Fix FS2014 duplicate .cctor error by renaming and delegating static constructors

[Copilot]

• Fix FS2014 duplicate .cctor error by renaming and delegating static constructors
• Updated cdef_cctorCode2CodeOrCreate function in il.fs to handle multiple .cctor methods
• Created delegating .cctor that calls renamed static constructors
• Added test case in Misc.fs to verify the fix generates proper IL
• Applied fantomas code formatting
• Removed unused DuplicateCctorFix.fs file (test code is embedded in Misc.fs)

Problem Resolved

Fixed discriminated unions with both static members and nullary cases failing compilation with "FS2014: duplicate entry '.cctor' in method table". The solution renames duplicate .cctor methods to unique static methods and creates a single .cctor that calls both, preserving all initialization semantics while ensuring only one .cctor exists in the final IL.

Changes Made

• Modified cdef_cctorCode2CodeOrCreate function to detect and rename duplicate .cctor methods
• Uses generic naming pattern (cctor_renamed_0, cctor_renamed_1) to avoid hardcoded assumptions
• Generated IL includes single .cctor method marked as rtspecialname that delegates to renamed methods
• All original initialization logic preserved through clean delegation pattern

This pull request was created as a result of the following prompt from Copilot chat.

Merge duplicate static constructors (.cctor) for discriminated unions with generic statics in F# compiler backend. When assembling ILTypeDef for a type, if multiple .cctor methods are present (one from incremental class typechecking, one from union erasure), rename each to a unique static method (e.g., cctor_IncrClass, cctor_UnionErasure), then synthesize a single .cctor that calls both. Ensure only one .cctor is marked as rtspecialname and static constructor. Add a test using verifyIL to assert that the generated IL contains a single .cctor which calls both renamed initializers. Example IL:
.method private specialname rtspecialname static void .cctor() {
call void cctor_IncrClass()
call void cctor_UnionErasure()
ret
}
.method private static void cctor_IncrClass() { ... }
.method private static void cctor_UnionErasure() { ... }
This resolves #18767.

---

💬 Share your feedback on Copilot coding agent for the chance to win a $200 gift card! Click here to start the survey.

[T-Gro]

/run fantomas

[github-actions]

❗ Release notes required

---

✅ Found changes and release notes in following paths:

Warning

No PR link found in some release notes, please consider adding it.

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/10.0.100.md	No current pull request URL (#18801) found, please consider adding it

[github-actions]

🔧 CLI Command Report

• Command: /run fantomas
• Outcome: success

✅ Patch applied:
- Files changed: 1
- Lines changed: 47

[Copilot]

/run fantomas

Done. Applied fantomas formatting in commit 063261c.