[ET Trac] [Einstein Toolkit] #1522: Improve determining make dependencies

[Einstein Toolkit]

#1522: Improve determining make dependencies
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  Reporter:  eschnett     |       Owner:                     
      Type:  enhancement  |      Status:  new                
  Priority:  major        |   Milestone:                     
 Component:  Cactus       |     Version:  development version
Resolution:               |    Keywords:                     
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Comment (by eschnett):

 Let's state the problem again. Assume we have a source tree consisting of
 two files, "header.h" and "source.c", and where source.c includes
 header.h. We build, everything is working fine, and the automatic
 dependency tracking records that source.c depends on header.h

 We then change the code, removing the file header.h, and chancing source.c
 so that it doesn't include header.h any more. This is still self-
 consistent, and if we say "make cleandeps", it will compile fine.

 However, without the cleandeps, the Cactus make system remembers that
 source.c depends on header.h. Since header.h does not exist any more, and
 since there is no rule for generating it automatically, make will abort
 with an error message. Yes, it will detect that source.c has changed and
 needs to be rebuilt, but it currently doesn't know that this also means
 that the dependencies are outdated and should be ignored.

 The proposed change tells make in this case that it should not worry about
 the missing file header.h. Thus make continues, decides that source.c
 needs to be rebuilt since it changed, and will also generate new, correct
 dependencies. All is fine.

 I did not understand Roland's text about "useA" and "change in a file", or
 why this would "circumvent make".

 We can also examine how the proposed new system behaves in the presence of
 errors. Assume that header.h has been deleted, and source.c has not been
 modified. Make will then treat header.h as changed (since it is not
 present), and rebuild source.c, leading to a compiler error pointing to
 the problem. This is also good.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1522#comment:13>
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