[CMake] CMake 2.8.6 --> 2.8.8 New TryCompile Fails on GCC-GNAT Ada Linking

[Matthew Schuchard]

The executable name does in fact have to match the name of the source file.
I could get into details, but the short summary is that gcc-gnat is a 
very headache-inducing compiler with poorly conceived input/output file 
behavior and arguments.

As per the first email, the general Ada link statement in 
CMakeAdaInformation is:

"${CMAKE_Ada_BUILDER} <LINK_FLAGS> <TARGET_BASE>.adb -cargs <FLAGS> 
-bargs ${CMAKE_Ada_BIND_FLAGS} -largs <CMAKE_Ada_LINK_FLAGS> 
<LINK_LIBRARIES>"

and the free to use one by Allen Irwin(?) follows the same basic 
methodology for linking, meaning his will break now also.  You can see 
why the target name has to match the primary source file name.  If you 
are wondering about executables with multiple source files, gnatmake 
hilariously goes through and builds whatever other Ada files it think 
are necessary for the executable based on the primary source file.

So this worked before because the generated function was:

ADD_EXECUTABLE(cmTryCompileExec 
"/users/ms503/gtsims/bld/CMakeFiles/CMakeTmp/cmTryCompileExec.adb")

which generated a link statement:

/usr/bin/gnatmake   cmTryCompileExec.adb -cargs
-gnatec/path/to/gnat.adc   -g -Wall   -bargs  -largs  -rdynamic


whereas now it is:

/usr/bin/gnatmake   cmTryCompileExec162931069.adb -cargs
-gnatec/path/to/gnat.adc   -g -Wall   -bargs  -largs  -rdynamic


Which fails due to non-existent file.

This also works because there is no need for the -aI flag instructing 
gnat as to the location of the input source file, since TryCompile 
builds in /path/to/CMakeTmp/, which is where the source file is located.
For all the local project CMakeLists, I have an overloaded 
add_ada_executable function which builds a nominal "hello world" object 
with gnat for the compilation step (free to use CMake Ada does something 
similar) and then asks gnatmake to do all the heavy lifting for the 
executable during build/bind/link.  Building objects for linking into a 
library is performed with gnat without any hacks and/or shenanigans.

If there was a way to continue naming the test file the same as the 
TryCompile target, I would be set.

The other possibility is to delve into the GNAT 4.1.x --> 4.4.x changes 
and see if any sanity was introduced into input/output file behavior and 
arguments.

On 07/02/2012 11:38 AM, Bill Hoffman wrote:
> On 7/2/2012 11:22 AM, Matthew Schuchard wrote:
>> Attached tarball of CMakeTmp after failed Ada TryCompile.
>>
>> Relevant from CMakeTestAdaCompiler:
>>
>> IF(NOT CMAKE_Ada_COMPILER_WORKS)
>>    PrintTestCompilerStatus("Ada" "")
>>    FILE(WRITE 
>> ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/cmTryCompileExec.adb
>>      "with Ada.Text_IO;\n"
>>      "use Ada.Text_IO;\n"
>>      "procedure cmTryCompileExec is\n"
>>      "begin\n"
>>      "Put(\"Hello World\");\n"
>>      "end cmTryCompileExec;\n")
>>    TRY_COMPILE(CMAKE_Ada_COMPILER_WORKS ${CMAKE_BINARY_DIR}
>>      
>> ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/cmTryCompileExec.adb
>>      OUTPUT_VARIABLE OUTPUT)
>>    SET(Ada_TEST_WAS_RUN 1)
>> ENDIF(NOT CMAKE_Ada_COMPILER_WORKS)
>
> So, the generated CMake file looks like this:
>
> ADD_EXECUTABLE(cmTryCompileExec2054790633 
> "/users/ms503/gtsims/bld/CMakeFiles/CMakeTmp/cmTryCompileExec.adb")
>
> That does not look bad to me.  However, since you did not include the 
> Platform ADA files you are using, the problem could be there.  Does 
> the executable name have to match the .adb file?
>
> -Bill