The following seems like a bug to me; if so, I'll report it as such.
But maybe it's a feature of the field property or isearch-yank-line
that I don't understand; if so, I'd appreciate a pointer to
documentation (I couldn't find anything apposite in either the Emacs
or Elisp manuals).
1. Type the following three lines in an empty buffer:
2. Now put the cursor at the beginning of the second line and type this:
`M-: (add-text-properties (point) (point-max) '(field test))'
3. Now type `C-s C-y'. The minibuffer contains the prompt "I-search:"
but the line is not yanked into the search string, and in fact nothing
else happens at all as long as you keep typing `C-y'.
This happens only with isearch-yank-line, and only at that position;
any other isearch command (including isearch-yank-word) at that
position works fine. Moreover, isearch-yank-line from any following
position also works fine, although they also have the field property;
isearch-yank-line from any preceding position works up to that
position and then stops as above.
This happens in both CVS Emacs and in Emacs 21.3. The two Emacsen
differ in the return value of field-string called with the cursor over
the first character with the field property: in Emacs 21.3 it is "",
while in CVS Emacs it is "test^J".