cmake: support BUILD_SHARED_LIBS built-in option

Support building internal libraries as shared. This reduces
development time by eliminating the need to re-link all
binaries every time non-interface code in the library changes.
Instead, can hack on libxyz, then `make libxyz`, and re-run
monerod.

By default BUILD_SHARED_LIBS is OFF in release build type,
and ON in debug build type, but can be overriden with -D.

CMakeLists.txt

@@ -49,6 +49,7 @@ if(NOT CMAKE_BUILD_TYPE)
   set(CMAKE_BUILD_TYPE Release CACHE STRING "Build type" FORCE)
   message(STATUS "Setting default build type: ${CMAKE_BUILD_TYPE}")
 endif()
+string(TOLOWER ${CMAKE_BUILD_TYPE} CMAKE_BUILD_TYPE_LOWER)
 
 # ARCH defines the target architecture, either by an explicit identifier or
 # one of the following two keywords. By default, ARCH a value of 'native':
@@ -179,6 +180,17 @@ else()
 endif()
 option(STATIC "Link libraries statically" ${DEFAULT_STATIC})
 
+# This is a CMake built-in switch that concerns internal libraries
+if (NOT DEFINED BUILD_SHARED_LIBS AND NOT STATIC AND CMAKE_BUILD_TYPE_LOWER STREQUAL "debug")
+    set(BUILD_SHARED_LIBS ON CACHE STRING "Build internal libs as shared")
+endif()
+if (BUILD_SHARED_LIBS)
+  message(STATUS "Building internal libraries as shared")
+  set(PIC_FLAG "-fPIC")
+else()
+  message(STATUS "Building internal libraries as static")
+endif()
+
 if(MINGW)
   string(REGEX MATCH "^[^/]:/[^/]*" msys2_install_path "${CMAKE_C_COMPILER}")
   message(STATUS "MSYS location: ${msys2_install_path}")
@@ -365,8 +377,8 @@ else()
     set(COVERAGE_FLAGS "-fprofile-arcs -ftest-coverage --coverage")
   endif()
 
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c11 -D_GNU_SOURCE ${MINGW_FLAG} ${STATIC_ASSERT_FLAG} ${WARNINGS} ${C_WARNINGS} ${ARCH_FLAG} ${COVERAGE_FLAGS}")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c11 -D_GNU_SOURCE ${MINGW_FLAG} ${STATIC_ASSERT_FLAG} ${WARNINGS} ${C_WARNINGS} ${ARCH_FLAG} ${COVERAGE_FLAGS} ${PIC_FLAG}")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -D_GNU_SOURCE ${MINGW_FLAG} ${WARNINGS} ${CXX_WARNINGS} ${ARCH_FLAG} ${COVERAGE_FLAGS}")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -D_GNU_SOURCE ${MINGW_FLAG} ${WARNINGS} ${CXX_WARNINGS} ${ARCH_FLAG} ${COVERAGE_FLAGS} ${PIC_FLAG}")
 
   # With GCC 6.1.1 the compiled binary malfunctions due to aliasing. Until that
   # is fixed in the code (Issue #847), force compiler to be conservative.

contrib/otshell_utils/CMakeLists.txt

@@ -9,6 +9,6 @@ file(GLOB otshell_utils_sources # All files in directory:
 	"*.cpp"
 )
 
-add_library (otshell_utils STATIC ${otshell_utils_sources})
+add_library (otshell_utils ${otshell_utils_sources})
 set_target_properties (otshell_utils PROPERTIES OUTPUT_NAME "otshell_utils")
 #target_link_libraries (upnpc-static ${LDLIBS}) # to add used libs

src/CMakeLists.txt

@@ -88,7 +88,7 @@ function (bitmonero_add_library name)
   # libwallet, which combines multiple components.
   set(objlib obj_${name})
   add_library(${objlib} OBJECT ${ARGN})
-  add_library("${name}" STATIC $<TARGET_OBJECTS:${objlib}>)
+  add_library("${name}" $<TARGET_OBJECTS:${objlib}>)
   set_property(TARGET "${name}"
     PROPERTY
       FOLDER "libs")