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romanett 14fba2d120 Fix instance TypeDefinition across dependency ModelDesign boundaries (#4355)
# Description

The model source generator crashed with `MODELGEN003` /
`NullReferenceException` whenever a `ModelDesign` instantiated an
`ObjectType` (or `VariableType`) declared in a **dependency** design
file, as soon as that type had children. The sibling of #4332 on the
instance-declaration path: #4335 linked dependency *data types*, but an
*instance* whose `TypeDefinition` lives in another design still crashed
in `NodeStateGenerator` on the type's inherited children.

Root cause: dependency design files load with `validateDictionary:
false`, so `ValidateInstance` / `ValidateType` never ran on them and
their types' children kept `TypeDefinitionNode` / `DataTypeNode` at
`null`. When the target instance merged those children into its
hierarchy (`BuildInstanceHierarchy` re-walks the dependency type's
`Children.Items`), the null references were copied along, and
`GetNodeStateClassName` dereferenced them while building the node state
factory list.

Changes:

- A new best-effort `LinkDependencyInstances` pass in
`ModelDesignValidator` links dependency-design instances the way
`ValidateInstance` / `ValidateType` do for the target model: the
`TypeDefinitionNode` / `DataTypeNode` of the types' children and
standalone instances (recursively), variable `DataType` / `ValueRank`
inheritance from the variable type, `DefaultValue` decoding,
`VariableTypeDesign.DataTypeNode` restrictions, and method arguments —
including creation of the `InputArguments` / `OutputArguments` argument
properties so method children materialise into the target hierarchy
exactly like local ones. Resolution is best effort (unresolvable
references stay `null`) and NodeSet2 dependencies remain excluded,
consistent with `LinkDependencyDataTypes`.
- The pass runs alongside `LinkDependencyDataTypes`: for upstream
dependencies after all of them are loaded and before the target
validates (so the hierarchy merge picks up the links), and for
downstream dependencies after they load.
- `docs/ModelDependencies.md` documents the instance linking.

Tests (all verified to fail with the exact reported NRE stack before the
fix):

- `CrossModelInstanceTypeDefinitionTests` (Core, 4 tests): the issue's
minimal repro end to end; an equivalence test asserting the cross-model
instance emits the **identical node-state factory set** as a locally
declared type (this is the issue's stated expectation, and it drove the
method-argument-property part of the fix); the flipped
upstream/downstream ordering; and validator-level assertions that the
merged hierarchy carries linked `TypeDefinitionNode` / `DataTypeNode`
references, including the data type inherited from a dependency
`VariableType`.
- `CrossModelInstanceTypeDefinitionGeneratorTests` (Roslyn driver, 2
tests): the issue's csproj repro shape — both `AdditionalFiles`
orderings, asserting no diagnostics and that the combined generated
output of both models **compiles** (the instance factories reference the
dependency model's typed state classes).

Verified locally on net10.0: `Opc.Ua.SourceGeneration.Core.Tests` 3800
passed, `Opc.Ua.SourceGeneration.Tests` 141 passed,
`Opc.Ua.SourceGeneration.Stack.Tests` 94 passed; 0-warning Release build
of `Opc.Ua.SourceGeneration.Core` (all TFMs incl. netstandard2.0);
`dotnet format whitespace --verify-no-changes` clean.

This removes the last generator blocker for source generating the
instance model of the `Workshop/DataTypes` sample
(OPCFoundation/UA-.NETStandard-Samples#814): its `ParkingLot` /
`DriverOfTheMonth` are instances of types declared in the other design
file.

## Related Issues

- Fixes #4353

## Checklist

_Put an `x` in the boxes that apply. You can complete these step by step
after opening the PR._

- [ ] I have signed the
[CLA](https://opcfoundation.org/license/cla/ContributorLicenseAgreementv1.0.pdf)
and read the
[CONTRIBUTING](https://github.com/OPCFoundation/UA-.NETStandard/blob/master/CONTRIBUTING.md)
doc.
- [x] I have added tests that prove my fix is effective or that my
feature works and increased code coverage.
- [x] I have added all necessary documentation.
- [x] I have verified that my changes do not introduce (new) build or
analyzer warnings.
- [ ] I ran **all** tests locally using the **UA.slnx** solution against
at least .net **framework** and .net **10**, and all passed.
- [ ] I fixed **all** failing and flaky tests in the CI pipelines and
**all** CodeQL warnings.
- [ ] I have addressed **all** PR feedback received.

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---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: Marc Schier <marcschier@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: marcschier <11168470+marcschier@users.noreply.github.com>
2026-08-31 09:47:08 +00:00
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