Calls to error or get_env with '\0' in string crash Mars

[Matt Giuca]

Expected:
?> error(['a', '\0', 'b'])
Runtime Error: ab

Actual:
?> error(['a', '\0', 'b'])
Uncaught Mercury exception:
univ_cons(univ_cons(univ_cons(software_error("string.from_char_list: null character in list"))))

This is due to a call to string.from_char_list in interpret.m:mars_value_to_string, which crashes Mercury if it has a '\0'. Mercury strings may not have null characters in them; Mars strings can. This should be solved on a builtin-by-builtin basis. mars_value_to_string should return a list(char) instead, and the builtins should deal with null characters accordingly. error should ignore the characters; get_env should return the empty string (as if a lookup failed).

The string.semidet_from_char_list predicate is useful.

[Matt Giuca (mgiuca)]

Fixed in trunk r981.