Add BUILD_BOTH_LIBRARIES option to build static and shared libs

Add a new CMake option BUILD_BOTH_LIBRARIES that allows building both
static and shared libraries in a single build directory.

This provides an alternative to the existing approach of building in
separate directories with BUILD_SHARED_LIBS=ON/OFF, while maintaining
backward compatibility with existing build scripts.

Usage:
  cmake .. -DBUILD_BOTH_LIBRARIES=ON

Produces:
  - libcpp_dotenv_static.a
  - libcpp_dotenv_shared.so (or .dylib on macOS)

Author: renecannao

CMakeLists.txt

@@ -12,36 +12,68 @@ else()
 endif()
 message(STATUS "Building CPP-DOTENV in ${CMAKE_BUILD_TYPE} mode")
 
+# Option to build both static and shared libraries
+option(BUILD_BOTH_LIBRARIES "Build both static and shared libraries" OFF)
+
 #------------------- SUBDIRECTORY ADDITION ------------------------------------
 
 add_subdirectory(common)
 add_subdirectory(src)
 
 #----------------------- LIBRARY CONFIGURATION --------------------------------
 
-set(CPP_DOTENV cpp_dotenv CACHE INTERNAL "")
 set(CPP_DOTENV_SRC
     src/dotenv.cpp
     include/dotenv.h
 )
 
-add_library(${CPP_DOTENV} ${CPP_DOTENV_SRC})
+# Common include directories
+set(CPP_DOTENV_INCLUDE_DIRS ${CMAKE_CURRENT_SOURCE_DIR}/include)
 
-target_link_libraries(${CPP_DOTENV}
-    ${ENVIRON_LIB}
-    ${PARSER_LIB}
-)
+# Common compile options
+if ("${CMAKE_BUILD_TYPE}" STREQUAL "DEBUG")
+    set(CPP_DOTENV_COMPILE_OPTIONS -g -Wall -O0)
+else()
+    set(CPP_DOTENV_COMPILE_OPTIONS -O3)
+endif()
 
-target_include_directories(${CPP_DOTENV} PUBLIC
-    ${CMAKE_CURRENT_SOURCE_DIR}/include
-)
+# Build both static and shared libraries if requested
+if(BUILD_BOTH_LIBRARIES)
+    # Static library
+    add_library(cpp_dotenv_static STATIC ${CPP_DOTENV_SRC})
+    target_link_libraries(cpp_dotenv_static
+        ${ENVIRON_LIB}
+        ${PARSER_LIB}
+    )
+    target_include_directories(cpp_dotenv_static PUBLIC ${CPP_DOTENV_INCLUDE_DIRS})
+    target_compile_options(cpp_dotenv_static PRIVATE ${CPP_DOTENV_COMPILE_OPTIONS})
 
-if ("${CMAKE_BUILD_TYPE}" STREQUAL "DEBUG")
-    target_compile_options(${CPP_DOTENV} PRIVATE
-        -g -Wall -O0
+    # Shared library
+    add_library(cpp_dotenv_shared SHARED ${CPP_DOTENV_SRC})
+    target_link_libraries(cpp_dotenv_shared
+        ${ENVIRON_LIB}
+        ${PARSER_LIB}
     )
+    target_include_directories(cpp_dotenv_shared PUBLIC ${CPP_DOTENV_INCLUDE_DIRS})
+    target_compile_options(cpp_dotenv_shared PRIVATE ${CPP_DOTENV_COMPILE_OPTIONS})
+
+    # Alias for compatibility - default to static
+    add_library(cpp_dotenv ALIAS cpp_dotenv_static)
 else()
+    # Single library (type determined by BUILD_SHARED_LIBS)
+    set(CPP_DOTENV cpp_dotenv CACHE INTERNAL "")
+    add_library(${CPP_DOTENV} ${CPP_DOTENV_SRC})
+
+    target_link_libraries(${CPP_DOTENV}
+        ${ENVIRON_LIB}
+        ${PARSER_LIB}
+    )
+
+    target_include_directories(${CPP_DOTENV} PUBLIC
+        ${CPP_DOTENV_INCLUDE_DIRS}
+    )
+
     target_compile_options(${CPP_DOTENV} PRIVATE
-        -O3
+        ${CPP_DOTENV_COMPILE_OPTIONS}
     )
 endif()