codebehind-class-body-location

Skill: Code-Behind Transform — Class Body Location Pattern

Summary

When a code-behind transform must locate the class body opening brace ({) to inject fields or members, it must use [^{]*\{ not \s*\{ between the class name and the brace.

Problem This Solves

Code-behind transforms run in Order sequence. Earlier transforms (e.g., BaseClassStripTransform at Order 200) modify the class declaration before later transforms see it. By Order 220+, a typical Page class looks like:

public partial class ShoppingCart : WebFormsPageBase
{

A regex like partial\s+class\s+\w+\s*\{ fails to match this because : WebFormsPageBase\n is not \s*. The transform silently returns the content unchanged — no injection happens, no error is raised.

Correct Pattern

// WRONG — fails when base class or interface list is present
private static readonly Regex ClassOpenRegex = new(
    @"partial\s+class\s+\w+\s*\{",
    RegexOptions.Compiled);

// CORRECT — [^{]* skips base class, interfaces, newlines, anything before {
private static readonly Regex ClassOpenRegex = new(
    @"partial\s+class\s+\w+[^{]*\{",
    RegexOptions.Compiled);

[^{]* matches : WebFormsPageBase, : Base, IInterface, spaces, newlines — everything up to (but not including) the first {.

When To Apply

• Any transform that injects members/fields/properties into a class body.
• Any transform that locates the class body to insert using statements or attributes near it.

Test Coverage Required

When authoring such a transform, always include these three test shapes:

1. Plain class — public partial class Foo { (baseline)
2. Class with base — public partial class Foo : WebFormsPageBase {
3. Brace on next line with base — public partial class Foo : WebFormsPageBase\n{

Real-World Example

ComponentRefCodeBehindTransform (Order 220) injects @ref backing fields. It was broken from inception because its ClassOpenRegex used \s*\{. After BaseClassStripTransform (Order 200) added : WebFormsPageBase, the regex never matched — causing 15+ CS0103 errors per page in WingtipToys Run 80.