-*-indented-text-*- First, for the purposes of this policy, some terminology: - a particular flavor of Emacs, for example: emacs xemacs21 add-on package - any package which wishes to use the emacsen-common infrastructure, usually in order to byte-compile itself for some subset of the currently installed emacs flavors. - the name of an add-on package, for example: auctex bbdb gnus 1) Guarding use of emacsen-common infrastructure Any use of the emacsen-common infrastructure must be guarded by a test for the existence of the emacsen-common installed state file. i.e.: if test -e /var/lib/emacsen-common/state/package/installed/emacsen-common then emacs-package-install ... fi Of course this requirement does not apply for the maintainer scripts of any package that depends on emacsen-common, which includes all add-on packages and all emacsen main packages: emacs-lucid, xemacs21, etc. So in practice, this guard should rarely be necessary. 2) Flavor indication Each flavor's binary must set the variable debian-emacs-flavor to be the same as the name of the debian-package. For example, the emacs-lucid package does this in startup.el: (defconst debian-emacs-flavor 'emacs "A symbol representing the particular debian flavor of emacs running. Something like 'emacs, 'xemacs21, etc.") For now, debian-emacs-flavor should be defined regardless of the use of -q or --no-site-file. 3) Emacs startup strategy On startup each emacsen must call (debian-startup ). During debian-startup, the relevant flavor-specific site-start.d files will be loaded via debian-run-directories, e.g: emacs: /etc/emacs/site-start.d xemacs21: /etc/xemacs21/site-start.d The next question is, "Where should we run debian-startup?" The safest possibility, and the one I had originally intended was to modify lisp/startup.el to do the right thing, and I had also intended that --no-site-file would disable all of the Debian startup bits, including calling Debian startup. So here's what emacs-lucid has in startup.el: ;; Debian startup (if site-run-file (progn ;; Load all the Debian package snippets. ;; It's in here because we want -q to kill it too. (if (load "debian-startup" t t nil) (debian-startup debian-emacs-flavor)) ;; Now the normal site file... (load site-run-file t t nil))) This makes sure that Debian's bits are setup as early as possible, and requires only minor modifications to the emacs source. At a minimum debian-startup calls debian-run-directories which collects the union of all the file base names (i.e. without any .el or .elc extension, and without the directory component: i.e. /etc/xemacs21/site-start.d/50foo.elc => 50foo), then temporarily augments the emacs load path to include /etc//site-start.d, and calls (load base-name) in string< order. 4) /usr/share//site-lisp/ This directory must be treated as part of the normal emacsen load path, and add-on packages should place their files there (see below), e.g.: emacs: /usr/share/emacs/site-lisp/ xemacs21: /usr/share/xemacs21/site-lisp/ 5) Emacs add-on package support (examples below should make this much clearer) A) Each add-on package must add a "Depends: emacsen-common (>= 2.0.8)" and include a file like this that indicates its emacsen-common compatibility level: /usr/lib/emacsen-common/packages/compat/ This file should contain a single integer, which at the moment should be 0. (Currently, the file is just used to distinguish between old-style packages and new-style packages.) B) Each add-on package may place a file named the same as the package in /usr/lib/emacsen-common/packages/install/ /usr/lib/emacsen-common/packages/remove/ and the package must make these calls from the given maintainer scripts: preinst: /usr/lib/emacsen-common/emacs-package-install --preinst postinst: /usr/lib/emacsen-common/emacs-package-install --postinst prerm: /usr/lib/emacsen-common/emacs-package-remove --prerm The postinst call must not be made until the package is completely configured and otherwise ready for use, and the prerm call must be made before any changes that would make the package not completely configured and ready for use. These calls will ensure that the add-on package's emacsen-common install and remove scripts are called at the appropriate times. In particular the postinst call will trigger the install script for every flavor of emacs that's already completely installed. If flavors are being installed simultaneously, the install script may be delayed until that flavor's postinst runs. When the install or remove script is called, the add-on package can assume that the flavor for which it is being invoked is completely installed (i.e. past the significant parts of its postinst). The install and remove scripts will be invoked with a single argument, the being installed or removed. So if emacs and xemacs21 flavors are fully installed, installing add-on foo will result in calls to: /usr/lib/emacsen-common/packages/install/foo emacs /usr/lib/emacsen-common/packages/install/foo xemacs21 emacs-package remove does the symmetric thing. C) Add-on packages need not declare a dependency on any emacs flavors, but they must declare a dependency on emacsen-common (see above, and (of course) must declare dependencies on any other relevant packages, including relevant add-on packages, or tools needed by the install/remove scripts. The emacsen-common infrastructure will ensure that the install/remove script invocations are ordered to respect inter-add-on package dependencies. D) Each add-on package has the right to place files into the following directories: /etc//site-start.d /usr/share//site-lisp/ E) If an add-on package compiles any of its Emacs Lisp sources (which must be compiled to a subdirectory of /usr/share//site-lisp/ -- see section 4 above), the corresponding .el file must be available in the same directory as the corresponding .elc file, either directly, via symlink, or hardlink. For example, if add-on package foo produces /usr/share/emacs/site-lisp/foo/bar.elc, then /usr/share/emacs/site-lisp/foo/bar.el must refer to the corresponding source file. This ensures that Emacs will be able to locate the source code for the add-on package when using M-x find-function, etc. F) Each emacsen main package (i.e. emacs-lucid, xemacs21, etc.) must depend on emacsen-common (>= 3.0.0). G) Each emacsen main package (i.e. emacs-lucid, emacs-nox, etc.) must make these calls from the given maintainer scripts: preinst: /usr/lib/emacsen-common/emacs-install --preinst postinst: /usr/lib/emacsen-common/emacs-install --postinst prerm: /usr/lib/emacsen-common/emacs-remove --prerm The postinst call must not be made until the package is completely configured and ready for use, and the prerm call must be made before any changes that would make the package not completely configured and ready for use. These calls will ensure that all of the relevant add-on packages' emacsen-common install and remove scripts are called at the appropriate times. In particular the postinst call may trigger the install scripts and the prerm script may trigger the remove scripts for any package that is ready. If add-on packages are being installed simultaneously, the add-on install scripts may be delayed until their postinst scripts are run. 6) Mandatory binary path Each emacsen must be available as /usr/bin/ in addition to any normal binary path so that when add-on package install/remove scripts are called, they can just use /usr/bin/"$1" to get the right binary for byte-compilation. 7) Virtual package Each emacsen main package must "Provides: emacsen", and packages that just need to make sure some flavor of emacs is installed should "Depends: emacsen". If they depend on specific flavors of emacs, then they should list those dependencies explicitly instead. 8) Emacs lisp load path. At a minimum, each emacs must have the following directories in this relative order in their load path: /usr/local/share//site-lisp /usr/share//site-lisp Emacs add-on packages may not modify load-path directly. They must use (debian-pkg-add-load-path-item ). This function will make sure that their additions end up in the right place -- before the emacs system directories, but after the /usr/local/ directories. 9) Usage of autoload instead of load in the site-start.d files. It's been suggested, and is probably a good idea that maintainers switch to using autoload rather than load when possible in their site-start.d files. For example, instead of (load "some-package"), you should use autoloads for all the top level, user visible functions. That's it. Hopefully this gives the add-on package maintainers the flexibility they need to be able to DTRT, and the common case won't be all that difficult. Examples: 1) xemacs21 and the add-on packages tm and auctex are already installed, and now someone installs emacs23. In its prerm, emacs23 would make this call: /usr/lib/emacsen-common/emacs-install --postinst emacs23 which would result in calls to /usr/lib/emacsen-common/packages/install/auctex emacs23 /usr/lib/emacsen-common/packages/emacs/install/tm emacs23 2) Now, given (1), assume that someone removes xemacs21. In its prerm, xemacs21 would make this call: /usr/lib/emacsen-common/emacs-remove --prerm xemacs21 which would result in calls to /usr/lib/emacsen-common/packages/remove/auctex xemacs21 /usr/lib/emacsen-common/packages/remove/tm xemacs21 3) Now assume emacs23 and xemacs21 are installed, and that someone removes tm. The call to emacsen-package-remove in tm's prerm will result in the following calls: /usr/lib/emacsen-common/packages/remove/tm emacs23 /usr/lib/emacsen-common/packages/remove/tm xemacs21 In the remove/tm file, tm is responsible for cleaning up any files it put into its allowed locations: /etc//site-start.d/ /usr/share//site-lisp/tm 4) Now assume that emacs and auctex are not installed, and that someone installs both at the same time. At some point during the installation, after emacs and auctex are fully configured, this command will be invoked: /usr/lib/emacsen-common/packages/remove/auctex emacs This call may happen from either emacs or auctex's postinst as a result of their respective calls to emacs-install and emacs-package-install. Which package causes the invocation will depend on the order in which dpkg decides to invoke their postint scripts. The emacsen-common infrastructure makes sure that the last one wins. 5) Finally, please see sample-package-install-foo and sample-package-remove-foo in /usr/share/doc/emacsen-common/. These are sample install and remove scripts for a hypothetical package "foo" that only needs to byte compile a list of files for each flavor.