tags-search raises error if a file is not found

[Drew Adams]

emacs -Q
M-x tags-search
Enter a regexp.
 
If the TAGS file refers to a source file that no longer exists, an
error is raised, preventing any search of the available files.
 
This is too drastic and too limiting. Emacs should be more forgiving
and degrade its service gracefully in this case. It should display a
message listing any unavailable files, but it should still search
those that are available.
 
The problem is in `tags-loop-continue', which calls `next-file', which
raises the error when it tries to (insert-file-contents
the-missing-file nil).
 
I don't know if the fix should be just for `tags-search' or for
`tags-loop-continue' or for `next-file'. Probably all uses of
`next-file' should be examined to see what TRT is. I don't have the
time for that, myself. At any rate, this is a silly limitation for
`tags-search', and it should at least be fixed for that case.
 
Note that some users might use a TAGS file that they obtained
elsewhere, they might not have all of the source files indexed in the
TAGS file, and they might not have a means or the knowledge or the
will to regenerate a TAGS file. Emacs should nevertheless let them
make use of the TAGS file, as far as possible.
 
This bug occurs at least as far back as Emacs 20. I'm surprised this
has not been seen to be a problem before now.
 

In GNU Emacs 22.1.90.1 (i386-mingw-nt5.1.2600)
 of 2008-01-30 on PRETEST
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4) --cflags -Ic:/gnuwin32/include'