XmlProvider: Error reading MS Office Custom UI Schema

[roboz0r]

I have copied the schema from https://docs.microsoft.com/en-us/openspecs/office_standards/ms-customui/5f3e35d6-70d6-47ee-9e11-f5499559f93a into a file and used the following code to access:

[<Literal>]
let RibbonXSDPath = @"C:\Projects\Ribbon CustomUI.xsd"

type RibbonBuilder = XmlProvider<Schema = RibbonXSDPath>

An error is reported in a dialogue box:

dotnet.exe - System Error
A new guard page for the stack cannot be created.

Not sure but I believe this is a stack overflow. Is this a bug or is there any workaround for this?

[giacomociti]

Likely a bug, maybe some circular definition not handled appropriately.
I noticed that the issue disappears when commenting out line 1413

<!-- <xsd:group ref="EG_MenuControlsBase"/> -->

which probably is not a workaround since it removes a piece of the schema

[github-actions]

🤖 This is an automated response from Repo Assist.

Thanks for the detailed report, and good catch by @giacomociti on the EG_MenuControlsBase group reference!

Root cause: In XsdInference.fs, when a (xsd:group ref="...") is encountered, the code resolves it by immediately recursing into the referenced group's particle:

| :? XmlSchemaGroupRef as grpRef -> parseParticle ctx grpRef.Particle

There's no cycle guard, so a schema where a group (directly or transitively) references itself causes infinite recursion → stack overflow (the "guard page for the stack cannot be created" error you saw).

The MS Office Custom UI schema has exactly this pattern: EG_MenuControlsBase is a group that references other groups which eventually reference EG_MenuControlsBase again.

Fix needed: The XSD inference pass needs to track visited XmlSchemaGroup names (or object references) and break cycles when detected — returning an empty or placeholder particle for the back-edge. This is a non-trivial change.

Workaround for now: As noted, commenting out the self-referential group line is the only practical option. If you need the full schema, you could pre-process the XSD to unroll or remove the cyclic group reference before passing it to the type provider.

This is a genuine bug worth tracking — labelling it bug + needs investigation.

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[dsyme]

Yes , implement the cycle guard

[github-actions]

🤖 This is an automated response from Repo Assist.

Good news — I've opened a draft PR implementing the cycle guard fix: #1626 (or browse here).

Summary of the fix: parseParticle in XsdInference.fs now tracks which group qualified names are currently being visited. When a GroupRef is encountered whose group is already on the stack, it returns Empty (an empty particle) to break the cycle instead of recursing infinitely.

@dsyme, happy for you to review when you get a chance!

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