[Lldb-commits] [PATCH] D13234: Use the correct Python lib for each build configuration generated by the Visual Studio CMake generator

[Zachary Turner via lldb-commits]

zturner accepted this revision.
zturner added a comment.
This revision is now accepted and ready to land.

If the above if / else is equivalent, I prefer if you change it to that before comitting.  If not, feel free to commit as is.


================
Comment at: cmake/modules/LLDBConfig.cmake:61
@@ +60,3 @@
+      # below, otherwise CMake will replace the whitespace with a semicolon in some contexts (which would stuff things up).
+      set (PYTHON_EXECUTABLE $<$<CONFIG:Debug>:${PYTHON_DEBUG_EXE}>$<$<NOT:$<CONFIG:Debug>>:${PYTHON_RELEASE_EXE}>)
+      set (PYTHON_LIBRARY $<$<CONFIG:Debug>:${PYTHON_DEBUG_LIB}>$<$<NOT:$<CONFIG:Debug>>:${PYTHON_RELEASE_LIB}>)
----------------
enlight wrote:
> zturner wrote:
> > This line is hard to parse mentally, and I'm not sure I've seen this kind of nested generator expression.  I trust you when you say it's right, but can you explain what this does?
> Sure thing.
> 
>   # `$<CONFIG:Debug>` evaluates to `1` when the `Debug` configuration is being generated, or `0` in all other cases.
>   # `$<$<CONFIG:Debug>:${PYTHON_DEBUG_EXE}>` expands to `${PYTHON_DEBUG_EXE}` when the `Debug` configuration is being generated, or nothing (literally) in all other cases.
>   # `$<$<NOT:$<CONFIG:Debug>>:${PYTHON_RELEASE_EXE}>` expands to `${PYTHON_RELEASE_EXE}` when any configuration other than `Debug` is being generated, or nothing in all other cases.
> 
> Since the conditionals in 2 & 3 are mutually exclusive, and a conditional expression that evaluates to `0` yields no value at all, it's possible to concatenate them to obtain a single value. This value will be `${PYTHON_DEBUG_EXE}` when generating the Debug configuration, or `${PYTHON_RELEASE_EXE}` when generating any other configuration.
Ahh, I understand.  Is it equivalent to write this:

    if ($<CONFIG:Debug> == 1)
      set(PYTHON_EXECUTABLE ${PYTHON_DEBUG_EXE})
    else()
      set(PYTHON_EXECUTABLE ${PYTHON_RELEASE_EXE})
    endif()

?  If so, I kind of prefer this way, if nothing else so that other people will be able to understand it in the future if they go to edit this code.


Repository:
  rL LLVM

http://reviews.llvm.org/D13234