bug#20629: 25.0.50; Regression: TAGS broken, can't find anything in C++ files.

[Dmitry Gutov]

On 05/27/2015 12:01 AM, Stefan Monnier wrote:

> BTW, it might be worthwhile to try and replace the obarray with
> a function which directly searches the corresponding tags buffers.
> Searching those buffers might not be significantly slower than searching
> the obarray, with the advantage that we avoid the "building the
> completion table" step.

Having the table always up-to-date would be nice. But here's some 
numbers with a rough patch.

The project is of moderate size: Linux kernel.

TAGS is 159097 lines long.

Pre-built tags-completion-table:

Build it -> 1.34 seconds
(all-completions "" (tags-completion-table)) after that -> 0.02 seconds

Dynamic completion table:

(all-completions "" (tags-completion-table)) -> 0.78 seconds
                 ^-- same with any longer prefix, in this implementation

Patch:

diff --git a/lisp/progmodes/etags.el b/lisp/progmodes/etags.el
index 9ff164e..19de126 100644
--- a/lisp/progmodes/etags.el
+++ b/lisp/progmodes/etags.el
@@ -753,31 +753,18 @@ Assumes the tags table is the current buffer."
       (setq tags-included-tables (funcall 
tags-included-tables-function))))
 
 (defun tags-completion-table ()
-  "Build `tags-completion-table' on demand.
+  "Return tags completion table.
 The tags included in the completion table are those in the current
 tags table and its (recursively) included tags tables."
-  (or tags-completion-table
-      ;; No cached value for this buffer.
-      (condition-case ()
-         (let (current-table combined-table)
-           (message "Making tags completion table for %s..." buffer-file-name)
-           (save-excursion
-             ;; Iterate over the current list of tags tables.
-             (while (visit-tags-table-buffer (and combined-table t))
-               ;; Find possible completions in this table.
-               (setq current-table (funcall tags-completion-table-function))
-               ;; Merge this buffer's completions into the combined table.
-               (if combined-table
-                   (mapatoms
-                    (lambda (sym) (intern (symbol-name sym) combined-table))
-                    current-table)
-                 (setq combined-table current-table))))
-           (message "Making tags completion table for %s...done"
-                    buffer-file-name)
-           ;; Cache the result in a buffer-local variable.
-           (setq tags-completion-table combined-table))
-       (quit (message "Tags completion table construction aborted.")
-             (setq tags-completion-table nil)))))
+  (completion-table-with-cache
+   (lambda (_string)
+     (let (cont tables)
+       (save-excursion
+         ;; Iterate over the current list of tags tables.
+         (while (visit-tags-table-buffer (or cont (progn (setq cont t) 
nil)))
+           ;; Find possible completions in this table.
+           (push (funcall tags-completion-table-function) tables)))
+       (nreverse (apply #'nconc tables))))))

 ;;;###autoload
 (defun tags-lazy-completion-table ()
@@ -1256,11 +1243,7 @@ buffer-local values of tags table format variables."


 (defun etags-tags-completion-table () ; Doc string?
-  (let ((table (make-vector 511 0))
-       (progress-reporter
-        (make-progress-reporter
-         (format "Making tags completion table for %s..." buffer-file-name)
-         (point-min) (point-max))))
+  (let ((table nil))
     (save-excursion
       (goto-char (point-min))
       ;; This monster regexp matches an etags tag line.
@@ -1276,12 +1259,11 @@ buffer-local values of tags table format variables."
 \\([-a-zA-Z0-9_+*$?:]+\\)[^-a-zA-Z0-9_+*$?:\177]*\\)\177\
 \\(\\([^\n\001]+\\)\001\\)?\\([0-9]+\\)?,\\([0-9]+\\)?\n"
              nil t)
-       (intern (prog1 (if (match-beginning 5)
+       (push   (prog1 (if (match-beginning 5)
                           ;; There is an explicit tag name.
                           (buffer-substring (match-beginning 5) (match-end 5))
                         ;; No explicit tag name.  Best guess.
-                        (buffer-substring (match-beginning 3) (match-end 3)))
-                 (progress-reporter-update progress-reporter (point)))
+                        (buffer-substring (match-beginning 3) (match-end 3))))
                table)))
     table))