bug#5303: 23.1.91; Cannot load .emacs-history from savehist.el

[Michael Albinus]

Lennart Borgman <lennart.borgman@gmail.com> writes:

> Yes, it is broken and it has been so for very long time. I just have
> not understood before that it was in the special case with a file in
> the root of a w32 drive.

I could break down the example file from Drew to the following contents:

(setq command-history '((describe-key "")))

When enabling traces of all Tramp functions, I see

======================================================================
1 -> tramp-completion-file-name-handler: operation=load 
args=("c:/emacs-history" nil nil t)
| 2 -> tramp-completion-run-real-handler: operation=load 
args=("c:/emacs-history" nil nil t)
| | 3 -> tramp-completion-file-name-handler: operation=substitute-in-file-name 
args=("c:/emacs-history")
| | | 4 -> tramp-completion-run-real-handler: operation=substitute-in-file-name 
args=("c:/emacs-history")
| | | 4 <- tramp-completion-run-real-handler: "c:/emacs-history"
| | 3 <- tramp-completion-file-name-handler: "c:/emacs-history"
| | 3 -> tramp-completion-file-name-handler: operation=expand-file-name 
args=("c:/emacs-history" "l:/usr/local/src/emacs-jabber")
| | | 4 -> tramp-completion-run-real-handler: operation=expand-file-name 
args=("c:/emacs-history" "l:/usr/local/src/emacs-jabber")
| | | 4 <- tramp-completion-run-real-handler: "c:/emacs-history"
| | 3 <- tramp-completion-file-name-handler: "c:/emacs-history"
| | 3 -> tramp-completion-file-name-handler: operation=expand-file-name 
args=("c:/emacs-history" nil)
| | | 4 -> tramp-completion-run-real-handler: operation=expand-file-name 
args=("c:/emacs-history" nil)
| | | 4 <- tramp-completion-run-real-handler: "c:/emacs-history"
| | 3 <- tramp-completion-file-name-handler: "c:/emacs-history"
| | 3 -> tramp-completion-file-name-handler: operation=file-readable-p 
args=("c:/emacs-history")
| | | 4 -> tramp-completion-run-real-handler: operation=file-readable-p 
args=("c:/emacs-history")
| | | | 5 -> tramp-completion-file-name-handler: operation=expand-file-name 
args=("c:/emacs-history" nil)
| | | | | 6 -> tramp-completion-run-real-handler: operation=expand-file-name 
args=("c:/emacs-history" nil)
| | | | | 6 <- tramp-completion-run-real-handler: "c:/emacs-history"
| | | | 5 <- tramp-completion-file-name-handler: "c:/emacs-history"
| | | 4 <- tramp-completion-run-real-handler: t
| | 3 <- tramp-completion-file-name-handler: t
| | 3 -> tramp-completion-file-name-handler: operation=expand-file-name 
args=("c:/emacs-history" "c:/")
| | | 4 -> tramp-completion-run-real-handler: operation=expand-file-name 
args=("c:/emacs-history" "c:/")
| | | 4 <- tramp-completion-run-real-handler: "c:/emacs-history"
| | 3 <- tramp-completion-file-name-handler: "c:/emacs-history"
| | 3 -> tramp-completion-file-name-handler: operation=file-directory-p 
args=("c:/emacs-history")
| | | 4 -> tramp-completion-run-real-handler: operation=file-directory-p 
args=("c:/emacs-history")
| | | | 5 -> tramp-completion-file-name-handler: operation=expand-file-name 
args=("c:/emacs-history" "c:/")
| | | | | 6 -> tramp-completion-run-real-handler: operation=expand-file-name 
args=("c:/emacs-history" "c:/")
| | | | | 6 <- tramp-completion-run-real-handler: "c:/emacs-history"
| | | | 5 <- tramp-completion-file-name-handler: "c:/emacs-history"
| | | 4 <- tramp-completion-run-real-handler: nil
| | 3 <- tramp-completion-file-name-handler: nil
| | 3 -> tramp-completion-file-name-handler: operation=file-truename 
args=("c:/emacs-history")
| | | 4 -> tramp-completion-run-real-handler: operation=file-truename 
args=("c:/emacs-history")
| | | | 5 -> tramp-completion-file-name-handler: operation=expand-file-name 
args=("c:/emacs-history" nil)
| | | | | 6 -> tramp-completion-run-real-handler: operation=expand-file-name 
args=("c:/emacs-history" nil)
| | | | | 6 <- tramp-completion-run-real-handler: "c:/emacs-history"
| | | | 5 <- tramp-completion-file-name-handler: "c:/emacs-history"
| | | 4 <- tramp-completion-run-real-handler: "c:/emacs-history"
| | 3 <- tramp-completion-file-name-handler: "c:/emacs-history"
======================================================================

As you can see, the error happens inside
`tramp-completion-file-name-handler'.  I've debugged it; the last action
I can see is disabling Tramp' file name completion handler, and calling
`load', again. The error does not seem to be caused inside a Tramp
function.

As I am not able to debug C sources on W32, I must let it to you. It
seems to be something inside FLoad.

> However I wonder why those files at all are interesting for tramp. I
> know little about tramp, but does not remote file names always start
> with something like "/ssh:", "/ftp:", "/telnet:" etc?
>
> If so why look for file names starting with "c:/"?

Some packages ( I don't remember which ones) do add the volume letter to
file names, which haven't one. Tramp silently removes the volume letter
then, and continues.

> And why does this file handler at all jump in during `load'? Shouldn't
> tramp-completion-file-name-handler just come in during completion? It
> should be invoked when the operations are file-name-completion or
> file-name-all-completion (see
> tramp-completion-file-name-handler-alist), but are these operations
> used during `load'?

In `tramp-completion-file-name-handler' it is checked, whether Emacs is
in (file name) completion mode. If not, Tramp's file name completion
handler is disables, and the function is re-called, recursively.

Best regards, Michael.