bug#63829: 29.0.90; project-find-file's future history breaks with common-parent-directory

[Dmitry Gutov <dmitry@gutov.dev>]

Hi!

On 02/06/2023 01:32, Spencer Baugh wrote:
> 
> 1. emacs -Q
> 2. Open a project where project-files only returns files in a certain
> subdirectory.  For example, a git repo /repo where the only file is
> "dir/file.txt".
> 3. Open dir/file.txt
> 4. C-x p f   ;; project-find file
> 5. Observe that the prompt is "Find file in /repo/dir: " which correctly
> contains the common parent directory between all the paths returned by
> project-files.
> 6. M-n       ;; next-history-element
> 7. The minibuffer now contains "dir/file.txt".  RET will fail to
> open the file.

Note that if you continue pressing 'M-n', you will see the corresponding 
proper relative file names. The first one comes from the value 
constructed in project-find-file. Which indeed looks problematic, since 
we remove context in there by creating a relative name.

> Instead, the common parent directory should be stripped from the "future
> history" element.

Try the patch at the end, please. It seems to fix the scenario you 
presented. Does it help with the feature you mention below, too?

It doesn't handle the case when (thing-at-point 'filename) returns a 
relative file name that includes a directory name, relative to the 
project root (where common-parent-directory differs), but that one seems 
even more ambiguous.

> (As a separate point: I ran into this while adding a feature for
> switching between projects with similar directory structures.  I want to
> include the relative path in the starting project in the "future
> history", so that when you have a file in projectA open, you can switch
> to the same file in projectB with C-x p p f M-n RET.  For example,
> switching between the same file in multiple clones of Emacs.  But sadly
> the future history doesn't work properly right now even in a single
> project)

diff --git a/lisp/progmodes/project.el b/lisp/progmodes/project.el
index 7c51778d5d4..184f2316074 100644
--- a/lisp/progmodes/project.el
+++ b/lisp/progmodes/project.el
@@ -1008,7 +1008,7 @@ project-find-file
           (dirs (list root)))
      (project-find-file-in
       (or (thing-at-point 'filename)
-         (and buffer-file-name (file-relative-name buffer-file-name root)))
+         buffer-file-name)
       dirs pr include-all)))

  ;;;###autoload
@@ -1062,6 +1062,10 @@ project--read-file-cpd-relative
                                 (delete common-parent-directory all-files))
                           t))
           (substrings (mapcar (lambda (s) (substring s cpd-length)) 
all-files))
+         (mb-default (if (and common-parent-directory
+                              (file-name-absolute-p mb-default))
+                         (file-relative-name mb-default 
common-parent-directory)
+                       mb-default))
           (_ (when included-cpd
                (setq substrings (cons "./" substrings))))
           (new-collection (project--file-completion-table substrings))