cli-transform-authoring

name	cli-transform-authoring
description	Create and register new CLI migration transforms for the webforms-to-blazor pipeline. Covers IMarkupTransform and ICodeBehindTransform interfaces, transform ordering, dual-registration in Program.cs and TestHelpers.cs, testing patterns, and when to use a transform vs. a semantic pattern. Use when adding a new markup or code-behind transform, debugging transform output, or understanding transform execution order. Use when this capability is needed.
metadata	{"author":"FritzAndFriends"}

CLI Transform Authoring

This skill covers creating new transforms for the webforms-to-blazor CLI migration pipeline.

Architecture Overview

The migration CLI uses two transform interfaces that run in sequence during file conversion:

1. Markup transforms (IMarkupTransform) — Convert .aspx/.ascx/.master markup to .razor syntax
2. Code-behind transforms (ICodeBehindTransform) — Convert .aspx.cs code-behind to .razor.cs

Both interfaces share the same contract:

public interface IMarkupTransform  // (or ICodeBehindTransform)
{
    string Name { get; }
    int Order { get; }
    string Apply(string content, FileMetadata metadata);
}

• Name — Human-readable identifier (used in logs and diagnostics)
• Order — Execution sequence (ascending). Lower numbers run first.
• Apply — Takes current content + file metadata, returns transformed content

Pipeline Execution Order

MigrationPipeline runs transforms in this order:

1. Markup transforms (sorted by Order ascending) — all run on .razor content
2. Code-behind transforms (sorted by Order ascending) — all run on .razor.cs content
3. Semantic patterns (SemanticPatternCatalog) — page-level rewrites after all transforms

FileMetadata

Every transform receives FileMetadata which carries context about the file being processed:

• OriginalPath — Source .aspx path
• OutputPath — Target .razor path
• PageDirectives — Parsed directive info (CodeBehind, Inherits, MasterPageFile)
• MarkupContent — Can be set by code-behind transforms to modify the markup file
• CodeBehindContent — The code-behind source
• IsUserControl / IsMasterPage — File type flags

Creating a New Transform

Step 1: Create the Transform Class

src/BlazorWebFormsComponents.Cli/Transforms/Markup/MyNewTransform.cs
    — or —
src/BlazorWebFormsComponents.Cli/Transforms/CodeBehind/MyNewTransform.cs

using BlazorWebFormsComponents.Cli.Pipeline;

namespace BlazorWebFormsComponents.Cli.Transforms.Markup;  // or .CodeBehind

public class MyNewTransform : IMarkupTransform  // or ICodeBehindTransform
{
    public string Name => "MyNewTransform";
    public int Order => 500;  // Choose based on dependencies

    public string Apply(string content, FileMetadata metadata)
    {
        // Return content unchanged if this transform doesn't apply
        if (!content.Contains("pattern-to-match"))
            return content;

        // Apply transformation
        return content.Replace("old-pattern", "new-pattern");
    }
}

Step 2: Register in BOTH Locations

⚠️ CRITICAL: Every transform must be registered in TWO places.

src/BlazorWebFormsComponents.Cli/Program.cs (runtime DI):

services.AddSingleton<IMarkupTransform, MyNewTransform>();
// — or —
services.AddSingleton<ICodeBehindTransform, MyNewTransform>();

tests/BlazorWebFormsComponents.Cli.Tests/TestHelpers.cs (test pipeline):

var markupTransforms = new List<IMarkupTransform>
{
    // ... existing transforms ...
    new MyNewTransform(),
};
// — or for code-behind —
var codeBehindTransforms = new List<ICodeBehindTransform>
{
    // ... existing transforms ...
    new MyNewTransform(),
};

Step 3: Write Tests

Create a test file at tests/BlazorWebFormsComponents.Cli.Tests/MyNewTransformTests.cs:

using BlazorWebFormsComponents.Cli.Pipeline;
using BlazorWebFormsComponents.Cli.Transforms.Markup;
using Xunit;

namespace BlazorWebFormsComponents.Cli.Tests;

public class MyNewTransformTests
{
    private readonly MyNewTransform _transform = new();

    [Fact]
    public void Apply_WithMatchingPattern_TransformsCorrectly()
    {
        var input = "<asp:CustomControl runat=\"server\" />";
        var metadata = new FileMetadata { OriginalPath = "Test.aspx" };

        var result = _transform.Apply(input, metadata);

        Assert.Contains("expected-output", result);
        Assert.DoesNotContain("asp:", result);
    }

    [Fact]
    public void Apply_WithoutMatchingPattern_ReturnsUnchanged()
    {
        var input = "<div>No Web Forms here</div>";
        var metadata = new FileMetadata { OriginalPath = "Test.aspx" };

        var result = _transform.Apply(input, metadata);

        Assert.Equal(input, result);
    }
}

Step 4: Run Tests

dotnet test tests\BlazorWebFormsComponents.Cli.Tests --nologo

Transform Ordering Guidelines

Order Range	Category	Examples
0–99	Directive stripping	PageDirectiveTransform, RegisterDirectiveTransform
100–199	Structural transforms	MasterPageTransform, ContentWrapperTransform
200–299	Prefix/attribute removal	AspPrefixTransform, AttributeStripTransform
300–399	Expression/binding rewrites	ExpressionTransform, DataBindingAttributeTransform
400–499	Template/column processing	TemplateFieldChildComponentsTransform, GridViewColumnItemTypeTransform
500–599	Event/form wiring	EventWiringTransform, FormWrapperTransform
600–699	URL/reference cleanup	UrlReferenceTransform, ScriptManagerStripTransform
700+	Post-processing	FormAntiforgeryPostProcessor, ValidatorGenericTypeTransform

Key ordering dependencies:

• AspPrefixTransform must run before AttributeStripTransform (strip asp: before removing runat)
• TemplateContextTransform must run before TemplateFieldChildComponentsTransform
• SelectMethodTransform must run before EventWiringTransform

Transform vs. Semantic Pattern

Use a Transform when...	Use a Semantic Pattern when...
Converting a specific Web Forms tag/attribute	Rewriting page-level structure
Change is mechanical (regex/string)	Change requires understanding page intent
Applies to ALL files universally	Applies only to specific page types (query, detail, action)
No context about surrounding markup needed	Needs to understand the full page layout
Example: stripping runat="server"	Example: converting a search form + GridView into a query page

Current Transform Inventory

• 24 markup transforms in src/BlazorWebFormsComponents.Cli/Transforms/Markup/
• 5 directive transforms in src/BlazorWebFormsComponents.Cli/Transforms/Directives/
• 27 code-behind transforms in src/BlazorWebFormsComponents.Cli/Transforms/CodeBehind/

Checklist

• Transform class implements IMarkupTransform or ICodeBehindTransform
• Order is set appropriately (check ordering dependencies)
• Registered in Program.cs DI container
• Registered in TestHelpers.cs test pipeline
• Unit tests cover: matching input, non-matching input, edge cases
• dotnet test tests\BlazorWebFormsComponents.Cli.Tests passes
• Benchmark regression check: run migration against current focus app

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Source: FritzAndFriends/BlazorWebFormsComponents — distributed by TomeVault.