fix regex.scan to work correclty with utf8 strings

2 files changed, 21 insertions, 6 deletions

diff --git a/src/gleam_stdlib.erl b/src/gleam_stdlib.erl
index dc3727c..04b73eb 100644
--- a/src/gleam_stdlib.erl
+++ b/src/gleam_stdlib.erl
@@ -200,16 +200,17 @@ regex_check(Regex, String) ->
 regex_split(Regex, String) ->
     re:split(String, Regex).
 
-regex_submatches(String, {S, L}) ->
-    SubMatch = string:slice(String, S, L),
-    case string:is_empty(SubMatch) of
+regex_submatches(String, {Start, Length}) ->
+    Binary = unicode:characters_to_binary(String, unicode, unicode),
+    BinarySlice = binary:part(Binary, {Start, Length}),
+    case string:is_empty(binary_to_list(BinarySlice)) of
         true -> none;
-        false -> {some, SubMatch}
+        false -> {some, BinarySlice}
     end.
 
-regex_matches(String, [{S, L} | Submatches]) ->
+regex_matches(String, [{Start, Length} | Submatches]) ->
     Submatches1 = lists:map(fun(X) -> regex_submatches(String, X) end, Submatches),
-    {match, binary:part(String, S, L), Submatches1}.
+    {match, binary:part(String, Start, Length), Submatches1}.
 
 regex_scan(Regex, String) ->
     case re:run(String, Regex, [global]) of
diff --git a/test/gleam/regex_test.gleam b/test/gleam/regex_test.gleam
index cdd6e68..30d197f 100644
--- a/test/gleam/regex_test.gleam
+++ b/test/gleam/regex_test.gleam
@@ -64,4 +64,18 @@ pub fn scan_test() {
     Match(content: "on a boat", submatches: [None, Some("boat")]),
     Match(content: "in a lake", submatches: [None, Some("lake")]),
   ])
+
+  assert Ok(re) = regex.from_string("answer (\\d+)")
+  regex.scan(re, "Is the answer 42?")
+  |> should.equal([Match(content: "answer 42", submatches: [Some("42")])])
+
+  assert Ok(re) = regex.from_string("(\\d+)")
+  regex.scan(re, "hello 42")
+  |> should.equal([Match(content: "42", submatches: [Some("42")])])
+
+  regex.scan(re, "你好 42")
+  |> should.equal([Match(content: "42", submatches: [Some("42")])])
+
+  regex.scan(re, "你好 42 世界")
+  |> should.equal([Match(content: "42", submatches: [Some("42")])])
 }