General PrinciplesKeyword arguments
All methods and functions in this API will support the use of keyword
arguments in calls, for the sake of explicitness and readability.
For brevity in the hands of experts, most methods and functions
will also support positional arguments for their most-commonly-used
arguments. As an explicit example, the following two lines will each
arrange for an executable program named foo (or
foo.exe on a Win32 system) to be compiled from
the foo.c source file:
env.Program(target = 'foo', source = 'foo.c')
env.Program('foo', 'foo.c')
Internal object representation
All methods and functions use internal (Python) objects that
represent the external objects (files, for example) for which they
perform dependency analysis.
All methods and functions in this API that accept an external object
as an argument will accept either a string
description or an object reference. For example, the two following
two-line examples are equivalent:
env.Object(target = 'foo.o', source = 'foo.c')
env.Program(target = 'foo', 'foo.o') # builds foo from foo.o
foo_obj = env.Object(target = 'foo.o', source = 'foo.c')
env.Program(target = 'foo', foo_obj) # builds foo from foo.o
&ConsEnvs
A &consenv; is the basic means by which a software system interacts
with the &SCons; Python API to control a build process.
A &consenv; is an object with associated methods for generating target
files of various types (&Builder; objects), other associated object
methods for automatically determining dependencies from the contents
of various types of source files (&Scanner; objects), and a dictionary
of values used by these methods.
Passing no arguments to the &Environment; instantiation creates a
&consenv; with default values for the current platform:
env = Environment()
&Consvars;
A &consenv; has an associated dictionary of &consvars; that control how
the build is performed. By default, the &Environment; method creates
a &consenv; with values that make most software build "out of the box"
on the host system. These default values will be generated at the
time &SCons; is installed using functionality similar to that provided
by GNU &Autoconf;.
It would be nice if we could avoid re-inventing the wheel here by
using some other Python-based tool &Autoconf replacement--like what
was supposed to come out of the Software Carpentry configuration
tool contest. It will probably be most efficient to roll our own
logic initially and convert if something better does come along.
At a minimum, there will be pre-configured sets of default values
that will provide reasonable defaults for UNIX and Windows NT.
The default &consenv; values may be overridden when a new &consenv; is
created by specifying keyword arguments:
env = Environment(CC = 'gcc',
CCFLAGS = '-g',
CPPPATH = ['.', 'src', '/usr/include'],
LIBPATH = ['/usr/lib', '.'])
Fetching &consvars;
A copy of the dictionary of &consvars; can be returned using
the &Dictionary; method:
env = Environment()
dict = env.Dictionary()
If any arguments are supplied, then just the corresponding value(s)
are returned:
ccflags = env.Dictionary('CCFLAGS')
cc, ld = env.Dictionary('CC', 'LD')
Copying a &consenv;
A method exists to return a copy of an existing environment, with
any overridden values specified as keyword arguments to the method:
env = Environment()
debug = env.Copy(CCFLAGS = '-g')
Multiple &consenvs;
Different external objects often require different build
characteristics. Multiple &consenvs; may be defined, each with
different values:
env = Environment(CCFLAGS = '')
debug = Environment(CCFLAGS = '-g')
env.Make(target = 'hello', source = 'hello.c')
debug.Make(target = 'hello-debug', source = 'hello.c')
Dictionaries of values from multiple &consenvs; may be passed to the
&Environment; instantiation or the &Copy; method, in which case the
last-specified dictionary value wins:
env1 = Environment(CCFLAGS = '-O', LDFLAGS = '-d')
env2 = Environment(CCFLAGS = '-g')
new = Environment(env1.Dictionary(), env2.Dictionary())
The new environment in the above example retains
LDFLAGS = '-d' from the env1
environment, and CCFLAGS = '-g' from the
env2 environment.
Variable substitution
Within a construction command, any variable from the &consenv; may
be interpolated by prefixing the name of the construction with
$:
MyBuilder = Builder(command = "$XX $XXFLAGS -c $_INPUTS -o $target")
env.Command(targets = 'bar.out', sources = 'bar.in',
command = "sed '1d' < $source > $target")
Variable substitution is recursive: the command line is expanded
until no more substitutions can be made.
Variable names following the $ may be enclosed in
braces. This can be used to concatenate an interpolated value with an
alphanumeric character:
VerboseBuilder = Builder(command = "$XX -${XXFLAGS}v > $target")
The variable within braces may contain a pair of parentheses
after a Python function name to be evaluated (for example,
${map()}). &SCons; will interpolate the return
value from the function (presumably a string):
env = Environment(FUNC = myfunc)
env.Command(target = 'foo.out', source = 'foo.in',
command = "${FUNC($<)}")
If a referenced variable is not defined in the &consenv;,
the null string is interpolated.
The following special variables can also be used:
$targets
All target file names. If multiple targets are specified in an
array, $targets expands to the entire list of
targets, separated by a single space.
Individual targets from a list may be extracted by enclosing
the targets keyword in braces and using the
appropriate Python array index or slice:
${targets[0]} # expands to the first target
${targets[1:]} # expands to all but the first target
${targets[1:-1]} # expands to all but the first and last targets
$target
A synonym for ${targets[0]}, the first target
specified.
$sources
All input file names. Any input file names that
are used anywhere else on the current command
line (via ${sources[0]},
${sources{[1]}, etc.) are removed from the
expanded list.
Any of the above special variables may be enclosed in braces and
followed immediately by one of the following attributes to select just
a portion of the expanded path name:
.base
Basename: the directory plus the file name, minus any file suffix.
.dir
The directory in which the file lives. This is a relative path,
where appropriate.
.file
The file name, minus any directory portion.
.suffix
The file name suffix (that is, the right-most dot in the file name,
and all characters to the right of that).
.filebase
The file name (no directory portion), minus any file suffix.
.abspath
The absolute path to the file.
&Builder; Objects
By default, &SCons; supplies (and uses) a number of pre-defined
&Builder; objects:
&Object;compile or assemble an object file&Library;archive files into a library&SharedLibrary;archive files into a shared library&Program;link objects and/or libraries into an executable&MakeBuilder;build according to file suffixes; see below
&Library; and &SharedLibrary; have nearly identical
semantics, just different
tools and &consenvs (paths, etc.) that they use.
In other words, you can construct a shared library
using just the &Library; &Builder; object
with a different environment.
I think that's a better way to do it.
Feedback?
A &consenv; can be explicitly initialized with associated &Builder;
objects that will be bound to the &consenv; object:
env = Environment(BUILDERS = ['Object', 'Program'])
&Builder; objects bound to a &consenv; can be called directly as
methods. When invoked, a &Builder; object returns a (list of) objects
that it will build:
obj = env.Object(target ='hello.o', source = 'hello.c')
lib = env.Library(target ='libfoo.a',
source = ['aaa.c', 'bbb.c'])
slib = env.SharedLibrary(target ='libbar.so',
source = ['xxx.c', 'yyy.c'])
prog = env.Program(target ='hello',
source = ['hello.o', 'libfoo.a', 'libbar.so'])
Specifying multiple inputs
Multiple input files that go into creating a target file may be passed
in as a single string, with the individual file names separated by
white space:
env.Library(target = 'foo.a', source = 'aaa.c bbb.c ccc.c')
env.Object(target = 'yyy.o', source = 'yyy.c')
env.Program(target = 'bar', source = 'xxx.c yyy.o foo.a')
Alternatively, multiple input files that go into creating a target
file may be passed in as an array. This allows input files to be
specified using their object representation:
env.Library(target = 'foo.a', source = ['aaa.c', 'bbb.c', 'ccc.c'])
yyy_obj = env.Object(target = 'yyy.o', source = 'yyy.c')
env.Program(target = 'bar', source = ['xxx.c', yyy_obj, 'foo.a'])
Individual string elements within an array of input files are
not further split into white-space separated
file names. This allows file names that contain white space to
be specified by putting the value into an array:
env.Program(target = 'foo', source = ['an input file.c'])
Specifying multiple targets
Conversely, the generated target may be a string listing multiple
files separated by white space:
env.Object(target = 'grammar.o y.tab.h', source = 'grammar.y')
An array of multiple target files can be used to mix string and object
representations, or to accomodate file names that contain white space:
env.Program(target = ['my program'], source = 'input.c')
File prefixes and suffixes
For portability, if the target file name does not already have an
appropriate file prefix or suffix, the &Builder; objects will
append one appropriate for the file type on the current system:
# builds 'hello.o' on UNIX, 'hello.obj' on Windows NT:
obj = env.Object(target ='hello', source = 'hello.c')
# builds 'libfoo.a' on UNIX, 'foo.lib' on Windows NT:
lib = env.Library(target ='foo', source = ['aaa.c', 'bbb.c'])
# builds 'libbar.so' on UNIX, 'bar.dll' on Windows NT:
slib = env.SharedLibrary(target ='bar', source = ['xxx.c', 'yyy.c'])
# builds 'hello' on UNIX, 'hello.exe' on Windows NT:
prog = env.Program(target ='hello',
source = ['hello.o', 'libfoo.a', 'libbar.so'])
&Builder; object exceptions
&Builder; objects raise the following exceptions on error:
LIST THESE ONCE WE FIGURE OUT WHAT THEY ARE FROM CODING THEM.
User-defined &Builder; objects
Users can define additional &Builder; objects for specific external
object types unknown to &SCons;. A &Builder; object may build its
target by executing an external command:
WebPage = Builder(command = 'htmlgen $HTMLGENFLAGS $sources > $target',
suffix = '.html',
src_suffix = '.in')
Alternatively, a &Builder; object may also build its target by
executing a Python function:
def update(dest):
# [code to update the object]
return 1
OtherBuilder1 = Builder(function = update,
src_suffix = ['.in', '.input'])
An optional argument to pass to the function may be specified:
def update_arg(dest, arg):
# [code to update the object]
return 1
OtherBuilder2 = Builder(function = update_arg,
function_arg = 'xyzzy',
src_suffix = ['.in', '.input'])
Both an external command and an internal function may be specified,
in which case the function will be called to build the object first,
followed by the command line.
NEED AN EXAMPLE HERE.
User-defined &Builder; objects can be used like the default &Builder;
objects to initialize &consenvs;.
WebPage = Builder(command = 'htmlgen $HTMLGENFLAGS $sources > $target',
suffix = '.html',
src_suffix = '.in')
env = Environment(BUILDERS = ['WebPage'])
env.WebPage(target = 'foo.html', source = 'foo.in')
# Builds 'bar.html' on UNIX, 'bar.htm' on Windows NT:
env.WebPage(target = 'bar', source = 'bar.in')
The command-line specification can interpolate variables from the
&consenv;; see "Variable substitution," above.
A &Builder; object may optionally be initialized with a list of:
the prefix of the target file (e.g., 'lib' for libraries)
the suffix of the target file (e.g., '.a' for libraries)
the expected suffixes of the input files
(e.g., '.o' for object files)
These arguments are used in automatic
dependency analysis and to generate output file names that don't
have suffixes supplied explicitly.
Copying &Builder; Objects
A &Copy; method exists to return a copy of an existing &Builder;
object, with any overridden values specified as keyword arguments to
the method:
build = Builder(function = my_build)
build_out = build.Copy(suffix = '.out')
Typically, &Builder; objects will be supplied by a tool-master or
administrator through a shared &consenv;.
Special-purpose build rules
A pre-defined &Command; builder exists to associate a target file with
a specific command or list of commands for building the file:
env.Command(target = 'foo.out', source =
command = 'foo.in', "foo.process $sources > $target")
commands = [ "bar.process -o .tmpfile $sources",
"mv .tmpfile $target" ]
env.Command(target = 'bar.out', source = 'bar.in', command = commands)
This is useful when it's too cumbersome to create a &Builder;
object just to build a single file in a special way.
The &MakeBuilder; &Builder;
A pre-defined &Builder; object named &MakeBuilder; exists to make
simple builds as easy as possible for users, at the expense of
sacrificing some build portability.
The following minimal example builds the 'hello' program from the
'hello.c' source file:
Environment().Make('hello', 'hello.c')
Users of the &MakeBuilder; &Builder; object are not required to
understand intermediate steps involved in generating a file--for
example, the distinction between compiling source code into an object
file, and then linking object files into an executable. The details
of intermediate steps are handled by the invoked method. Users that
need to, however, can specify intermediate steps explicitly:
env = Environment()
env.Make(target = 'hello.o', source = 'hello.c')
env.Make(target = 'hello', source = 'hello.o')
The &MakeBuilder; method understands the file suffixes specified and
"does the right thing" to generate the target object and program
files, respectively. It does this by examining the specified output
suffixes for the &Builder; objects bound to the environment.
Because file name suffixes in the target and source file names
must be specified, the &MakeBuilder; method can't be used
portably across operating systems. In other words, for the
example above, the &MakeBuilder; builder will not generate
hello.exe on Windows NT.
&Builder; maps
Do we even need this anymore?
Now that the individual builders
have specified suffix
and src_suffix values,
all of the information we need to support
the &MakeBuilder; builder is right there in the environment.
I think this is a holdover from before I
added the suffix arguments.
If you want &MakeBuilder; to do something different,
you set it up with another environment...
The env.Make method "does the right thing" to
build different file types because it uses a dictionary from the
&consenv; that maps file suffixes to the appropriate &Builder; object.
This &BUILDERMAP; can be initialized at instantiation:
env = Environment(BUILDERMAP = {
'.o' : Object,
'.a' : Library,
'.html' : WebPage,
'' : Program,
})
With the &BUILDERMAP; properly initialized, the
env.Make method can be used to build additional
file types:
env.Make(target = 'index.html', source = 'index.input')
&Builder; objects referenced in the &BUILDERMAP; do not need to be
listed separately in the &BUILDERS; variable. The &consenv; will
bind the union of the &Builder; objects listed in both variables.
DependenciesAutomatic dependencies
By default, &SCons; assumes that a target file has automatic
dependencies on the:
tool used to build the target filecontents of the input filescommand line used to build the target file
If any of these changes, the target file will be rebuilt.
Implicit dependencies
Additionally, &SCons; can scan the contents of files for
implicit dependencies on other files. For
example, &SCons; will scan the contents of a .c
file and determine that any object created from it is
dependent on any .h files specified via
#include. &SCons;, therefore, "does the right
thing" without needing to have these dependencies listed explicitly:
% cat Construct
env = Environment()
env.Program('hello', 'hello.c')
% cat hello.c
#include "hello_string.h"
main()
{
printf("%s\n", STRING);
}
% cat > hello_string.h
#define STRING "Hello, world!\n"
% scons .
gcc -c hello.c -o hello.o
gcc -o hello hello.c
% ./hello
Hello, world!
% cat > hello_string.h
#define STRING "Hello, world, hello!\n"
% scons .
gcc -c hello.c -o hello.o
gcc -o hello hello.c
% ./hello
Hello, world, hello!
%
Ignoring dependencies
Undesirable automatic dependencies or
implicit dependencies may be ignored:
env.Program(target = 'bar', source = 'bar.c')
env.Ignore('bar', '/usr/bin/gcc', 'version.h')
In the above example, the bar program will not
be rebuilt if the /usr/bin/gcc compiler or the
version.h file change.
Explicit dependencies
Dependencies that are unknown to &SCons; may be specified explicitly
in an &SCons; configuration file:
env.Dependency(target = 'output1', dependency = 'input_1 input_2')
env.Dependency(target = 'output2', dependency = ['input_1', 'input_2'])
env.Dependency(target = 'output3', dependency = ['white space input'])
env.Dependency(target = 'output_a output_b', dependency = 'input_3')
env.Dependency(target = ['output_c', 'output_d'], dependency = 'input_4')
env.Dependency(target = ['white space output'], dependency = 'input_5')
Just like the target keyword argument, the
dependency keyword argument may be specified as a
string of white-space separated file names, or as an array.
A dependency on an &SCons; configuration file itself may be specified
explicitly to force a rebuild whenever the configuration file changes:
env.Dependency(target = 'archive.tar.gz', dependency = 'SConstruct')
&Scanner; Objects
Analagous to the previously-described &Builder; objects, &SCons;
supplies (and uses) &Scanner; objects to search the contents of
a file for implicit dependency files:
CScanscan .{c,C,cc,cxx,cpp} files for #include dependencies
A &consenv; can be explicitly initialized with
associated &Scanner; objects:
env = Environment(SCANNERS = ['CScan', 'M4Scan'])
&Scanner; objects bound to a &consenv; can be
associated directly with specified files:
env.CScan('foo.c', 'bar.c')
env.M4Scan('input.m4')
User-defined &Scanner; objects
A user may define a &Scanner; object to scan a type of file for
implicit dependencies:
def scanner1(file_contents):
# search for dependencies
return dependency_list
FirstScan = Scanner(function = scanner1)
The scanner function must return a list of dependencies that its finds
based on analyzing the file contents it is passed as an argument.
The scanner function, when invoked, will be passed the calling
environment. The scanner function can use &consenvs; from the passed
environment to affect how it performs its dependency scan--the
canonical example being to use some sort of search-path construction
variable to look for dependency files in other directories:
def scanner2(file_contents, env):
path = env.{'SCANNERPATH'} # XXX
# search for dependencies using 'path'
return dependency_list
SecondScan = Scanner(function = scanner2)
The user may specify an additional argument when the &Scanner; object
is created. When the scanner is invoked, the additional argument
will be passed to the scanner funciton, which can be used in any way
the scanner function sees fit:
def scanner3(file_contents, env, arg):
# skip 'arg' lines, then search for dependencies
return dependency_list
Skip_3_Lines_Scan = Scanner(function = scanner2, argument = 3)
Skip_6_Lines_Scan = Scanner(function = scanner2, argument = 6)
Copying &Scanner; Objects
A method exists to return a copy of an existing &Scanner; object,
with any overridden values specified as keyword arguments to the
method:
scan = Scanner(function = my_scan)
scan_path = scan.Copy(path = '%SCANNERPATH')
Typically, &Scanner; objects will be supplied by a tool-master or
administrator through a shared &consenv;.
&Scanner; maps
If the &BUILDERMAP; proves unnecessary,
we could/should get rid of this one, too,
by adding a parallel src_suffix
argument to the &Scanner; factory...
Comments?
Each &consenv; has a &SCANNERMAP;, a dictionary that associates
different file suffixes with a scanner object that can be used to
generate a list of dependencies from the contents of that file. This
&SCANNERMAP; can be initialized at instantiation:
env = Environment(SCANNERMAP = {
'.c' : CScan,
'.cc' : CScan,
'.m4' : M4Scan,
})
&Scanner; objects referenced in the &SCANNERMAP; do not need to
be listed separately in the &SCANNERS; variable. The &consenv;
will bind the union of the &Scanner; objects listed
in both variables.
Targets
The methods in the build engine API described so far merely
establish associations that describe file dependencies, how a
file should be scanned, etc. Since the real point is to actually
build files, &SCons; also has methods that
actually direct the build engine to build, or otherwise manipulate,
target files.
Building targets
One or more targets may be built as follows:
env.Build(target = ['foo', 'bar'])
Note that specifying a directory (or other collective object) will
cause all subsidiary/dependent objects to be built as well:
env.Build(target = '.')
env.Build(target = 'builddir')
By default, &SCons; explicitly removes a target file before
invoking the underlying function or command(s) to build it.
Removing targets
A "cleanup" operation of removing generated (target) files is
performed as follows:
env.Clean(target = ['foo', 'bar'])
Like the &Build; method, the &Clean; method may be passed a
directory or other collective object, in which case the subsidiary
target objects under the directory will be removed:
env.Clean(target = '.')
env.Clean(target = 'builddir')
(The directories themselves are not removed.)
Suppressing build-target removal
As mentioned, by default, &SCons; explicitly removes a target
file before invoking the underlying function or command(s) to build
it. Files that should not be removed before rebuilding can be
specified via the &Precious; method:
env.Library(target = 'libfoo.a', source = ['aaa.c', 'bbb.c', 'ccc.c'])
env.Precious('libfoo.a')
Default targets
The user may specify default targets that will be built if there are no
targets supplied on the command line:
env.Default('install', 'src')
Multiple calls to the &Default; method (typically one per &SConscript;
file) append their arguments to the list of default targets.
File installation
Files may be installed in a destination directory:
env.Install('/usr/bin', 'program1', 'program2')
Files may be renamed on installation:
env.InstallAs('/usr/bin/xyzzy', 'xyzzy.in')
Multiple files may be renamed on installation by specifying
equal-length lists of target and source files:
env.InstallAs(['/usr/bin/foo', '/usr/bin/bar'],
['foo.in', 'bar.in'])
Target aliases
In order to provide convenient "shortcut" target names that expand to
a specified list of targets, aliases may be established:
env.Alias(alias = 'install',
targets = ['/sbin', '/usr/lib', '/usr/share/man'])
In this example, specifying a target of install
will cause all the files in the associated directories to be built
(that is, installed).
An &Alias; may include one or more other &Aliases; in its list:
env.Alias(alias = 'libraries', targets = ['lib'])
env.Alias(alias = 'programs', targets = ['libraries', 'src'])
Customizing output
Take this whole section with a grain of salt.
I whipped it up without a great deal of thought
to try to add a "competitive advantage"
for the second round of the Software Carpentry contest.
In particular, hard-coding the
analysis points and the keywords that specify them
feels inflexible,
but I can't think of another way it would be
done effectively.
I dunno, maybe this is fine as it is...
The &SCons; API supports the ability to customize, redirect, or
suppress its printed output through user-defined functions.
&SCons; has several pre-defined points in its build process at
which it calls a function to (potentially) print output. User-defined
functions can be specified for these call-back points when &Build;
or &Clean;is invoked:
env.Build(target = '.',
on_analysis = dump_dependency,
pre_update = my_print_command,
post_update = my_error_handler)
on_error = my_error_handler)
The specific call-back points are:
on_analysis
Called for every object, immediately after the object has been
analyzed to see if it's out-of-date. Typically used to print a
trace of considered objects for debugging of unexpected dependencies.
pre_update
Called for every object that has been determined to be out-of-date
before its update function or command is executed. Typically used
to print the command being called to update a target.
post_update
Called for every object after its update function or command has
been executed. Typically used to report that a top-level specified
target is up-to-date or was not remade.
on_error
Called for every error returned by an update function or command.
Typically used to report errors with some string that will be
identifiable to build-analysis tools.
Functions for each of these call-back points all take the same
arguments:
my_dump_dependency(target, level, status, update, dependencies)
where the arguments are:
target
The target object being considered.
level
Specifies how many levels the dependency analysis has
recursed in order to consider the target.
A value of 0 specifies a top-level
target (that is, one passed to the
&Build; or &Clean; method). Objects which a top-level
target is directly dependent upon have a
level of <1>, their direct dependencies have a
level of <2>, etc. Typically used to indent
output to reflect the recursive levels.
status
A string specifying the current status of the target
("unknown", "built",
"error", "analyzed", etc.). A
complete list will be enumerated and described during implementation.
update
The command line or function name that will be (or has been) executed
to update the target.
dependencies
A list of direct dependencies of the target.
Separate source and build trees
I've never liked Cons' use of the name Link
for this functionality,
mainly because the term is overloaded
with linking object files into an executable.
Yet I've never come up with anything better.
Any suggestions?
Also, I made this an &Environment; method because
it logically belongs in the API reference
(the build engine needs to know about it),
and I thought it was clean to have
everything in the build-engine API
be called through an &Environment; object.
But &Link isn't really
associated with a specific environment
(the &Cons; classic implementation just
leaves it as a bare function call),
so maybe we should just follow that example
and not call it through an environment...
&SCons; allows target files to be built completely separately from
the source files by "linking" a build directory to an underlying
source directory:
env.Link('build', 'src')
SConscript('build/SConscript')
&SCons; will copy (or hard link) necessary files (including the
&SConscript; file) into the build directory hierarchy. This allows the
source directory to remain uncluttered by derived files.
Variant builds
The &Link; method may be used in conjunction with multiple
&consenvs; to support variant builds. The following
&SConstruct; and &SConscript; files would build separate debug and
production versions of the same program side-by-side:
% cat SConstruct
env = Environment()
env.Link('build/debug', 'src')
env.Link('build/production', 'src')
flags = '-g'
SConscript('build/debug/SConscript', Export(env))
flags = '-O'
SConscript('build/production/SConscript', Export(env))
% cat src/SConscript
env = Environment(CCFLAGS = flags)
env.Program('hello', 'hello.c')
The following example would build the appropriate program for the current
compilation platform, without having to clean any directories of object
or executable files for other architectures:
% cat SConstruct
build_platform = os.path.join('build', sys.platform)
Link(build_platform, 'src')
SConscript(os.path.join(build_platform, 'SConscript'))
% cat src/SConscript
env = Environment
env.Program('hello', 'hello.c')
Code repositories
Like &Link;, &Repository; and &Local; are part of the
API reference, but not really tied to any specific environment.
Is it better to be consistent about calling
everything in the API through an environment,
or to leave these independent so as
not to complicate their calling interface?
&SCons; may use files from one or more shared code repositories in order
to build local copies of changed target files. A repository would
typically be a central directory tree, maintained by an integrator,
with known good libraries and executables.
Repository('/home/source/1.1', '/home/source/1.0')
Specified repositories will be searched in-order for any file
(configuration file, input file, target file) that does not exist
in the local directory tree. When building a local target file,
&SCons; will rewrite path names in the build command to use the
necessary repository files. This includes modifying lists of
or flags to specify an
appropriate set of include paths for dependency analysis.
&SCons; will modify the Python sys.path variable to
reflect the addition of repositories to the search path, so that any
imported modules or packages necessary for the build can be found in a
repository, as well.
If an up-to-date target file is found in a code repository, the file
will not be rebuilt or copied locally. Files that must exist locally
(for example, to run tests) may be specified:
Local('program', 'libfoo.a')
in which case &SCons; will copy or link an up-to-date copy of the
file from the appropriate repository.
Derived-file caching
There should be extensions to this part of the API for
auxiliary functions like cleaning the cache.
&SCons; can maintain a cache directory of target files which may be
shared among multiple builds. This reduces build times by allowing
developers working on a project together to share common target
files:
Cache('/var/tmp/build.cache/i386')
When a target file is generated, a copy is added to the cache.
When generating a target file, if &SCons; determines that a file
that has been built with the exact same dependencies already exists
in the specified cache, &SCons; will copy the cached file rather
than re-building the target.
Command-line options exist to modify the &SCons; caching behavior
for a specific build, including disabling caching, building
dependencies in random order, and displaying commands as if cached
files were built.
Job management
This has been completely superseded by
the more sophisticated &Task; manager
that Anthony Roach has contributed.
I need to write that up...
A simple API exists to inform the Build Engine how many jobs may
be run simultaneously:
Jobs(limit = 4)