namespace-migration

name	namespace-migration
description	Migrate C# types between namespaces across the solution. Updates usings, refs, and verifies build.
when_to_use	migrate namespace, rename namespace, namespace refactor, move types to namespace.
argument-hint	<OldNamespace> <NewNamespace>

Namespace Migration

You migrate C# types to new namespaces across the entire solution, updating usings and refs and verifying the build.

Step 1: Build the mapping table

From $ARGUMENTS or the conversation, extract the namespace mapping. Expected format: OldNamespace → NewNamespace (one or more pairs).

If the mapping is unclear, ask once:

What's the namespace mapping? Example:
  Foo.Core → Foo.Pipeline
  Foo.Core.Models → Foo.Pipeline.Models

Step 2: Audit impact

For each old namespace, find affected files:

rg -l "namespace {OldNamespace}" src/ -g "*.cs" | sort
rg -l "using {OldNamespace}" src/ tests/ -g "*.cs" | wc -l

Also check for InternalsVisibleTo implications:

rg -l "InternalsVisibleTo" src/ -g "*.csproj" -g "*.cs"

Print the impact summary inline and proceed immediately:

## Migration Impact: {OldNamespace} → {NewNamespace}

- Source files with namespace declaration: {N}
- Files with using directives: {M}
- InternalsVisibleTo affected: {Y/N — list if yes}
- Estimated build risk: LOW/MEDIUM/HIGH

Step 3: Apply migration

Produce a clean build with all namespace references updated and git history preserved.

• Use git mv for any file moves (plain mv loses history; if git mv errors on untracked files, git add first)
• Use Edit tool for namespace declarations and using directives (not sed/awk — can corrupt encoding)
• Update every occurrence: namespace declarations, using directives, fully-qualified references {OldNamespace}.TypeName, <RootNamespace>/<AssemblyName> in .csproj/.props, and any InternalsVisibleTo strings

Convention: Namespace.Sub.Name maps to src/{Project}/Sub/Name/.

Verify with:

scripts/build.sh

If build errors remain, they are almost always residual using directives or fully-qualified type references. Read the error, find the file, apply the fix. Re-run until clean.

Output the test command — do not run it:

scripts/test.sh --all

Report completion:

## Migration Complete: {OldNamespace} → {NewNamespace}

- Files moved: {N}
- using directives updated: {M}
- Build status: CLEAN
- Test command: {command}

Notes

• Never use mv — always git mv to preserve history
• If git mv errors on untracked files, git add the file first
• After a large migration, scripts/format.sh --changed may reorder using directives — that's expected
• InternalsVisibleTo uses assembly names, not namespace names — check both
• If the old namespace is a prefix of another (e.g. Foo and Foo.Core), be precise with grep patterns: use \bFoo\b or namespace Foo; to avoid partial matches