Minor cmake fix & cleanup (#1754)

* Reorder cmake docs a bit

Just wanted to group the more related build options together.

Also removed a pointless reference to the old reasoning for the required
min ver since it's 3.14 now anyways.

* Fix outdated cmake comment

We don't use Git to find the version string anymore.
Just updated to match what it's actually used for now.

* Group options and build-tree vars in Cmake

Doesn't really change anything, I just wanted to clean these up a bit.

* Fix how we set HTTPLIB_IS_USING_XXX vars in Cmake

Prevents us acidentally using libs when the user didn't want them
actually used. This could happen if they set the option to OFF but their
own project itself is using the lib, thus we'd find and use it anyways.

Ref #1602 to see an example of this already happening before.
This is merely apply that kind of fix to all 3 of our deps, instead of
just OpenSSL.

* Minor formatting/comment change to Cmake

Pointless, but these things were bothering me..

CMakeLists.txt

@@ -3,11 +3,11 @@
 	* BUILD_SHARED_LIBS (default off) builds as a shared library (if HTTPLIB_COMPILE is ON)
 	* HTTPLIB_USE_OPENSSL_IF_AVAILABLE (default on)
 	* HTTPLIB_USE_ZLIB_IF_AVAILABLE (default on)
+	* HTTPLIB_USE_BROTLI_IF_AVAILABLE (default on)
 	* HTTPLIB_REQUIRE_OPENSSL (default off)
 	* HTTPLIB_REQUIRE_ZLIB (default off)
-	* HTTPLIB_USE_BROTLI_IF_AVAILABLE (default on)
-	* HTTPLIB_USE_CERTS_FROM_MACOSX_KEYCHAIN (default on)
 	* HTTPLIB_REQUIRE_BROTLI (default off)
+	* HTTPLIB_USE_CERTS_FROM_MACOSX_KEYCHAIN (default on)
 	* HTTPLIB_COMPILE (default off)
 	* HTTPLIB_INSTALL (default on)
 	* HTTPLIB_TEST (default off)
@@ -59,7 +59,6 @@
 
 	-------------------------------------------------------------------------------
 
-	FindPython3 requires Cmake v3.12
 	ARCH_INDEPENDENT option of write_basic_package_version_file() requires Cmake v3.14
 ]]
 cmake_minimum_required(VERSION 3.14.0 FATAL_ERROR)
@@ -69,20 +68,19 @@ cmake_minimum_required(VERSION 3.14.0 FATAL_ERROR)
 # This is so the maintainer doesn't actually need to update this manually.
 file(STRINGS httplib.h _raw_version_string REGEX "CPPHTTPLIB_VERSION \"([0-9]+\\.[0-9]+\\.[0-9]+)\"")
 
-# Needed since git tags have "v" prefixing them.
-# Also used if the fallback to user agent string is being used.
+# Extracts just the version string itself from the whole string contained in _raw_version_string
+# since _raw_version_string would contain the entire line of code where it found the version string
 string(REGEX MATCH "([0-9]+\\.?)+" _httplib_version "${_raw_version_string}")
 
 project(httplib VERSION ${_httplib_version} LANGUAGES CXX)
 
-# Lets you disable C++ exception during CMake configure time.
-# The value is used in the install CMake config file.
-option(HTTPLIB_NO_EXCEPTIONS "Disable the use of C++ exceptions" OFF)
-
 # Change as needed to set an OpenSSL minimum version.
 # This is used in the installed Cmake config file.
 set(_HTTPLIB_OPENSSL_MIN_VER "3.0.0")
 
+# Lets you disable C++ exception during CMake configure time.
+# The value is used in the install CMake config file.
+option(HTTPLIB_NO_EXCEPTIONS "Disable the use of C++ exceptions" OFF)
 # Allow for a build to require OpenSSL to pass, instead of just being optional
 option(HTTPLIB_REQUIRE_OPENSSL "Requires OpenSSL to be found & linked, or fails build." OFF)
 option(HTTPLIB_REQUIRE_ZLIB "Requires ZLIB to be found & linked, or fails build." OFF)
@@ -94,10 +92,6 @@ option(HTTPLIB_USE_ZLIB_IF_AVAILABLE "Uses ZLIB (if available) to enable Zlib co
 option(HTTPLIB_COMPILE "If ON, uses a Python script to split the header into a compilable header & source file (requires Python v3)." OFF)
 # Lets you disable the installation (useful when fetched from another CMake project)
 option(HTTPLIB_INSTALL "Enables the installation target" ON)
-# Just setting this variable here for people building in-tree
-if(HTTPLIB_COMPILE)
-	set(HTTPLIB_IS_COMPILED TRUE)
-endif()
 option(HTTPLIB_TEST "Enables testing and builds tests" OFF)
 option(HTTPLIB_REQUIRE_BROTLI "Requires Brotli to be found & linked, or fails build." OFF)
 option(HTTPLIB_USE_BROTLI_IF_AVAILABLE "Uses Brotli (if available) to enable Brotli decompression support." ON)
@@ -110,45 +104,48 @@ if (BUILD_SHARED_LIBS AND WIN32 AND HTTPLIB_COMPILE)
 	set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)
 endif()
 
+# Set some variables that are used in-tree and while building based on our options
+set(HTTPLIB_IS_COMPILED ${HTTPLIB_COMPILE})
+set(HTTPLIB_IS_USING_CERTS_FROM_MACOSX_KEYCHAIN ${HTTPLIB_USE_CERTS_FROM_MACOSX_KEYCHAIN})
+
 # Threads needed for <thread> on some systems, and for <pthread.h> on Linux
-set(THREADS_PREFER_PTHREAD_FLAG true)
+set(THREADS_PREFER_PTHREAD_FLAG TRUE)
 find_package(Threads REQUIRED)
 # Since Cmake v3.11, Crypto & SSL became optional when not specified as COMPONENTS.
 if(HTTPLIB_REQUIRE_OPENSSL)
 	find_package(OpenSSL ${_HTTPLIB_OPENSSL_MIN_VER} COMPONENTS Crypto SSL REQUIRED)
+	set(HTTPLIB_IS_USING_OPENSSL TRUE)
 elseif(HTTPLIB_USE_OPENSSL_IF_AVAILABLE)
 	find_package(OpenSSL ${_HTTPLIB_OPENSSL_MIN_VER} COMPONENTS Crypto SSL QUIET)
-endif()
-# Just setting this variable here for people building in-tree
-if(OPENSSL_FOUND AND NOT DEFINED HTTPLIB_IS_USING_OPENSSL)
-	set(HTTPLIB_IS_USING_OPENSSL TRUE)
+	# Avoid a rare circumstance of not finding all components but the end-user did their
+	# own call for OpenSSL, which might trick us into thinking we'd otherwise have what we wanted
+	if (TARGET OpenSSL::SSL AND TARGET OpenSSL::Crypto)
+		set(HTTPLIB_IS_USING_OPENSSL ${OPENSSL_FOUND})
+	else()
+		set(HTTPLIB_IS_USING_OPENSSL FALSE)
+	endif()
 endif()
 
 if(HTTPLIB_REQUIRE_ZLIB)
 	find_package(ZLIB REQUIRED)
+	set(HTTPLIB_IS_USING_ZLIB TRUE)
 elseif(HTTPLIB_USE_ZLIB_IF_AVAILABLE)
 	find_package(ZLIB QUIET)
-endif()
-# Just setting this variable here for people building in-tree
-# FindZLIB doesn't have a ZLIB_FOUND variable, so check the target.
-if(TARGET ZLIB::ZLIB)
-	set(HTTPLIB_IS_USING_ZLIB TRUE)
+	# FindZLIB doesn't have a ZLIB_FOUND variable, so check the target.
+	if(TARGET ZLIB::ZLIB)
+		set(HTTPLIB_IS_USING_ZLIB TRUE)
+	endif()
 endif()
 
 # Adds our cmake folder to the search path for find_package
+# This is so we can use our custom FindBrotli.cmake
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
 if(HTTPLIB_REQUIRE_BROTLI)
 	find_package(Brotli COMPONENTS encoder decoder common REQUIRED)
+	set(HTTPLIB_IS_USING_BROTLI TRUE)
 elseif(HTTPLIB_USE_BROTLI_IF_AVAILABLE)
 	find_package(Brotli COMPONENTS encoder decoder common QUIET)
-endif()
-# Just setting this variable here for people building in-tree
-if(Brotli_FOUND)
-	set(HTTPLIB_IS_USING_BROTLI TRUE)
-endif()
-
-if(HTTPLIB_USE_CERTS_FROM_MACOSX_KEYCHAIN)
-	set(HTTPLIB_IS_USING_CERTS_FROM_MACOSX_KEYCHAIN TRUE)
+	set(HTTPLIB_IS_USING_BROTLI ${Brotli_FOUND})
 endif()
 
 # Used for default, common dirs that the end-user can change (if needed)
@@ -204,9 +201,7 @@ endif()
 add_library(${PROJECT_NAME}::${PROJECT_NAME} ALIAS ${PROJECT_NAME})
 
 # Require C++11
-target_compile_features(${PROJECT_NAME} ${_INTERFACE_OR_PUBLIC}
-	cxx_std_11
-)
+target_compile_features(${PROJECT_NAME} ${_INTERFACE_OR_PUBLIC} cxx_std_11)
 
 target_include_directories(${PROJECT_NAME} SYSTEM ${_INTERFACE_OR_PUBLIC}
     $<BUILD_INTERFACE:${_httplib_build_includedir}>
@@ -273,9 +268,7 @@ if(HTTPLIB_INSTALL)
 	# Creates the export httplibTargets.cmake
 	# This is strictly what holds compilation requirements
 	# and linkage information (doesn't find deps though).
-	install(TARGETS ${PROJECT_NAME}
-		EXPORT httplibTargets
-	)
+	install(TARGETS ${PROJECT_NAME} EXPORT httplibTargets)
 
 	install(FILES "${_httplib_build_includedir}/httplib.h" TYPE INCLUDE)