[CMake] avoid rebuilding targets depending on generated source files

Ajay Panyala ajay at csc.lsu.edu
Sun Mar 4 14:02:17 EST 2012 

The following project is a boiled-down version of yours but doesn't
need any programs except for CMake - that's what I actually meant
with "minimal but complete" as I don't have the org.antlr.Tool
Java program:

I am sorry. I was mainly trying to cleanup the big CMakeLists file
I had and removed about 10 different targets - all of which were
rebuilt because the 5 files (test*.*) were overwritten.

If you want to try running the test project on your system

test.g is at http://pastie.org/private/agzor3ibzoa5pom6q31qq

org.antlr.Tool is at www.antlr.org/download/antlr-3.4-complete.jar

After configuration, you can run the target by "make X=0" and check the
timestamps by "ls -l --full-time test.tokens parser src". Issuing "make
X=0" again reveals that the copied files aren't rewritten as it happens
after "make X=1". Thus, AFAICS, everything works as expected. Could you
check if the above-noted example also works on your system?

It does not work. The files are still overwritten.

What exactly does not work with your example? You wrote:

>>> I have 4 cmake -E copy_if_different commands, one for each file.
>>> Only the last file is not copied (if similar). [...]

Does this mean that the last file out of four - in fact, your example
handles five files - is not copied *although* the source file and the
destination file are different, i.e. similar but not equal?

Yes the file test.tokens is not copied overwritten since they are
exactly (diff) similar files. This is the case with the other 4 files as
well,
but they are still copied over and rewritten.


You wrote further:

>>> [...] The others are copied
>>> even if they are the same.
>>>
>>> I verfied that they are the same with a diff.

Does this mean that source files are copied *although* they are equal
to their respective destination file? How do you determine that they
have been copied? Do you check the timestamps? With --full-time?

Yes, I do check with ls -l --full-time. Except test.tokens, all the other
files
are copied over (rewritten) even though they are exactly the same (diff
same I mean).

This is what is confusing me about the behavior of copy_if_different.
that is why it works only with test.tokens and not others.

PS: Does org.antlr.Tool write to the source tree? If so: Don't do that.

Yes, it generates the files in the source dir itself (where test.g is
present)
I now modified CMakeLists to copy test.g to the project build folder and
run it there. The new CMakeLists is at

http://pastie.org/private/p1yi0l8so9cqimqlywfmhw


Thank You
Ajay

On Sun, Mar 4, 2012 at 12:52 AM, Michael Hertling <mhertling at online.de>wrote:

> On 03/04/2012 01:06 AM, Ajay Panyala wrote:
> > Please provide a minimal but complete example for this issue.
> >
> > Please find it in the following link
> > http://pastie.org/private/pd13u33s9xpfihf2dbzc1q
>
>


> The following project is a boiled-down version of yours but doesn't
> need any programs except for CMake - that's what I actually meant
> with "minimal but complete" as I don't have the org.antlr.Tool
> Java program:
>
> CMAKE_MINIMUM_REQUIRED(VERSION 2.8 FATAL_ERROR)
> PROJECT(P NONE)
> SET(CMAKE_VERBOSE_MAKEFILE ON)
>
> SET(GrammarSource ${PROJECT_BINARY_DIR}/src)
> FILE(MAKE_DIRECTORY ${PROJECT_BINARY_DIR}/src)
>
> ADD_CUSTOM_TARGET(GrammarBuild ALL
>    COMMAND ${CMAKE_COMMAND} -E echo "\${X}"
>        > ${GrammarSource}/testLexer.h
>    COMMAND ${CMAKE_COMMAND} -E echo "\${X}"
>        > ${GrammarSource}/testLexer.c
>    COMMAND ${CMAKE_COMMAND} -E echo "\${X}"
>        > ${GrammarSource}/testParser.h
>    COMMAND ${CMAKE_COMMAND} -E echo "\${X}"
>        > ${GrammarSource}/testParser.c
>    COMMAND ${CMAKE_COMMAND} -E echo "\${X}"
>        > ${PROJECT_BINARY_DIR}/test.tokens
> )
>
> ADD_CUSTOM_COMMAND(TARGET GrammarBuild POST_BUILD
>    COMMAND ${CMAKE_COMMAND} -E copy_if_different
>        ${GrammarSource}/testLexer.h
>        ${PROJECT_BINARY_DIR}/parser/testLexer.h
>    COMMAND ${CMAKE_COMMAND} -E copy_if_different
>        ${GrammarSource}/testLexer.c
>        ${PROJECT_BINARY_DIR}/parser/testLexer.c
>    COMMAND ${CMAKE_COMMAND} -E copy_if_different
>        ${GrammarSource}/testParser.h
>        ${PROJECT_BINARY_DIR}/parser/testParser.h
>    COMMAND ${CMAKE_COMMAND} -E copy_if_different
>        ${GrammarSource}/testParser.c
>        ${PROJECT_BINARY_DIR}/parser/testParser.c
>    COMMAND ${CMAKE_COMMAND} -E copy_if_different
>        ${PROJECT_BINARY_DIR}/test.tokens
>        ${PROJECT_BINARY_DIR}/parser/test.tokens
> )
>
> After configuration, you can run the target by "make X=0" and check the
> timestamps by "ls -l --full-time test.tokens parser src". Issuing "make
> X=0" again reveals that the copied files aren't rewritten as it happens
> after "make X=1". Thus, AFAICS, everything works as expected. Could you
> check if the above-noted example also works on your system?
>
> What exactly does not work with your example? You wrote:
>
> >>> I have 4 cmake -E copy_if_different commands, one for each file.
> >>> Only the last file is not copied (if similar). [...]
>
> Does this mean that the last file out of four - in fact, your example
> handles five files - is not copied *although* the source file and the
> destination file are different, i.e. similar but not equal?
>
> You wrote further:
>
> >>> [...] The others are copied
> >>> even if they are the same.
> >>>
> >>> I verfied that they are the same with a diff.
>
> Does this mean that source files are copied *although* they are equal
> to their respective destination file? How do you determine that they
> have been copied? Do you check the timestamps? With --full-time?
>
> Regards,
>
> Michael
>
> PS: Does org.antlr.Tool write to the source tree? If so: Don't do that.
>
> > On Sat, Mar 3, 2012 at 3:54 PM, Michael Hertling <mhertling at online.de
> >wrote:
> >
> >> On 03/04/2012 12:14 AM, Ajay Panyala wrote:
> >>> No, it wouldn't; check it out:
> >>>
> >>> % touch a
> >>> % rm -f b
> >>> % ls b
> >>> ls: cannot access b: No such file or directory
> >>> % cmake -E copy_if_different a b
> >>> % ls b
> >>> b
> >>> % cksum a b
> >>> 4294967295 0 a
> >>> 4294967295 0 b
> >>>
> >>> It works with one file, but I have 4 files that are generated.
> >>> I have 4 cmake -E copy_if_different commands, one for each file.
> >>> Only the last file is not copied (if similar). The others are copied
> >>> even if they are the same.
> >>>
> >>> I verfied that they are the same with a diff.
> >>>
> >>> Any idea what might be happening here ?
> >>
> >> Please provide a minimal but complete example for this issue.
> >>
> >> Regards,
> >>
> >> Michael
> >>
> >>> On Sat, Mar 3, 2012 at 2:47 PM, Michael Hertling <mhertling at online.de
> >>> wrote:
> >>>
> >>>> On 03/03/2012 10:36 PM, Ajay Panyala wrote:
> >>>>> Try "cmake -E copy_if_different ..."
> >>>>>
> >>>>> cmake -E copy_if_different build/test1.c build/tests/test1.c
> >>>>>
> >>>>> That would work when make is run atleast once.
> >>>>> When running make for the 1st time test1.c was never
> >>>>> copied to build/tests before. So I would be comparing a file with
> >>>>> another non-existant file and that would result in an error halting
> >>>>> the make process.
> >>>>
> >>>> No, it wouldn't; check it out:
> >>>>
> >>>> % touch a
> >>>> % rm -f b
> >>>> % ls b
> >>>> ls: cannot access b: No such file or directory
> >>>> % cmake -E copy_if_different a b
> >>>> % ls b
> >>>> b
> >>>> % cksum a b
> >>>> 4294967295 0 a
> >>>> 4294967295 0 b
> >>>>
> >>>> Regards,
> >>>>
> >>>> Michael
> >>>>
> >>>>> On Sat, Mar 3, 2012 at 1:20 PM, Hendrik Sattler <
> >> post at hendrik-sattler.de
> >>>>> wrote:
> >>>>>
> >>>>>> Am Samstag, 3. März 2012, 21:41:49 schrieb Ajay Panyala:
> >>>>>>> I have a custom target which runs a command to generate
> >>>>>>> a C source file say test1.c
> >>>>>>>
> >>>>>>> ADD_CUSTOM_TARGET(TestGen ALL
> >>>>>>> COMMAND genExec ${PROJECT_SOURCE_DIR}/Main.java
> >>>>>>> DEPENDS ${PROJECT_SOURCE_DIR}/Main.java
> >>>>>>> )
> >>>>>>>
> >>>>>>> And I have a custom command that moves the generated *test1.c *
> >>>>>>> to a new directory inside the build directory.
> >>>>>>>
> >>>>>>> ADD_CUSTOM_COMMAND(
> >>>>>>> TARGET TestGen
> >>>>>>> POST_BUILD
> >>>>>>> COMMAND mv
> >>>>>>> ARGS ${PROJECT_BINARY_DIR}/test1.c ${PROJECT_BINARY_DIR}/tests/
> >>>>>>> )
> >>>>>>>
> >>>>>>> Each time I run make, the custom target is run (since custom
> targets
> >>>> are
> >>>>>>> always
> >>>>>>> out-of-date). But I want to avoid moving the new test1.c generated
> >> each
> >>>>>>> time if build/test1.c is the same as build/tests/test1.c since
> there
> >>>> are
> >>>>>>> other targets
> >>>>>>> like add_executable and add_library later in the CMakelists file
> that
> >>>> are
> >>>>>>>  re-built
> >>>>>>> each time since they depend on test1.c
> >>>>>>
> >>>>>> Try "cmake -E copy_if_different ..."
> >>>>>>
> >>>>>> HS
> --
>
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