Hi Carsten and Friends of Org-mode,


appended is the ongoing caching stuff as patch against the current
master.

Please everyone: test this patch and report not _if_ it breaks
something, but _what_ it actually breaks :-P
It is meant to make life as a "publisher" easier (or at least faster
... or longer even?).



* What it does

It writes the information gathered during publishing to disk and
re-loads it from there the next time you publish the same project.

All those informations, currently titles and publishing-timestamps,
will survive a restart of emacs.

One cache file per publishing project is used. The contents of that file
is the elisp that fills the new variable `org-publish-cache'. The cache
is loaded using `load-file', once a project is to be published.

The cache file is named like the project with `.cache' appended and
lives in `org-timestamp-directory' [1]


`org-publish-cache' stores key value pairs:

  - "timestamp-filename" => time of last publishing as integer
    "timestamp-filename" is that sha1 hash of the filename,
    publishing-directory and publishing-function.

  - Absolute filename => plist
    Currently this plist holds just one property: `:title'
    to speed up sitemap generation.


The publishing is meant to keep working the exact way it did before.


Some minor quirks remain:

  - The cache file is written, even if
    `org-publish-use-timestamps-flag' is nil.

  - `org-publish-cache-file-needs-publishing' could replace
    `org-publish-needed-p' or it's body could go there.

  - In case of an error, the cache is not always written and
    cleared. This causes no trouble though.

  - We should add functions to clear the cache from old stuff. Now it's
    growing each time a file is added or renamed, but it won't shrink
    once a file is removed.
    The only way to clear the cache is to remove all cache files using
    `org-publish-remove-all-timestamps'



* Changes/Fixes:

  - Function `initialize-files-alist' and the variable
    `org-publish-files-alist' are not used anymore in favour of the
    reloadable cache and the functions for handling it. Removed
    therefor.

  - `org-publish-validate-link' was not used. Removed.

  - `org-publish-get-base-files'
    Added the variable `sitemap-requested' to avoid sorting where
    possible (see end of `org-publish-get-base-files-1').

  - `org-publish-get-project-from-filename'
    does not depend on a list of files anymore. Before, all files of
    all projects had to be loaded which took too much time here (my
    org-publish-project-alist is constantly growing).
    Instead of that, we walk `org-publish-project-alist' until we find
    a project, where the properties :base-directory, :recursive,
    :base-extension, :include and :exclude match.

    This must especially be tested in different setups, since a failure
    might expose private files to the public.

  - `org-publish-file'
    takes an additional parameter to avoid superfloues loading and
    writing of the cache file when used to publish a part of a project.

  - Everting below.



* Internal usage of the cache:

   - org-publish-reset-cache ()
     Ensure the cache is nil.

   - org-publish-initialize-cache (project-name)
     Initialize the cache for a certain project.

   - org-publish-write-cache-file ()
     Write the cache to file.

  To get and set values, four functions are provided:

    - org-publish-cache-set (key value)
      Simple key => value association.
    - org-publish-cache-get (key)
      Dito.

    - org-publish-cache-set-file-property (file prop value)
      Set a property to value in plist associated with file.
    - org-publish-cache-get-file-property (file prop value)
      Get a property's value out of plist associated with file.

  Helpers:

    - org-publish-cache-ctime-of-src (filename)
      Return the ctime of file filename as integer.