refactor: replace_makeprg (#19570)

src/nvim/strings.c

@@ -1528,3 +1528,45 @@ char_u *reverse_text(char_u *s)
 
   return rev;
 }
+
+/// Replace all occurrences of "what" with "rep" in "src". If no replacement happens then NULL is
+/// returned otherwise return a newly allocated string.
+///
+/// @param[in] src  Source text
+/// @param[in] what Substring to replace
+/// @param[in] rep  Substring to replace with
+///
+/// @return [allocated] Copy of the string.
+char *strrep(const char *src, const char *what, const char *rep)
+{
+  char *pos = (char *)src;
+  size_t whatlen = STRLEN(what);
+
+  // Count occurrences
+  size_t count = 0;
+  while ((pos = strstr(pos, what)) != NULL) {
+    count++;
+    pos += whatlen;
+  }
+
+  if (count == 0) {
+    return NULL;
+  }
+
+  size_t replen = STRLEN(rep);
+  char *ret = xmalloc(STRLEN(src) + count * (replen - whatlen) + 1);
+  char *ptr = ret;
+  while ((pos = strstr(src, what)) != NULL) {
+    size_t idx = (size_t)(pos - src);
+    memcpy(ptr, src, idx);
+    ptr += idx;
+    STRCPY(ptr, rep);
+    ptr += replen;
+    src = pos + whatlen;
+  }
+
+  // Copy remaining
+  STRCPY(ptr, src);
+
+  return ret;
+}