[lldb/cmake] Enable more verbose find_package output.

[mattd]

Summary

The purpose of this patch is to make identifying missing dependencies clearer to the user.
find_package will report if a package is not found, that output, combined with the exiting
status message, is clearer than not having the additional verbosity.

If the SWIG dependency is required {LLDB_ENABLE_PYTHON, LLDB_ENABLE_LUA}
and SWIG is not available, fail the configuration step. Terminate the
configure early rather than later with a clear error message.

We could possibly modify:
llvm-project/lldb/cmake/modules/FindPythonInterpAndLibs.cmake
However, the patch here seems clear in my opinion.

[JDevlieghere]

It should never be possible for LLDB_ENABLE_PYTHON to be true but SWIG_FOUND to be false. The modules FindPythonInterpAndLibs.cmake and FindLuaAndSwig.cmake should fail early when SWIG isn't found.

[mattd]

In D74917#1885590, @JDevlieghere wrote:

It should never be possible for LLDB_ENABLE_PYTHON to be true but SWIG_FOUND to be false. The modules FindPythonInterpAndLibs.cmake and FindLuaAndSwig.cmake should fail early when SWIG isn't found.

Thanks for taking a look. Would you be okay with making the status message() in FindPythonInterpAndLibs.cmake and FindLuaAndSwig.cmake fatal, that way the dependency error is clearer?

[JDevlieghere]

In D74917#1885615, @mattd wrote:

In D74917#1885590, @JDevlieghere wrote:

It should never be possible for LLDB_ENABLE_PYTHON to be true but SWIG_FOUND to be false. The modules FindPythonInterpAndLibs.cmake and FindLuaAndSwig.cmake should fail early when SWIG isn't found.

Thanks for taking a look. Would you be okay with making the status message() in FindPythonInterpAndLibs.cmake and FindLuaAndSwig.cmake fatal, that way the dependency error is clearer?

That would defeat the purpose of auto-detecting these dependencies. Please take a look at D71306 for all the details. The summary is that all optional dependencies default to Auto: where we enable them if we can find them. You can override this behavior by passing LLDB_ENABLE_PYTHON=ON to CMake, in which case not finding Python (or SWIG) will be a fatal error.

I agree that it can be confusing to figure out that Python got disabled because SWIG wasn't found. Currently we call find_package with QUIET from FindPythonInterpAndLibs.cmake and FindLuaAndSwig.cmake. I think we should remove that so that the user gets more information in CMake's configuration output. Would that address your concerns?

[mattd]

In D74917#1885621, @JDevlieghere wrote:

In D74917#1885615, @mattd wrote:

In D74917#1885590, @JDevlieghere wrote:

It should never be possible for LLDB_ENABLE_PYTHON to be true but SWIG_FOUND to be false. The modules FindPythonInterpAndLibs.cmake and FindLuaAndSwig.cmake should fail early when SWIG isn't found.

Thanks for taking a look. Would you be okay with making the status message() in FindPythonInterpAndLibs.cmake and FindLuaAndSwig.cmake fatal, that way the dependency error is clearer?

That would defeat the purpose of auto-detecting these dependencies. Please take a look at D71306 for all the details. The summary is that all optional dependencies default to Auto: where we enable them if we can find them. You can override this behavior by passing LLDB_ENABLE_PYTHON=ON to CMake, in which case not finding Python (or SWIG) will be a fatal error.

Thanks for the clarification there.

I agree that it can be confusing to figure out that Python got disabled because SWIG wasn't found. Currently we call find_package with QUIET from FindPythonInterpAndLibs.cmake and FindLuaAndSwig.cmake. I think we should remove that so that the user gets more information in CMake's configuration output. Would that address your concerns?

Ah, yes, dropping the QUIET produces meaningful insight as to what might be missing. I think others, who might not have all the dependencies, might find this level of verbosity clearer, so that they can more quickly understand what is missing in their build environment.

[JDevlieghere]

LGMT. Thank you!

lldb/cmake/modules/FindLuaAndSwig.cmake

 #.rst:
 # FindLuaAndSwig
 # --------------
 #
 # Find Lua and SWIG as a whole.
 
 if(LUA_LIBRARIES AND LUA_INCLUDE_DIR AND SWIG_EXECUTABLE)
   set(LUAANDSWIG_FOUND TRUE)
 else()
-  find_package(SWIG 2.0 QUIET)
+  find_package(SWIG 2.0)
   if (SWIG_FOUND)
-    find_package(Lua QUIET)
+    find_package(Lua)
     if(LUA_FOUND AND SWIG_FOUND)
       mark_as_advanced(
         LUA_LIBRARIES
         LUA_INCLUDE_DIR
         SWIG_EXECUTABLE)
     endif()
   else()
     message(STATUS "SWIG 2 or later is required for Lua support in LLDB but could not be found")

lldb/cmake/modules/FindPythonInterpAndLibs.cmake

 #.rst:
 # FindPythonInterpAndLibs
 # -----------
 #
 # Find the python interpreter and libraries as a whole.
 
 if(PYTHON_LIBRARIES AND PYTHON_INCLUDE_DIRS AND PYTHON_EXECUTABLE AND SWIG_EXECUTABLE)
   set(PYTHONINTERPANDLIBS_FOUND TRUE)
 else()
-  find_package(SWIG 2.0 QUIET)
+  find_package(SWIG 2.0)
   if (SWIG_FOUND)
     if ("${CMAKE_SYSTEM_NAME}" STREQUAL "Windows")
-      find_package(Python3 COMPONENTS Interpreter Development QUIET)
+      find_package(Python3 COMPONENTS Interpreter Development)
       if (Python3_FOUND AND Python3_Interpreter_FOUND)
         set(PYTHON_LIBRARIES ${Python3_LIBRARIES})
         set(PYTHON_INCLUDE_DIRS ${Python3_INCLUDE_DIRS})
         set(PYTHON_EXECUTABLE ${Python3_EXECUTABLE})
         mark_as_advanced(
           PYTHON_LIBRARIES
           PYTHON_INCLUDE_DIRS
           PYTHON_EXECUTABLE
           SWIG_EXECUTABLE)
       endif()
     else()
-      find_package(PythonInterp QUIET)
-      find_package(PythonLibs QUIET)
+      find_package(PythonInterp)
+      find_package(PythonLibs)
       if(PYTHONINTERP_FOUND AND PYTHONLIBS_FOUND AND SWIG_FOUND)
         if (NOT CMAKE_CROSSCOMPILING)
           string(REPLACE "." ";" pythonlibs_version_list ${PYTHONLIBS_VERSION_STRING})
           list(GET pythonlibs_version_list 0 pythonlibs_major)
           list(GET pythonlibs_version_list 1 pythonlibs_minor)
 
           # Ignore the patch version. Some versions of macOS report a different
           # patch version for the system provided interpreter and libraries.