{
"schema": "https://ai-atoms.com/schemas/skill-v1.json",
"type": "skill",
"id": "skill/property-patterns",
"version": "1.0.0",
"name": "property-patterns",
"description": "MSBuild property definition patterns: conditional defaults, composition/concatenation, path normalization, trailing slash handling, TFM detection helpers, and property evaluation order. Only activate in MSBuild/.NET build context. USE FOR: diagnosing and fixing MSBuild property definition issues in .props or .csproj files, reviewing and fixing shared property configuration anti-patterns, fixing DefineConstants or NoWarn being overwritten instead of appended, fixing unconditional property assignments that prevent project-level overrides, fixing unquoted conditions that fail when properties are empty, fixing hardcoded paths that break cross-platform builds, setting property defaults that can be overridden, understanding property evaluation order and last-write-wins semantics. DO NOT USE FOR: props vs targets placement (use directory-build-organization), item operations (use item-management), target structure (use target-authoring), general anti-patterns (use msbuild-antipatterns), non...",
"system_prompt_fragment": "# MSBuild Property Patterns\n\nCanonical property definition and manipulation patterns from the MSBuild repository.\n\n## Conditional Defaults — The Foundational Pattern\n\nSet a property **only if not already set**, allowing callers to override:\n\n```xml\n\n Debug\n AnyCPU\n true\n\n```\n\n### Rules\n\n- Always quote both sides: `'$(Prop)' == ''`\n- In `.props`: creates overridable defaults. In `.targets`: creates fallbacks.\n- Properties without the condition **cannot be overridden** by earlier imports.\n\n## Nested Conditional Groups\n\nGroup related properties under a shared condition:\n\n```xml\n\n $(DefineConstants);FEATURE_APARTMENT_STATE\n $(DefineConstants);FEATURE_APM\n true\n\n\n\n true\n $(DefineConstants);RUNTIME_TYPE_NETCORE\n\n```\n\nUse the outer `Condition` on `PropertyGroup` to avoid repeating the same condition on every property.\n\n> **Warning:** `$(TargetFramework)` is empty in `.props` files for single-targeting projects until the project body is evaluated. Place `TargetFramework`-conditioned property groups in `.targets` files (or the project file itself), where the value is always available.\n\n## Composition — Semicolon Concatenation\n\nProperties that hold lists use semicolons. Always include the existing value when appending:\n\n```xml\n\n $(DefineConstants);MY_FEATURE\n $(NoWarn);NU5131;IDE0005\n $(FullFrameworkTFM);$(LatestDotNetCoreForMSBuild);netstandard2.0\n\n```\n\n## Path Normalization and Trailing Slashes\n\n```xml\n\n\n $(OutDir)\\\n\n\n\n\n $([MSBuild]::NormalizePath('$(TargetDir)', 'ref', '$(TargetFileName)'))\n\n\n\n\n \n $([System.IO.Path]::Combine('$(MSBuildProjectDirectory)', '$(MSBuildProjectExtensionsPath)'))\n \n\n```\n\n### Preferred path functions\n\n| Function | Purpose |\n|---|---|\n| `$([MSBuild]::NormalizePath(...))` | Combine and normalize (cross-platform) |\n| `$([System.IO.Path]::Combine(...))` | Combine path segments |\n| `$([System.IO.Path]::IsPathRooted(...))` | Check if absolute |\n| `HasTrailingSlash(...)` | Check for trailing slash |\n| `$([MSBuild]::GetDirectoryNameOfFileAbove(...))` | Walk up directory tree |\n| `$(MSBuildThisFileDirectory)` | Directory of current file |\n\n## Target Framework Detection Helpers\n\n```xml\n\n\n true\n\n\n\n\n true\n\n\n\n\n $(DefineConstants);TEST_ISWINDOWS\n\n```\n\n## Guard Properties\n\nMark that a file has been imported to prevent double-imports:\n\n```xml\n\n\n true\n\n\n\n\n```\n\n## Feature Gating by MSBuild Version\n\n```xml\n\n true\n\n```\n\n## Fallback Chains\n\nSet via primary source first, then fall back:\n\n```xml\n\n $([Microsoft.Build.Utilities.ToolLocationHelper]::GetPathToDotNetFrameworkSdkFile('tlbexp.exe'))\n $(_NetFxToolsDir)TlbExp.exe\n\n```\n\n## Last Write Wins — Evaluation Order\n\nMSBuild evaluates properties top-to-bottom. The last assignment wins:\n\n```xml\n\nvalue1 \n\nvalue2 \n\nvalue3 \n```\n\nProperties in `.targets` (imported late) override properties in `.props` (imported early) and the project file.\n\n## Common Pitfalls\n\n- **Unquoted conditions** (`$(X)==true`) fail when the property is empty. Always quote both sides.\n- **Overwriting DefineConstants** (`MY_CONST`) drops all prior constants. Always append with `$(DefineConstants);`.\n- **Hardcoded absolute paths** break portability. Use `$(MSBuildThisFileDirectory)` or `$([MSBuild]::NormalizePath(...))`.\n- **Missing `Condition` on defaults** makes properties non-overridable. Add `Condition=\"'$(Prop)' == ''\"` for values meant to be defaults.",
"applicable_domains": [
"code",
"dotnet",
"engineering"
],
"invocation": [
"/property-patterns"
],
"tags": [
"dotnet-msbuild",
"dotnet",
"csharp",
"microsoft"
],
"authored_by": "anthropics",
"source_url": "https://github.com/dotnet/skills/blob/main/plugins/dotnet-msbuild/skills/property-patterns/SKILL.md",
"lifecycle": "stable",
"category": "dotnet",
"provenance": {
"source": "dotnet/skills",
"source_url": "https://github.com/dotnet/skills/blob/main/plugins/dotnet-msbuild/skills/property-patterns/SKILL.md",
"author": "Microsoft / .NET Foundation",
"license": "MIT",
"notes": "Imported by scripts/import-anthropic-skills.py."
}
}