# __FILE__ __REVISION__ __DATE__ __DEVELOPER__
SCons - a software construction tool
This is a beta release of SCons, a tool for building software (and other
files). SCons is implemented in Python, and its "configuration files"
are actually Python scripts, allowing you to use the full power of a
real scripting language to solve build problems. You do not, however,
need to know Python to use SCons effectively.
So that everyone using SCons can help each other learn how to use it
more effectively, please sign up for the scons-users mailing list at:
RELEASE 0.96.96 - Thu, 12 Apr 2007 12:36:25 -0500
This is a pre-release for testing the eighth beta release of SCons.
Please consult the CHANGES.txt file for a list of specific changes
since last release.
Please note the following important changes since release 0.96.93:
-- THE --debug=memoizer OPTION NOW REQUIRES PYTHON 2.2 OR LATER
The --debug=memoizer option now prints a warning message and
does nothing if SCons is run on a version of Python that does
not support metaclasses (earlier than Python 2.2).
-- THE --debug=nomemoizer OPTION DOES NOTHING AND IS NOW DEPRECATED
The --debug=nomemoizer no longer does anything and instead
now generates a warning message about being deprecated. The
--debug=nomemoizer will be removed completely in a future release.
Please note the following important changes since release 0.96.91:
-- /opt/bin AND /sw/bin ADDED TO DEFAULT EXECUTION PATH VARIABLES
On all POSIX systems, the default execution PATH variable has had
the /opt/bin directory added after the /usr/local/bin directory
and before /bin and /usr/bin directories. This may cause SCons
to find and/or different compilers, linkers, etc. if you have
any same-named utilities installed in /opt/bin that it previously
found in /bin or /usr/bin.
On Mac OS X (Darwin) systems, the /sw/bin directory has been added
to the end of the default execution PATH. This may cause SCons
to find compilers, linkers and other utilities it previously did
not, although it should not otherwise change existing behavior.
-- Configure.Checklib() ARGUMENTS HAVE CHANGED TO MATCH DOCUMENTATION
The order of the arguments to the Configure.CheckLib() function
has changed to put the "autoadd" keyword argument last, matching
the documentation in the man page. This could cause problems
for any calls to Configure.Checklib() that were relying on the
order of the arguments. Specifying all arguments as keyword
arguments will work on both older and newer versions of SCons.
-- env.subst() NO LONGER EXPANDS $TARGET, $SOURCES, etc. BY DEFAULT
Calls to the env.subst() method to interpolate construction
variables in strings no longer automatically expand the special
variables $TARGET, $TARGETS, $SOURCE and $SOURCES. The keyword
variables "target" and "source" must now be set to the lists
of target and source files to be used in expansion of those
variables, when desired.
This is most likely necessary for any env.subst() calls within
a Python function being used as an SCons action for a Builder:
def build_it(env, target, source):
env.subst('$STRING', target=targets, source=sources)
MyBuilder = Builder(action=build_it)
The "target" and "source" keyword arguments are backwards
compatible and can be added to SConscript files without breaking
builds on systems using older SCons releases.
-- INTERNAL FUNCTIONS AND CLASSES HAVE MOVED FROM SCons.Util
All internal functions and classes related to string substitution
have been moved out of the SCons.Util module into their own
SCons.Subst module. The following classes have been moved:
And the following functions have moved:
If your SConscript files have been using any of these function
directly from the SCons.Util module (which they ultimately should
not be!), you will need to modify them.
Please note the following important changes since release 0.96.90:
-- SIGNATURES ARE NOW STORED IN AN SConsignFile() BY DEFAULT,
CAUSING LIKELY REBUILDS; SPECIAL NOTE CONCERNING INTERACTION
The default behavior has been changed to store signature
information in a single .sconsign.dblite file in the top-level
SConstruct file. This will cause rebuilds on upgrade to 0.97,
unless you were already calling the SConsignFile() function in
your SConscript files.
The previous default behavior was to store signature information
in a .sconsign file in each directory that contained target
files that SCons knew about. The old behavior may be preserved
in any SConscript file.
If you are using the Repository feature, and are not already
using the SConsignFile() function in your build, you *must*
add "SConsignFile(None)" to your build configuration to keep
interoperating with an existing Repository that uses the old
behavior of a .sconsign file in each directory. Alternatively,
you can rebuild the Repository with the new default behavior.
-- OTHER SIGNATURE CHANGES WILL CAUSE LIKELY REBUILDS AFTER UPGRADE
This release adds several changes to the signature mechanism that
will cause SCons to rebuild most configurations after upgrading
(and when switching back to an earlier release from 0.97).
These changes are:
-- NORMALIZED PATHS IN SConsignFile() DATABASES ON WINDOWS
When using an SConsignFile() database, instead of individual
.sconsign files in each directory, the path names are
stored in normalized form with / (forward slash) separating
the elements. This may cause rebuilds on Windows systems
with hierarchical configurations.
-- STORED DEPENDENCY PATHS ARE NOW RELATIVE TO THE TARGET
SCons used to store the paths of all source files and
dependencies relative to the top-level SConstruct directory.
It now stores them relative to the directory of the
associated target file. This makes it possible to use
content signatures to subdivide a dependency tree without
causing unnecessary rebuilds due to an intermediate file in
one build being treated as a source file in a nother build.
This a step towards making it possible to write a hierarchy
of SConstruct files that allow developers to build just
one portion of a tree wherever there's an SConstruct file.
(Note that this would still require some specific code at
the top of each SConstruct file, but we hope to make this
an easier/more naturally supported thing in the future.)
-- PYTHON FUNCTION ACTION SIGNATURES HAVE CHANGED TO AVOID
FUTURE REBUILDS AND REBUILDS BETWEEN PYTHON VERSIONS
SCons Actions for Python functions use the functions byte
code to generate their signature. The byte code in older
versions of Python includes indications of the line numbers
at which the function's code appeared in its original
source file, which means that changes in the location of
an otherwise unmodified Python function would trigger
rebuilds. The line number byte codes are now removed
from the signature, which will cause any targets built by
Python function Actions (including various pre-supplied
SCons Actions) be rebuilt.
-- REMOVED CONVERSION FROM PRE-0.96 .sconsign FORMATS
Because this release involves so many other signature
changes that cause rebuilds, the support for automatically
converting signature information from .sconsign files
written by SCons versions prior to 0.96 has been removed.
-- ORDER OF -o FLAGS ON CERTAIN LINK COMMAND LINES HAS CHANGED
The -o flag that specifies an output file has been moved on
certain linker command lines to place it consistently after
the link command itself. This will cause recompilation
of target files created by these changed lines.
-- F95 AND F90 COMPILERS ARE NOW PREFERRED OVER F77
SCons now searches for Fortran 95 and Fortran 90 compilers first
in preference to Fortran 77. This may result in a different
Fortran compiler being used by default, although as Fortran 95 and
Fortran 90 are backwards compatible with Fortran 77, this should
not cause problems for standards-compliant Fortran programs.
On systems that have multiple versions of Fortran installed,
the Fortran 77 compiler may be explicitly selected by specifying
it when creating the construction environment:
env = Environment(tools = ['default', 'f77'])
-- SOLARIS DEFAULT SHARED OBJECT PREFIXES AND SUFFIXES HAVE CHANGED
On Solaris, SCons now builds shared objects from C and C++ source
files with a default prefix of "so_" and a default suffix of ".o".
The previous default suffix of ".os" caused problems when trying
to use SCons with Sun WorkShop.
-- CACHED Configure() RESULTS ARE STORED IN A DIFFERENT FILE
The Configure() subsystem now stores its cached results in a
different file. This may cause configuration tests to be re-run
the first time after you install 0.97.
-- setup.py INSTALLS VERSION-NUMBERED SCRIPTS AND DIRS BY DEFAULT
The setup.py script has been changed to always install SCons in
a version-numbered directory (e.g. /usr/local/lib/scons-0.97
or D:\Python23\scons-0.97) and with a version-numbered script
name (scons-0.97) in addition to the usual installation of an
"scons" script name. A number of new setup.py options allow
control over what does or does not get installed, and where.
See the README.txt or README files for additional information.
-- setup.py NOW INSTALLS MAN PAGES ON UNIX AND Linux SYSTEMS
The SCons setup.py script now installs the "scons.1" and
"sconsign.1" man pages on UNIX and Linux systems. A
-- BUILDERS RETURN A LIST-LIKE OBJECT, NOT A REGULAR LIST
Builder calls now return an object that behaves like a list
(and which provides some other functionality), not an underlying
Python list. In general, this should not cause any problems,
although it introduces a subtle change in the following behavior:
obj += env.Object('foo.c')
If "obj" is a regular Python list, Python will no longer update
the "obj" in place, because the return value from env.Object()
is no longer the same type. Python will instead allocate a
new object and assign the local variable "obj" to it. If "obj"
is defined in an SConscript file that calls another SConscript
file containing the above code, "obj" in the first SConscript
file will not contain the object file nodes created by the
You can guarantee that a list will be updated in place regardless
of which SConscript file defines it and which adds to it by
using the list append() method as follows:
Please note the following important changes since release 0.96.1:
-- DIRECTORY TREES ARE NO LONGER AUTOMATICALLY SCANNED FOR CHANGES
Custom builders and Command() calls that accept directories as
source arguments no longer scan entire on-disk directory trees by
default. This means that their targets will not be automatically
rebuilt if a file changes on disk *unless* SCons already knows
about the file from a specific Builder or File() call. Note that
the targets will still be rebuilt correctly if a file changes
that SCons already knows about due to a Builder or other call.
The existing behavior of scanning on-disk directory trees for
any changed file can be maintained by passing the new DirScanner
global directory scanner as the source_scanner keyword argument
to the Builder call:
bld = Builder("build < $SOURCE > $TARGET",
source_scanner = DirScanner)
The same keyword argument can also be supplied to any Command()
calls that need to scan directory trees on-disk for changed files:
"archiver -o $TARGET $SOURCE",
source_scanner = DirScanner)
This change was made because scanning directories by default
could cause huge slowdowns if a configurable directory like /usr
or /usr/local was passed as the source to a Builder or Command()
call, in which case SCons would scan the entire directory tree.
-- ParseConfig() METHOD ADDS LIBRARY FILE NAMES TO THE $LIBS VARIABLE
The ParseConfig() method now adds library file names returned
by the specified *-config command to the $LIBS construction
variable, instead of returning them (the same way it handles
the -l option).
-- ParseConfig() METHOD DOESN'T ADD DUPLICATES TO CONSTRUCTION VARIABLES
By default, the ParseConfig() method now avoids adding duplicate
entries to construction variables. The old behavior may be
specified using a new "unique=0" keyword argument.
-- WINDOWS %TEMP% and %TMP% VARIABLES ARE PROPAGATED AUTOMATICALLY
The %TEMP% and %TMP% external environment variables are now
propagated automatically to the command execution environment on
-- OUTPUT OF Configure() SUBSYSTEM CHANGED SLIGHTLY
The Configure() subsystem now reports tests results as "yes" and
"no" instead of "ok" and "failed." This might interfere with any
scripts that automatically parse the Configure() output from SCons.
-- VISUAL STUDIO ATL AND MFC DIRECTORIES NOT ADDED BY DEFAULT
When compiling with Microsoft Visual Studio, SCons no longer
adds the ATL and MFC directories to the INCLUDE and LIB
environment variables by default. If you want these directories
included in your environment variables, you should now set the
$MSVS_USE_MFC_DIRS *construction* variable when initializing
env = Environment(MSVS_USE_MFC_DIRS = 1)
-- DEPRECATED GLOBAL FUNCTIONS HAVE BEEN REMOVED
The following deprecated global functions have been removed:
ParseConfig(), SetBuildSignatureType(), SetContentSignatureType(),
SetJobs() and GetJobs().
-- DEPRECATED "validater" KEYWORD HAS BEEN REMOVED
The deprecated "validater" keyword to the Options.Add() method
has been removed.
Please note the following important changes since release 0.95:
-- BUILDERS NOW ALWAYS RETURN A LIST OF TARGETS
All Builder calls (both built-in like Program(), Library(),
etc. and customer Builders) now always return a list of target
Nodes. If the Builder only builds one target, the Builder
call will now return a list containing that target Node, not
the target Node itself as it used to do.
This change should be invisibile to most normal uses of the
return values from Builder calls. It will cause an error if the
SConscript file was performing some direct manipulation of the
returned Node value. For example, an attempt to print the name
of a target returned by the Object() Builder:
target = Object('foo.c')
# OLD WAY
Will now need to access the first element in the list returned by
the Object() call:
target = Object('foo.c')
# NEW WAY
This change was introduced to make the data type returned by Builder
calls consistent (always a list), regardless of platform or number
of returned targets.
-- DEFAULT SConsignFile() DATABASE SCHEME HAS CHANGED
The SConsignFile() function now uses an internally-supplied
SCons.dblite module as the default DB scheme for the .sconsign file.
If you are using the SConsignFile() function without an explicitly
specified dbm_module argument, this will cause all of your targets
to be recompiled the first time you use SCons 0.96. To preserve the
previous behavior, specify the "anydbm" module explicitly:
-- INTERNAL .sconsign FILE FORMAT HAS CHANGED
The internal format of .sconsign files has been changed. This might
cause warnings about "ignoring corrupt .sconsign files" and rebuilds
when you use SCons 0.96 for the first time in a tree that was
previously built with SCons 0.95 or earlier.
-- INTERFACE CHANGE OF scan_check FUNCTION TO CUSTOM SCANNERS
The scan_check function that can be supplied to a custom Scanner now
must take two arguments, the Node to be checked and a construction
environment. It previously only used the Node as an argument.
-- DEFAULT SCANNERS NO LONGER HEED INTERNAL Scanner.add_skey() METHOD
The internal Scanner.add_skey() method no longer works for the
default scanners, which now use construction variables to hold their
lists of suffixes. If you had a custom Tool specification that was
reaching into the internals in this way to add a suffix to one of
the following scanner, you must now add the suffix to a construction
environment through which you plan to call the scanner, as follows:
CScan.add_skey('.x') => env.Append(CPPSUFFIXES = ['.x'])
DScan.add_skey('.x') => env.Append(DSUFFIXES = ['.x'])
FortranScan.add_skey('.x') => env.Append(FORTRANSUFFIXES = ['.x'])
-- KEYWORD ARGUMENTS TO Builder() HAVE BEEN REMOVED
The "node_factory" and "scanner" keyword arguments to the Builder()
function have been removed. In their place, the separate and more
flexible "target_factory," "source_factory," "target_scanner" and
"source scanner" keywords should be used instead.
-- ALL-DIGIT FILE "EXTENSIONS" ARE NOW PART OF THE FILE BASENAME
SCons now treats file "extensions" that contain all digits (for
example, "file.123") as part of the file basename, for easier
handling of version numbers in the names of shared libraries
and other files. Builders will now add their file extensions to
file names specified with all-digit extensions. If you need to
generate a file with an all-digit extension using a Builder that
adds a file extension, you can preserve the previous behavior by
wrapping the file name in a File() call.
-- Append()/Prepend() METHODS CHANGED WHEN USING UserList OBJECTS
The behavior of the env.Append() and env.Prepend() methods has
changed when appending a string value to a UserList, or vice versa.
They now behave like normal Python addition of a string to
a UserList. Given an initialization and an env.Append() call like:
env = Environment(VAR1=UserList(['foo']), VAR2='foo')
The resulting values of $VAR1 and $VAR2 will now be ['foo', 'b',
'a', 'r'] and ['f', 'o', 'o', 'bar'], respectively. This is because
Python UserList objects treat strings as sequences of letters when
adding them to the value of the UserList.
The old behavior of yielding $VAR1 and $VAR2 values of ['foo',
'bar'] when either variable is a UserList object now requires that
the string variables be enclosed in a list:
env = Environment(VAR1=UserList(['foo']), VAR2=['foo'])
Note that the SCons behavior when appending to normal lists has
*not* changed, and the behavior of all of the default values that
SCons uses to initialize all construction variables has *not*
changed. This change *only* affects any cases where you explicitly
use UserList objects to initialize or append to a variable.
Please note the following planned, future changes:
-- SCANNER NAMES HAVE BEEN DEPRECATED AND WILL BE REMOVED
Several internal variable names in SCons.Defaults for various
pre-made default Scanner objects have been deprecated and will
be removed in a future revision. In their place are several new
global variable names that are now part of the publicly-supported
NEW NAME DEPRECATED NAME
Of these, only ObjSourceScan was probably used at all, to add
new mappings of file suffixes to other scanners for use by the
Object() Builder. This should now be done as follows:
-- THE env.Copy() METHOD WILL CHANGE OR GO AWAY ENTIRELY
The env.Copy() method (to make a copy of a construction
environment) is being replaced by the env.Clone() method.
In some future release, a deprecation warning will be added
to current uses of the env.Copy() method. At some point after
the deprecation warning, the env.Copy() method will either be
removed entirely or have its behavior changed.
You can prepare for this by changing all your uses of env.Copy()
to env.Clone(), which has the exact same calling arguments.
NOTE: CHANGING USES OF env.Copy() TO env.Clone() WILL MAKE YOUR
SConscript FILES NOT WORK ON EARLIER VERSIONS OF SCons.
If you change SConscript files in software that you make available
for download or otherwise distribute, other users may try to
build your software with an earlier version of SCons that does
not have the env.Clone() method. We recommend preparing for
this in one of two ways:
-- Make your SConscript files backwards-compatible by
including the following code near the beginning of your
top-level SConstruct file:
SCons.Environment.Environment.Clone = \
-- Use the EnsureSConsVersion() function to provide a
descriptive error message if your SConscript files
are executed by an earlier version of SCons:
EnsureSConsVersion(0, 96, 93)
SCons is developed with an extensive regression test suite, and a
rigorous development methodology for continually improving that suite.
Because of this, SCons is of sufficient quality that you can use it
for real work. The "beta" status of the release reflects that we
still may change interfaces in future releases, which may require
modifications to your SConscript files. We strive to hold these
changes to a minimum.
Nevertheless, please heed the following disclaimers:
- Please report any bugs or other problems that you find to our bug
tracker at our SourceForge project page:
We have a reliable bug-fixing methodology already in place and
strive to respond to problems relatively quickly.
- Documentation is spottier than we'd like. You may need to dive
into the source code to figure out how to do something. Asking
questions on the scons-users mailing list is also welcome. We
will be addressing the documentation in upcoming releases, but
would be more than glad to have your assistance in correcting this
In particular, the "SCons Design" documentation on the SCons web
site is currently out of date, as we made significant changes to
portions of the interface as we figured out what worked and what
didn't during implementation.
- There may be performance issues. Improving SCons performance
is an ongoing priority. If you still find the performance
unacceptable, we would very much like to hear from you and learn
more about your configuration so we can optimize the right things.
- Error messages don't always exist where they'd be helpful.
Please let us know about any errors you ran into that would
have benefitted from a (more) descriptive message.
KNOWN PROBLEMS IN THIS RELEASE:
For a complete list of known problems, consult the SCons bug tracker
page at SourceForge:
- Support for parallel builds (-j) does not work on WIN32 systems
prior to *official* Python release 2.2 (not 2.2 pre-releases).
Prior to Python 2.2, there is a bug in Python's Win32
implementation such that when a thread spawns an external command,
it blocks all threads from running. This breaks the SCons
multithreading architecture used to support -j builds.
We have included a patch file, os_spawnv_fix.diff, that you can
use if you you want to fix your version of Python to support
parallel builds in SCons.
- Again, the "SCons Design" documentation on the SCons web
site is currently out of date. Take what you read there with a
grain of salt.
- On Win32 systems, you must put a space between the redirection
characters < and >, and the specified files (or construction
command < $SOURCE > $TARGET
If you don't supply a space (for example, "<$SOURCE"), SCons will
not recognize the redirection.
- MSVC .res files are not rebuilt when icons change.
- The -c option does not clean up .sconsign files or directories
created as part of the build, and also does not clean up
SideEffect files (for example, Visual Studio .pdb files).
- Switching content signatures from "MD5" to "timestamp" and back
again can cause unusual errors. These errors can be cleared up by
removing all .sconsign files.
- When using multiple Repositories, changing the name of an include
file can cause an old version of the file to be used.
- There is currently no way to force use of a relative path (../*)
for directories outside the top-level SConstruct file.
- The Jar() Builder will, on its second or subsequent invocation,
package up the .sconsign files that SCons uses to track signatures.
You can work around this by using the SConsignFile() function
to collect all of the .sconsign information into a single file
outside of the directory being packaged by Jar().
- SCons does not currently have a way to detect that an intermediate
file has been corrupted from outside and should be rebuilt.
- Unicode characters in path names do not work in all circumstances.
- A stray source file in a BuildDir can prevent targets from being
(re)built when they should.
- SCons does not automatically rebuild LaTeX files when the file
has an undefined reference on the first build.
- Use of --implicit-cache with TargetSignatures('content') can,
for some changes, not rebuild a file when necessary.
- SCons does not currently automatically check out SConstruct or
SConscript files from SCCS, RCS or BitKeeper.
- No support yet for the following planned command-line options:
-d -e -l --list-actions --list-derived --list-where
-o --override -p -r -R -w --write-filenames
Thank you for your interest, and please let us know how we can help
improve SCons for your needs.
knight at baldmt dot com
With plenty of help from the SCons Development team: