SCons / doc / user / hierarchy.in

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
<!--

  __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.

-->

<!--


=head2 The Build command

By default, Cons does not change its working directory to the directory
containing a subsidiary F<Conscript> file it is including.  This behavior
can be enabled for a build by specifying, in the top-level F<Construct>
file:

  Conscript_chdir 1;

When enabled, Cons will change to the subsidiary F<Conscript> file's
containing directory while reading in that file, and then change back
to the top-level directory once the file has been processed.

It is expected that this behavior will become the default in some future
version of Cons.  To prepare for this transition, builds that expect
Cons to remain at the top of the build while it reads in a subsidiary
F<Conscript> file should explicitly disable this feature as follows:

  Conscript_chdir 0;

=head2 Relative, top-relative, and absolute file names

(There is another file prefix, ``!'', that is interpreted specially by
Cons.  See discussion of the C<Link> command, below, for details.)


=head2 Using modules in build scripts

You may pull modules into each F<Conscript> file using the normal Perl
C<use> or C<require> statements:

  use English;
  require My::Module;

Each C<use> or C<require> only affects the one F<Conscript> file in which
it appears.  To use a module in multiple F<Conscript> files, you must
put a C<use> or C<require> statement in each one that needs the module.


=head2 Scope of variables

The top-level F<Construct> file and all F<Conscript> files begin life in
a common, separate Perl package.  B<Cons> controls the symbol table for
the package so that, the symbol table for each script is empty, except
for the F<Construct> file, which gets some of the command line arguments.
All of the variables that are set or used, therefore, are set by the
script itself, not by some external script.

Variables can be explicitly B<imported> by a script from its parent
script. To import a variable, it must have been B<exported> by the parent
and initialized (otherwise an error will occur).


=head2 The Export command

The C<Export> command is used as in the following example:

  $env = new cons();
  $INCLUDE = "#export/include";
  $LIB = "#export/lib";
  Export qw( env INCLUDE LIB );
  Build qw( util/Conscript );

The values of the simple variables mentioned in the C<Export> list will be
squirreled away by any subsequent C<Build> commands. The C<Export> command
will only export Perl B<scalar> variables, that is, variables whose name
begins with C<$>. Other variables, objects, etc. can be exported by
reference, but all scripts will refer to the same object, and this object
should be considered to be read-only by the subsidiary scripts and by the
original exporting script. It's acceptable, however, to assign a new value
to the exported scalar variable, that won't change the underlying variable
referenced. This sequence, for example, is OK:

  $env = new cons();
  Export qw( env INCLUDE LIB );
  Build qw( util/Conscript );
  $env = new cons(CFLAGS => '-O');
  Build qw( other/Conscript );

It doesn't matter whether the variable is set before or after the C<Export>
command. The important thing is the value of the variable at the time the
C<Build> command is executed. This is what gets squirreled away. Any
subsequent C<Export> commands, by the way, invalidate the first: you must
mention all the variables you wish to export on each C<Export> command.


=head2 The Import command

Variables exported by the C<Export> command can be imported into subsidiary
scripts by the C<Import> command. The subsidiary script always imports
variables directly from the superior script. Consider this example:

  Import qw( env INCLUDE );

This is only legal if the parent script exported both C<$env> and
C<$INCLUDE>. It also must have given each of these variables values. It is
OK for the subsidiary script to only import a subset of the exported
variables (in this example, C<$LIB>, which was exported by the previous
example, is not imported).

All the imported variables are automatically re-exported, so the sequence:

  Import qw ( env INCLUDE );
  Build qw ( beneath-me/Conscript );

will supply both C<$env> and C<$INCLUDE> to the subsidiary file. If only
C<$env> is to be exported, then the following will suffice:

  Import qw ( env INCLUDE );
  Export qw ( env );
  Build qw ( beneath-me/Conscript );

Needless to say, the variables may be modified locally before invoking
C<Build> on the subsidiary script.

=head2 Build script evaluation order

The only constraint on the ordering of build scripts is that superior
scripts are evaluated before their inferior scripts. The top-level
F<Construct> file, for instance, is evaluated first, followed by any
inferior scripts. This is all you really need to know about the evaluation
order, since order is generally irrelevant. Consider the following C<Build>
command:

  Build qw(
	drivers/display/Conscript
	drivers/mouse/Conscript
	parser/Conscript
	utilities/Conscript
  );

We've chosen to put the script names in alphabetical order, simply because
that's the most convenient for maintenance purposes. Changing the order will
make no difference to the build.

-->

  <para>

  The source code for large software projects
  rarely stays in a single directory,
  but is nearly always divided into a
  hierarchy of directories.
  Organizing a large software build using &SCons;
  involves creating a hierarchy of build scripts
  using the &SConscript; function.

  </para>

  <section>
  <title>&SConscript; Files</title>

    <para>

    As we've already seen,
    the build script at the top of the tree is called &SConstruct;.
    The top-level &SConstruct; file can
    use the &SConscript; function to
    include other subsidiary scripts in the build.
    These subsidiary scripts can, in turn,
    use the &SConscript; function
    to include still other scripts in the build.
    By convention, these subsidiary scripts are usually
    named &SConscript;.
    For example, a top-level &SConstruct; file might
    arrange for four subsidiary scripts to be included
    in the build as follows:

    </para>

    <sconstruct>
      SConscript(['drivers/display/SConscript',
                  'drivers/mouse/SConscript',
                  'parser/SConscript',
                  'utilities/SConscript'])
    </sconstruct>

    <para>

    In this case, the &SConstruct; file
    lists all of the &SConscript; files in the build explicitly.
    (Note, however, that not every directory in the tree
    necessarily has an &SConscript; file.)
    Alternatively, the <literal>drivers</literal>
    subdirectory might contain an intermediate
    &SConscript; file,
    in which case the &SConscript; call in
    the top-level &SConstruct; file
    would look like:

    </para>

    <sconstruct>
      SConscript(['drivers/SConscript',
                  'parser/SConscript',
                  'utilities/SConscript'])
    </sconstruct>

    <para>

    And the subsidiary &SConscript; file in the
    <literal>drivers</literal> subdirectory
    would look like:

    </para>

    <sconstruct>
      SConscript(['display/SConscript',
                  'mouse/SConscript'])
    </sconstruct>

    <para>

    Whether you list all of the &SConscript; files in the
    top-level &SConstruct; file,
    or place a subsidiary &SConscript; file in
    intervening directories,
    or use some mix of the two schemes,
    is up to you and the needs of your software.

    </para>

  </section>

  <section>
  <title>Path Names Are Relative to the &SConscript; Directory</title>

    <para>

    Subsidiary &SConscript; files make it easy to create a build
    hierarchy because all of the file and directory names
    in a subsidiary &SConscript; files are interpreted
    relative to the directory in which the &SConscript; file lives.
    Typically, this allows the &SConscript; file containing the
    instructions to build a target file
    to live in the same directory as the source files
    from which the target will be built,
    making it easy to update how the software is built
    whenever files are added or deleted
    (or other changes are made).

    </para>

    <para>

    For example, suppose we want to build two programs
    &prog1; and &prog2; in two separate directories
    with the same names as the programs.
    One typical way to do this would be
    with a top-level &SConstruct; file like this:

    </para>

    <scons_example name="ex1">
      <file name="SConstruct" printme="1">
      SConscript(['prog1/SConscript',
                  'prog2/SConscript'])
      </file>
      <file name="prog1/SConscript">
      env = Environment()
      env.Program('prog1', ['main.c', 'foo1.c', 'foo2.c'])
      </file>
      <file name="prog2/SConscript">
      env = Environment()
      env.Program('prog2', ['main.c', 'bar1.c', 'bar2.c'])
      </file>
      <directory name="prog1"></directory>
      <file name="prog1/main.c">
      x
      </file>
      <file name="prog1/foo1.c">
      x
      </file>
      <file name="prog1/foo2.c">
      x
      </file>
      <directory name="prog2"></directory>
      <file name="prog2/main.c">
      x
      </file>
      <file name="prog2/bar1.c">
      x
      </file>
      <file name="prog2/bar2.c">
      x
      </file>
    </scons_example>

    <para>

    And subsidiary &SConscript; files that look like this:

    </para>

    <scons_example_file example="ex1" name="prog1/SConscript">
    </scons_example_file>

    <para>

    And this:

    </para>

    <scons_example_file example="ex1" name="prog2/SConscript">
    </scons_example_file>

    <para>

    Then, when we run &SCons; in the top-level directory,
    our build looks like:

    </para>

    <scons_output example="ex1">
       <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <para>

    Notice the following:

    First, you can have files with the same names
    in multiple directories, like main.c in the above example.

    Second, unlike standard recursive use of &Make;,
    &SCons; stays in the top-level directory
    (where the &SConstruct; file lives)
    and issues commands that use the path names
    from the top-level directory to the
    target and source files within the hierarchy.

    </para>

  </section>

  <section>
  <title>Top-Level Path Names in Subsidiary &SConscript; Files</title>

    <para>

    If you need to use a file from another directory,
    it's sometimes more convenient to specify
    the path to a file in another directory
    from the top-level &SConstruct; directory,
    even when you're using that file in
    a subsidiary &SConscript; file in a subdirectory.
    You can tell &SCons; to interpret a path name
    as relative to the top-level &SConstruct; directory,
    not the local directory of the &SConscript; file,
    by appending a &hash; (hash mark)
    to the beginning of the path name:

    </para>

    <scons_example name="ex2">
       <file name="SConstruct">
       SConscript('src/prog/SConscript')
       </file>
       <file name="src/prog/SConscript" printme="1">
       env = Environment()
       env.Program('prog', ['main.c', '#lib/foo1.c', 'foo2.c'])
       </file>
       <file name="src/prog/main.c">
       x
       </file>
       <file name="lib/foo1.c">
       x
       </file>
       <file name="src/prog/foo2.c">
       x
       </file>
    </scons_example>

    <para>

    In this example,
    the <literal>lib</literal> directory is
    directly underneath the top-level &SConstruct; directory.
    If the above &SConscript; file is in a subdirectory
    named <literal>src/prog</literal>,
    the output would look like:

    </para>

    <scons_output example="ex2">
       <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <para>

    (Notice that the <literal>lib/foo1.o</literal> object file
    is built in the same directory as its source file.
    See <xref linkend="chap-separate"></xref>, below,
    for information about
    how to build the object file in a different subdirectory.)

    </para>

  </section>

  <section>
  <title>Absolute Path Names</title>

    <para>

    Of course, you can always specify
    an absolute path name for a file--for example:

    </para>

    <scons_example name="ex3">
       <file name="SConstruct">
       SConscript('src/prog/SConscript')
       </file>
       <file name="src/prog/SConscript" printme="1">
       env = Environment()
       env.Program('prog', ['main.c', '__ROOT__/usr/joe/lib/foo1.c', 'foo2.c'])
       </file>
       <file name="src/prog/main.c">
       x
       </file>
       <file name="__ROOT__/usr/joe/lib/foo1.c">
       x
       </file>
       <file name="src/prog/foo2.c">
       x
       </file>
    </scons_example>

    <para>

    Which, when executed, would yield:

    </para>

    <scons_output example="ex3">
       <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <para>

    (As was the case with top-relative path names,
    notice that the <literal>/usr/joe/lib/foo1.o</literal> object file
    is built in the same directory as its source file.
    See <xref linkend="chap-separate"></xref>, below,
    for information about
    how to build the object file in a different subdirectory.)

    </para>

  </section>

  <section>
  <title>Sharing Environments (and Other Variables) Between &SConscript; Files</title>

    <para>

    In the previous example,
    each of the subsidiary &SConscript; files
    created its own construction environment
    by calling &Environment; separately.
    This obviously works fine,
    but if each program must be built
    with the same construction variables,
    it's cumbersome and error-prone to initialize
    separate construction environments
    in the same way over and over in each subsidiary
    &SConscript; file.

    </para>

    <para>

    &SCons; supports the ability to <emphasis>export</emphasis> variables
    from a parent &SConscript; file
    to its subsidiary &SConscript; files,
    which allows you to share common initialized
    values throughout your build hierarchy.

    </para>

    <section>
    <title>Exporting Variables</title>

      <para>

      There are two ways to export a variable,
      such as a construction environment,
      from an &SConscript; file,
      so that it may be used by other &SConscript; files.
      First, you can call the &Export;
      function with a list of variables,
      or a string of white-space separated variable names.
      Each call to &Export; adds one
      or more variables to a global list
      of variables that are available for import
      by other &SConscript; files.

      </para>

      <sconstruct>
        env = Environment()
        Export('env')
      </sconstruct>

      <para>

      You may export more than one variable name at a time:

      </para>

      <sconstruct>
        env = Environment()
        debug = ARGUMENTS['debug']
        Export('env', 'debug')
      </sconstruct>

      <para>

      Because white space is not legal in Python variable names,
      the &Export; function will even automatically split
      a string into separate names for you:

      </para>

      <sconstruct>
        Export('env debug')
      </sconstruct>

      <para>

      Second, you can specify a list of
      variables to export as a second argument
      to the &SConscript; function call:

      </para>

      <sconstruct>
        SConscript('src/SConscript', 'env')
      </sconstruct>

      <para>

      Or as the &exports; keyword argument:

      </para>

      <sconstruct>
        SConscript('src/SConscript', exports='env')
      </sconstruct>

      <para>

      These calls export the specified variables
      to only the listed &SConscript; files.
      You may, however, specify more than one
      &SConscript; file in a list:

      </para>

      <sconstruct>
        SConscript(['src1/SConscript',
                    'src2/SConscript'], exports='env')
      </sconstruct>

      <para>

      This is functionally equivalent to
      calling the &SConscript; function
      multiple times with the same &exports; argument,
      one per &SConscript; file.

      </para>

    </section>

    <section>
    <title>Importing Variables</title>

      <para>

      Once a variable has been exported from a calling
      &SConscript; file,
      it may be used in other &SConscript; files
      by calling the &Import; function:

      </para>

      <sconstruct>
        Import('env')
        env.Program('prog', ['prog.c'])
      </sconstruct>

      <para>

      The &Import; call makes the <literal>env</literal> construction
      environment available to the &SConscript; file,
      after which the variable can be used to build
      programs, libraries, etc.

      </para>

      <para>

      Like the &Export; function,
      the &Import; function can be used
      with multiple variable names:

      </para>

      <sconstruct>
        Import('env', 'debug')
        env = env.Clone(DEBUG = debug)
        env.Program('prog', ['prog.c'])
      </sconstruct>

      <para>

      And the &Import; function will similarly
      split a string along white-space
      into separate variable names:

      </para>

      <sconstruct>
        Import('env debug')
        env = env.Clone(DEBUG = debug)
        env.Program('prog', ['prog.c'])
      </sconstruct>

      <para>

      Lastly, as a special case,
      you may import all of the variables that
      have been exported by supplying an asterisk
      to the &Import; function:

      </para>

      <sconstruct>
        Import('*')
        env = env.Clone(DEBUG = debug)
        env.Program('prog', ['prog.c'])
      </sconstruct>

      <para>

      If you're dealing with a lot of &SConscript; files,
      this can be a lot simpler than keeping
      arbitrary lists of imported variables in each file.

      </para>

    </section>

    <section>
    <title>Returning Values From an &SConscript; File</title>

      <para>

      Sometimes, you would like to be able to
      use information from a subsidiary
      &SConscript file in some way.
      For example,
      suppose that you want to create one
      library from source files
      scattered throughout a number
      of subsidiary &SConscript; files.
      You can do this by using the &Return;
      function to return values
      from the subsidiary &SConscript; files
      to the calling file.

      </para>

      <para>

      If, for example, we have two subdirectories
      &foo; and &bar;
      that should each contribute a source
      file to a Library,
      what we'd like to be able to do is
      collect the object files
      from the subsidiary &SConscript; calls
      like this:

      </para>

      <scons_example name="Return">
        <file name="SConstruct" printme="1">
          env = Environment()
          Export('env')
          objs = []
          for subdir in ['foo', 'bar']:
              o = SConscript('%s/SConscript' % subdir)
              objs.append(o)
          env.Library('prog', objs)
        </file>
        <directory name="foo"></directory>
        <directory name="bar"></directory>
        <file name="foo/SConscript">
          Import('env')
          obj = env.Object('foo.c')
          Return('obj')
        </file>
        <file name="bar/SConscript">
          Import('env')
          obj = env.Object('bar.c')
          Return('obj')
        </file>
        <file name="foo/foo.c">
          void foo(void) { printf("foo/foo.c\n"); }
        </file>
        <file name="bar/bar.c">
          void bar(void) { printf("bar/bar.c\n"); }
        </file>
      </scons_example>

      <para>

      We can do this by using the &Return;
      function in the
      <literal>foo/SConscript</literal> file like this:

      </para>

      <scons_example_file example="Return" name="foo/SConscript">
      </scons_example_file>

      <para>

      (The corresponding
      <literal>bar/SConscript</literal>
      file should be pretty obvious.)
      Then when we run &SCons;,
      the object files from the subsidiary subdirectories
      are all correctly archived in the desired library:

      </para>

      <scons_output example="Return">
        <scons_output_command>scons -Q</scons_output_command>
      </scons_output>

      <!--
      XXX Return(stop=False)
      -->

    </section>

  </section>

  <!--

  <section>
  <title>Executing From a Subdirectory:  the -D, -u and -U Options</title>

    <para>

    XXX -D, -u and -U

    </para>

  </section>

  -->
Tip: Filter by directory path e.g. /media app.js to search for public/media/app.js.
Tip: Use camelCasing e.g. ProjME to search for ProjectModifiedEvent.java.
Tip: Filter by extension type e.g. /repo .js to search for all .js files in the /repo directory.
Tip: Separate your search with spaces e.g. /ssh pom.xml to search for src/ssh/pom.xml.
Tip: Use ↑ and ↓ arrow keys to navigate and return to view the file.
Tip: You can also navigate files with Ctrl+j (next) and Ctrl+k (previous) and view the file with Ctrl+o.
Tip: You can also navigate files with Alt+j (next) and Alt+k (previous) and view the file with Alt+o.