Add automatic migration for deprecated packages

claude.md

@@ -12,6 +12,59 @@ PackageUpdate is a .NET global tool that updates NuGet packages for all solution
 - Uses C# preview language features (`LangVersion>preview`)
 - Central Package Management (CPM) is required for all target solutions
 
+## Coding Conventions
+
+### Lambda Expressions
+
+Always use underscore `_` for single-parameter lambda expressions instead of named parameters:
+
+```csharp
+// ✅ Correct
+packages.Where(_ => _.Id == "MyPackage")
+packages.FirstOrDefault(_ => _.Version == "1.0.0")
+packages.OrderByDescending(_ => _)
+elements.Any(_ => _.IsEnabled)
+
+// ❌ Incorrect - don't use named parameters
+packages.Where(p => p.Id == "MyPackage")
+packages.FirstOrDefault(pkg => pkg.Version == "1.0.0")
+elements.Any(e => e.IsEnabled)
+```
+
+This applies even when the parameter is used multiple times in the expression:
+
+```csharp
+// ✅ Correct
+xml.Descendants("PackageVersion")
+    .FirstOrDefault(_ =>
+        string.Equals(
+            _.Attribute("Include")?.Value,
+            packageName,
+            StringComparison.OrdinalIgnoreCase))
+
+// ❌ Incorrect
+xml.Descendants("PackageVersion")
+    .FirstOrDefault(e =>
+        string.Equals(
+            e.Attribute("Include")?.Value,
+            packageName,
+            StringComparison.OrdinalIgnoreCase))
+```
+
+**Exception:** Use descriptive parameter names when creating complex anonymous types or when the lambda body is long and clarity would benefit from a meaningful name:
+
+```csharp
+// Named parameter acceptable for complex Select projections
+var packageVersions = xml.Descendants("PackageVersion")
+    .Select(element => new
+    {
+        Element = element,
+        Package = element.Attribute("Include")?.Value,
+        CurrentVersion = element.Attribute("Version")?.Value,
+        Pinned = element.Attribute("Pinned")?.Value == "true"
+    })
+```
+
 ## Build and Test Commands
 
 ```bash
@@ -46,10 +99,11 @@ packageupdate --build
 
 ### Key Components
 
-- **Updater.cs**: Core update logic
+- **Updater.cs**: Core update and migration logic
   - Parses `Directory.Packages.props` XML
   - Respects `Pinned="true"` attribute to skip packages
   - Queries NuGet sources for latest versions via NuGet.Protocol API
+  - Detects deprecated packages and auto-migrates to alternatives when current version is deprecated
   - Preserves file formatting (newlines, indentation, trailing newlines)
   - Only considers stable versions when current version is stable
   - Only considers pre-release versions when current version is pre-release
@@ -93,6 +147,50 @@ The tool only works with CPM. Each solution must have a `Directory.Packages.prop
 
 Packages with `Pinned="true"` attribute are never updated, even when explicitly targeted via `--package` flag.
 
+### Package Migration
+
+The tool automatically detects and migrates deprecated packages when an alternative is available.
+
+#### How It Works
+
+When updating packages, PackageUpdate checks if the **current version** of a package is marked as deprecated in NuGet. If the package has an alternative specified and that alternative is available in configured NuGet sources, the tool will automatically migrate:
+
+1. Replaces the `Include` attribute with the alternative package name
+2. Sets the `Version` to the latest version of the alternative (or the minimum version from the range if specified)
+3. Logs the migration with deprecation reason
+
+#### Migration Examples
+
+```xml
+<!-- Before -->
+<PackageVersion Include="WindowsAzure.Storage" Version="9.3.3" />
+
+<!-- After (migrated) -->
+<PackageVersion Include="Azure.Storage.Common" Version="12.26.0" />
+```
+
+#### Migration Behavior
+
+- **Pinned packages**: Never migrated (Pinned="true" is respected)
+- **No alternative available**: Package version updated normally, warning logged
+- **Alternative not found**: Package version updated normally, warning logged
+- **Alternative already exists**: Migration skipped, warning logged, both packages remain
+- **--package flag**: Migrations still occur for specified deprecated packages
+- **Current version check**: Only migrates if the **current** version is deprecated, not if only newer versions are deprecated
+
+#### Migration Logging
+
+Successful migration:
+```
+Migrated WindowsAzure.Storage -> Azure.Storage.Common (Version: 12.26.0) [Deprecated: Legacy]
+```
+
+Deprecation warnings (when no migration possible):
+```
+Package WindowsAzure.Storage is deprecated but has no alternative. Reasons: Legacy
+Package WindowsAzure.Storage is deprecated with alternative Azure.Storage.Common, but alternative already exists
+```
+
 ### Version Selection Logic
 
 - Uses `FindPackageByIdResource` to query all versions efficiently

readme.md

@@ -317,6 +317,199 @@ The next time you run the updater, it will update to the latest version.
 - Comments and formatting around pinned packages are preserved during updates
 
 
+## Automatic Package Migration
+
+
+### Overview
+
+PackageUpdate automatically detects and migrates deprecated NuGet packages to their recommended alternatives. When a package is marked as deprecated on NuGet.org with an alternative package specified, the tool will automatically replace it during updates.
+
+
+### How It Works
+
+When updating packages, PackageUpdate:
+
+1. Checks if the **current version** of each package is marked as deprecated
+2. If an alternative package is specified in the deprecation metadata:
+   - Verifies the alternative package exists in configured NuGet sources
+   - Checks that the alternative doesn't already exist in `Directory.Packages.props`
+   - Replaces the package reference with the alternative
+   - Sets the version to the latest available version of the alternative
+3. Logs the migration with the deprecation reason
+
+
+### Example Migration
+
+**Before:**
+
+```xml
+<Project>
+  <ItemGroup>
+    <PackageVersion Include="WindowsAzure.Storage" Version="9.3.3" />
+    <PackageVersion Include="Newtonsoft.Json" Version="13.0.1" />
+  </ItemGroup>
+</Project>
+```
+
+**After running `packageupdate`:**
+
+```xml
+<Project>
+  <ItemGroup>
+    <PackageVersion Include="Azure.Storage.Common" Version="12.26.0" />
+    <PackageVersion Include="Newtonsoft.Json" Version="13.0.3" />
+  </ItemGroup>
+</Project>
+```
+
+Console output:
+
+```
+Migrated WindowsAzure.Storage -> Azure.Storage.Common (Version: 12.26.0) [Deprecated: Legacy]
+Updated Newtonsoft.Json: 13.0.1 -> 13.0.3
+```
+
+
+### Migration Behavior
+
+
+#### Automatic by Default
+
+Migrations happen automatically without requiring any flags or configuration. The tool detects deprecated packages and migrates them seamlessly.
+
+
+#### Pinned Packages Are Never Migrated
+
+If a package is pinned, it will not be migrated even if it's deprecated:
+
+```xml
+<PackageVersion Include="WindowsAzure.Storage" Version="9.3.3" Pinned="true" />
+```
+
+This package will remain unchanged.
+
+
+#### When Alternative Already Exists
+
+If the alternative package already exists in `Directory.Packages.props`, the migration is skipped:
+
+```xml
+<Project>
+  <ItemGroup>
+    <PackageVersion Include="WindowsAzure.Storage" Version="9.3.3" />
+    <PackageVersion Include="Azure.Storage.Common" Version="12.0.0" />
+  </ItemGroup>
+</Project>
+```
+
+Output:
+
+```
+Package WindowsAzure.Storage is deprecated with alternative Azure.Storage.Common, but alternative already exists
+```
+
+Both packages remain in the file, and only `Azure.Storage.Common` gets updated to the latest version.
+
+
+#### When No Alternative is Available
+
+If a package is deprecated but has no alternative specified, the tool logs a warning and continues with normal version update:
+
+```
+Package SomeDeprecatedPackage is deprecated but has no alternative. Reasons: Legacy
+```
+
+
+#### Current Version Check
+
+The tool only migrates if the **current** version you're using is deprecated. If you're on an older, non-deprecated version, and only newer versions are deprecated, no migration occurs. This prevents unnecessary migrations when you're deliberately staying on an older version.
+
+
+#### Specific Package Flag
+
+The migration feature works with the `--package` flag:
+
+```bash
+packageupdate --package WindowsAzure.Storage
+```
+
+If `WindowsAzure.Storage` is deprecated with an alternative, it will be migrated automatically.
+
+
+### Common Scenarios
+
+
+#### Scenario 1: Microsoft Azure SDK Packages
+
+Many older Azure SDK packages have been deprecated in favor of the new Azure SDK:
+
+- `WindowsAzure.Storage` → `Azure.Storage.Common` or `Azure.Storage.Blobs`
+- `Microsoft.Azure.Storage.Blob` → `Azure.Storage.Blobs`
+- `Microsoft.Azure.DocumentDB` → `Microsoft.Azure.Cosmos`
+
+These migrations happen automatically when you run `packageupdate`.
+
+
+#### Scenario 2: Preventing Migration
+
+If you want to prevent migration of a deprecated package (e.g., you're not ready to migrate yet), pin the package:
+
+```xml
+<!-- Pinned: Not ready to migrate to Azure.Storage.Blobs yet -->
+<PackageVersion Include="WindowsAzure.Storage" Version="9.3.3" Pinned="true" />
+```
+
+
+#### Scenario 3: Manual Review After Migration
+
+After automatic migration, you may want to:
+
+1. Review the changes in `Directory.Packages.props`
+2. Update your code to use the new package's API (if breaking changes exist)
+3. Test thoroughly before committing
+
+The migration updates the package reference but doesn't modify your source code.
+
+
+### Logging
+
+
+#### Successful Migration
+
+```
+Migrated WindowsAzure.Storage -> Azure.Storage.Common (Version: 12.26.0) [Deprecated: Legacy]
+```
+
+
+#### Migration Skipped (Alternative Exists)
+
+```
+Package WindowsAzure.Storage is deprecated with alternative Azure.Storage.Common, but alternative already exists
+```
+
+
+#### Migration Skipped (No Alternative)
+
+```
+Package MyOldPackage is deprecated but has no alternative. Reasons: Legacy, Critical Bugs
+```
+
+
+#### Migration Skipped (Alternative Not Found)
+
+```
+Package OldPackage is deprecated with alternative NewPackage, but alternative not found in sources
+```
+
+
+### Technical Details
+
+- Migration uses NuGet's official deprecation metadata API (`PackageDeprecationMetadata`)
+- The `AlternatePackage` information comes directly from package authors via NuGet.org
+- File formatting, comments, and XML structure are preserved during migration
+- Migrations are logged distinctly from version updates for clarity
+
+
 ## Icon
 
 [Update](https://thenounproject.com/search/?q=update&i=2060555) by [Andy Miranda](https://thenounproject.com/andylontuan88) from [The Noun Project](https://thenounproject.com/).