[cmake-developers] generator expression for path slash conversion

[Kislinskiy, Stefan]

I see. I would suggest that I add another output flag to cmOutputConverter like SHELL_NO_ESCAPE then. If this flag is passed to ConvertToOutputFormat() instead of SHELL, the call of EscapeForShell() will be circumvented. This way there wouldn't be code duplication and we would still cover the MSYS case (drive letter conversion).

Something that just came to my mind: Isn't it possible to specify parameters for generator expressions? - How about something like $<SHELL_PATH:c:/this/is/an/example,ESCAPE>?

-----Original Message-----
From: Brad King [mailto:brad.king at kitware.com] 
Sent: Mittwoch, 23. September 2015 15:56
To: Kislinskiy, Stefan
Cc: cmake-developers at cmake.org
Subject: Re: [cmake-developers] generator expression for path slash conversion

On 09/23/2015 08:40 AM, Kislinskiy, Stefan wrote:
> I wrote the documentation, added a genex test that checks it the given 
> path is converted as expected on different platforms, and added 
> another ExternalProject test for Windows that invokes pushd, which is 
> is command sensitive to the path style.

Thanks.  I needed to fix a typo to get the latter test to run:

-    add_test(ExternalProjectShellPathGenex ${CMAKE_TEST_COMMAND}
+    add_test(ExternalProjectShellPathGenex ${CMAKE_CTEST_COMMAND}

However, it fails when there is a space in the path because the conversion result ends up as something like

  "\"c:\path with space\...\""

The problem is that the genex evaluates and adds the quotes and then the custom command generator escapes the argument for the shell again.  The problem is that ConvertToOutputFormat is meant as the final conversion step when writing a path into a shell command in the generator, so it quotes values with spaces and may add other escapes ad needed for the build system script (e.g. the Makefile).  The custom command generator will then repeat all that with another layer.  Therefore ConvertToOutputFormat is not the right implementation for SHELL_PATH.  I think we want just the slash conversion to be done by the genex.

Unfortunately the proper sequence of path escaping steps depends on the context in which the path will be written.  When using $<SHELL_PATH:...> inside add_custom_command we want it to do just the slash conversion because add_custom_command will take care of the rest of the layers of escaping.  However, in case of using file(GENERATE) for a .cmd file then we would want the quoting too.  Perhaps we can defer that use case to later work with a separate $<SHELL_ESCAPE:...> genex.

> I wasn't sure about the VERSION I am supposed to write into the
> cmake_minimum_required() line in
> Tests/ExternalProjectShellPathGenex/CMakeLists.txt, so I chose 
> 3.3.20150923.

That's fine.

Thanks,
-Brad