Add the first Conan-based dependecies

add_conan_lib cmake function is defined, that allows to add a dependency using Conan with two possible system fallbacks:

1. pkg_check_modules is invoked, if `PGK_CONFIG ...` is present
2. find_package is invoked if `FIND_PACKAGE_OPTIONS` is present and `pkg_check_modules` has failed

If `ALWAYS_ALLOW_CONAN_FALLBACK` is present - `obey_system_dependencies` will be ignored for the package

Currently, the following dependencies are retrieved using Conan:

* zlib
* expat
* wxwidgets
* libmp3lame
* libid3tag
* libmad

The last three libraries are included in this commit, as they depend on zlib.
Properly pass **arch** and **os.version** to Conan

CMakeLists.txt

@@ -97,7 +97,18 @@ if( APPLE )
 endif()
 
 # Add our module path
-set( CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/cmake-proxies/cmake-modules)
+# CMAKE_BINARY_DIR is required for Conan to work
+set( AUDACITY_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake-proxies/cmake-modules")
+set( CMAKE_MODULE_PATH 
+   ${AUDACITY_MODULE_PATH}
+   ${CMAKE_BINARY_DIR}
+   ${CMAKE_MODULE_PATH} 
+)
+
+set( CMAKE_PREFIX_PATH
+   ${CMAKE_BINARY_DIR}
+   ${CMAKE_PREFIX_PATH}
+)
 
 # This "is a good thing" but greatly increases link time on Linux
 #set( CMAKE_INTERPROCEDURAL_OPTIMIZATION ON )
@@ -116,6 +127,9 @@ if( CCACHE_PROGRAM )
    set_property( GLOBAL PROPERTY RULE_LAUNCH_COMPILE "${CCACHE_PROGRAM}" )
 endif()
 
+# Define option() prefix
+set( _OPT "audacity_" )
+
 # Our very own project
 project( Audacity )
 
@@ -125,7 +139,7 @@ include( AudacityFunctions )
 # Allow user to globally set the library preference
 cmd_option( ${_OPT}lib_preference
             "Library preference [system (if available), local]"
-            "local"
+            "system"
             STRINGS "system" "local"
 )
 
@@ -215,9 +229,6 @@ endif()
 message( STATUS "  Current Commit: ${GIT_COMMIT_SHORT}" )
 message( STATUS )
 
-# Define option() prefix
-set( _OPT "audacity_" )
-
 # Organize subdirectories/targets into folders for the IDEs
 set_property( GLOBAL PROPERTY USE_FOLDERS ON )
 
@@ -437,6 +448,7 @@ find_package( Python3 )
 if( Python3_FOUND )
    set( PYTHON "${Python3_EXECUTABLE}" )
 elseif( CMAKE_SYSTEM_NAME MATCHES "Windows" )
+   # This is an odd case now, as Conan requires Python as well
    nuget_package( pkgdir "python3" "3.7.7" )
    file( TO_NATIVE_PATH "${pkgdir}/tools/python.exe" PYTHON )
 endif()
@@ -447,6 +459,10 @@ include( "src/Experimental.cmake" )
 
 # Add our children
 add_subdirectory( "cmake-proxies" )
+
+# Conan uses find_package and does not set GLOBAL flag
+resolve_conan_dependencies()
+
 add_subdirectory( "help" )
 add_subdirectory( "images" )
 add_subdirectory( "libraries" )

cmake-proxies/CMakeLists.txt

@@ -1,22 +1,96 @@
-# Allow user to globally set the library preference
-cmd_option( ${_OPT}lib_preference
-            "Library preference [system (if available), local]"
-            "system"
-            STRINGS "system" "local"
+add_conan_lib(
+   ZLIB
+   zlib/1.2.11
+   REQUIRED
+   PGK_CONFIG "zlib >= 1.2.11"
+   INTERFACE_NAME ZLIB::ZLIB
+   OPTION_NAME zlib
+   CONAN_OPTIONS 
+      zlib:shared=True
 )
 
-# Special mode, that will force dependencies to the packages provided by system unless they were set to local explicitly.
-cmd_option( ${_OPT}obey_system_dependencies
-            "Use system packages to satisfy dependencies"
-            Off
+add_conan_lib(
+   expat
+   expat/2.2.9
+   REQUIRED
+   PGK_CONFIG "expat >= 2.1.0"
+   CONAN_OPTIONS 
+      expat:shared=True
 )
 
+set(wx_zlib "zlib")
+set(wx_png "libpng")
+
+if (${_OPT}use_zlib STREQUAL "system")
+   set(wx_zlib "sys")
+   # To prevent linking conflicts - we need to use system libpng as well.
+   # wxWdigets will attempt to resolve it using find_package
+   set(wx_png "sys")
+endif()
+
+set(wx_expat "expat")
+
+if (${_OPT}use_expat STREQUAL "system")
+   set(wx_expat "sys")
+endif()
+
+add_conan_lib( 
+   wxWidgets 
+   wxwidgets/3.1.3-audacity 
+   REQUIRED 
+   ALWAYS_ALLOW_CONAN_FALLBACK
+   OPTION_NAME wxwidgets
+   FIND_PACKAGE_OPTIONS COMPONENTS adv base core html qa xml net
+   INTERFACE_NAME wxwidgets::wxwidgets
+   CONAN_OPTIONS 
+      wxwidgets:shared=True
+      wxwidgets:zlib=${wx_zlib}
+      wxwidgets:expat=${wx_expat}
+      wxwidgets:compatibility=3.0
+      wxwidgets:png=${wx_png}
+      wxwidgets:tiff=off
+      wxwidgets:secretstore=False
+      wxwidgets:opengl=False
+      wxwidgets:propgrid=False
+      wxwidgets:ribbon=False
+      wxwidgets:richtext=False
+      wxwidgets:stc=False
+      wxwidgets:webview=False
+      wxwidgets:help=False
+      wxwidgets:html_help=False
+      wxwidgets:fs_inet=False
+      wxwidgets:protocol=False
+)
+
+add_conan_lib(
+   libmp3lame
+   libmp3lame/3.100
+   REQUIRED
+   INTERFACE_NAME libmp3lame::libmp3lame
+   PGK_CONFIG "lame >= 3.100"
+)
+
+add_conan_lib(
+   libid3tag
+   libid3tag/0.15.1b
+   OPTION_NAME id3tag
+   HAS_ONLY_DEBUG_RELEASE
+   PGK_CONFIG "id3tag >= 0.15.1b"
+)
+
+add_conan_lib(
+   libmad
+   libmad/0.15.1b
+   OPTION_NAME mad
+   HAS_ONLY_DEBUG_RELEASE
+   PGK_CONFIG "mad >= 0.15.1b"
+)
+
+set_conan_vars_to_parent()
+
 # Required libraries
 #
 #       directory          option      symbol      req   chk   version
-addlib( wxWidgets          wxwidgets   WX          YES   NO    "" ) # must be first
-addlib( expat              expat       EXPAT       YES   YES   "expat >= 2.1.0" )
-addlib( lame               lame        LAME        YES   YES   "lame >= 3.100" )
 addlib( libsndfile         sndfile     SNDFILE     YES   YES   "sndfile >= 1.0.28" )
 addlib( libsoxr            soxr        SOXR        YES   YES   "soxr >= 0.1.1" )
 addlib( portaudio-v19      portaudio   PORTAUDIO   YES   YES   "" )
@@ -26,8 +100,6 @@ addlib( sqlite             sqlite      SQLITE      YES   YES   "sqlite3 >= 3.32.
 #
 #       directory          option      symbol      req   chk   version
 addlib( ffmpeg             ffmpeg      FFMPEG      NO    NO    "libavcodec >= 51.53" "libavformat >= 52.12" "libavutil >= 52.66" )
-addlib( libid3tag          id3tag      LIBID3TAG   NO    YES   "id3tag >= 0.15.1b" )
-addlib( libmad             mad         LIBMAD      NO    YES   "mad >= 0.15.1b" )
 addlib( libnyquist         nyquist     NYQUIST     NO    YES   "" )
 addlib( libvamp            vamp        VAMP        NO    YES   "vamp >= 2.5" "vamp-hostsdk >= 2.5" )
 addlib( libogg             ogg         LIBOGG      NO    YES   "ogg >= 1.3.1" )
@@ -53,4 +125,3 @@ addlib( portsmf            portsmf     PORTSMF     NO    YES   "portSMF >= 0.1"
 addlib( libsbsms           sbsms       SBSMS       NO    YES   "sbsms >= 2.2.0" )
 addlib( soundtouch         soundtouch  SOUNDTOUCH  NO    YES   "soundtouch >= 1.7.1" )
 addlib( twolame            twolame     LIBTWOLAME  NO    YES   "twolame >= 0.3.13" )
-