# Description
Nullable reference types are now enabled once, in `common.props`, and
every project in the repository builds warning-clean with them.
**Configuration**
- `<Nullable>enable</Nullable>` lives in `common.props`. All per-project
`<Nullable>` settings are removed: 178 project files (enable,
annotations, and the `disable` in the three Aot test projects).
- 419 per-file `#nullable enable`/`restore` directives and the 4
`#nullable disable` directives are removed.
- Kept on purpose:
- The 5 `<auto-generated>` schema files (`UANodeSet.cs`, `UA Type
Dictionary.cs`, `OPCBinarySchema.cs`, `SecuredApplication.cs`,
`PInvokeHelper.cs`) keep `#nullable enable`. The compiler ignores the
project setting in generated code, so the directive is required there.
- `tests/Opc.Ua.Interop.LegacyPeer` keeps `disable`. It builds against
the 1.5.378 packages and does not import the repository props.
- `docs/DeveloperGuide.md` and `.github/copilot-instructions.md` now
describe the central setting.
**Migration** (the 43 unset and 13 annotations-only projects, roughly
10k diagnostics)
- **Production code: annotated at the declarations.** Covers
`tools/Opc.Ua.SourceGeneration.Core`, `src/Opc.Ua.Lds.Server` and the
LDS sample.
- Members, parameters and returns are nullable where null actually
flows.
- Null-check helpers carry `[NotNullWhen]` (`IsNull`, `IsValidXmlName`,
`IsMethodTypeDesign`).
- `CoreUtils.Format`, `Utils.Format`, `ITemplateWriter.WriteLine` take
`params object?[]`. `Template.AddReplacement` takes `string?` (rendering
already skips null replacements).
- `IRegisteredServerStore.RegisterAsync` returns
`Task<RegistrationEntry?>`: it returns null when a registration is
removed.
- Dereferences backed by an invariant (for example, the validated model)
use `!`, so runtime behaviour is unchanged.
- **Behavioural changes in production code** (small, deliberate):
- `NodeSetToModelDesign` throws `InvalidOperationException` when the
file is not a NodeSet. Before, it threw a NullReferenceException on the
next line.
- `ModelDesignValidator` starts its lookup tables empty instead of null.
A redundant `if (m_nodes == null) return;` guard is gone.
- **Test code: minimal annotations.**
- `?` on values that can be null, `!` where the test asserts non-null.
- `= null!` for fixture members assigned in SetUp.
- `TryGetStructure<T>(out T? x)` where the inferred `T?` broke the
`IEncodeable` constraint.
- A few redundant `== null` checks on structs (`NodeId`, `ArrayOf<T>`)
folded into the adjacent `IsNull`/`Count` checks.
**Notes for reviewers**
- The diff is large (~1,500 files) but almost entirely mechanical: `?`,
`!` and directive removal. The non-annotation changes are listed above.
- Known follow-up, not done here:
`IModelDesign.Namespaces/TargetNamespace/NamespaceUris` stay
non-nullable even though the validator returns null before it loads a
dictionary. Making them nullable would ripple through every generator
call site.
## Related Issues
- Fixes#4439
## Checklist
- [ ] 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.
- [ ] 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.
The "no new warnings" box covers net10.0 and net48: full non-incremental
builds of `UA.slnx`, `tools/SourceGeneration.slnx`,
`tools/MigrationAnalyzer.slnx` and the Aot test projects finished with 0
warnings and 0 errors under the repository's warnings-as-errors
settings. net9.0 and net8.0 also had no nullable diagnostics, but they
were not rebuilt after the final fixes. Tests have not been run locally
yet.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
# Description
Drops support for **netstandard2.1** and **.NET Framework 4.7.2**.
Libraries now target `net48`, `net8.0`, `net9.0` and `net10.0`.
`Opc.Ua.Types` and `Opc.Ua.SourceGeneration.Core` still also target
`netstandard2.0`, but only because the Roslyn source generators load
them. There is no general netstandard2.0 support.
**Preprocessor directives** (112 files)
- Every `#if`/`#elif` mentioning `NETSTANDARD2_1*`, `NET472*`,
`NET_STANDARD_TESTS`, `SKIP_ECC_CERTIFICATE_REQUEST_SIGNING` or
`NETSTANDARD*` was evaluated against the remaining TFM set (net48,
net8/9/10, plus netstandard2.0 inside `Opc.Ua.Types`/`tools`) and
simplified. Dead branches were removed.
- Example: `NETSTANDARD2_1 || NET8_0_OR_GREATER` → `NET8_0_OR_GREATER`.
- Example: `NET8_0_OR_GREATER || NET472_OR_GREATER` → removed (always
true).
- Netstandard-only code was removed: `UnixFileModeShim`, the CRDT
reflection path in `ReplicatedGossipOptions.CreateReaderOptions`, and
the netstandard2.1-only test variants.
**Custom test logic**
- `targets.props` drops the `net472`, `netstandard2.0` and
`netstandard2.1` `CustomTestTarget` profiles, `NetStandardTests` and
`SKIP_ECC_CERTIFICATE_REQUEST_SIGNING`. Supported values are now
`net48`, `net8.0`, `net9.0`, `net10.0`.
- The `NET_STANDARD_TESTS` define is removed from 29 test projects.
- The "build netstandard shells as net10.0" overrides are removed from
18 projects.
- `RestrictForLegacyTfm` now only applies to `net48`.
- `tests/customtest.bat` is updated to the new values.
**Build / packaging / CI**
- MSBuild TFM conditions are simplified: Kestrel package choice, MQTTnet
v4 (net48 only), BouncyCastle, Di/OpenUsd/Vision/Stress test excludes,
and `System.IO.FileSystem.AccessControl` (dropped from Core).
- The MigrationAnalyzer nuspec drops its net472/netstandard2.1 lib
groups. The Azure signing lists are updated.
- `get-ci-matrix.ps1` removes the net472/netstandard test profiles
(including the PR-gating `linux-netstandard2.1`) and the matching build
legs.
**Breaking API change (2.0 preview):** removed
`HttpsTransportListener.IsWssTransportSupported` and
`ReplicatedGossipOptions.IsGossipStateDecodingSupported`. They only
returned `false` on netstandard2.1 and are now always `true`. The test
guards that used them were removed as well.
**Docs**
- NuGet READMEs, `README.md`, `DeveloperGuide.md`, `PubSub.md`, the
certificate/ECC/identity docs and the 2.0 migration guide (plus its
`.agents` skill mirror) are updated.
- The migration guide notes that 4.7.2 consumers must move to 4.8 and
netstandard2.1 consumers to net8.0+.
### Reviewer notes
- The `System.IO.FileSystem.AccessControl` `PackageVersion` pin is left
in `Directory.Packages.props`. It has no direct reference any more, but
transitive pinning is on, so it was kept to avoid shifting resolved
versions.
- The `#if` rewrite was done mechanically by a truth-table evaluator.
The diff in the `.cs` files is limited to directive lines, removed dead
branches, and stale-comment updates.
### Verified locally
- `dotnet build UA.slnx -p:CustomTestTarget=net48`: 0 errors.
- `dotnet build UA.slnx -p:CustomTestTarget=net10.0`: 0 errors.
- Default multi-target builds (no `CustomTestTarget`) of Opc.Ua.Types,
Bindings.Https, PubSub.Mqtt and Redundancy.Server succeeded.
- net10.0 tests:
- Opc.Ua.Redundancy.Server.Tests: 840/840 passed.
- Opc.Ua.Types.Tests: 11363 passed, 1 skipped.
- ModelDependencyScanner tests: 20/20 passed.
- The full test suite was **not** run locally.
## Related Issues
- None
## Checklist
- [ ] 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.
- [ ] 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.
- [ ] 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.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
romanett