lib: fix semantic on has_substring on extreme cases

And avoid illegal access outside the string.

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/lib/standard/string.nit b/lib/standard/string.nit
index f78c0ac..b18e698 100644 (file)
--- a/lib/standard/string.nit
+++ b/lib/standard/string.nit
@@ -181,8 +181,25 @@ abstract class Text
        #
        #     assert "abcd".has_substring("bc",1)            ==  true
        #     assert "abcd".has_substring("bc",2)            ==  false
+       #
+       # Returns true iff all characters of `str` are presents
+       # at the expected index in `self.`
+       # The first character of `str` being at `pos`, the second
+       # character being at `pos+1` and so on...
+       #
+       # This means that all characters of `str` need to be inside `self`.
+       #
+       #     assert "abcd".has_substring("xab", -1)         == false
+       #     assert "abcd".has_substring("cdx", 2)          == false
+       #
+       # And that the empty string is always a valid substring.
+       #
+       #     assert "abcd".has_substring("", 2)             == true
+       #     assert "abcd".has_substring("", 200)           == true
        fun has_substring(str: String, pos: Int): Bool
        do
+               if str.is_empty then return true
+               if pos < 0 or pos + str.length > length then return false
                var myiter = self.chars.iterator_from(pos)
                var itsiter = str.chars.iterator
                while myiter.is_ok and itsiter.is_ok do