Merged revisions 2136-2200,2202-2290,2292-2301 via svnmerge from

http://scons.tigris.org/svn/scons/branches/core

........
  r2145 | stevenknight | 2007-07-17 09:15:12 -0500 (Tue, 17 Jul 2007) | 3 lines

  Don't put null strings (from variable expansion) in a path list.
  (They get turned into the current directory on later expansion.)
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  r2146 | stevenknight | 2007-07-17 10:47:39 -0500 (Tue, 17 Jul 2007) | 3 lines

  Add support for optional arguments on command-line long options
  by specifying nargs='?'.
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  r2149 | stevenknight | 2007-07-17 15:22:24 -0500 (Tue, 17 Jul 2007) | 2 lines

  Remove left-over Optik mentions.
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  r2150 | stevenknight | 2007-07-17 15:39:34 -0500 (Tue, 17 Jul 2007) | 4 lines

  Add a $SWIGPATH variable for finding SWIG dependencies, with
  $SWIGINC{PREFIX,SUFFIX} for adding them to the command line.
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  r2154 | stevenknight | 2007-07-18 20:05:31 -0500 (Wed, 18 Jul 2007) | 2 lines

  Fix variable misspellings in the doc added for $SWIGOUTPUT.
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  r2155 | stevenknight | 2007-07-18 20:07:28 -0500 (Wed, 18 Jul 2007) | 2 lines

  Add the Python eggs info file to the RPM packaging build.
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  r2156 | stevenknight | 2007-07-18 20:15:08 -0500 (Wed, 18 Jul 2007) | 2 lines

  Convert documentation from DocBook SGML to XML.
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  r2158 | stevenknight | 2007-07-19 17:16:19 -0500 (Thu, 19 Jul 2007) | 3 lines

  Conditionally add the .egg-info the RPM file list only if the distutils
  in the version of Python that rpmbuild will execute knows about them.
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  r2161 | stevenknight | 2007-07-19 19:12:29 -0500 (Thu, 19 Jul 2007) | 5 lines

  Capture a test case (contributed by Tilo Prutz) where instantiation of
  a private class causes javac to generate an additional anonymous inner
  class file.  (No solution yet, but there's no sense throwing away the
  preparatory work.)
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  r2162 | stevenknight | 2007-07-20 11:29:56 -0500 (Fri, 20 Jul 2007) | 3 lines

  Support passing a list of .java files as source to the Java() builder.
  (Leanid Nazdrynau)
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  r2163 | garyo | 2007-07-20 12:00:35 -0500 (Fri, 20 Jul 2007) | 1 line

  Fixed cut-n-paste error in Touch factory method doc in users guide.
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  r2167 | stevenknight | 2007-07-21 22:59:40 -0500 (Sat, 21 Jul 2007) | 2 lines

  Don't execute the SWIGOUTDIR test if swig isn't installed.
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  r2168 | stevenknight | 2007-07-21 23:14:17 -0500 (Sat, 21 Jul 2007) | 2 lines

  Fix the test's ability to run under a path name containing spaces.
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  r2171 | stevenknight | 2007-07-24 15:54:41 -0500 (Tue, 24 Jul 2007) | 2 lines

  Handle white space in key file names in the packaging build.
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  r2172 | stevenknight | 2007-07-24 21:41:15 -0500 (Tue, 24 Jul 2007) | 2 lines

  More efficient copying of construction environments.
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  r2173 | stevenknight | 2007-07-25 10:56:02 -0500 (Wed, 25 Jul 2007) | 2 lines

  Update the SCons build for Subversion and general clean-up.
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  r2174 | stevenknight | 2007-07-25 11:35:16 -0500 (Wed, 25 Jul 2007) | 3 lines

  Suppress the [brackets] around a node in the --tree=prune output if
  the node is a source.
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  r2175 | stevenknight | 2007-07-25 12:52:18 -0500 (Wed, 25 Jul 2007) | 3 lines

  Commonize the skip_test() method and make its behavior configurable
  via a TESTCOMMON_PASS_SKIPS environment variable.
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  r2178 | stevenknight | 2007-07-25 21:43:47 -0500 (Wed, 25 Jul 2007) | 3 lines

  Add $JAVACLASSPATH and $JAVASOURCEPATH construction variables.  (Leanid
  Nazdrynau)
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  r2182 | stevenknight | 2007-07-30 12:10:20 -0500 (Mon, 30 Jul 2007) | 3 lines

  Refactor Builder suffix-adjusting into its own method, so we can
  (potentially) re-use it for Builders with attached source Builders.
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  r2183 | stevenknight | 2007-07-30 14:51:53 -0500 (Mon, 30 Jul 2007) | 2 lines

  More efficient source-builder suffix matching.
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  r2184 | stevenknight | 2007-07-30 16:01:42 -0500 (Mon, 30 Jul 2007) | 4 lines

  Encapsulate initialization of the default FS object by an accessor
  function in SCons.Node.FS.  (This also gets rid of an unnecessary
  reference to SCons.Node.FS.default_fs in the LaTeX scanner.)
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  r2193 | stevenknight | 2007-07-30 18:24:07 -0500 (Mon, 30 Jul 2007) | 3 lines

  Fix interpretation of source arguments that have no suffix when the
  called Builder has both a src_suffix and a src_builder.
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  r2194 | stevenknight | 2007-07-31 10:25:31 -0500 (Tue, 31 Jul 2007) | 2 lines

  Increase the number of tries for random output from three to ten.
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  r2195 | stevenknight | 2007-07-31 10:52:28 -0500 (Tue, 31 Jul 2007) | 3 lines

  Skip the test gracefully if the zipfile module can't read the file it
  just wrote (which is the case for Python 2.1 on 64-bit systems).
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  r2196 | stevenknight | 2007-07-31 13:06:21 -0500 (Tue, 31 Jul 2007) | 2 lines

  Move the "import zipfile" so it doesn't fail on Python <= 2.0.
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  r2197 | stevenknight | 2007-07-31 14:51:50 -0500 (Tue, 31 Jul 2007) | 3 lines

  Commonize initialization of the various Java builders so they can be
  hooked up into a multi-stage Builder chain.  (Leanid Nazdrynau)
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  r2198 | stevenknight | 2007-07-31 16:15:18 -0500 (Tue, 31 Jul 2007) | 3 lines

  Fix use of ${TARGET.dir} and ${SOURCE.dir} expansions in $FORTRANMODDIR
  $JARCHDIR, $JARFLAGS, $LEXFLAGS, $SWIGFLAGS, $SWIGOUTDIR and $YACCFLAGS.
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  r2199 | stevenknight | 2007-07-31 16:25:48 -0500 (Tue, 31 Jul 2007) | 2 lines

  Remove left-over Trace() call.
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  r2202 | stevenknight | 2007-08-01 12:31:48 -0500 (Wed, 01 Aug 2007) | 3 lines

  Bail out via test.skip_test() if wix ("candle") isn't found.
  Put the main body of code flush left instead of under an if: block.
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  r2203 | stevenknight | 2007-08-01 15:35:55 -0500 (Wed, 01 Aug 2007) | 5 lines

  Fix Tool.packaging.rpm.package() so it doesn't always overwrite
  $RPMFLAGS with -ta.
  Set --buildroot in RPM packaging tests so they don't overwrite
  each other when run simultaneously.
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  r2204 | stevenknight | 2007-08-01 15:37:36 -0500 (Wed, 01 Aug 2007) | 2 lines

  Fix a nested scope issue with the internal build_sources() function.
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  r2205 | stevenknight | 2007-08-01 15:46:08 -0500 (Wed, 01 Aug 2007) | 5 lines

  Normalize (X out) the CreationDate field inside embedded, compressed
  PostScript streams within the generated PDF files.  Also normalize
  preceding Length field, since compression length is affected by different
  patterns of input, including the variable CreationDate value.
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  r2211 | stevenknight | 2007-08-02 08:52:06 -0500 (Thu, 02 Aug 2007) | 2 lines

  Add the new modules from branches/packaging to the SCons packaging build.
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  r2212 | stevenknight | 2007-08-02 19:59:01 -0500 (Thu, 02 Aug 2007) | 2 lines

  Fix the JAVACLASSPATH test when javah isn't on the default $PATH.
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  r2214 | stevenknight | 2007-08-03 15:05:21 -0500 (Fri, 03 Aug 2007) | 4 lines

  Hook up the Java builders into a multi-step chain underneath a Java()
  pseudo-builder (wrapper) that examines its arguments and calls the
  appropriate underlying file-or-dir builder.
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  r2215 | stevenknight | 2007-08-03 15:49:58 -0500 (Fri, 03 Aug 2007) | 2 lines

  Fix for old Python versions:  use apply() instead of *args, **kw.
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  r2216 | stevenknight | 2007-08-03 16:49:31 -0500 (Fri, 03 Aug 2007) | 2 lines

  Hook up the SWIG builder as a source builder for .java files.
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  r2217 | stevenknight | 2007-08-03 17:28:19 -0500 (Fri, 03 Aug 2007) | 2 lines

  Don't use .endswith(), which didn't appear until later Python versions.
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  r2218 | stevenknight | 2007-08-03 17:29:38 -0500 (Fri, 03 Aug 2007) | 2 lines

  Replace tabs with spaces.
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  r2219 | stevenknight | 2007-08-04 08:06:23 -0500 (Sat, 04 Aug 2007) | 3 lines

  Initialize a loop-invariant lambda for matching .java suffixes outside
  the loop.
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  r2220 | stevenknight | 2007-08-07 15:06:13 -0500 (Tue, 07 Aug 2007) | 2 lines

  Refactor parallel class-generation loops into one.
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  r2221 | stevenknight | 2007-08-07 16:04:06 -0500 (Tue, 07 Aug 2007) | 5 lines

  Have the Java multi-step builder test actually check for generated files,
  and fix the generation of .java and .class file names, and interaction
  with the SWIG builder, so that the files are generated in the correct
  place.
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  r2222 | stevenknight | 2007-08-07 16:45:05 -0500 (Tue, 07 Aug 2007) | 3 lines

  Fix dependencies on SWIG-generated .java files so they don't have to
  be built in multiple passes.
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  r2226 | stevenknight | 2007-08-07 18:00:22 -0500 (Tue, 07 Aug 2007) | 2 lines

  Fix SWIG when used with BuildDir().
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  r2227 | stevenknight | 2007-08-07 22:15:55 -0500 (Tue, 07 Aug 2007) | 5 lines

  User's guide updates:
  - Make the multiple files example match its text.
  - Expand a truncated sentence about being able to use Python function actions
    in the Command() Builder.
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  r2228 | stevenknight | 2007-08-07 23:25:18 -0500 (Tue, 07 Aug 2007) | 3 lines

  Don't generate an error if a #include file matches a same-named
  directory in $CPPPATH (or $FORTRANPATH, etc.).
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  r2229 | stevenknight | 2007-08-07 23:40:00 -0500 (Tue, 07 Aug 2007) | 2 lines

  Fix a code example.  (Gary Oberbrunner)
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  r2230 | stevenknight | 2007-08-08 00:05:43 -0500 (Wed, 08 Aug 2007) | 3 lines

  Capture a test case to make sure AddPostAction() doesn't interfere
  with normal linking.  (Matt Doar, Gary Oberbrunner)
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  r2233 | stevenknight | 2007-08-08 14:15:44 -0500 (Wed, 08 Aug 2007) | 2 lines

  Fix documentation typo in a construction variable cross-reference.
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  r2234 | stevenknight | 2007-08-08 17:03:25 -0500 (Wed, 08 Aug 2007) | 2 lines

  Changes to SCons packaging to support checkpoint releases.
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  r2235 | stevenknight | 2007-08-09 10:10:01 -0500 (Thu, 09 Aug 2007) | 2 lines

  Sidestep false negatives on heavily loaded systems.
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  r2236 | garyo | 2007-08-09 11:16:26 -0500 (Thu, 09 Aug 2007) | 1 line

  Allow unpackaged files (e.g. *.pyo) to exist in the build dir without being packaged in the RPM.  Without this, on some systems the rpmbuild may error out.
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  r2237 | stevenknight | 2007-08-09 11:27:56 -0500 (Thu, 09 Aug 2007) | 5 lines

  Fix test/SWIG/build-dir.py so it works on old Python versions without
  distutils.sysconfig.
  Instead of just cutting-and-pasting initialization code from other
  SWIG tests, centralize it in some new TestSCons methods.
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  r2238 | garyo | 2007-08-09 11:30:58 -0500 (Thu, 09 Aug 2007) | 1 line

  Use docbook 4.3 instead of 4.4 for the XML doctype since some older(?) jade parsers can't handle new 4-byte Unicode chars in the 4.4 version of isogrk4.ent.
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  r2240 | stevenknight | 2007-08-09 16:35:06 -0500 (Thu, 09 Aug 2007) | 2 lines

  User's Guide updates (post packaging changes).
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  r2243 | stevenknight | 2007-08-10 10:31:51 -0500 (Fri, 10 Aug 2007) | 3 lines

  Fix the User's Guide build to use openjade, and to accomodate a change
  in the name of the main generated file (book1.html => index.html).
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  r2245 | stevenknight | 2007-08-10 11:09:16 -0500 (Fri, 10 Aug 2007) | 2 lines

  Update the {CHANGES,RELEASE}.txt datestamp lines.
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  r2253 | stevenknight | 2007-08-10 16:21:54 -0500 (Fri, 10 Aug 2007) | 2 lines

  Fix the wix Tool module's ability to handle null entries in $PATH.
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  r2261 | stevenknight | 2007-08-11 23:08:12 -0500 (Sat, 11 Aug 2007) | 3 lines

  Remove unnecessary files (.svnt/*, .{ae,cvs}ignore, www/*) from the
  scons-src packages.
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  r2262 | stevenknight | 2007-08-11 23:24:49 -0500 (Sat, 11 Aug 2007) | 2 lines

  Add missing __revision__ lines.
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  r2263 | stevenknight | 2007-08-11 23:33:42 -0500 (Sat, 11 Aug 2007) | 2 lines

  Skip the test if the MANIFEST file hasn't been built.
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  r2264 | stevenknight | 2007-08-11 23:36:30 -0500 (Sat, 11 Aug 2007) | 2 lines

  Add recent compatibility modules to the relevant exceptions lists.
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  r2265 | stevenknight | 2007-08-11 23:39:00 -0500 (Sat, 11 Aug 2007) | 3 lines

  Update __VERSION__ strings in the QMTest/*.py modules, so that packaging
  tests (src/test_*.py) will pass after builds of checkpoint releases.
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  r2266 | stevenknight | 2007-08-12 07:36:19 -0500 (Sun, 12 Aug 2007) | 2 lines

  Add a comment about why we construct the __VERSION__ string at run time.
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  r2267 | stevenknight | 2007-08-12 07:42:30 -0500 (Sun, 12 Aug 2007) | 2 lines

  Avoid reading the MANIFEST file twice.  (Courtesy review by Greg Noel.)
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  r2268 | stevenknight | 2007-08-12 08:14:53 -0500 (Sun, 12 Aug 2007) | 3 lines

  Shift Install() and InstallAs() from being documented as functions
  to being documented as Builders.
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  r2269 | garyo | 2007-08-13 08:49:52 -0500 (Mon, 13 Aug 2007) | 1 line

  Tests: Skip some more Java tests if javac is not installed on the test machine so they don't get marked as failing.
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  r2270 | garyo | 2007-08-13 11:09:39 -0500 (Mon, 13 Aug 2007) | 1 line

  Fixed typo in test (shows up on non-Linux platforms).
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  r2271 | garyo | 2007-08-13 14:09:05 -0500 (Mon, 13 Aug 2007) | 4 lines

  Test portability fixes for Darwin/OSX and IRIX.
  This does not make all the tests pass on those OSes,
  but it takes care of some of the more obvious errors that
  I have time for right now.  More to come.
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  r2272 | stevenknight | 2007-08-13 15:33:29 -0500 (Mon, 13 Aug 2007) | 2 lines

  Tab => space fix.
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  r2273 | stevenknight | 2007-08-13 15:33:52 -0500 (Mon, 13 Aug 2007) | 2 lines

  Test for swig, too, which is used to build from the .i file.
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  r2277 | garyo | 2007-08-14 10:40:00 -0500 (Tue, 14 Aug 2007) | 8 lines

  Test portability on IRIX: test/Actions/pre-post creates target file
  before building target, then IRIX CC does not chmod +x afterwards.
  I think this change is safe on all OSes.

  test/AS/ml.py: I think this is only supposed to be run on win32
  (not skipped only on win32); the sense of the skip test was backwards.
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  r2278 | stevenknight | 2007-08-14 11:04:40 -0500 (Tue, 14 Aug 2007) | 2 lines

  Add -tt when running tests, to catch inconsistent tab usage.
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  r2279 | stevenknight | 2007-08-14 14:00:43 -0500 (Tue, 14 Aug 2007) | 2 lines

  Minor refactor of logic in File.retrieve_from_cache().
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  r2280 | stevenknight | 2007-08-15 01:11:40 -0500 (Wed, 15 Aug 2007) | 2 lines

  Refactor CacheDir support into its own module.
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  r2281 | stevenknight | 2007-08-15 07:24:51 -0500 (Wed, 15 Aug 2007) | 2 lines

  Move the cachepath() method from FS.File to the CacheDir class.
........
  r2282 | stevenknight | 2007-08-15 08:31:34 -0500 (Wed, 15 Aug 2007) | 2 lines

  Python 1.5.2 fix in the new Null class.
........
  r2283 | stevenknight | 2007-08-15 10:45:53 -0500 (Wed, 15 Aug 2007) | 5 lines

  Refactor CacheDir unit tests to:
  - restore functionality that was dropped in the transition;
  - commonize creation of test Nodes and other (mock) objects
  - separate CacheDir tests from tests of CacheDir through Node.FS.File.
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  r2284 | stevenknight | 2007-08-15 11:46:38 -0500 (Wed, 15 Aug 2007) | 3 lines

  Replace the Executor.Null.NullEnvironment object with a real Null object,
  so it will absorb the CacheDir method calls as well.
........
  r2285 | stevenknight | 2007-08-15 11:52:57 -0500 (Wed, 15 Aug 2007) | 5 lines

  Add a get_CacheDir() method to a construction environment, which will
  be used to fetch per-environment CacheDir specifications.  (Right now
  all calls to it still just return the one attached to underlying default
  FS object.)
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  r2286 | stevenknight | 2007-08-15 15:15:46 -0500 (Wed, 15 Aug 2007) | 2 lines

  Support per-construction-environment configuration of CacheDir().
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  r2287 | stevenknight | 2007-08-15 15:33:04 -0500 (Wed, 15 Aug 2007) | 2 lines

  Move the tests of CacheDir()-related command-line options into test/CacheDir.
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  r2293 | stevenknight | 2007-08-16 11:14:49 -0500 (Thu, 16 Aug 2007) | 3 lines

  Add the Package() builder description to the documentation build,
  fixing the XML so that it will build.
........
  r2294 | stevenknight | 2007-08-16 12:51:19 -0500 (Thu, 16 Aug 2007) | 3 lines

  Reorganize packaging documentation:  alphabetize the variable definitions
  (and function names), document Tag() as a function, not a builder.
........
  r2296 | stevenknight | 2007-08-16 12:55:01 -0500 (Thu, 16 Aug 2007) | 2 lines

  Add a build command.
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  r2300 | stevenknight | 2007-08-16 16:49:13 -0500 (Thu, 16 Aug 2007) | 2 lines

  First cut at documenting packaging variables.
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  r2301 | stevenknight | 2007-08-16 16:51:21 -0500 (Thu, 16 Aug 2007) | 3 lines

  Construct the .src.rpm and .arch.rpm file names independnetly, not
  by trying to massage one into the other.
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1 files changed, 461 insertions, 0 deletions

diff --git a/doc/user/separate.xml b/doc/user/separate.xml
new file mode 100644
index 0000000..57acd48
--- /dev/null
+++ b/doc/user/separate.xml
@@ -0,0 +1,461 @@
+<!--
+
+  __COPYRIGHT__
+
+  Permission is hereby granted, free of charge, to any person obtaining
+  a copy of this software and associated documentation files (the
+  "Software"), to deal in the Software without restriction, including
+  without limitation the rights to use, copy, modify, merge, publish,
+  distribute, sublicense, and/or sell copies of the Software, and to
+  permit persons to whom the Software is furnished to do so, subject to
+  the following conditions:
+
+  The above copyright notice and this permission notice shall be included
+  in all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
+  KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
+  WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+-->
+
+<!--
+
+=head1 Separating source and build trees
+
+It's often desirable to keep any derived files from the build completely
+separate from the source files. This makes it much easier to keep track of
+just what is a source file, and also makes it simpler to handle B<variant>
+builds, especially if you want the variant builds to co-exist.
+
+=head2 Separating build and source directories using the Link command
+
+Cons provides a simple mechanism that handles all of these requirements. The
+C<Link> command is invoked as in this example:
+
+  Link 'build' => 'src';
+
+The specified directories are ``linked'' to the specified source
+directory. Let's suppose that you setup a source directory, F<src>, with the
+sub-directories F<world> and F<hello> below it, as in the previous
+example. You could then substitute for the original build lines the
+following:
+
+  Build qw(
+	build/world/Conscript
+	build/hello/Conscript
+  );
+
+Notice that you treat the F<Conscript> file as if it existed in the build
+directory. Now if you type the same command as before, you will get the
+following results:
+
+  % cons export
+  Install build/world/world.h as export/include/world.h
+  cc -Iexport/include -c build/hello/hello.c -o build/hello/hello.o
+  cc -Iexport/include -c build/world/world.c -o build/world/world.o
+  ar r build/world/libworld.a build/world/world.o
+  ar: creating build/world/libworld.a
+  ranlib build/world/libworld.a
+  Install build/world/libworld.a as export/lib/libworld.a
+  cc -o build/hello/hello build/hello/hello.o -Lexport/lib -lworld
+  Install build/hello/hello as export/bin/hello
+
+Again, Cons has taken care of the details for you. In particular, you will
+notice that all the builds are done using source files and object files from
+the build directory. For example, F<build/world/world.o> is compiled from
+F<build/world/world.c>, and F<export/include/world.h> is installed from
+F<build/world/world.h>. This is accomplished on most systems by the simple
+expedient of ``hard'' linking the required files from each source directory
+into the appropriate build directory.
+
+The links are maintained correctly by Cons, no matter what you do to the
+source directory. If you modify a source file, your editor may do this ``in
+place'' or it may rename it first and create a new file. In the latter case,
+any hard link will be lost. Cons will detect this condition the next time
+the source file is needed, and will relink it appropriately.
+
+You'll also notice, by the way, that B<no> changes were required to the
+underlying F<Conscript> files. And we can go further, as we shall see in the
+next section.
+
+=head2 Explicit references to the source directory
+
+When using the C<Link> command on some operating systems or with some
+tool chains, it's sometimes useful to have a command actually use
+the path name to the source directory, not the build directory.  For
+example, on systems that must copy, not "hard link," the F<src/> and
+F<build/> copies of C<Linked> files, using the F<src/> path of a file
+name might make an editor aware that a syntax error must be fixed in the
+source directory, not the build directory.
+
+You can tell Cons that you want to use the "source path" for a file by
+preceding the file name with a ``!'' (exclamation point).  For example,
+if we add a ``!'' to the beginning of a source file:
+
+  Program $env "foo", "!foo.c";	# Notice initial ! on foo.c
+
+Cons will compile the target as follows:
+
+  cc -c src/foo.c -o build/foo.o
+  cc -o build/foo build/foo.o
+
+Notice that Cons has compiled the program from the the F<src/foo.c>
+source file.  Without the initial ``!'', Cons would have compiled the
+program using the F<build/foo.c> path name.
+
+-->
+
+  <para>
+
+  It's often useful to keep any built files completely
+  separate from the source files.
+  This is usually done by creating one or more separate
+  <emphasis>build directories</emphasis>
+  that are used to hold the built objects files, libraries,
+  and executable programs, etc.
+  for a specific flavor of build.
+  &SCons; provides two ways to do this,
+  one through the &SConscript; function that we've already seen,
+  and the second through a more flexible &BuildDir; function.
+
+  </para>
+
+  <section>
+  <title>Specifying a Build Directory as Part of an &SConscript; Call</title>
+
+    <para>
+
+    The most straightforward way to establish a build directory
+    uses the fact that the usual way to
+    set up a build hierarchy is to have an
+    &SConscript; file in the source subdirectory.
+    If you then pass a &build_dir; argument to the
+    &SConscript; function call:
+
+    </para>
+
+    <programlisting>
+      SConscript('src/SConscript', build_dir='build')
+    </programlisting>
+
+    <para>
+
+    &SCons; will then build all of the files in
+    the &build; subdirectory:
+
+    </para>
+
+    <screen>
+      % <userinput>ls src</userinput>
+      SConscript  hello.c
+      % <userinput>scons -Q</userinput>
+      cc -o build/hello.o -c build/hello.c
+      cc -o build/hello build/hello.o
+      % <userinput>ls build</userinput>
+      SConscript  hello  hello.c  hello.o
+    </screen>
+
+    <para>
+
+    But wait a minute--what's going on here?
+    &SCons; created the object file
+    <filename>build/hello.o</filename>
+    in the &build; subdirectory,
+    as expected.
+    But even though our &hello_c; file lives in the &src; subdirectory,
+    &SCons; has actually compiled a
+    <filename>build/hello.c</filename> file
+    to create the object file.
+
+    </para>
+
+    <para>
+
+    What's happened is that &SCons; has <emphasis>duplicated</emphasis>
+    the &hello_c; file from the &src; subdirectory
+    to the &build; subdirectory,
+    and built the program from there.
+    The next section explains why &SCons; does this.
+
+    </para>
+
+  </section>
+
+  <section>
+  <title>Why &SCons; Duplicates Source Files in a Build Directory</title>
+
+    <para>
+
+    &SCons; duplicates source files in build directories
+    because it's the most straightforward way to guarantee a correct build
+    <emphasis>regardless of include-file directory paths,
+    relative references between files,
+    or tool support for putting files in different locations</emphasis>,
+    and the &SCons; philosophy is to, by default,
+    guarantee a correct build in all cases.
+
+    </para>
+
+    <para>
+
+    The most direct reason to duplicate source files
+    in build directories
+    is simply that some tools (mostly older vesions)
+    are written to only build their output files
+    in the same directory as the source files.
+    In this case, the choices are either
+    to build the output file in the source directory
+    and move it to the build directory,
+    or to duplicate the source files in the build directory.
+
+    </para>
+
+    <para>
+
+    Additionally,
+    relative references between files
+    can cause problems if we don't
+    just duplicate the hierarchy of source files
+    in the build directory.
+    You can see this at work in
+    use of the C preprocessor <literal>#include</literal>
+    mechanism with double quotes, not angle brackets:
+
+    </para>
+
+    <programlisting>
+      #include "file.h"
+    </programlisting>
+
+    <para>
+
+    The <emphasis>de facto</emphasis> standard behavior
+    for most C compilers in this case
+    is to first look in the same directory
+    as the source file that contains the <literal>#include</literal> line,
+    then to look in the directories in the preprocessor search path.
+    Add to this that the &SCons; implementation of
+    support for code repositories
+    (described below)
+    means not all of the files
+    will be found in the same directory hierarchy,
+    and the simplest way to make sure
+    that the right include file is found
+    is to duplicate the source files into the build directory,
+    which provides a correct build
+    regardless of the original location(s) of the source files.
+
+    </para>
+
+    <para>
+
+    Although source-file duplication guarantees a correct build
+    even in these end-cases,
+    it <emphasis>can</emphasis> usually be safely disabled.
+    The next section describes
+    how you can disable the duplication of source files
+    in the build directory.
+
+    </para>
+
+  </section>
+
+  <section>
+  <title>Telling &SCons; to Not Duplicate Source Files in the Build Directory</title>
+
+    <para>
+
+    In most cases and with most tool sets,
+    &SCons; can place its target files in a build subdirectory
+    <emphasis>without</emphasis>
+    duplicating the source files
+    and everything will work just fine.
+    You can disable the default &SCons; behavior
+    by specifying <literal>duplicate=0</literal>
+    when you call the &SConscript; function:
+
+    </para>
+
+    <programlisting>
+      SConscript('src/SConscript', build_dir='build', duplicate=0)
+    </programlisting>
+
+    <para>
+
+    When this flag is specified,
+    &SCons; uses the build directory
+    like most people expect--that is,
+    the output files are placed in the build directory
+    while the source files stay in the source directory:
+
+    </para>
+
+    <screen>
+      % <userinput>ls src</userinput>
+      SConscript
+      hello.c
+      % <userinput>scons -Q</userinput>
+      cc -c src/hello.c -o build/hello.o
+      cc -o build/hello build/hello.o
+      % <userinput>ls build</userinput>
+      hello
+      hello.o
+    </screen>
+
+  </section>
+
+  <section>
+  <title>The &BuildDir; Function</title>
+
+    <para>
+
+    Use the &BuildDir; function to establish that target
+    files should be built in a separate directory
+    from the source files:
+
+    </para>
+
+    <programlisting>
+      BuildDir('build', 'src')
+      env = Environment()
+      env.Program('build/hello.c')
+    </programlisting>
+
+    <para>
+
+    Note that when you're not using
+    an &SConscript; file in the &src; subdirectory,
+    you must actually specify that
+    the program must be built from
+    the <filename>build/hello.c</filename>
+    file that &SCons; will duplicate in the
+    &build; subdirectory.
+
+    </para>
+
+    <para>
+
+    When using the &BuildDir; function directly,
+    &SCons; still duplicates the source files
+    in the build directory by default:
+
+    </para>
+
+    <screen>
+      % <userinput>ls src</userinput>
+      hello.c
+      % <userinput>scons -Q</userinput>
+      cc -o build/hello.o -c build/hello.c
+      cc -o build/hello build/hello.o
+      % <userinput>ls build</userinput>
+      hello  hello.c  hello.o
+    </screen>
+
+    <para>
+
+    You can specify the same <literal>duplicate=0</literal> argument
+    that you can specify for an &SConscript; call:
+
+    </para>
+
+    <programlisting>
+      BuildDir('build', 'src', duplicate=0)
+      env = Environment()
+      env.Program('build/hello.c')
+    </programlisting>
+
+    <para>
+
+    In which case &SCons;
+    will disable duplication of the source files:
+
+    </para>
+
+    <screen>
+      % <userinput>ls src</userinput>
+      hello.c
+      % <userinput>scons -Q</userinput>
+      cc -o build/hello.o -c src/hello.c
+      cc -o build/hello build/hello.o
+      % <userinput>ls build</userinput>
+      hello  hello.o
+    </screen>
+
+  </section>
+
+  <section>
+  <title>Using &BuildDir; With an &SConscript; File</title>
+
+    <para>
+
+    Even when using the &BuildDir; function,
+    it's much more natural to use it with
+    a subsidiary &SConscript; file.
+    For example, if the
+    <filename>src/SConscript</filename>
+    looks like this:
+
+    </para>
+
+    <programlisting>
+      env = Environment()
+      env.Program('hello.c')
+    </programlisting>
+
+    <para>
+
+    Then our &SConstruct; file could look like:
+
+    </para>
+
+    
+    <programlisting>
+      BuildDir('build', 'src')
+      SConscript('build/SConscript')
+      </programlisting>
+
+    <para>
+
+    Yielding the following output:
+
+    </para>
+
+    <screen>
+      % <userinput>ls src</userinput>
+      SConscript  hello.c
+      % <userinput>scons -Q</userinput>
+      cc -o build/hello.o -c build/hello.c
+      cc -o build/hello build/hello.o
+      % <userinput>ls build</userinput>
+      SConscript  hello  hello.c  hello.o
+    </screen>
+
+    <para>
+
+    Notice that this is completely equivalent
+    to the use of &SConscript; that we
+    learned about in the previous section.
+
+    </para>
+
+  </section>
+
+  <!--
+
+  <section>
+  <title>Why You'd Want to Call &BuildDir; Instead of &SConscript;</title>
+
+    <para>
+
+    XXX why call BuildDir() instead of SConscript(build_dir=)
+
+    </para>
+
+  </section>
+
+  -->