Improve ext/com_dotnet extension configuration

The <mscoree.h> is part of the .NET Framework (.NET Framework versions 4
and earlier). The current .NET implementations (version 5 don't have
this header and API anymore).

This at least errors out to make the user aware of this and what needs
to be installed.

Author: petk

cmake/cmake/platforms/Windows.cmake

@@ -109,7 +109,6 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Windows")
   set(HAVE_MMAP FALSE)
   set(HAVE_MPROTECT FALSE)
   set(HAVE_MREMAP FALSE)
-  set(HAVE_MSCOREE_H TRUE)
   set(HAVE_NET_IF_H FALSE)
   set(HAVE_NETDB_H FALSE)
   set(HAVE_NETINET_IN_H FALSE)

cmake/ext/com_dotnet/CMakeLists.txt

@@ -8,19 +8,46 @@ This extension provides the Component Object Model (COM) and .NET support.
 > [!NOTE]
 > This extension is available only when the target system is Windows.
 
-## PHP_EXT_COM_DOTNET
+## Requirements
+
+To build this extension, Windows SDK needs to be installed, which includes
+the COM support.
+
+To enable also the .NET support in this extension (e.g., the `dotnet` PHP
+class), the .NET framework needs to be installed, which provides the
+`<mscoree.h>` header. This can be done in several ways:
+
+* in Visual Studio by installing the .NET desktop development workload
+* in Visual Studio by installing the .NET framework 4.x component only
+* Download and install
+  [.NET framework](https://dotnet.microsoft.com/en-us/download/dotnet-framework)
+  manually.
+
+The .NET version 5 and later are not supported as they have removed the
+`<mscoree.h>` API.
+
+## Configuration options
+
+### PHP_EXT_COM_DOTNET
 
 * Default: `ON`
 * Values: `ON|OFF`
 
-Enable the extension.
+Enables the extension.
 
-## PHP_EXT_COM_DOTNET_SHARED
+### PHP_EXT_COM_DOTNET_SHARED
 
 * Default: `OFF`
 * Values: `ON|OFF`
 
-Build extension as shared.
+Builds extension as shared.
+
+### PHP_EXT_COM_DOTNET_ENABLE_DOTNET
+
+* Default: `ON`
+* Values: `ON|OFF`
+
+Enables the .NET Framework support.
 #]=============================================================================]
 
 cmake_minimum_required(VERSION 3.29...4.0)
@@ -54,6 +81,14 @@ cmake_dependent_option(
   OFF
 )
 
+cmake_dependent_option(
+  PHP_EXT_COM_DOTNET_ENABLE_DOTNET
+  "Enable .NET support"
+  ON
+  PHP_EXT_COM_DOTNET
+  OFF
+)
+
 if(NOT PHP_EXT_COM_DOTNET)
   return()
 endif()
@@ -91,7 +126,20 @@ target_compile_definitions(
 
 target_link_libraries(php_ext_com_dotnet PRIVATE oleaut32)
 
-check_include_files(mscoree.h HAVE_MSCOREE_H)
+if(PHP_EXT_COM_DOTNET_ENABLE_DOTNET)
+  check_include_files(mscoree.h PHP_EXT_COM_DOTNET_HAS_MSCOREE_H)
+
+  if(NOT PHP_EXT_COM_DOTNET_HAS_MSCOREE_H)
+    message(
+      FATAL_ERROR
+      "<mscoree.h> not found. Please install the .NET Framework or disable the "
+      ".NET support with by setting 'PHP_EXT_COM_DOTNET_ENABLE_DOTNET' to "
+      "'OFF'."
+    )
+  endif()
+
+  set(HAVE_MSCOREE_H TRUE)
+endif()
 
 set(HAVE_COM_DOTNET TRUE)