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MSBuild Anti-Pattern Catalog

A numbered catalog of common MSBuild anti-patterns. Each entry follows the format:

• Smell : What to look for
• Why it's bad : Impact on builds, maintainability, or correctness
• Fix : Concrete transformation

Use this catalog when scanning project files for improvements.

AP-01: <Exec> for Operations That Have Built-in Tasks

Smell : <Exec Command="mkdir ..." />, <Exec Command="copy ..." />, <Exec Command="del ..." />

Why it's bad : Built-in tasks are cross-platform, support incremental build, emit structured logging, and handle errors consistently. <Exec> is opaque to MSBuild.

<!-- BAD -->
<Target Name="PrepareOutput">
  <Exec Command="mkdir $(OutputPath)logs" />
  <Exec Command="copy config.json $(OutputPath)" />
  <Exec Command="del $(IntermediateOutputPath)*.tmp" />
</Target>

<!-- GOOD -->
<Target Name="PrepareOutput">
  <MakeDir Directories="$(OutputPath)logs" />
  <Copy SourceFiles="config.json" DestinationFolder="$(OutputPath)" />
  <Delete Files="@(TempFiles)" />
</Target>

Built-in task alternatives:

AP-02: Unquoted Condition Expressions

Smell : Condition="$(Foo) == Bar" — either side of a comparison is unquoted.

Why it's bad : If the property is empty or contains spaces/special characters, the condition evaluates incorrectly or throws a parse error. MSBuild requires single-quoted strings for reliable comparisons.

<!-- BAD -->
<PropertyGroup Condition="$(Configuration) == Release">
  <Optimize>true</Optimize>
</PropertyGroup>

<!-- GOOD -->
<PropertyGroup Condition="'$(Configuration)' == 'Release'">
  <Optimize>true</Optimize>
</PropertyGroup>

Rule : Always quote both sides of == and != comparisons with single quotes.

AP-03: Hardcoded Absolute Paths

Smell : Paths like C:\tools\, D:\packages\, /usr/local/bin/ in project files.

Why it's bad : Breaks on other machines, CI environments, and other operating systems. Not relocatable.

<!-- BAD -->
<PropertyGroup>
  <ToolPath>C:\tools\mytool\mytool.exe</ToolPath>
</PropertyGroup>
<Import Project="C:\repos\shared\common.props" />

<!-- GOOD -->
<PropertyGroup>
  <ToolPath>$(MSBuildThisFileDirectory)tools\mytool\mytool.exe</ToolPath>
</PropertyGroup>
<Import Project="$(RepoRoot)eng\common.props" />

Preferred path properties:

AP-04: Restating SDK Defaults

Smell : Properties set to values that the .NET SDK already provides by default.

Why it's bad : Adds noise, hides intentional overrides, and makes it harder to identify what's actually customized. When defaults change in newer SDKs, the redundant properties may silently pin old behavior.

<!-- BAD: All of these are already the default -->
<PropertyGroup>
  <OutputType>Library</OutputType>
  <EnableDefaultItems>true</EnableDefaultItems>
  <EnableDefaultCompileItems>true</EnableDefaultCompileItems>
  <RootNamespace>MyLib</RootNamespace>       <!-- matches project name -->
  <AssemblyName>MyLib</AssemblyName>         <!-- matches project name -->
  <AppendTargetFrameworkToOutputPath>true</AppendTargetFrameworkToOutputPath>
</PropertyGroup>

<!-- GOOD: Only non-default values -->
<PropertyGroup>
  <TargetFramework>net8.0</TargetFramework>
</PropertyGroup>

AP-05: Manual File Listing in SDK-Style Projects

Smell : <Compile Include="File1.cs" />, <Compile Include="File2.cs" /> in SDK-style projects.

Why it's bad : SDK-style projects automatically glob **/*.cs (and other file types). Explicit listing is redundant, creates merge conflicts, and new files may be accidentally missed if not added to the list.

<!-- BAD -->
<ItemGroup>
  <Compile Include="Program.cs" />
  <Compile Include="Services\MyService.cs" />
  <Compile Include="Models\User.cs" />
</ItemGroup>

<!-- GOOD: Remove entirely — SDK includes all .cs files by default.
     Only use Remove/Exclude when you need to opt out: -->
<ItemGroup>
  <Compile Remove="LegacyCode\**" />
</ItemGroup>

Exception : Non-SDK-style (legacy) projects require explicit file includes. If migrating, see msbuild-modernization skill.

AP-06: Using <Reference> with HintPath for NuGet Packages

Smell : <Reference Include="..." HintPath="..\packages\SomePackage\lib\..." />

Why it's bad : This is the legacy packages.config pattern. It doesn't support transitive dependencies, version conflict resolution, or automatic restore. The packages/ folder must be committed or restored separately.

<!-- BAD -->
<ItemGroup>
  <Reference Include="Newtonsoft.Json">
    <HintPath>..\packages\Newtonsoft.Json.13.0.3\lib\netstandard2.0\Newtonsoft.Json.dll</HintPath>
  </Reference>
</ItemGroup>

<!-- GOOD -->
<ItemGroup>
  <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
</ItemGroup>

Note : <Reference> without HintPath is still valid for .NET Framework GAC assemblies like WindowsBase, PresentationCore, etc.

AP-07: Missing PrivateAssets="all" on Analyzer/Tool Packages

Smell : <PackageReference Include="StyleCop.Analyzers" Version="..." /> without PrivateAssets="all".

Why it's bad : Without PrivateAssets="all", analyzer and build-tool packages flow as transitive dependencies to consumers of your library. Consumers get unwanted analyzers or build-time tools they didn't ask for.

See references/private-assets.md for BAD/GOOD examples and the full list of packages that need this.

AP-08: Copy-Pasted Properties Across Multiple .csproj Files

Smell : The same <PropertyGroup> block appears in 3+ project files.

Why it's bad : Maintenance burden — a change must be made in every file. Inconsistencies creep in over time.

<!-- BAD: Repeated in every .csproj -->
<!-- ProjectA.csproj, ProjectB.csproj, ProjectC.csproj all have: -->
<PropertyGroup>
  <LangVersion>latest</LangVersion>
  <Nullable>enable</Nullable>
  <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
  <ImplicitUsings>enable</ImplicitUsings>
</PropertyGroup>

<!-- GOOD: Define once in Directory.Build.props at the repo/src root -->
<!-- Directory.Build.props -->
<Project>
  <PropertyGroup>
    <LangVersion>latest</LangVersion>
    <Nullable>enable</Nullable>
    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>
</Project>

See directory-build-organization skill for full guidance on structuring Directory.Build.props / Directory.Build.targets.

AP-09: Scattered Package Versions Without Central Package Management

Smell : <PackageReference Include="X" Version="1.2.3" /> with different versions of the same package across projects.

Why it's bad : Version drift — different projects use different versions of the same package, leading to runtime mismatches, unexpected behavior, or diamond dependency conflicts.

<!-- BAD: Version specified in each project, can drift -->
<!-- ProjectA.csproj -->
<PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
<!-- ProjectB.csproj -->
<PackageReference Include="Newtonsoft.Json" Version="13.0.3" />

Fix: Use Central Package Management. See https://learn.microsoft.com/en-us/nuget/consume-packages/central-package-management for details.

AP-10: Monolithic Targets (Too Much in One Target)

Smell : A single <Target> with 50+ lines doing multiple unrelated things.

Why it's bad : Can't skip individual steps via incremental build, hard to debug, hard to extend, and the target name becomes meaningless.

<!-- BAD -->
<Target Name="PrepareRelease" BeforeTargets="Build">
  <WriteLinesToFile File="version.txt" Lines="$(Version)" Overwrite="true" />
  <Copy SourceFiles="LICENSE" DestinationFolder="$(OutputPath)" />
  <Exec Command="signtool sign /f cert.pfx $(OutputPath)*.dll" />
  <MakeDir Directories="$(OutputPath)docs" />
  <Copy SourceFiles="@(DocFiles)" DestinationFolder="$(OutputPath)docs" />
  <!-- ... 30 more lines ... -->
</Target>

<!-- GOOD: Single-responsibility targets -->
<Target Name="WriteVersionFile" BeforeTargets="CoreCompile"
        Inputs="$(MSBuildProjectFile)" Outputs="$(IntermediateOutputPath)version.txt">
  <WriteLinesToFile File="$(IntermediateOutputPath)version.txt" Lines="$(Version)" Overwrite="true" />
</Target>

<Target Name="CopyLicense" AfterTargets="Build">
  <Copy SourceFiles="LICENSE" DestinationFolder="$(OutputPath)" SkipUnchangedFiles="true" />
</Target>

<Target Name="SignAssemblies" AfterTargets="Build" DependsOnTargets="CopyLicense"
        Condition="'$(SignAssemblies)' == 'true'">
  <Exec Command="signtool sign /f cert.pfx %(AssemblyFiles.Identity)" />
</Target>

AP-11: Custom Targets Missing Inputs and Outputs

Smell : <Target Name="MyTarget" BeforeTargets="Build"> with no Inputs / Outputs attributes.

Why it's bad : The target runs on every build, even when nothing changed. This defeats incremental build and slows down no-op builds.

See references/incremental-build-inputs-outputs.md for BAD/GOOD examples and the full pattern including FileWrites registration.

See incremental-build skill for deep guidance on Inputs/Outputs, FileWrites, and up-to-date checks.

AP-12: Setting Defaults in .targets Instead of .props

Smell : <PropertyGroup> with default values inside a .targets file.

Why it's bad : .targets files are imported late (after project files). By the time they set defaults, other .targets files may have already used the empty/undefined value. .props files are imported early and are the correct place for defaults.

<!-- BAD: custom.targets -->
<PropertyGroup>
  <MyToolVersion>2.0</MyToolVersion>
</PropertyGroup>
<Target Name="RunMyTool">
  <Exec Command="mytool --version $(MyToolVersion)" />
</Target>

<!-- GOOD: Split into .props (defaults) + .targets (logic) -->
<!-- custom.props (imported early) -->
<PropertyGroup>
  <MyToolVersion Condition="'$(MyToolVersion)' == ''">2.0</MyToolVersion>
</PropertyGroup>

<!-- custom.targets (imported late) -->
<Target Name="RunMyTool">
  <Exec Command="mytool --version $(MyToolVersion)" />
</Target>

Rule : .props = defaults and settings (evaluated early). .targets = build logic and targets (evaluated late).

AP-13: Import Without Exists() Guard

Smell : <Import Project="some-file.props" /> without a Condition="Exists('...')" check.

Why it's bad : If the file doesn't exist (not yet created, wrong path, deleted), the build fails with a confusing error. Optional imports should always be guarded.

<!-- BAD -->
<Import Project="$(RepoRoot)eng\custom.props" />

<!-- GOOD: Guard optional imports -->
<Import Project="$(RepoRoot)eng\custom.props" Condition="Exists('$(RepoRoot)eng\custom.props')" />

<!-- ALSO GOOD: Sdk attribute imports don't need guards (they're required by design) -->
<Project Sdk="Microsoft.NET.Sdk">

Exception : Imports that are required for the build to work correctly should fail fast — don't guard those. Guard imports that are optional or environment-specific (e.g., local developer overrides, CI-specific settings).

AP-14: Using Backslashes in Paths (Cross-Platform Issue)

Smell : <Import Project="$(RepoRoot)\eng\common.props" /> with backslash separators in .props/.targets files meant to be cross-platform.

Why it's bad : Backslashes work on Windows but fail on Linux/macOS. MSBuild normalizes forward slashes on all platforms.

<!-- BAD: Breaks on Linux/macOS -->
<Import Project="$(RepoRoot)\eng\common.props" />
<Content Include="assets\images\**" />

<!-- GOOD: Forward slashes work everywhere -->
<Import Project="$(RepoRoot)/eng/common.props" />
<Content Include="assets/images/**" />

Note : $(MSBuildThisFileDirectory) already ends with a platform-appropriate separator, so $(MSBuildThisFileDirectory)tools/mytool works on both platforms.

AP-15: Unconditional Property Override in Multiple Scopes

Smell : A property set unconditionally in both Directory.Build.props and a .csproj — last write wins silently.

Why it's bad : Hard to trace which value is actually used. Makes the build fragile and confusing for anyone reading the project files.

<!-- BAD: Directory.Build.props sets it, csproj silently overrides -->
<!-- Directory.Build.props -->
<PropertyGroup>
  <OutputPath>bin\custom\</OutputPath>
</PropertyGroup>
<!-- MyProject.csproj -->
<PropertyGroup>
  <OutputPath>bin\other\</OutputPath>
</PropertyGroup>

<!-- GOOD: Use a condition so overrides are intentional -->
<!-- Directory.Build.props -->
<PropertyGroup>
  <OutputPath Condition="'$(OutputPath)' == ''">bin\custom\</OutputPath>
</PropertyGroup>
<!-- MyProject.csproj can now intentionally override or leave the default -->

For additional anti-patterns (AP-16 through AP-21) and a quick-reference checklist, see additional-antipatterns.md.

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