[asdf-devel] asdf output locations

[Tobias C. Rittweiler]

Faré <...> writes:

> My plan for ASDF 1.600 is to rename the (recently) builtin
> asdf-binary-locations to asdf-output-locations and make a few
> incompatible changes to it.
> * These changes will allow for configuration through an API similar to
> the one I introduced for the source-registry in 1.500.
> * I don't think many people use bleeding-edge enough ASDF to have the
> builtin ABL and these kinds of people would easily adapt anyway
> * This API will allow the future common-lisp-controller to plug nicely
> into ASDF through a supported API that doesn't break other stuff and
> isn't broken by it.
> * It will also bring all the binary location advantages of
> asdf-binary-locations, common-lisp-controller or CL-launch to everyone
> with a single, well-documented, supported configuration mechanism.
>
> I committed the following document to explain my current plans, and
> would appreciate comments:
>
> http://common-lisp.net/gitweb?p=projects/xcvb/asdf.git;a=blob;f=README.asdf-output-locations;h=82b8299246ed77b8c9c5c6e689911ae954737baa;hb=29e4b8e6919d5281b6fb5198388e3cfd5bbbe402
>
> [ François-René ÐVB Rideau | Reflection&Cybernethics | http://fare.tunes.org ]
> Wishing without work is like fishing without bait.
>         — Frank Tyger

Thanks for time you're investing in this. I think you could just have
appended the writeup to your mail, as it results in one step less people
have to take to read it, and it's easier to reply in context.

I'll do so. The PS is README.asdf-output-locations written by Fare.

  -T.

PS.

=====================
ASDF Output Locations
=====================

This file specifies how ASDF stores "binary" outputs for its operations,
typically Lisp FASL files, but also any other files
that may be generated, e.g. C files and executables from CFFI-GROVEL.

Configurations
==============

Configurations specify mappings from source locations to binary locations.

  1- An application may explicitly initialize the binary-locations
     configuration using the `Configuration API`_ below,
     in which case this takes precedence.
     It may itself compute this configuration from the command-line,
     from a script, from its own configuration file, etc.

  2- The source registry will be configured from
     the environment variable ``ASDF_OUTPUT_LOCATIONS`` if it exists.

  3- The source registry will be configured from
     user configuration file
	``~/.config/common-lisp/asdf-output-locations.conf``
     if it exists.

  4- The source registry will be configured from
     user configuration directory
	``~/.config/common-lisp/asdf-output-locations.conf.d/``
     if it exists.

  5- The source registry will be configured from
     system configuration file
	``/etc/common-lisp/asdf-output-locations.conf``
     if it exists.

  6- The source registry will be configured from
     system configuration directory
	``/etc/common-lisp/asdf-output-locations.conf.d/``
     if it exists.

Each of these configurations is specified as a SEXP
in a trival domain-specific language (defined below).
Additionally, a more shell-friendly syntax is available
for the environment variable (defined yet below).

Each of these configurations is only used if the previous
configuration explicitly or implicitly specifies that it
includes its inherited configuration.

Additionally, some implementation-specific directories
may be automatically added to whatever mappings are specified
in configuration files, no matter if the last one inherits or not.


Backward Compatibility
======================

We purposefully do not provide backward compatibility with earlier versions of
asdf-binary-locations (8 Sept 2009),
common-lisp-controller (6.17) or
cl-launch (2.35),
each of which had similar general capabilities.

Future versions of same packages (if any)
will hopefully use the new ASDF API as defined below.

Indeed, few people use and customize these packages;
these people are experts who can trivially adapt to the new configuration.
Other people will experience software that "just works".


Configuration DSL
=================

Here is the grammar of the SEXP DSL for asdf-output-locations configuration:

;; A configuration is single SEXP starting with keyword :source-registry
;; followed by a list of directives.
CONFIGURATION := (:asdf-output-locations DIRECTIVE ...)

;; A directive is one of the following:
DIRECTIVE :=
    ;; add a single directory to be scanned (no recursion)
    (:map DIRECTORY-DESIGNATOR DIRECTORY-DESIGNATOR) |

    (:include PATHNAME-DESIGNATOR)

    ;; Your configuration expression MUST contain
    ;; exactly one of either of these:
    (:inherit-configuration) | ; splices contents of inherited configuration
    (:ignore-inherited-configuration) ; drop contents of inherited configuration

DIRECTORY-DESIGNATOR :=
    ABSOLUTE-COMPONENT-DESIGNATOR |
    (ABSOLUTE-COMPONENT-DESIGNATOR RELATIVE-COMPONENT-DESIGNATOR ...)

ABSOLUTE-COMPONENT-DESIGNATOR :=
    STRING ;; namestring (directory is assumed, better be absolute or bust)
    PATHNAME ;; pathname (better be an absolute directory or bust)
    :HOME ;; designates the user-homedir-pathname ~/
    :USER-CACHE ;; designates the default location for the user cache
    :SYSTEM-CACHE ;; designates the default location for the system cache
    :ROOT ;; the root of the filesystem hierarchy

RELATIVE-COMPONENT-DESIGNATOR :=
    STRING ;; namestring (directory is assumed)
    PATHNAME ;; pathname (better be a directory or bust)
    :IMPLEMENTATION ;; a directory based on implementation, e.g. sbcl-1.0.32.30-linux-x86-64

Relative components better be either relative
or subdirectories of the path before them, or bust.

You may use #+features to customize the configuration file.

Include statements cause the search to recurse with the path specifications
from the file specified.

An inherit-configuration statement cause the search to recurse with the path
specifications from the next configuration
(see section Configurations_ above).


Configuration Directories
=========================

Configuration directories consist in files each contains
a list of directives without any enclosing ``(:asdf-binary-locations ...)`` form.
The files will be sorted by namestring as if by #'string< and
the lists of directives of these files with be concatenated in order.
An implicit ``:inherit-configuration`` will be included
at the end of the list.

This allows for packaging software that has file granularity
(e.g. Debian's ``dpkg`` or some future version of ``clbuild``)
to easily include configuration information about distributed software.

Directories may be included by specifying a directory pathname
or namestring in an ``:include`` directive, e.g.::
	(:include "/foo/bar/")


Shell-friendly syntax for configuration
=======================================

When considering environment variable ``ASDF_OUTPUT_LOCATIONS``
ASDF will skip to next configuration if it's an empty string.
It will ``READ`` the string as a SEXP in the DSL
if it begins with a paren ``(``
and it will be interpreted as a colon-separated list of directories.
Directories should come in pairs, each pair indicating a :map directive.

The magic ``!`` entry indicates the splicing of inherited configuration
rather than one of entry in a mapping pair.


Semantics of Output Location Mappings
=====================================

>From the specified configuration, a list of mappings is extracted
in a straightforward way:
mappings are collected in order, recursing through
included or inherited configuration as specified.
To this list is prepended some implementation-specific mappings,
and is appended a global default.

The list is then compiled to a mapping table as follows:
for each entry, in order, resolve the first designated directory
into an actual directory pathname for source locations.
If no mapping was specified yet for that location,
resolve the second designated directory to an output location directory
add a mapping to the table mapping the source location to the output location,
and add another mapping from the output location to itself
(unless a mapping already exists for the output location).

Based on the table, a mapping function is defined,
mapping source pathnames to output pathnames:
given a source pathname, locate the longest matching prefix
in the source column of the mapping table.
Replace that prefix by the corresponding output column
in the same row of the table, and return the result.
If no match is found, return the source pathname.
(A global default mapping the filesystem root to itself
may ensure that there will always be a match,
with same fall-through semantics).

Caching Results
===============

The implementation is allowed to either eagerly compute the information
from the configurations and file system, or to lazily re-compute it
every time, or to cache any part of it as it goes.
To explicitly flush any information cached by the system, use the API below.


Output location API
===================

The specified functions are exported from package ASDF.

(initialize-output-locations)
   will read the configuration and initialize all internal variables.

(clear-output-locations)
   undoes any output location configuration
   and clears any cache for the mapping algorithm.
   You might want to call that before you
   dump an image that would be resumed with a different configuration,
   and return an empty configuration.
   Note that this does not include clearing information about
   systems defined in the current image, only about
   where to look for systems not yet defined.

(ensure-output-locations)
   checks whether output locations have been initialized.
   If not, initialize them.
   This function will be called before any attempt to operate on a system.
   If your application wants to override the provided defaults,
   it will have to use the below function process-output-locations.

(process-output-locations X &key inherit collect)
   If X is a CONS, parse it as a SEXP in the configuration DSL,
   and extend or override inheritted configuration.
   If X is a STRING, first parse it into a SEXP
   as for the ASDF_OUTPUT_LOCATIONS
   environment variable (see above) then process it.
   If X is a PATHNAME, read the file as a single SEXP and process it.
   The inheritted configuration is provided in keyword argument inherit,
   itself a list of functions that take inherit
   and collect keyword arguments
   and defaulting to a list of functions
   that implements the default behavior.

(translate-output-locations PATHNAME)
   Applies the configured output location translations to PATHNAME
   (calls ensure-output-locations for the locations).

Credits
=======

Thanks a lot to Bjorn Lindberg and Gary King for ASDF-Binary-Locations,
and to Peter van Eynde for Common Lisp Controller.

All bad design ideas and implementation bugs are to mine, not theirs.
But so are good design ideas and elegant implementation tricks.

 -- Francois-Rene Rideau <...>