Added build capability switches in the shared Windows props file so optional components are only enabled when their prerequisites exist:

Python3Enabled (python executable + import lib + cffi)
   PerlEnabled (perl executable + perl runtime DLL + gendef.exe)
   InstallerEnabled (Inno Setup iscc.exe).
Updated the Python plugin project to compile only when Python3Enabled is true, and otherwise emit a clear skip message instead of failing prebuild/import steps.
Updated the Perl plugin project similarly to gate build steps on PerlEnabled and print a skip message when prerequisites are missing.
Updated the installer project so it only uses C++ targets when InstallerEnabled is true, with a fallback skip message when Inno Setup is unavailable.

plugins/perl/perl.vcxproj

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project DefaultTargets="Build" ToolsVersion="12.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup Label="Configuration">
     <PlatformToolset>v142</PlatformToolset>
@@ -27,7 +27,7 @@
     <TargetName>hcperl</TargetName>
     <OutDir>$(ZoiteChatRel)plugins\</OutDir>
   </PropertyGroup>
-  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+  <ItemDefinitionGroup Condition="'$(PerlEnabled)'=='true' and '$(Configuration)|$(Platform)'=='Release|Win32'">
     <ClCompile>
       <PreprocessorDefinitions>WIN32;NDEBUG;_WINDOWS;_USRDLL;PERL520_EXPORTS;HAS_BOOL;$(OwnFlags);%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <AdditionalIncludeDirectories>$(IntDir);..\..\src\common;$(ZoiteChatLib);$(PerlPath)\lib\CORE;$(Glib);%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
@@ -47,7 +47,7 @@ move irc.pm.h "$(IntDir)"
 move zoitechat.pm.h "$(IntDir)"</Command>
     </PreBuildEvent>
   </ItemDefinitionGroup>
-  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
+  <ItemDefinitionGroup Condition="'$(PerlEnabled)'=='true' and '$(Configuration)|$(Platform)'=='Release|x64'">
     <ClCompile>
       <PreprocessorDefinitions>WIN32;_WIN64;_AMD64_;NDEBUG;_WINDOWS;_USRDLL;PERL520_EXPORTS;HAS_BOOL;$(OwnFlags);%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <AdditionalIncludeDirectories>$(IntDir);..\..\src\common;$(ZoiteChatLib);$(PerlPath)\lib\CORE;$(Glib);%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
@@ -70,8 +70,11 @@ move zoitechat.pm.h "$(IntDir)"</Command>
   <ItemGroup>
     <None Include="perl.def" />
   </ItemGroup>
-  <ItemGroup>
+  <ItemGroup Condition="'$(PerlEnabled)'=='true'">
     <ClCompile Include="perl.c" />
   </ItemGroup>
-  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" Condition="'$(PerlEnabled)'=='true'" />
+  <Target Name="Build" Condition="'$(PerlEnabled)'!='true'">
+    <Message Text="Perl build prerequisites not found (perl/gendef/runtime); skipping Perl plugin build." Importance="high" />
+  </Target>
 </Project>

plugins/python/python3.vcxproj

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project DefaultTargets="Build" ToolsVersion="12.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup Label="Configuration">
     <PlatformToolset>v142</PlatformToolset>
@@ -27,7 +27,7 @@
     <TargetName>$(Python3Output)</TargetName>
     <OutDir>$(ZoiteChatRel)plugins\</OutDir>
   </PropertyGroup>
-  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+  <ItemDefinitionGroup Condition="'$(Python3Enabled)'=='true' and '$(Configuration)|$(Platform)'=='Release|Win32'">
     <ClCompile>
       <PreprocessorDefinitions>WIN32;NDEBUG;_WINDOWS;_USRDLL;PYTHON_EXPORTS;$(OwnFlags);%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <AdditionalIncludeDirectories>$(Glib);$(Python3Path)\include;..\..\src\common;$(ZoiteChatLib);%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
@@ -41,7 +41,7 @@
       <Command>"$(Python3Path)\python.exe" generate_plugin.py ..\..\src\common\zoitechat-plugin.h python.py "$(IntDir)python.c"</Command>
     </PreBuildEvent>
   </ItemDefinitionGroup>
-  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
+  <ItemDefinitionGroup Condition="'$(Python3Enabled)'=='true' and '$(Configuration)|$(Platform)'=='Release|x64'">
     <ClCompile>
       <PreprocessorDefinitions>WIN32;_WIN64;_AMD64_;NDEBUG;_WINDOWS;_USRDLL;PYTHON_EXPORTS;$(OwnFlags);%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <AdditionalIncludeDirectories>$(Glib);$(Python3Path)\include;..\..\src\common;$(ZoiteChatLib);%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
@@ -63,8 +63,11 @@
     <None Include="xchat.py" />
     <None Include="_zoitechat.py" />
   </ItemGroup>
-  <ItemGroup>
+  <ItemGroup Condition="'$(Python3Enabled)'=='true'">
     <ClCompile Include="$(IntDir)python.c" />
   </ItemGroup>
-  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" Condition="'$(Python3Enabled)'=='true'" />
+  <Target Name="Build" Condition="'$(Python3Enabled)'!='true'">
+    <Message Text="Python 3 build prerequisites not found (python/cffi/libs); skipping Python plugin build." Importance="high" />
+  </Target>
 </Project>

win32/installer/installer.vcxproj

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project DefaultTargets="Build" ToolsVersion="12.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup Label="Configuration">
     <PlatformToolset>v142</PlatformToolset>
@@ -49,5 +49,8 @@ $(IsccPath) /dPROJECTDIR="$(ProjectDir)" /dAPPARCH="$(Platform)" "$(ZoiteChatBin
     <None Include="wizardsmallimage.bmp" />
     <None Include="zoitechat.iss" />
   </ItemGroup>
-  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" Condition="'$(InstallerEnabled)'=='true'" />
+  <Target Name="Build" Condition="'$(InstallerEnabled)'!='true'">
+    <Message Text="Inno Setup (iscc.exe) not found; skipping installer build." Importance="high" />
+  </Target>
 </Project>

win32/zoitechat.props

@@ -29,6 +29,12 @@
 		<Python3Path>$(YourPython3Path)\$(PlatformName)</Python3Path>
 		<Python3Lib>python314</Python3Lib>
 		<Python3Output>hcpython3</Python3Output>
+		<Python3Enabled Condition="Exists('$(Python3Path)\\python.exe') and Exists('$(Python3Path)\\libs\\$(Python3Lib).lib') and Exists('$(Python3Path)\\Lib\\site-packages\\cffi')">true</Python3Enabled>
+		<Python3Enabled Condition="'$(Python3Enabled)'==''">false</Python3Enabled>
+		<PerlEnabled Condition="Exists('$(PerlPath)\\bin\\perl.exe') and Exists('$(PerlPath)\\bin\\$(PerlLib).dll') and Exists('$(GendefPath)\\gendef.exe')">true</PerlEnabled>
+		<PerlEnabled Condition="'$(PerlEnabled)'==''">false</PerlEnabled>
+		<InstallerEnabled Condition="Exists($(IsccPath))">true</InstallerEnabled>
+		<InstallerEnabled Condition="'$(InstallerEnabled)'==''">false</InstallerEnabled>
 		<LuaInclude>$(DepsRoot)\include\luajit-2.1;$(DepsRoot)\include\lua;$(DepsRoot)\include\lua5.1;$(DepsRoot)\include\lua54;$(DepsRoot)\include\lua5.4;$(DepsRoot)\include\lua-5.4;$(SolutionDir)..\plugins\lua\luajit\src;$(SolutionDir)..\plugins\lua\luajit\src\jit</LuaInclude>
 		<LuaOutput>hclua</LuaOutput>
 		<LuaEnabled Condition="Exists('$(DepsRoot)\\include\\lua.h')">true</LuaEnabled>