Skip to content
Snippets Groups Projects
asdf.texinfo 201 KiB
Newer Older
@section 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.


@section Configuration API

The specified functions are exported from your build system's package.
Thus for ASDF the corresponding functions are in package ASDF,
and for XCVB the corresponding functions are in package XCVB.

@defun initialize-source-registry @Aoptional PARAMETER
   will read the configuration and initialize all internal variables.
Francois-Rene Rideau's avatar
Francois-Rene Rideau committed
   You may extend or override configuration
   from the environment and configuration files
   with the given @var{PARAMETER}, which can be
   @code{nil} (no configuration override),
Francois-Rene Rideau's avatar
Francois-Rene Rideau committed
   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).
@end defun

@defun clear-source-registry
   undoes any source registry configuration
   and clears any cache for the search algorithm.
   You might want to call this function
   (or better, @code{clear-configuration})
   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.
@end defun

@defun ensure-source-registry @Aoptional PARAMETER
   checks whether a source registry has been initialized.
Francois-Rene Rideau's avatar
Francois-Rene Rideau committed
   If not, initialize it with the given @var{PARAMETER}.
Every time you use ASDF's @code{find-system}, or
anything that uses it (such as @code{operate}, @code{load-system}, etc.),
@code{ensure-source-registry} is called with parameter @code{nil},
which the first time around causes your configuration to be read.
If you change a configuration file,
you need to explicitly @code{initialize-source-registry} again,
or maybe simply to @code{clear-source-registry} (or @code{clear-configuration})
which will cause the initialization to happen next time around.


@subsection *source-registry-parameter* variable
@vindex *source-registry-parameter*

We have made available the variable @code{*source-registry-parameter*}
that can be used by code that wishes to introspect about the (past)
configuration of ASDF's source registry.  @strong{This variable should
never be set!}  It will be set as a side-effect of calling
@code{initialize-source-registry}; user code should treat it as
read-only.
@subsection Information about system dependencies

ASDF makes available three functions to read system interdependencies.
These are intended to aid programmers who wish to perform dependency
analyses.

@defun system-defsystem-depends-on system
@end defun

@defun system-depends-on system
@end defun

@defun system-weakly-depends-on system
Returns a list of names of systems that are weakly depended on by
@var{system}.  Weakly depended on systems are optionally loaded only if
Robert P. Goldman's avatar
Robert P. Goldman committed
ASDF can find them; failure to find such systems does @emph{not} cause an
error in loading.

Note that the return value for @code{system-weakly-depends-on} is simpler
than the return values of the other two system dependency introspection
functions.
@end defun

@section Status
This mechanism is vastly successful, and we have declared
that @code{asdf:*central-registry*} is not recommended anymore,
though we will continue to support it.
All hooks into implementation-specific search mechanisms
have been integrated in the @code{wrapping-source-registry}
that everyone uses implicitly.


@section Rejected ideas

Alternatives I considered and rejected included:

@enumerate
@item Keep @code{asdf:*central-registry*} as the master with its current semantics,
   and somehow the configuration parser expands the new configuration
   language into a expanded series of directories of subdirectories to
   lookup, pre-recursing through specified hierarchies. This is kludgy,
   and leaves little space of future cleanups and extensions.

@item Keep @code{asdf:*central-registry*} remains the master but extend its semantics
   in completely new ways, so that new kinds of entries may be implemented
   as a recursive search, etc. This seems somewhat backwards.

@item Completely remove @code{asdf:*central-registry*}
   and break backwards compatibility.
   Hopefully this will happen in a few years after everyone migrate to
   a better ASDF and/or to XCVB, but it would be very bad to do it now.

@item Replace @code{asdf:*central-registry*} by a symbol-macro with appropriate magic
   when you dereference it or setf it. Only the new variable with new
   semantics is handled by the new search procedure.
   Complex and still introduces subtle semantic issues.
@end enumerate


I've been suggested the below features, but have rejected them,
for the sake of keeping ASDF no more complex than strictly necessary.

@itemize
@item
  More syntactic sugar: synonyms for the configuration directives, such as
  @code{(:add-directory X)} for @code{(:directory X)}, or @code{(:add-directory-hierarchy X)}
  or @code{(:add-directory X :recurse t)} for @code{(:tree X)}.

@item
   The possibility to register individual files instead of directories.

@item
  Integrate Xach Beane's tilde expander into the parser,
  or something similar that is shell-friendly or shell-compatible.
  I'd rather keep ASDF minimal. But maybe this precisely keeps it
  minimal by removing the need for evaluated entries that ASDF has?
  i.e. uses of @code{USER-HOMEDIR-PATHNAME} and @code{$SBCL_HOME}
  Hopefully, these are already superseded by the @code{:default-registry}

@item
  Using the shell-unfriendly syntax @code{/**} instead of @code{//} to specify recursion
  down a filesystem tree in the environment variable.
  It isn't that Lisp friendly either.
@end itemize

@section TODO

@itemize
@item Add examples
@end itemize


@section Credits for the source-registry

Thanks a lot to Stelian Ionescu for the initial idea.

Thanks to Rommel Martinez for the initial implementation attempt.

Robert P. Goldman's avatar
Robert P. Goldman committed
All bad design ideas and implementation bugs are mine, not theirs.
But so are good design ideas and elegant implementation tricks.

 --- Francois-Rene Rideau @email{fare@@tunes.org}, Mon, 22 Feb 2010 00:07:33 -0500



@node Controlling where ASDF saves compiled files, Error handling, Controlling where ASDF searches for systems, Top
@comment  node-name,  next,  previous,  up
@chapter Controlling where ASDF saves compiled files
@cindex asdf-output-translations
@vindex ASDF_OUTPUT_TRANSLATIONS
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 @file{fasl}s, @file{dfsl}s, @file{cfsl}s 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.
Since ASDF 2, ASDF includes the @code{asdf-output-translations} facility
@section Configurations
Configurations specify mappings from input locations to output locations.
Once again we rely on the XDG base directory specification for configuration.
@xref{Controlling where ASDF searches for systems,,XDG base directory}.
@item
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.

@item
An application may explicitly initialize the output-translations
configuration using the Configuration API
in which case this takes precedence.
(@pxref{Controlling where ASDF saves compiled files,,Configuration API}.)
It may itself compute this configuration from the command-line,
from a script, from its own configuration file, etc.

@item
The source registry will be configured from
the environment variable @code{ASDF_OUTPUT_TRANSLATIONS} if it exists.

@item
The source registry will be configured from
user configuration file
@file{$XDG_CONFIG_DIRS/common-lisp/asdf-output-translations.conf}
(which defaults to
@file{~/.config/common-lisp/asdf-output-translations.conf})
if it exists.

@item
The source registry will be configured from
user configuration directory
@file{$XDG_CONFIG_DIRS/common-lisp/asdf-output-translations.conf.d/}
(which defaults to
@file{~/.config/common-lisp/asdf-output-translations.conf.d/})
if it exists.

@item
The source registry will be configured from
system configuration file
@file{/etc/common-lisp/asdf-output-translations.conf}
if it exists.

@item
The source registry will be configured from
system configuration directory
@file{/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.
@cindex ASDF-BINARY-LOCATIONS compatibility


We purposefully do NOT provide backward compatibility with earlier versions of
@code{ASDF-Binary-Locations} (8 Sept 2009),
@code{common-lisp-controller} (7.0) or
@code{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 @code{asdf-output-translations} API as defined below:
@code{common-lisp-controller} (7.2) and @code{cl-launch} (3.000).
@code{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
@code{common-lisp-controller} and/or @code{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 are a fan of @code{ASDF-Binary-Locations},
we provide a limited emulation mode:

@defun enable-asdf-binary-locations-compatibility @Akey centralize-lisp-binaries default-toplevel-directory include-per-user-information map-all-source-files source-to-target-mappings
This function will initialize the new @code{asdf-output-translations} facility in a way
that emulates the behavior of the old @code{ASDF-Binary-Locations} facility.
Where you would previously set global variables
@var{*centralize-lisp-binaries*},
@var{*default-toplevel-directory*},
@var{*include-per-user-information*},
@var{*map-all-source-files*} or @var{*source-to-target-mappings*}
you will now have to pass the same values as keyword arguments to this function.
Note however that as an extension the @code{:source-to-target-mappings} keyword argument
will accept any valid pathname designator for @code{asdf-output-translations}
instead of just strings and pathnames.
@end defun

If you insist, you can also keep using the old @code{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),
but first you must disable @code{asdf-output-translations}
with @code{(asdf:disable-output-translations)},
or you might experience ``interesting'' issues.

Also, note that output translation is enabled by default.
To disable it, use @code{(asdf:disable-output-translations)}.
Here is the grammar of the SEXP DSL
for @code{asdf-output-translations} configuration:

@verbatim
;; 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 :=
    ;; Your configuration expression MUST contain
    ;; exactly one of either of these:
    :inherit-configuration | ; splices inherited configuration (often specified last)
    :ignore-inherited-configuration | ; drop inherited configuration (specified anywhere)

    ;; forward compatibility directive (since ASDF 2.011.4), useful when
    ;; you want to use new configuration features but have to bootstrap a
    ;; the newer required ASDF from an older release that doesn't sport said features:
    :ignore-invalid-entries | ; drops subsequent invalid entries instead of erroring out

    ;; include a configuration file or directory
    (:include PATHNAME-DESIGNATOR) |
    ;; enable global cache in ~/.common-lisp/cache/sbcl-1.0.45-linux-amd64/ 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)

    ;; use a function to return the translation of a directory designator
    (DIRECTORY-DESIGNATOR (:function TRANSLATION-FUNCTION))
    NIL | ;; As source: skip this entry. As destination: same as source
    T | ;; as source matches anything, as destination leaves pathname unmapped.
    ABSOLUTE-COMPONENT-DESIGNATOR ;; same as in the source-registry language

TRANSLATION-FUNCTION :=
    SYMBOL | ;; symbol of a function that takes two arguments,
             ;; the pathname to be translated and the matching DIRECTORY-DESIGNATOR
    LAMBDA   ;; A form which evalutates to a function taking two arguments consisting of
             ;; the pathname to be translated and the matching DIRECTORY-DESIGNATOR

@end verbatim

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 @file{/**/*.*}.
You can specify more fine-grained patterns
by using a pathname object as the last component
e.g. @file{#p"some/path/**/foo*/bar-*.fasl"}

You may use @code{#+features} to customize the configuration file.

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

When the first designator is @code{t},
the mapping always matches.
When the first designator starts with @code{:root},
the mapping matches any host and device.
In either of these cases, if the second designator
isn't @code{t} and doesn't start with @code{:root},
then strings indicating the host and pathname are somehow copied
in the beginning of the directory component of the source pathname
before it is translated.

When the second designator is @code{t}, the mapping is the identity.
the mapping preserves the host and device of the original pathname.
Notably, this allows you to map files
to a subdirectory of the whichever directory the file is in.
Though the syntax is not quite as easy to use as we'd like,
you can have an (source destination) mapping entry such as follows
in your configuration file,
or you may use @code{enable-asdf-binary-locations-compatibility}
with @code{:centralize-lisp-binaries nil}
which will do the same thing internally for you:
@verbatim
  #.(let ((wild-subdir (make-pathname :directory '(:relative :wild-inferiors)))
          (wild-file (make-pathname :name :wild :version :wild :type :wild)))
     `((:root ,wild-subdir ,wild-file) ;; Or using the implicit wildcard, just :root
       (:root ,wild-subdir :implementation ,wild-file)))
@end verbatim
Starting with ASDF 2.011.4, you can use the simpler:
	@code{`(:root (:root :**/ :implementation :*.*.*))}

@code{:include} statements cause the search to recurse with the path specifications
from the file specified.

If the @code{translate-pathname} mechanism cannot achieve a desired
translation, the user may provide a function which provides the
required algorithim.  Such a translation function is specified by
supplying a list as the second @code{directory-designator}
the first element of which is the keyword @code{:function},
and the second element of which is
either a symbol which designates a function or a lambda expression.
The function designated by the second argument must take two arguments,
the first being the pathname of the source file,
the second being the wildcard that was matched.
The result of the function invocation should be the translated pathname.
An @code{:inherit-configuration} statement cause the search to recurse with the path
specifications from the next configuration.
@xref{Controlling where ASDF saves compiled files,,Configurations}, above.
@code{:enable-user-cache} is the same as @code{(t :user-cache)}.
@code{:disable-cache} is the same as @code{(t t)}.
@item
@code{:user-cache} uses the contents of variable @code{asdf::*user-cache*}
which by default is the same as using
@code{(:home ".cache" "common-lisp" :implementation)}.
@section Configuration Directories

Configuration directories consist in files each contains
a list of directives without any enclosing
Francois-Rene Rideau's avatar
Francois-Rene Rideau committed
The files will be sorted by namestring as if by @code{string<} and
the lists of directives of these files with be concatenated in order.
An implicit @code{:inherit-configuration} will be included

This allows for packaging software that has file granularity
(e.g. Debian's @command{dpkg} or some future version of @command{clbuild})
to easily include configuration information about software being distributed.
Francois-Rene Rideau's avatar
Francois-Rene Rideau committed
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 @code{"conf"}
and as a limitation of some implementations, the type cannot be @code{nil}.
Directories may be included by specifying a directory pathname
or namestring in an @code{:include} directive, e.g.:
@verbatim
	(:include "/foo/bar/")
@end verbatim

@section Shell-friendly syntax for configuration

When considering environment variable @code{ASDF_OUTPUT_TRANSLATIONS}
ASDF will skip to next configuration if it's an empty string.
It will @code{READ} the string as an SEXP in the DSL
if it begins with a paren @code{(}
and it will be interpreted as a list of directories.
Directories should come by pairs, indicating a mapping directive.
Entries are separated
by a @code{:} (colon) on Unix platforms (including cygwin),
by a @code{;} (semicolon) on other platforms (mainly, Windows).
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).


@section 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).

@section 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.


@section Output location API

The specified functions are exported from package ASDF.

@defun initialize-output-translations @Aoptional 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 @var{PARAMETER}, which can be
   @code{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).
@defun disable-output-translations
   will initialize output translations in a way
   that maps every pathname to itself,
   effectively disabling the output translation facility.
@end defun

@defun clear-output-translations
   undoes any output translation configuration
   and clears any cache for the mapping algorithm.
   You might want to call this function
   (or better, @code{clear-configuration})
   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.
@defun ensure-output-translations @Aoptional PARAMETER
   checks whether output translations have been initialized.
   If not, initialize them with the given @var{PARAMETER}.
   This function will be called before any attempt to operate on a system.
@defun apply-output-translations PATHNAME
   Applies the configured output location translations to @var{PATHNAME}
   (calls @code{ensure-output-translations} for the translations).
Every time you use ASDF's @code{output-files}, or
anything that uses it (that may compile, such as @code{operate}, @code{perform}, etc.),
@code{ensure-output-translations} is called with parameter @code{nil},
which the first time around causes your configuration to be read.
If you change a configuration file,
you need to explicitly @code{initialize-output-translations} again,
or maybe @code{clear-output-translations} (or @code{clear-configuration}),
which will cause the initialization to happen next time around.

@section Credits for output translations
Thanks a lot to Bjorn Lindberg and Gary King for @code{ASDF-Binary-Locations},
and to Peter van Eynde for @code{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 @email{fare@@tunes.org}

@c @section Default locations
@c @findex output-files-for-system-and-operation

@c The default binary location for each Lisp implementation
@c is a subdirectory of each source directory.
@c To account for different Lisps, Operating Systems, Implementation versions,
@c and so on, ASDF borrows code from SLIME
@c to create reasonable custom directory names.
@c Here are some examples:

@c @itemize
@c @item
@c SBCL, version 1.0.45 on Mac OS X for Intel: @code{sbcl-1.0.45-darwin-x86}

@c @item
@c Franz Allegro, version 8.0, ANSI Common Lisp: @code{allegro-8.0a-macosx-x86}

@c @item
@c Franz Allegro, version 8.1, Modern (case sensitive) Common Lisp: @code{allegro-8.1m-macosx-x86}
@c @end itemize

@c By default, all output file pathnames will be relocated
@c to some thus-named subdirectory of @file{~/.cache/common-lisp/}.

@c See the document @file{README.asdf-output-translations}
@c for a full specification on how to configure @code{asdf-output-translations}.
@node  Error handling, Miscellaneous additional functionality, Controlling where ASDF saves compiled files, Top
@comment  node-name,  next,  previous,  up
@chapter Error handling
@findex SYSTEM-DEFINITION-ERROR
@findex OPERATION-ERROR

If ASDF detects an incorrect system definition, it will signal a generalised instance of
@code{SYSTEM-DEFINITION-ERROR}.

Operations may go wrong (for example when source files contain errors).
These are signalled using generalised instances of
@code{OPERATION-ERROR}.

@section Compilation error and warning handling
@vindex *compile-file-warnings-behaviour*
@vindex *compile-file-errors-behavior*

ASDF checks for warnings and errors when a file is compiled.
The variables @var{*compile-file-warnings-behaviour*} and
@var{*compile-file-errors-behavior*}
control the handling of any such events.
The valid values for these variables are
@code{:error}, @code{:warn}, and @code{:ignore}.
@node  Miscellaneous additional functionality, Getting the latest version, Error handling, Top
@comment  node-name,  next,  previous,  up
@chapter Miscellaneous additional functionality
ASDF includes several additional features that are generally
useful for system definition and development.

@section Controlling file compilation
@cindex :around-compile
@cindex around-compile keyword
@cindex compile-check keyword
@cindex :compile-check
@findex compile-file*

When declaring a component (system, module, file),
you can specify a keyword argument @code{:around-compile function}.
If left unspecified (and therefore unbound),
the value will be inherited from the parent component if any,
or with a default of @code{nil}
if no value is specified in any transitive parent.

The argument must be a either @code{nil}, a fbound symbol,
a lambda-expression (e.g. @code{(lambda (thunk) ...(funcall thunk ...) ...)})
a function object (e.g. using @code{#.#'} but that's discouraged
because it prevents the introspection done by e.g. asdf-dependency-grovel),
or a string that when @code{read} yields a symbol or a lambda-expression.
@code{nil} means the normal compile-file function will be called.
A non-nil value designates a function of one argument
that will be called with a function that will
invoke @code{compile-file*} with various arguments;
the around-compile hook may supply additional keyword arguments
to pass to that call to @code{compile-file*}.
One notable argument that is heeded by @code{compile-file*} is
@code{:compile-check},
a function called when the compilation was otherwise a success,
with the same arguments as @code{compile-file};
the function shall return true if the compilation
and its resulting compiled file respected all system-specific invariants,
and false (@code{nil}) if it broke any of those invariants;
it may issue warnings or errors before it returns @code{nil}.
(NB: The ability to pass such extra flags
is only available starting with ASDF 2.22.3.)
This feature is notably exercised by asdf-finalizers.

By using a string, you may reference
that will only be created later during the build, but
isn't yet present at the time the defsystem form is evaluated.
However, if your entire system is using such a hook, you may have to
explicitly override the hook with @code{nil} for all the modules and files
that are compiled before the hook is defined.

Using this hook, you may achieve such effects as:
locally renaming packages,
binding @var{*readtables*} and other syntax-controlling variables,
handling warnings and other conditions,
proclaiming consistent optimization settings,
saving code coverage information,
maintaining meta-data about compilation timings,
setting gensym counters and PRNG seeds and other sources of non-determinism,
overriding the source-location and/or timestamping systems,
checking that some compile-time side-effects were properly balanced,
etc.

Note that there is no around-load hook. This is on purpose.
Some implementations such as ECL, GCL or MKCL link object files,
which allows for no such hook.
Other implementations allow for concatenating FASL files,
which doesn't allow for such a hook either.
We aim to discourage something that's not portable,
and has some dubious impact on performance and semantics
even when it is possible.
Things you might want to do with an around-load hook
are better done around-compile,
though it may at times require some creativity
(see e.g. the @code{package-renaming} system).


@section Controlling source file character encoding

Starting with ASDF 2.21, components accept a @code{:encoding} option
so authors may specify which character encoding should be used
to read and evaluate their source code.
When left unspecified, the encoding is inherited
from the parent module or system;
if no encoding is specified at any point,
the default @code{:autodetect} is assumed.
By default, only @code{:default}, @code{:utf-8}
and @code{:autodetect} are accepted.
@code{:autodetect}, the default, calls
@code{*encoding-detection-hook*} which by default always returns
@code{*default-encoding*} which itself defaults to @code{:default}.
In other words, there now are plenty of extension hooks, but
by default ASDF follows the backwards compatible behavior
of using whichever @code{:default} encoding your implementation uses,
which itself may or may not vary based on environment variables
and other locale settings.
In practice this means that only source code that only uses ASCII
is guaranteed to be read the same on all implementations
independently from any user setting.
Additionally, for backward-compatibility with older versions of ASDF
and/or with implementations that do not support unicode and its many encodings,
you may want to use
the reader conditionals @code{#+asdf-unicode #+asdf-unicode}
to protect any @code{:encoding @emph{encoding}} statement
as @code{:asdf-unicode} will be present in @code{*features*}
only if you're using a recent ASDF
on an implementation that supports unicode.
We recommend that you avoid using unprotected @code{:encoding} specifications
until after ASDF 2.21 or later becomes widespread, hopefully by the end of 2012.

While it offers plenty of hooks for extension,
and one such extension is being developed (see below),
ASDF itself only recognizes one encoding beside @code{:default},
and that is @code{:utf-8}, which is the @emph{de facto} standard,
already used by the vast majority of libraries that use more than ASCII.
On implementations that do not support unicode,
the feature @code{:asdf-unicode} is absent, and
the @code{:default} external-format is used
to read even source files declared as @code{:utf-8}.
On these implementations, non-ASCII characters
intended to be read as one CL character
may thus end up being read as multiple CL characters.
In most cases, this shouldn't affect the software's semantics:
comments will be skipped just the same, strings with be read and printed
with slightly different lengths, symbol names will be accordingly longer,
but none of it should matter.
But a few systems that actually depend on unicode characters
may fail to work properly, or may work in a subtly different way.
See for instance @code{lambda-reader}.

We invite you to embrace UTF-8
as the encoding for non-ASCII characters starting today,
even without any explicit specification in your @code{.asd} files.
Indeed, on some implementations and configurations,
UTF-8 is already the @code{:default},
and loading your code may cause errors if it is encoded in anything but UTF-8.
Therefore, even with the legacy behavior,
non-UTF-8 is guaranteed to break for some users,
whereas UTF-8 is pretty much guaranteed not to break anywhere
(provided you do @emph{not} use a BOM),
although it might be read incorrectly on some implementations.
In the future, we intend to make @code{:utf-8}
the default value of @code{*default-encoding*},
to be enforced everywhere, so at least the code is guaranteed
to be read correctly everywhere it can be.
If you need non-standard character encodings for your source code,
use the extension system @code{asdf-encodings}, by specifying
@code{:defsystem-depends-on (:asdf-encodings)} in your @code{defsystem}.
This extension system will register support for more encodings using the
@code{*encoding-external-format-hook*} facility,
so you can explicitly specify @code{:encoding :latin1}
in your @code{.asd} file.
Using the @code{*encoding-detection-hook*} it will also
eventually implement some autodetection of a file's encoding
from an emacs-style @code{-*- mode: lisp ; coding: latin1 -*-} declaration,
or otherwise based on an analysis of octet patterns in the file.
At this point, asdf-encoding only supports the encodings
that are supported as part of your implementation.
Since the list varies depending on implementations,
we once again recommend you use @code{:utf-8} everywhere,
which is the most portable (next is @code{:latin1}).

If you're not using a version of Quicklisp that has it,
you may get the source for @code{asdf-encodings} using git:
@kbd{git clone git://common-lisp.net/projects/asdf/asdf-encodings.git}
or
@kbd{git clone ssh://common-lisp.net/project/asdf/git/asdf-encodings.git}.
You can also browse the repository on
@url{http://common-lisp.net/gitweb?p=projects/asdf/asdf-encodings.git}.

In the future, we intend to change the default @code{*default-encoding*}
to @code{:utf-8}, which is already the de facto standard
for most libraries that use non-ASCII characters:
utf-8 works everywhere and was backhandedly enforced by
a lot of people using SBCL and utf-8 and sending reports to authors
so they make their packages compatible.
A survey showed only about a handful few libraries
are incompatible with non-UTF-8, and then, only in comments,
and we believe that authors will adopt UTF-8 when prompted.
See the April 2012 discussion on the asdf-devel mailing-list.
For backwards compatibility with users who insist on a non-UTF-8 encoding,
but cannot immediately transition to using @code{asdf-encodings}
(maybe because it isn't ready), it will still be possible to use
the @code{:encoding :default} option in your @code{defsystem} form
to restore the behavior of ASDF 2.20 and earlier.
This shouldn't be required in libraries,
because user pressure as mentioned above will already have pushed
library authors towards using UTF-8;
but authors of end-user programs might care.

When you use @code{asdf-encodings}, any further loaded @code{.asd} file
will use the autodetection algorithm to determine its encoding;
yet if you depend on this detection happening,
you may want to explicitly load @code{asdf-encodings} early in your build,
for by the time you can use @code{:defsystem-depends-on},
it is already too late to load it.
In practice, this means that the @code{*default-encoding*}
is usually used for @code{.asd} files.
Currently, this defaults to @code{:default} for backwards compatibility,
and that means that you shouldn't rely on non-ASCII characters in a .asd file.
Since component (path)names are the only real data in these files,
and non-ASCII characters are not very portable for file names,
this isn't too much of an issue.
We still encourage you to use either plain ASCII or UTF-8
in @code{.asd} files,
as we intend to make @code{:utf-8} the default encoding in the future.
This might matter, for instance, in meta-data about author's names.
@section Miscellaneous Functions

These functions are exported by ASDF for your convenience.
@anchor{system-relative-pathname}
@defun system-relative-pathname system name @Akey type
It's often handy to locate a file relative to some system.
The @code{system-relative-pathname} function meets this need.

It takes two mandatory arguments @var{system} and @var{name}
and a keyword argument @var{type}:
@var{system} is name of a system, whereas @var{name} and optionally @var{type}
specify a relative pathname, interpreted like a component pathname specifier
by @code{coerce-pathname}. @xref{The defsystem grammar,,Pathname specifiers}.

It returns a pathname built from the location of the system's
source directory and the relative pathname. For example:
> (asdf:system-relative-pathname 'cl-ppcre "regex.data")
#P"/repository/other/cl-ppcre/regex.data"
@end lisp

ASDF does not provide a turnkey solution for locating
data (or other miscellaneous) files
that are distributed together with the source code of a system.
Programmers can use @code{system-source-directory} to find such files.
Returns a pathname object.
The @var{system-designator} may be a string, symbol, or ASDF system object.
@defun clear-system system-designator

It is sometimes useful to force recompilation of a previously loaded system.
In these cases, it may be useful to @code{(asdf:clear-system :foo)}
to remove the system from the table of currently loaded systems;
the next time the system @code{foo} or one that depends on it is re-loaded,
@code{foo} will then be loaded again.
Alternatively, you could touch @code{foo.asd} or
remove the corresponding fasls from the output file cache.
(It was once conceived that one should provide
a list of systems the recompilation of which to force
as the @code{:force} keyword argument to @code{load-system};
but this has never worked, and though the feature was fixed in ASDF 2.000,
it remains @code{cerror}'ed out as nobody ever used it.)

Note that this does not and cannot by itself undo the previous loading
of the system. Common Lisp has no provision for such an operation,
and its reliance on irreversible side-effects to global datastructures
makes such a thing impossible in the general case.
If the software being re-loaded is not conceived with hot upgrade in mind,
this re-loading may cause many errors, warnings or subtle silent problems,
as packages, generic function signatures, structures, types, macros, constants, etc.
are being redefined incompatibly.
It is up to the user to make sure that reloading is possible and has the desired effect.
In some cases, extreme measures such as recursively deleting packages,
unregistering symbols, defining methods on @code{update-instance-for-redefined-class}
and much more are necessary for reloading to happen smoothly.
ASDF itself goes through notable pains to make such a hot upgrade possible
with respect to its own code, and what it does is ridiculously complex;
look at the beginning of @file{asdf.lisp} to see what it does.
@end defun
@defun register-preloaded-system name @Arest keys
A system with name @var{name},
created by @code{make-instance} with extra keys @var{keys}
(e.g. @code{:version}),
is registered as @emph{preloaded}.
That is, its code has already been loaded into the current image,
and if at some point some other system @code{:depends-on} it yet no source code is found,
it is considered as already provided,
and ASDF will not raise a @code{missing-component} error.

This function is particularly useful if you distribute your code
as fasls with either @code{fasl-op} or @code{monolithic-fasl-op},
and want to register systems so that dependencies will work uniformly
whether you're using your software from source or from fasl.
@end defun

@defun run-shell-command control-string @Arest args

This function is obsolete and present only for the sake of backwards-compatibility:
``If it's not backwards, it's not compatible''. We @emph{strongly} discourage its use.
Its current behavior is only well-defined on Unix platforms
(which include MacOS X and cygwin). On Windows, anything goes.
The following documentation is only for the purpose of your migrating away from it
in a way that preserves semantics.

Instead we recommend the use @code{run-program}, described in the next section, and
available as part of ASDF since ASDF 3.

@code{run-shell-command} takes as arguments a format @code{control-string}
and arguments to be passed to @code{format} after this control-string
to produce a string.
This string is a command that will be evaluated with a POSIX shell if possible;
yet, on Windows, some implementations will use CMD.EXE,
while others (like SBCL) will make an attempt at invoking a POSIX shell
(and fail if it is not present).
@end defun

@section Some Utility Functions

The below functions are not exported by ASDF itself, but by UIOP, available since ASDF 3.
Some of them have precursors in ASDF 2, but we recommend
you rely on ASDF 3 for active developments.
UIOP provides many, many more utility functions, and we recommend
you read its README and sources for more information.


@defun parse-unix-namestring name @Akey type defaults dot-dot ensure-directory @AallowOtherKeys
Coerce NAME into a PATHNAME using standard Unix syntax.

Unix syntax is used whether or not the underlying system is Unix;
on such non-Unix systems it is only usable but for relative pathnames;
but especially to manipulate relative pathnames portably, it is of crucial
to possess a portable pathname syntax independent of the underlying OS.
This is what @code{parse-unix-namestring} provides, and why we use it in ASDF.

When given a @code{pathname} object, just return it untouched.
When given @code{nil}, just return @code{nil}.
When given a non-null @code{symbol}, first downcase its name and treat it as a string.
When given a @code{string}, portably decompose it into a pathname as below.

@code{#\/} separates directory components.

The last @code{#\/}-separated substring is interpreted as follows:
1- If @var{type} is @code{:directory} or @var{ensure-directory} is true,
 the string is made the last directory component, and its @code{name} and @code{type} are @code{nil}.
 if the string is empty, it's the empty pathname with all slots @code{nil}.
2- If @var{type} is @code{nil}, the substring is a file-namestring,
 and its @code{name} and @code{type} are separated by @code{split-name-type}.
3- If @var{type} is a string, it is the given @code{type}, and the whole string is the @code{name}.

Directory components with an empty name the name @code{.} are removed.
Any directory named @code{..} is read as @var{dot-dot},