[m-rev.] diff: do not allow unterminated octal escapes

[Julien Fischer]

Do not allow unterminated octal escapes in string literals.

library/lexer.m:
 	Fix an old XXX: do not allow unterminated octal escapes in string
 	literals; we haven't needed to preserve bug-for-bug compatibility
 	with NU-Prolog for a very long time.

tests/hard_coded/special_char.m:
 	Terminate octal escapes.

tests/invalid/Mmakefile:
tests/invalid/unterminated_octal_escape.{m,err_exp}:
 	Check for an error if an unterminated octal escape is encountered.

Julien.

diff --git a/library/lexer.m b/library/lexer.m
index 1d0bd0c..b7c2a28 100644
--- a/library/lexer.m
+++ b/library/lexer.m
@@ -1431,12 +1431,7 @@ get_octal_escape(Stream, QuoteChar, Chars, OctalChars, Token, !IO) :-
              finish_octal_escape(Stream, QuoteChar, Chars,
                  OctalChars, Token, !IO)
          ;
-            % XXX We don't report this as an error since we need bug-for-bug
-            % compatibility with NU-Prolog.
-            % Token = error("unterminated octal escape")
-            io.putback_char(Stream, Char, !IO),
-            finish_octal_escape(Stream, QuoteChar, Chars, OctalChars, Token,
-                !IO)
+            Token = error("unterminated octal escape")
          )
      ).

@@ -1454,12 +1449,8 @@ string_get_octal_escape(String, Len, QuoteChar, Chars, OctalChars,
              string_finish_octal_escape(String, Len, QuoteChar, Chars,
                  OctalChars, Posn0, Token, Context, !Posn)
          ;
-            % XXX We don't report this as an error since we need bug-for-bug
-            % compatibility with NU-Prolog.
-            % Token = error("unterminated octal escape")
-            string_ungetchar(String, !Posn),
-            string_finish_octal_escape(String, Len, QuoteChar, Chars,
-                OctalChars, Posn0, Token, Context, !Posn)
+            string_get_context(Posn0, Context, !Posn),
+            Token = error("unterminated octal escape")
          )
      ;
          Token = eof,
diff --git a/tests/hard_coded/special_char.m b/tests/hard_coded/special_char.m
index efb51d3..9676752 100644
--- a/tests/hard_coded/special_char.m
+++ b/tests/hard_coded/special_char.m
@@ -12,7 +12,7 @@ main -->
  	print("Hello world\r\n"),
  	print("\r\n"),
  	print("\a\b\v\f\t\n"),
-	print("\077"),
-	print("\0123"),
-	print("\0321"),
+	print("\077\"),
+	print("\0123\"),
+	print("\0321\"),
  	print("\n").
diff --git a/tests/invalid/Mmakefile b/tests/invalid/Mmakefile
index 2c7c1e5..086dc46 100644
--- a/tests/invalid/Mmakefile
+++ b/tests/invalid/Mmakefile
@@ -263,6 +263,7 @@ SINGLEMODULE= \
  	unsatisfiable_constraint_bug \
  	unsatisfiable_constraint_msg \
  	unsatisfiable_super \
+	unterminated_octal_escape \
  	user_eq_dummy \
  	uu_type \
  	vars_in_wrong_places \
diff --git a/tests/invalid/unterminated_octal_escape.err_exp b/tests/invalid/unterminated_octal_escape.err_exp
new file mode 100644
index 0000000..67dd16a
--- /dev/null
+++ b/tests/invalid/unterminated_octal_escape.err_exp
@@ -0,0 +1,2 @@
+unterminated_octal_escape.m:009: Error: no clauses for predicate `main'/2.
+unterminated_octal_escape.m:014: Syntax error: unterminated octal escape.
diff --git a/tests/invalid/unterminated_octal_escape.m b/tests/invalid/unterminated_octal_escape.m
new file mode 100644
index 0000000..fbd385b
--- /dev/null
+++ b/tests/invalid/unterminated_octal_escape.m
@@ -0,0 +1,15 @@
+% Older versions of Mercury used to accept unterminated octal escapes
+% in order to be bug-for-bug compatible with NU-Prolog.
+%
+:- module unterminated_octal_escape.
+:- interface.
+
+:- import_module io.
+
+:- pred main(io::di, io::uo) is det.
+
+:- implementation.
+
+main(!IO) :-
+    io.write_string("\43", !IO),
+    io.nl(!IO).