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8 Controlling where ASDF saves compiled files

Each Common Lisp implementation has its own format for compiled files (fasls for short, short for “fast loading”). If you use multiple implementations (or multiple versions of the same implementation), you'll soon find your source directories littered with various fasls, dfsls, cfsls and so on. Worse yet, some implementations use the same file extension while changing formats from version to version (or platform to platform) which means that you'll have to recompile binaries as you switch from one implementation to the next.

ASDF 2 includes the asdf-output-translations facility to mitigate the problem.

8.1 Configurations

Configurations specify mappings from input locations to output locations. Once again we rely on the XDG base directory specification for configuration. See XDG base directory.

  1. Some hardcoded wrapping output translations configuration may be used. This allows special output translations (or usually, invariant directories) to be specified corresponding to the similar special entries in the source registry.
  2. An application may explicitly initialize the output-translations configuration using the Configuration API in which case this takes precedence. (see Configuration API.) It may itself compute this configuration from the command-line, from a script, from its own configuration file, etc.
  3. The source registry will be configured from the environment variable ASDF_OUTPUT_TRANSLATIONS if it exists.
  4. The source registry will be configured from user configuration file $XDG_CONFIG_DIRS/common-lisp/asdf-output-translations.conf (which defaults to ~/.config/common-lisp/asdf-output-translations.conf) if it exists.
  5. The source registry will be configured from user configuration directory $XDG_CONFIG_DIRS/common-lisp/asdf-output-translations.conf.d/ (which defaults to ~/.config/common-lisp/asdf-output-translations.conf.d/) if it exists.
  6. The source registry will be configured from system configuration file /etc/common-lisp/asdf-output-translations.conf if it exists.
  7. The source registry will be configured from system configuration directory /etc/common-lisp/asdf-output-translations.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.

Note that by default, a per-user cache is used for output files. This allows the seamless use of shared installations of software between several users, and takes files out of the way of the developers when they browse source code, at the expense of taking a small toll when developers have to clean up output files and find they need to get familiar with output-translations first.

8.2 Backward Compatibility

We purposefully do NOT provide backward compatibility with earlier versions of ASDF-Binary-Locations (8 Sept 2009), common-lisp-controller (7.0) or cl-launch (2.35), each of which had similar general capabilities. The previous APIs of these programs were not designed for configuration by the end-user in an easy way with configuration files. Recent versions of same packages use the new asdf-output-translations API as defined below: common-lisp-controller (7.1) and cl-launch (3.00); ASDF-Binary-Locations is fully superseded and not to be used anymore.

This incompatibility shouldn't inconvenience many people. Indeed, few people use and customize these packages; these few people are experts who can trivially adapt to the new configuration. Most people are not experts, could not properly configure these features (except inasmuch as the default configuration of common-lisp-controller and/or cl-launch might have been doing the right thing for some users), and yet will experience software that “just works”, as configured by the system distributor, or by default.

Nevertheless, if you want to use the old ASDF-Binary-Locations (the one available as an extension to load of top of ASDF, not the one built into a few old versions of ASDF), it may still work if you just make sure you disable the new builtin asdf-output-translations. But if you configure both ASDF's new builtin and ASDF-Binary-Locations (or an old common-lisp-controller or cl-launch), you may experience “interesting” issues, so don't do it.

Also, note that this feature is enabled by default.

8.3 Configuration DSL

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

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

;; A directive is one of the following:
DIRECTIVE :=
    ;; include a configuration file or directory
    (: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

    ;; enable global cache in ~/.common-lisp/cache/sbcl-1.0.35-x86-64/ or something.
    :enable-user-cache |
    ;; Disable global cache. Map / to /
    :disable-cache |

    ;; add a single directory to be scanned (no recursion)
    (DIRECTORY-DESIGNATOR DIRECTORY-DESIGNATOR)


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

ABSOLUTE-COMPONENT-DESIGNATOR :=
    NULL | ;; As source: skip this entry. As destination: same as source
    STRING | ;; namestring (directory is assumed, better be absolute or bust, ``/**/*.*'' added)
    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
    :CURRENT-DIRECTORY ;; the current directory

RELATIVE-COMPONENT-DESIGNATOR :=
    STRING | ;; namestring, directory is assumed. If the last component, /**/*.* is added
    PATHNAME | ;; pathname unless last component, directory is assumed.
    :IMPLEMENTATION | ;; a directory based on implementation, e.g. sbcl-1.0.32.30-linux-x86-64
    :IMPLEMENTATION-TYPE | ;; a directory based on lisp-implementation-type only, e.g. sbcl
    :CURRENT-DIRECTORY | ;; all components of the current directory, without the :absolute
    :UID | ;; current UID -- not available on Windows
    :USER ;; current USER name -- NOT IMPLEMENTED(!)

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

The last component, if not a pathname, is notionally completed by /**/*.*. You can specify more fine-grained patterns by using a pathname object as the last component e.g. #p"some/path/**/foo*/bar-*.fasl"

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

The second designator of a mapping may be NIL, indicating that files are not mapped to anything but themselves (same as if the second designator was the same as the first).

: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 Configurations, above.

8.4 Configuration Directories

Configuration directories consist in files each contains a list of directives without any enclosing (:output-translations ...) 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 software being distributed.

The convention is that, for sorting purposes, the names of files in such a directory begin with two digits that determine the order in which these entries will be read. Also, the type of these files is conventionally "conf" and as a limitation of some implementations, the type cannot be NIL.

Directories may be included by specifying a directory pathname or namestring in an :include directive, e.g.:

	(:include "/foo/bar/")

8.5 Shell-friendly syntax for configuration

When considering environment variable ASDF_OUTPUT_TRANSLATIONS ASDF will skip to next configuration if it's an empty string. It will READ the string as an 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 by pairs, indicating a mapping directive.

The magic empty entry, if it comes in what would otherwise be the first entry in a pair, indicates the splicing of inherited configuration. If it comes as the second entry in a pair, it indicates that the directory specified first is to be left untranslated (which has the same effect as if the directory had been repeated).

8.6 Semantics of Output Translations

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).

8.7 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.

8.8 Output location API

The specified functions are exported from package ASDF.

— Function: initialize-output-translations PARAMETER

will read the configuration and initialize all internal variables. You may extend or override configuration from the environment and configuration files with the given PARAMETER, which can be NIL (no configuration override), or a SEXP (in the SEXP DSL), a string (as in the string DSL), a pathname (of a file or directory with configuration), or a symbol (fbound to function that when called returns one of the above).

— Function: clear-output-translations

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.

— Function: ensure-output-translations PARAMETER

checks whether output translations have been initialized. If not, initialize them with the given PARAMETER. This function will be called before any attempt to operate on a system.

— Function: apply-output-translations PATHNAME

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

8.9 Credits for output translations

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 fare@tunes.org