Enable nullability and warnings-as-errors globally

[rolfbjarne]

Summary

Enable nullable reference types, treat-warnings-as-errors, and use the latest C# language version globally across the entire repository via Directory.Build.props.

Changes

Global settings (Directory.Build.props)

• Set <Nullable>enable</Nullable> globally.
• Set <TreatWarningsAsErrors>true</TreatWarningsAsErrors> globally.
• Set <LangVersion>latest</LangVersion> globally (when not already set).

Cleanup: remove per-project redundant settings

• Remove per-project <Nullable>enable</Nullable> from ~100+ .csproj files, since it's now set globally.
• Remove per-project <TreatWarningsAsErrors> and <WarningsAsErrors> settings that are now redundant.
• Remove per-project <LangVersion> settings that are now covered by the global default.

Fix nullability warnings in test code

• bindings-test: Fix nullability issues in ProtocolTest.cs, Registrar.cs, RuntimeTest.cs.
• dont-link: Fix nullability issues across multiple test files.
• link all: Fix nullability issues in link-all tests.
• link sdk: Fix nullability issues in link-sdk tests.
• BundledResources: Fix nullability in ResourcesTest.cs.
• F# tests: Fix nullability issues in F# test code.
• Other: Minor nullability fix in generate-frameworks-constants.cs.

🤖 Pull request created by Copilot

With this change, nullability is fully enabled everywhere, so:

• Fixes [Foundation] Missing nullability in some base types. #17285.
• Fixes Add C# 8 nullability annotations to bindings #6154.

[vs-mobiletools-engineering-service2]

✅ [PR Build #71b9d62] Build passed (Detect API changes) ✅

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Hash: 71b9d6217664cef7b4312842ddc9011bc391d1b1 [PR build]

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🔥 Failed to compare API and create generator diff 🔥

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Hash: 71b9d6217664cef7b4312842ddc9011bc391d1b1 [PR build]

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✅ [PR Build #71b9d62] Build passed (Build packages) ✅

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Hash: 71b9d6217664cef7b4312842ddc9011bc391d1b1 [PR build]

[vs-mobiletools-engineering-service2]

✅ [CI Build #71b9d62] Build passed (Build macOS tests) ✅

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Hash: 71b9d6217664cef7b4312842ddc9011bc391d1b1 [PR build]

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🔥 [CI Build #71b9d62] Test results 🔥

Test results

❌ Tests failed on VSTS: test results

2 tests crashed, 5 tests failed, 133 tests passed.

Failures

❌ dotnettests tests (iOS)

1 tests failed, 0 tests passed.

Failed tests

• DotNet tests: Failed (Execution failed with exit code 1)
  • Xamarin.Tests.AppIconTest.AlternateAppIcon(iOS,"ios-arm64"): 'dotnet build' failed with exit code 1
    Full command: /Users/builder/azdo/_work/5/s/macios/builds/downloads/dotnet-sdk-10.0.300-p...
  • Xamarin.Tests.AppIconTest.AlternateAppIcon(iOS,"iossimulator-x64...: 'dotnet build' failed with exit code 1
    Full command: /Users/builder/azdo/_work/5/s/macios/builds/downloads/dotnet-sdk-10.0.300-p...
  • Xamarin.Tests.AppIconTest.AlternateAppIcons(iOS,"ios-arm64"): 'dotnet build' failed with exit code 1
    Full command: /Users/builder/azdo/_work/5/s/macios/builds/downloads/dotnet-sdk-10.0.300-p...
  • ... and 37 more

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❌ dotnettests tests (MacCatalyst)

1 tests failed, 0 tests passed.

Failed tests

• DotNet tests: Failed (Execution failed with exit code 1)
  • Xamarin.Tests.AppSizeTest.MonoVM_Interpreter(MacCatalyst,"maccat...: 'dotnet build' failed with exit code 1
    Full command: /Users/builder/azdo/_work/3/s/macios/builds/downloads/dotnet-sdk-10.0.300-p...
  • Xamarin.Tests.AppSizeTest.MonoVM(MacCatalyst,"maccatalyst-arm64"...: 'dotnet build' failed with exit code 1
    Full command: /Users/builder/azdo/_work/3/s/macios/builds/downloads/dotnet-sdk-10.0.300-p...
  • Xamarin.Tests.AppSizeTest.NativeAOT(MacCatalyst,"maccatalyst-arm...: 'dotnet build' failed with exit code 1
    Full command: /Users/builder/azdo/_work/3/s/macios/builds/downloads/dotnet-sdk-10.0.300-p...
  • ... and 8 more

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❌ dotnettests tests (macOS)

1 tests failed, 0 tests passed.

Failed tests

• DotNet tests: Failed (Execution failed with exit code 1)
  • Xamarin.Tests.DotNetProjectTest.BuildProjectsWithExtensions(MacO...: 'dotnet build' failed with exit code 1
    Full command: /Users/builder/azdo/_work/3/s/macios/builds/downloads/dotnet-sdk-10.0.300-p...
  • Xamarin.Tests.DotNetProjectTest.BuildProjectsWithExtensions(MacO...: 'dotnet build' failed with exit code 1
    Full command: /Users/builder/azdo/_work/3/s/macios/builds/downloads/dotnet-sdk-10.0.300-p...
  • Xamarin.Tests.DotNetProjectTest.BuildProjectsWithExtensions(MacO...: 'dotnet build' failed with exit code 1
    Full command: /Users/builder/azdo/_work/3/s/macios/builds/downloads/dotnet-sdk-10.0.300-p...
  • ... and 7 more

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❌ dotnettests tests (tvOS)

1 tests failed, 0 tests passed.

Failed tests

• DotNet tests: Failed (Execution failed with exit code 1)
  • Xamarin.Tests.AppIconTest.AlternateAppIcon(TVOS,"tvos-arm64"): 'dotnet build' failed with exit code 1
    Full command: /Users/builder/azdo/_work/4/s/macios/builds/downloads/dotnet-sdk-10.0.300-p...
  • Xamarin.Tests.AppIconTest.AlternateAppIcon(TVOS,"tvossimulator-x...: 'dotnet build' failed with exit code 1
    Full command: /Users/builder/azdo/_work/4/s/macios/builds/downloads/dotnet-sdk-10.0.300-p...
  • Xamarin.Tests.AppIconTest.AlternateAppIcons(TVOS,"tvos-arm64"): 'dotnet build' failed with exit code 1
    Full command: /Users/builder/azdo/_work/4/s/macios/builds/downloads/dotnet-sdk-10.0.300-p...
  • ... and 28 more

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❌ monotouch tests (MacCatalyst)

🔥 Failed catastrophically on VSTS: test results - monotouch_maccatalyst (no summary found).

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❌ windows tests

🔥 Failed catastrophically on VSTS: test results - windows (no summary found).

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❌ xtro tests

1 tests failed, 0 tests passed.

Failed tests

• Xtro: BuildFailure

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Successes

✅ cecil: All 1 tests passed. Html Report (VSDrops) Download
✅ dotnettests (Multiple platforms): All 1 tests passed. Html Report (VSDrops) Download
✅ framework: All 2 tests passed. Html Report (VSDrops) Download
✅ fsharp: All 4 tests passed. Html Report (VSDrops) Download
✅ generator: All 5 tests passed. Html Report (VSDrops) Download
✅ interdependent-binding-projects: All 4 tests passed. Html Report (VSDrops) Download
✅ introspection: All 6 tests passed. Html Report (VSDrops) Download
✅ linker: All 44 tests passed. Html Report (VSDrops) Download
✅ monotouch (iOS): All 11 tests passed. Html Report (VSDrops) Download
✅ monotouch (macOS): All 12 tests passed. Html Report (VSDrops) Download
✅ monotouch (tvOS): All 11 tests passed. Html Report (VSDrops) Download
✅ msbuild: All 2 tests passed. Html Report (VSDrops) Download
✅ sharpie: All 1 tests passed. Html Report (VSDrops) Download
✅ xcframework: All 4 tests passed. Html Report (VSDrops) Download

macOS tests

✅ Tests on macOS Monterey (12): All 5 tests passed. Html Report (VSDrops) Download
✅ Tests on macOS Ventura (13): All 5 tests passed. Html Report (VSDrops) Download
✅ Tests on macOS Sonoma (14): All 5 tests passed. Html Report (VSDrops) Download
✅ Tests on macOS Sequoia (15): All 5 tests passed. Html Report (VSDrops) Download
✅ Tests on macOS Tahoe (26): All 5 tests passed. Html Report (VSDrops) Download

Linux Build Verification

✅ Linux build succeeded

Pipeline on Agent
Hash: 71b9d6217664cef7b4312842ddc9011bc391d1b1 [PR build]