replace,
         }
 
         rc = regexec (regex, result + start_offset, 100, eval_regex.match, 0);
-        /*
-         * no match found: exit the loop (if rm_eo == 0, it is an empty match
-         * at beginning of string: we consider there is no match, to prevent an
-         * infinite loop)
-         */
-        if ((rc != 0)
-            || (eval_regex.match[0].rm_so < 0)
-            || (eval_regex.match[0].rm_eo <= 0))
-        {
+
+        /* no match found: exit the loop */
+        if ((rc != 0) || (eval_regex.match[0].rm_so < 0))
             break;
+
+        /*
+         * if empty string is matching, continue only if empty replace is
+         * still allowed (to prevent infinite loop)
+         */
+        if (eval_regex.match[0].rm_eo <= 0)
+        {
+            if (!empty_replace_allowed)
+                break;
+            empty_replace_allowed = 0;
         }
 
         /* adjust the start/end offsets */
@@ -1183,6 +1192,9 @@ eval_replace_regex (const char *string, regex_t *regex, const char *replace,
             break;
 
         start_offset = eval_regex.match[0].rm_so + length_replace;
+
+        if (!result[start_offset])
+            break;
     }
 
     return result;

tests/unit/core/test-eval.cpp

@@ -452,6 +452,18 @@ TEST(CoreEval, EvalReplaceRegex)
                              NULL, NULL);
     CHECK(options);
 
+    /* replace regex by empty string (on empty string) */
+    hashtable_remove (pointers, "regex");
+    hashtable_set (options, "regex", ".*");
+    hashtable_set (options, "regex_replace", "");
+    WEE_CHECK_EVAL("", "");
+
+    /* replace regex (on empty string) */
+    hashtable_remove (pointers, "regex");
+    hashtable_set (options, "regex", ".*");
+    hashtable_set (options, "regex_replace", "test");
+    WEE_CHECK_EVAL("test", "");
+
     /* replace regex by empty string */
     hashtable_remove (pointers, "regex");
     hashtable_set (options, "regex", ".*");