[CMake] avoid rebuilding targets depending on generated source files

[Michael Hertling]

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 out-of-date).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