[m-rev.] for review: Document that string.to_utf8_code_unit_list throws exceptions.

[Mark Brown]

This looks fine.

On Mon, Nov 4, 2019 at 4:52 PM Peter Wang <novalazy at gmail.com> wrote:
>
> library/string.m:
>     Document that string.to_utf8_code_unit_list throws an exception
>     if the string contains an unpaired surrogate code point.
> ---
>  library/string.m | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/library/string.m b/library/string.m
> index 9adabf662..657494f5f 100644
> --- a/library/string.m
> +++ b/library/string.m
> @@ -210,6 +210,8 @@
>  :- pred to_code_unit_list(string::in, list(int)::out) is det.
>
>      % Convert a string into a list of UTF-8 code units.
> +    % Throws an exception if the string contains an unpaired surrogate code
> +    % point, as the encoding of surrogate code points is prohibited in UTF-8.
>      %
>  :- pred to_utf8_code_unit_list(string::in, list(int)::out) is det.
>
> @@ -1973,10 +1975,6 @@ to_code_unit_list_loop(String, Index, End, List) :-
>
>  %---------------------%
>
> -% XXX ILSEQ Behaviour differs according to target language.
> -%   - java: throws exception on unpaired surrogate (correct as written)
> -%   - csharp: infinite loop on string containing unpaired surrogate
> -
>  to_utf8_code_unit_list(String, CodeList) :-
>      ( if internal_encoding_is_utf8 then
>          to_code_unit_list(String, CodeList)
> @@ -1990,7 +1988,7 @@ encode_utf8(Char, CodeList0, CodeList) :-
>      ( if char.to_utf8(Char, CharCodes) then
>          CodeList = CharCodes ++ CodeList0
>      else
> -        unexpected($pred, "char.to_utf8 failed")
> +        unexpected($pred, "surrogate code point")
>      ).
>
>  %---------------------%
> --
> 2.23.0
>
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