Steven Knight  committed 44100a3

Add a -t (timing) option to (Baptiste Lepilleur) Add sections to the README to describe better how to change and execute SCons in-place.

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                  SCons - a software construction tool
-Welcome to the SCons development tree.  The real purpose of this tree is
-to package SCons for production distribution in a variety of formats,
+Welcome to the SCons development tree.  The real purpose of this tree
+is to package SCons for production distribution in a variety of formats,
 not just to hack SCons code.
-To that extent, the normal development cycle (enforced by Aegis) is not
-to test the code directly, but to package SCons, unpack the package,
-"install" SCons in a test subdirectory, and then to run the tests
-against the unpacked and installed software.  This helps eliminate
-problems caused by, for example, failure to update the list of files to
-be packaged.
+If all you want to do is install and run SCons, it will be easier for you
+to download and install the scons-{version}.tar.gz or scons-{version}.zip
+package rather than to work with the packaging logic in this tree.
-Note that if all you want to do is install and run SCons, it
-will probably be easier for you to download and install the
-scons-{version}.tar.gz or scons-{version}.zip package rather than to
-work with the packaging logic in this tree.
+To the extent that this tree is about building SCons packages, the
+*full* development cycle (enforced by Aegis) is not to test the code
+directly, but to package SCons, unpack the package, "install" SCons in
+a test subdirectory, and then to run the tests against the unpacked and
+installed software.  This helps eliminate problems caused by, for example,
+failure to update the list of files to be packaged.
+For just working on making an individual change to the SCons source,
+however, you don't actually need to build or install SCons; you
+*can* actually edit and execute SCons in-place.  See the following
+sections below for more information:
+        How to edit and executing SCons in-place.
+        Tips for debugging problems in SCons.
+        How to use the automated regression tests.
+        An example of how to put the edit/execute/test pieces
+        together in a reasonable development workflow.
+    NOTE: You don't need to build SCons packages or install SCons if
+    you just want to work on developing a patch.  See the sections
+    about MAKING CHANGES and TESTING below if you just want to submit
+    a bug fix or some new functionality.  See the sections below about
+    BUILDING PACKAGES and TESTING PACKAGES if your enhancement involves
+    changing the way in which SCons is packaged and/or installed on an
+    end-user system.
 Assuming your system satisfies the installation requirements in the
 previous section, install SCons from this package by first populating
 the build/scons/ subdirectory.  (For an easier way to install SCons,
 library in $HOME/lib/scons, for example.
+Because SCons is implemented in a scripting language, you don't need to
+build it in order to make changes and test them.
+Virtually all of the SCons functionality exists in the "build engine,"
+the src/engine/SCons subdirectory hierarchy that contains all of the
+modules that make up SCons.  The src/script/ wrapper script exists
+mainly to find the appropriate build engine library and then execute it.
+In order to make your own change locally and test them by hand, simply
+edit modules in the local src/engine/SCons and set the SCONS_LIB_DIR
+to point to that directory.  Here is one way you can set up environment
+variables to do this on a UNIX or Linux system:
+    $ setenv MYSCONS=`pwd`/src
+    $ setenv SCONS_LIB_DIR=$MYSCONS
+    $ python $MYSCONS/script/ [arguments]
+Or on Windows:
+    C:\scons>set MYSCONS=%cd%\src
+    C:\scons>set SCONS_LIB_DIR=%MYSCONS%
+    C:\scons>python %MYSCONS%\script\ [arguments]
+You can use the -C option to have SCons change directory to another
+location where you already have a build configuration set up (for example,
+if the SCons configuration for your project seems to be blocked by
+an SCons bug, and you want to see if a patch you make actually fixes
+that bug):
+    $ python $MYSCONS/script/ -C /some/other/location [arguments]
+Lastly, if you want to be able to just execute your modified version
+of SCons from the command line, you can make it executable and add its
+directory to your $PATH like so:
+    $ chmod 755 src/script/
+    $ export PATH=$PATH:`pwd`/src/script
+You should then be able to run this version of SCons by just typing
+"" at your UNIX or Linux command line.
+Note that the regular SCons development process makes heavy use of
+automated testing.  See the TESTING and DEVELOPMENT WORKFLOW sections
+below for more information about the automated regression tests and how
+they can be used in a development cycle to validate that your changes
+don't break existing functionality.
+Python comes with a good interactive debugger.  When debugging changes
+by hand (i.e., when not using the automated tests), you can invoke SCons
+under control of the Python debugger by specifying the --debug=pdb option:
+    $ scons --debug=pdb [arguments]
+    > /home/knight/SCons/src/engine/SCons/Script/
+    -> default_warnings = [ SCons.Warnings.CorruptSConsignWarning,
+    (Pdb) 
+Once in the debugger, you can set breakpoints at lines in files in the
+build engine modules by providing the path name of the file relative to
+the src/engine subdirectory (that is, including the SCons/ as the first
+directory component):
+    (Pdb) b SCons/Tool/
+The debugger also supports single stepping, stepping into functions,
+printing variables, etc.
+Trying to debug problems found by running the automated tests (see the
+TESTING section, below) is more difficult, because the test automation
+harness re-invokes SCons and captures output. Consequently, there isn't an
+easy way to invoke the Python debugger in a useful way on any particular
+SCons call within a test script.
+The most effective technique for debugging problems that occur during an
+automated test is to use the good old tried-and-true technique of adding
+statements to print tracing information.  But note that you can't just use
+"print" statement, or even "sys.stdout.write()," because those change the
+SCons output, and the automated tests usually look for matches of specific
+output strings to decide if a given SCons invocations passes the test.
+To deal with this, SCons supports a Trace() function that (by default)
+will print messages to your console screen ("/dev/tty" on UNIX or Linux,
+"con" on Windows).  By adding Trace() calls to the SCons source code:
+    def sample_method(self, value):
+        fromn SCons.Debug import Trace
+        Trace('called sample_method(%s, %s)\n' % (self, value))
+You can then run automated tests that print any arbitrary information
+you wish about what's going on inside SCons, without interfering with
+the test automation.
+The Trace() function can also redirect its output to a file, rather than
+the screen:
+    def sample_method(self, value):
+        fromn SCons.Debug import Trace
+        Trace('called sample_method(%s, %s)\n' % (self, value),
+              file='trace.out')
+Where the Trace() function sends its output is stateful: once you use the
+"file=" argument, all subsequent calls to Trace() send their output to
+the same file, until another call with a "file=" argument is reached.
         $ python test/ test/
-Alternatively, the script takes a -a option that searches
-the tree for all of the tests and runs them:
+You also use the -f option to execute just the tests listed in a specified
+text file:
+        $ cat testlist.txt
+        test/
+        test/
+        $ python -f testlist.txt
+One test must be listed per line, and any lines that begin with '#'
+will be ignored (allowing you, for example, to comment out tests that
+are currently passing and then uncomment all of the tests in the file
+for a final validation run).
+The script also takes a -a option that searches the tree for
+all of the tests and runs them:
         $ python -a
 PACKAGES" section below.
+    CAVEAT:  The point of this section isn't to describe one dogmatic
+    workflow.  Just running the test suite can be time-consuming, and
+    getting a patch to pass all of the tests can be more so.  If you're
+    genuinely blocked, it may make more sense to submit a patch with
+    a note about which tests still fail, and how.  Someone else may be
+    able to take your "initial draft" and figure out how to improve it
+    to fix the rest of the tests.  So there's plenty of room for use of
+    good judgement.
+The various techniques described in the above sections can be combined
+to create simple and effective workflows that allow you to validate
+that patches you submit to SCons don't break existing functionality and
+have adequate testing, thereby increasing the speed with which they can
+be integrated.
+For example, suppose your project's SCons configuration is blocked by
+an SCons bug, and you decide you want to fix it and submit the patch.
+Here's one possible way to go about doing that (using UNIX/Linux as the
+development platform, Windows users can translate as appropriate)):
+    --  Change to the top of your checked-out SCons tree and set
+        $SCONS_LIB_DIR to point to its build engine:
+            $ setenv SCONS_LIB_DIR=`pwd`/src
+    --  Confirm that the bug still exists in this version of SCons
+        by using the -C option to run the broken build:
+            $ python script/ -C /home/me/broken_project .
+    --  Fix the bug in SCons by editing appropriate module files
+        underneath src/engine/SCons.
+    --  Confirm that you've fixed the bug affecting your project:
+            $ python script/ -C /home/me/broken_project .
+    --  Test to see if your fix had any unintended side effects
+        that break existing functionality:
+            $ python -a
+        Be patient, there are more than 500 test scripts in the
+        whole suite.
+        If any test scripts fail, they will be listed in a summary at
+        the end of the run.  Some test scripts may also report NO RESULT
+        because (for example) your local system is the wrong type or
+        doesn't have some installed utilities necessary to run the
+        script.  In general, you can ignore the NO RESULT list.
+    --  Cut-and-paste the list of failed tests into a file:
+            $ cat > failed.txt
+            test/
+            test/
+            test/
+            ^D
+            $
+   --   Now debug the test failures and fix them, either by changing
+        SCons, or by making necessary changes to the tests (if, for
+        example, you have a strong reason to change functionality, or
+        if you find that the bug really is in the test script itself).
+        After each change, use the -f option to examine the
+        effects of the change on the subset of tests that originally
+        failed:
+            $ [edit]
+            $ python -f failed.txt
+        Repeat this until all of the tests that originally failed
+        now pass.
+   --   Now you need to go back and validate that any changes you
+        made while getting the tests to pass didn't break the fix you
+        originally put in, or introduce any *additional* unintended side
+        effects that broke other tests:
+            $ python script/ -C /home/me/broken_project .
+            $ python -a
+        If you find any newly-broken tests, add them to your "failed.txt"
+        file and go back to the previous step.
+Of course, the above is only one suggested workflow.  In practice, there's
+a lot of room for judgment and experience to make things go quicker.
+For example, if you're making a change to just the Java support, you
+might start looking for regressions by just running the test/Java/*.py
+tests instead of running all of " -a".
 	test $? -le 1";
- * We use a script to execute tests.  This takes care of
+ * We use a script to execute tests.  This takes care of
  * massaging environment variables and the like to test against the
  * unpacked package in the current directory.
  * is set appropriately during a baseline test.  So we just use the
  * proper aesub variable to comment out the expanded $spe.
-test_command = "python1.5 ${Source Absolute} -p tar-gz -v ${SUBSTitute '\\.[CD][0-9]+$' '' ${VERsion}} -q ${File_Name}";
+test_command = "python1.5 ${Source Absolute} -p tar-gz -t -v ${SUBSTitute '\\.[CD][0-9]+$' '' ${VERsion}} -q ${File_Name}";
-batch_test_command = "python1.5 ${Source Absolute} -p tar-gz -v ${SUBSTitute '\\.[CD][0-9]+$' '' ${VERsion}} -o ${Output} --aegis ${File_Names} ${COMment $spe}";
+batch_test_command = "python1.5 ${Source Absolute} -p tar-gz -t -v ${SUBSTitute '\\.[CD][0-9]+$' '' ${VERsion}} -o ${Output} --aegis ${File_Names} ${COMment $spe}";
 new_test_filename = "test/";
 #                       command line it will execute before
 #                       executing it.  This suppresses that print.
+#       -t              Print the execution time of each test.
 #       -X              The scons "script" is an executable; don't
 #                       feed it to Python.
 import stat
 import string
 import sys
+import time
 all = 0
 debug = ''
 outputfile = None
 testlistfile = None
 version = ''
+print_time = lambda fmt, time: None
 if == 'java':
     python = os.path.join(sys.prefix, 'jython')
                                 zip           .zip distribution
   --passed                    Summarize which tests passed.
   -q, --quiet                 Don't print the test being executed.
+  -t, --time                  Print test execution time.
   -v version                  Specify the SCons version.
   -X                          Test script is executable, don't feed to Python.
   -x SCRIPT, --exec SCRIPT    Test SCRIPT.
   --xml                       Print results in SCons XML format.
-opts, args = getopt.getopt(sys.argv[1:], "adf:ho:P:p:qv:Xx:",
+opts, args = getopt.getopt(sys.argv[1:], "adf:ho:P:p:qv:Xx:t",
                             ['all', 'aegis',
                              'debug', 'file=', 'help', 'output=',
                              'package=', 'passed', 'python=', 'quiet',
-                             'version=', 'exec=',
+                             'version=', 'exec=', 'time',
 for o, a in opts:
         python = a
     elif o == '-q' or o == '--quiet':
         printcommand = 0
+    elif o == '-t' or o == '--time':
+        print_time = lambda fmt, time: sys.stdout.write(fmt % time)
     elif o == '-v' or o == '--version':
         version = a
     elif o == '-X':
         f.write('      <exit_status>%s</exit_status>\n' % self.status)
         f.write('      <stdout>%s</stdout>\n' % self.stdout)
         f.write('      <stderr>%s</stderr>\n' % self.stderr)
+        f.write('      <time>%.1f</time>\n' % self.test_time)
         f.write('    </test>\n')
     def footer(self, f):
+        f.write('  <time>%.1f</time>\n' % self.total_time)
         f.write('  </results>\n')
 format_class = {
 sys.stdout = Unbuffered(sys.stdout)
+# time.clock() is the suggested interface for doing benchmarking timings,
+# but time.time() does a better job on Linux systems, so let that be
+# the non-Windows default.
+if sys.platform == 'win32':
+    time_func = time.clock
+    time_func = time.time
+total_start_time = time_func()
 for t in tests:
     t.command_args = [python, '-tt']
     if debug:
     t.command_str = string.join(map(escape, t.command_args), " ")
     if printcommand:
         sys.stdout.write(t.command_str + "\n")
+    test_start_time = time_func()
+    t.test_time = time_func() - test_start_time
+    print_time("Test execution time: %.1f seconds\n",  t.test_time)
+if len(tests) > 0:
+    tests[0].total_time = time_func() - total_start_time
+    print_time("Total execution time for all tests: %.1f seconds\n",  tests[0].total_time)
 passed = filter(lambda t: t.status == 0, tests)
 fail = filter(lambda t: t.status == 1, tests)