/msbuild-antipatterns

name: msbuild-antipatterns
description: "Detect and fix MSBuild anti-patterns in project and build files. USE WHEN asked to review, audit, lint, clean up, or code-review a .csproj/.vbproj/.fsproj/.props/.targets/.proj (or Directory.Build.props/.targets) file, when asked 'is this project file correct?' or 'what's wrong with my build file?', or when hunting subtle build bugs caused by how a project is authored. Each anti-pattern has a symptom and a concrete BAD→GOOD fix. DO NOT USE FOR: non-MSBuild build systems (npm, Maven, CMake), or migrating a project to SDK-style (use msbuild-modernization)."
license: MIT

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:**

| Shell Command | MSBuild Task | |--------------|--------------| | `mkdir` | `<MakeDir>` | | `copy` / `cp` | `<Copy>` | | `del` / `rm` | `<Delete>` | | `move` / `mv` | `<Move>` | | `echo text > file` | `<WriteLinesToFile>` | | `touch` | `<Touch>` | | `xcopy /s` | `<Copy>` with item globs |

---

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:**

| Property | Meaning | |----------|---------| | `$(MSBuildThisFileDirectory)` | Directory of the current .props/.targets file | | `$(MSBuildProjectDirectory)` | Directory of the .csproj | | `$([MSBuild]::GetDirectoryNameOfFileAbove(...))` | Walk up to find a marker file | | `$([MSBuild]::NormalizePath(...))` | Combine and normalize path segments |

---

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.

**Exception (F# / `.fsproj`)**: F# compilation is order-dependent — the compiler processes `<Compile Include>` items sequentially and a file can only reference types/modules declared in files listed above it. `.fsproj` files must therefore list every source file explicitly, in dependency order (utility/leaf modules at the top, the entry point such as `Program.fs` at the bottom). If a `.fsi` signature file is used, it must appear **immediately before** its companion `.fs` implementation file.

---

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