Fix 2011-12-03 regression. The freeform directive code

relies on lazy_str_get_trailing_list and the behavior
of that function changed because (split-str "" any-separator)
changed from returning nil to returning the empty string.
The resulting behavior change of lazy_str_get_trailing_list was later
described in the documentation, thereby codifying it.

This patch changes the lazy_str_get_trailing_list behavior,
which is poor, and causes infinite looping. We do not want
an extra empty string prepended, because it looks like
a spurious line.

* lib.c (lazy_str_get_trailing_list): if split_str produces
a the list (""), then just return the unmaterialized list from
the lazy string without prepending that one-element list to it.

* txr.1: Updated documentation for lazy-str-get-trailing-list.

3 files changed, 42 insertions, 12 deletions

diff --git a/ChangeLog b/ChangeLog
index 961af894..50bfaabb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,23 @@
+2014-10-08  Kaz Kylheku  <kaz@kylheku.com>
+
+	Fix 2011-12-03 regression. The freeform directive code
+	relies on lazy_str_get_trailing_list and the behavior
+	of that function changed because (split-str "" any-separator)
+	changed from returning nil to returning the empty string.
+	The resulting behavior change of lazy_str_get_trailing_list was later
+	described in the documentation, thereby codifying it.
+
+	This patch changes the lazy_str_get_trailing_list behavior,
+	which is poor, and causes infinite looping. We do not want
+	an extra empty string prepended, because it looks like
+	a spurious line.
+
+	* lib.c (lazy_str_get_trailing_list): if split_str produces
+	a the list (""), then just return the unmaterialized list from
+	the lazy string without prepending that one-element list to it.
+
+	* txr.1: Updated documentation for lazy-str-get-trailing-list.
+
 2014-10-05  Kaz Kylheku  <kaz@kylheku.com>
 
 	Version 99.
diff --git a/lib.c b/lib.c
index 0b107c93..d121177a 100644
--- a/lib.c
+++ b/lib.c
@@ -4987,6 +4987,9 @@ val lazy_str_get_trailing_list(val lstr, val index)
     val split_suffix = split_str(sub_str(lstr->ls.prefix, index, nil),
                                  or2(car(lstr->ls.opts), lit("\n")));
 
+    if (!cdr(split_suffix) && equal(car(split_suffix), null_string))
+      return lstr->ls.list;
+
     return nappend2(split_suffix, lstr->ls.list);
   }
 }
diff --git a/txr.1 b/txr.1
index 101f464d..7f4b5cb8 100644
--- a/txr.1
+++ b/txr.1
@@ -16376,30 +16376,37 @@ materialized lazy string.
 .desc
 The
 .code lazy-str-get-trailing-list
-function is a sort of inverse operation to
-the lazy string from its associated list.
+function can be considered, in some way, an inverse operation to
+the production of the lazy string from its associated list.
 
-First, the string is forced up through the position
+First,
+.meta string
+is forced up through the position
 .metn index .
+That is the only extent to which
+.meta string
+is modified by this function.
 
-Next, the materialized part of the string starting at position
+Next, the suffix of the materialized part of the lazy string starting at
+position
 .metn index ,
-through to the end, is split into pieces on occurrences of the terminator
-character, which had been given as the
+is split into pieces on occurrences of the
+terminator character (which had been given as the
 .meta terminator
 argument in the
 .code lazy-str
-constructor, and defaults to the newline character.
+constructor, and defaults to newline).   If the
+.meta index
+position is beyond the part of the string which can be materialized
+(in adherence with the lazy string's
+.meta limit-count
+constructor parameter), then the list of pieces is considered
+to be empty.
 
 Finally, a list is returned consisting of the pieces produced by the split,
 to which is appended the remaining list of the string which has not yet been
 forced to materialize.
 
-If
-.meta index
-is a position which cannot be forced, then the lazy string's
-remaining list is returned, with single null string prepended to it.
-
 .coNP Functions @, length-str-> @, length-str->= @ length-str-< and @ length-str-<=
 .synb
 .mets (length-str-> < string << len )