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SKILL.md
npx skills add dotnet/skills --skill item-management
Patterns for managing MSBuild item groups: Include/Remove/Update semantics, item metadata, batching with %(Metadata), transforms, per-item filtering, and cross-product batching pitfalls. USE FOR: diagnosing and fixing item group anti-patterns in .csproj files, reviewing item management for correctness, fixing CS2002 duplicate file warnings from SDK globbing, fixing targets that run more times than expected due to cross-product batching, fixing Include vs Update misuse on SDK-globbed items, fixing FileWrites registration for generated file clean support, moving generated files to IntermediateOutputPath. DO NOT USE FOR: target chain architecture (use target-authoring), property patterns (use property-patterns), incrementality (use incremental-build), general anti-patterns (use msbuild-antipatterns), non-MSBuild build systems.
npx skills add dotnet/skills --skill item-management
Canonical patterns for working with item groups, from Microsoft.Common.CurrentVersion.targets.
| Operation | Purpose | When to use |
|---|---|---|
Include | Add new items to the group | Creating items with identity + metadata |
Remove | Remove items matching a pattern | Excluding files or clearing a group |
Update | Modify metadata on existing items | Adding/changing metadata without re-adding |
Update does not add items — it only modifies items already in the group.
When %(Metadata) appears in target attributes or task parameters, MSBuild batches execution per unique metadata value.
%(Metadata) in Condition or Outputs → target batches per unique value.%(Metadata) in task parameters → task batches per unique value.%() from different item groups in the same expression — this causes a cross-product (see Common Pitfalls).Transforms create new item lists by applying an expression to each item:
Exclude only works on Include — it cannot be used with Update or Remove.
Referencing %(Metadata) from two different item groups creates O(N×M) executions:
Write to $(IntermediateOutputPath) (obj/), not the source directory. Source-tree generation pollutes version control and can cause duplicate compilation via globs.
Every file created during a target must be added to @(FileWrites) for dotnet clean support.