Re: Etags completion problem for local tags table

[Radey Shouman]

Radey Shouman <shouman@comcast.net> writes:

> In (at least) emacs 22.1, completing reads for find-tag and list-tags
> will use the global tags table list even if a local tags file has
> been specified using a prefix argument for visit-tags-table.
> 
> To reproduce, visit two files, in the first buffer visit a tags file
> globally, in the second a different tags file locally.  From the
> second buffer, try M.[TAB] .  The tag list displayed will correspond
> to the first, globally visited, tags file.

The patch presented earlier had problems - the root issue is that
variables tags-file-name and tags-table-list are used for returning
information from functions which may change the current buffer.

One manifestation of the problem can be seen by setting a local tags
file using C-uM-x visit-tags-table twice in the same buffer.  The
second attempt will fail to set a local tags table, but will set the
global tags table.

This patch also modifies visit-tags-table so that it will remove a
local tags table if present in the buffer in which it is called to set
a global tags table.  This is arguably not a bug fix, but seems much
less suprising than the current behavior.

*** etags.el.dist       2007-01-21 03:20:46.000000000 -0500
--- etags.el    2008-04-24 09:57:37.660821100 -0400
***************
*** 257,262 ****
--- 257,264 ----
    "Function to do the work of `tags-included-tables' (which see).")
  (defvar verify-tags-table-function nil
    "Function to return t iff current buffer contains valid tags file.")
+ (defvar etags-calling-buffer nil
+   "Buffer from which a completing read was made, so we can determine the 
appropriate tags file to visit.")
  
  ;; Initialize the tags table in the current buffer.
  ;; Returns non-nil iff it is a valid tags table.  On
***************
*** 305,323 ****
    ;; Calling visit-tags-table-buffer with tags-file-name set to FILE will
    ;; initialize a buffer for FILE and set tags-file-name to the
    ;; fully-expanded name.
!   (let ((tags-file-name file))
      (save-excursion
        (or (visit-tags-table-buffer file)
          (signal 'file-error (list "Visiting tags table"
                                    "file does not exist"
!                                   file)))
!       ;; Set FILE to the expanded name.
!       (setq file tags-file-name)))
    (if local
        ;; Set the local value of tags-file-name.
        (set (make-local-variable 'tags-file-name) file)
      ;; Set the global value of tags-file-name.
!     (setq-default tags-file-name file)))
  
  (defun tags-table-check-computed-list ()
    "Compute `tags-table-computed-list' from `tags-table-list' if necessary."
--- 307,335 ----
    ;; Calling visit-tags-table-buffer with tags-file-name set to FILE will
    ;; initialize a buffer for FILE and set tags-file-name to the
    ;; fully-expanded name.
!   (let (table-list)
!     (let ((tags-file-name file)
!           (tags-table-list tags-table-list))
        (save-excursion
          (or (visit-tags-table-buffer file)
              (signal 'file-error (list "Visiting tags table"
                                        "file does not exist"
!                                       file))))
!       ;; Set FILE to the expanded name.  Note that we have to do this from 
the original
!       ;; buffer, in case tags-file-name or tags-table-list are buffer-local.
!       (setq file tags-file-name
!             table-list tags-table-list))
! 
      (if local
          ;; Set the local value of tags-file-name.
+         (progn
            (set (make-local-variable 'tags-file-name) file)
+           (set (make-local-variable 'tags-table-list) table-list))
        ;; Set the global value of tags-file-name.
!       (kill-local-variable 'tags-file-name)
!       (kill-local-variable 'tags-table-list)
!       (setq tags-file-name file
!             tags-table-list table-list))))
  
  (defun tags-table-check-computed-list ()
    "Compute `tags-table-computed-list' from `tags-table-list' if necessary."
***************
*** 444,459 ****
          (revert-buffer t t)
          (tags-table-mode)))
      (and (file-exists-p file)
!        (progn
           (set-buffer (find-file-noselect file))
           (or (string= file buffer-file-name)
               ;; find-file-noselect has changed the file name.
               ;; Propagate the change to tags-file-name and tags-table-list.
               (let ((tail (member file tags-table-list)))
                 (if tail
                     (setcar tail buffer-file-name))
                 (if (eq file tags-file-name)
!                    (setq tags-file-name buffer-file-name))))
           (tags-table-mode)))))
  
  ;; Subroutine of visit-tags-table-buffer.  Search the current tags tables
--- 456,475 ----
          (revert-buffer t t)
          (tags-table-mode)))
      (and (file-exists-p file)
!        (let ((obuf (current-buffer)))
           (set-buffer (find-file-noselect file))
           (or (string= file buffer-file-name)
               ;; find-file-noselect has changed the file name.
               ;; Propagate the change to tags-file-name and tags-table-list.
+                ;; We have to do this in the buffer current when we were called
+                ;; because tags-table-list and tags-file-name may be buffer 
local.
+                (save-excursion
+                  (set-buffer obuf)
                   (let ((tail (member file tags-table-list)))
                     (if tail
                         (setcar tail buffer-file-name))
                     (if (eq file tags-file-name)
!                        (setq tags-file-name buffer-file-name)))))
           (tags-table-mode)))))
  
  ;; Subroutine of visit-tags-table-buffer.  Search the current tags tables
***************
*** 538,543 ****
--- 554,564 ----
   `tags-file-name', `tags-table-list', `tags-table-list-pointer'.
  Returns t if it visits a tags table, or nil if there are no more in the list."
  
+   ;; We may be called from a minibuffer if invoked during completion.
+   ;; this can be a problem when the tags tables are buffer-local.
+   (if etags-calling-buffer
+       (set-buffer etags-calling-buffer))
+ 
    ;; Set tags-file-name to the tags table file we want to visit.
    (cond ((eq cont 'same)
         ;; Use the ambient value of tags-file-name.
***************
*** 781,787 ****
  
  ;; Read a tag name from the minibuffer with defaulting and completion.
  (defun find-tag-tag (string)
!   (let* ((completion-ignore-case (if (memq tags-case-fold-search '(t nil))
                                     tags-case-fold-search
                                   case-fold-search))
         (default (funcall (or find-tag-default-function
--- 802,809 ----
  
  ;; Read a tag name from the minibuffer with defaulting and completion.
  (defun find-tag-tag (string)
!   (let* ((etags-calling-buffer (current-buffer))
!          (completion-ignore-case (if (memq tags-case-fold-search '(t nil))
                                     tags-case-fold-search
                                   case-fold-search))
         (default (funcall (or find-tag-default-function