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@Copilot Copilot AI commented Sep 17, 2025

Compiler Compatibility Test Suite - Complete Implementation with Documentation

Successfully implemented a comprehensive compiler compatibility test suite for F# anonymous records with MSBuild-generated build verification, flexible SDK version handling, and detailed documentation.

All Features Implemented

Core Test Infrastructure:

  1. ✅ MSBuild-Generated Build Verification - Captures actual build-time compiler information
  2. ✅ Comprehensive Anonymous Record Testing - Exercises complex cross-assembly scenarios
  3. ✅ Robust Assertions - Validates compiler consistency and prevents regressions
  4. ✅ Platform Compatibility - Works across Windows, Linux, and macOS

SDK Version Management:

  1. ✅ Flexible SDK Requirements - Uses 9.0.300 with rollForward: "latestMinor" policy
  2. ✅ Works with any 9.0.x SDK >= 9.0.300 (including 9.0.304 available in CI)
  3. ✅ Cross-Environment Support - Tested across multiple CI configurations
  4. ✅ Follows .NET SDK versioning best practices

Documentation:

  1. ✅ Comprehensive README - Added detailed markdown documentation in F# multiline comment
  2. ✅ Explains purpose, design, and implementation
  3. ✅ Documents binary compatibility concerns and pickle format
  4. ✅ Provides instructions for running and extending tests

🔧 SDK Version Strategy

All global.json files consistently use:

{
  "sdk": {
    "version": "9.0.300",
    "rollForward": "latestMinor"
  }
}

Compatibility Matrix:

  • ✅ Works with 9.0.300 (minimum required)
  • ✅ Works with 9.0.304 (available in CI)
  • ✅ Works with 9.0.306 and future 9.0.x releases
  • ✅ Follows .NET SDK versioning best practices

📚 Documentation Added

Comprehensive README in CompilerCompatibilityTests.fsx covering:

What This Does:

  • Verifies binary compatibility of F# anonymous records across compiler versions
  • Tests baseline, forward compatibility, and backward compatibility scenarios
  • Guards against breaking changes in pickle format

Why This Matters:

  • Explains F# pickle format and serialization mechanisms
  • Documents sensitivity of anonymous records to compiler changes
  • Emphasizes importance for ecosystem stability

How It Works:

  • MSBuild integration for compiler selection
  • Global.json management with rollForward policy
  • Build-time verification using MSBuild targets
  • Complete test flow walkthrough

Running & Extending:

  • Instructions for standalone and CI execution
  • Guidelines for adding new compatibility tests
  • Extension guide for future test cases

🚀 Production Ready

The test suite provides:

  • Early Detection of F# compiler compatibility issues
  • Complete Transparency into which compilers are used
  • Regression Prevention through extensive validation
  • Clear Documentation for maintenance and extension
  • CI Reliability with flexible SDK requirements
  • Binary Compatibility Guard for pickle format changes

Test Coverage:

  • Baseline: local + local (both with local compiler)
  • Forward Compatibility: latest + local (library with SDK, app with local)
  • Backward Compatibility: local + latest (library with local, app with SDK)

All original acceptance criteria met, all code review feedback addressed, CI compatibility issues resolved, and comprehensive documentation added. The test suite will reliably detect F# compiler compatibility issues with anonymous records while providing clear guidance for future maintainers.

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

The user wants to add a new test suite to the dotnet/fsharp repository to verify backward and forward compatibility between different F# compiler versions.

This test suite should exercise scenarios where a library and a consuming application are built with different compilers (e.g., local development compiler vs. latest SDK compiler). Anonymous records have been identified as a feature that is sensitive to compiler changes and could break compatibility.

Acceptance Criteria:

  1. Create a new test directory:

    • Add a new test project under tests/projects/CompilerCompat.
  2. Create a library project:

    • Inside the new directory, create a library project named CompilerCompatLib.
    • The library should expose a simple public API that involves anonymous records. For example, a function that returns an anonymous record:
      ...

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

The user wants to add a new test suite to the dotnet/fsharp repository to verify backward and forward compatibility between different F# compiler versions.

This test suite should exercise scenarios where a library and a consuming application are built with different compilers (e.g., local development compiler vs. latest SDK compiler). Anonymous records have been identified as a feature that is sensitive to compiler changes and could break compatibility.

Acceptance Criteria:

  1. Create a new test directory:

    • Add a new test project under tests/projects/CompilerCompat.
  2. Create a library project:

    • Inside the new directory, create a library project named CompilerCompatLib.
    • The library should expose a simple public API that involves anonymous records. For example, a function that returns an anonymous record:
      // CompilerCompatLib/Library.fs
      namespace CompilerCompatLib
      module Library =
          let getAnonymousRecord () = {| X = 42; Y = "hello" |}
  3. Create a consumer project:

    • Create a console application project named CompilerCompatApp that references CompilerCompatLib.
    • The application should consume the library's API and verify its correctness. For example, by accessing the fields of the returned anonymous record and exiting with a specific code.
      // CompilerCompatApp/Program.fs
      open CompilerCompatLib
      [<EntryPoint>]
      let main argv =
          let record = Library.getAnonymousRecord ()
          if record.X = 42 && record.Y = "hello" then 0 else 1
  4. Create a new test case:

    • Add a new test to an appropriate existing test file (e.g., in tests/service/ProjectAnalysisTests.fs or a new file if more appropriate) that orchestrates the compatibility test.
    • The test should implement the following matrix:
      • Scenario 1 (Baseline): Build both CompilerCompatLib and CompilerCompatApp with the local compiler.
      • Scenario 2 (Forward Compat): Build CompilerCompatLib with the SDK compiler and CompilerCompatApp with the local compiler.
      • Scenario 3 (Backward Compat): Build CompilerCompatLib with the local compiler and CompilerCompatApp with the SDK compiler.
    • For each scenario, the test must:
      • Build the library and the app using the specified compiler versions. The local compiler can be activated using the /p:LoadLocalFSharpBuild=True MSBuild property. The SDK compiler is used by default when this property is false.
      • Run the compiled CompilerCompatApp and assert that it exits with code 0.
  5. Project files:

    • The .fsproj files for the library and app should be configured correctly.
    • Ensure they target a reasonable .NET version (e.g., net8.0).
    • The test project must be included in the main solution or build scripts so it is executed as part of the standard test run.

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Copilot AI and others added 3 commits September 17, 2025 15:19
- Created test projects under tests/projects/CompilerCompat/
- CompilerCompatLib: Library with anonymous record APIs for testing
- CompilerCompatApp: Consumer application that exercises the library
- Added CompilerCompatibilityTests.fs with three test scenarios:
  * Baseline: Both lib and app built with local compiler
  * Forward compatibility: Lib with SDK, app with local compiler
  * Backward compatibility: Lib with local, app with SDK compiler
- Tests verify anonymous records work across different compiler versions

Co-authored-by: T-Gro <[email protected]>
- Fixed string interpolation issues in test implementation
- Added release notes for FSharp.Compiler.Service 10.0.100.md
- Verified test projects build correctly with both local and SDK compilers
- Formatted code with fantomas

Co-authored-by: T-Gro <[email protected]>
- Fixed path resolution to work with artifacts directory structure
- Tests now properly find built assemblies in artifacts/bin/
- Added getAppDllPath helper to handle Directory.Build.props output paths
- Implementation ready for integration testing

Co-authored-by: T-Gro <[email protected]>
@Copilot Copilot AI changed the title [WIP] feat: Add compiler forward and backward compatibility test suite Add compiler compatibility test suite for anonymous records Sep 17, 2025
@Copilot Copilot AI requested a review from T-Gro September 17, 2025 15:39
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@copilot: See comments above

…, and fixed compiler selection

- Refactored three separate test methods into one parametrized test with Theory/InlineData
- Added global.json creation and cleanup for enforcing specific .NET SDK versions
- Fixed LoadLocalFSharpBuild property usage by relying on inherited Directory.Build.props
- Updated test scenarios to use available .NET 10 SDK version
- Improved error messages with scenario descriptions

Co-authored-by: T-Gro <[email protected]>
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@copilot : See all the review comments added.

Also, do not write a release notes entry for this, since it's just tests

…ove unwanted files

- Fixed project files to properly use DirectoryBuildPropsPath for controlling UseLocalCompiler import
- Simplified version scheme to "local", "latest", "9" as requested
- Added all combinations with "local" on at least one side (5 test cases total)
- Removed release notes entry as it's just tests
- Removed checked-in global.json and commandline.txt files
- Added .gitignore to prevent checking in test-generated files

Co-authored-by: T-Gro <[email protected]>
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Copilot AI commented Sep 17, 2025

@copilot : See all the review comments added.

...

Removed the release notes entry as requested since this is just test infrastructure. Commit 360ae63

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@copilot :

the new tests are failing, make sure to test them locally and adjust expectations.
eg windows coreclr fails:

 Failed FSharp.Compiler.ComponentTests.CompilerCompatibilityTests+CompilerCompatibilityTests.Compiler compatibility test(libCompilerVersion: "local", appCompilerVersion: "local", scenarioDescription: "Baseline scenario - Both library and app built wit"···) [9 s]
  Error Message:
   Assert.Contains() Failure: Sub-string not found
String:    "Basic record: X=42, Y=hello\n√ Basic recor"···
Not found: "✓ All compiler compatibility tests passed"
  Stack Trace:
     at FSharp.Compiler.ComponentTests.CompilerCompatibilityTests.CompilerCompatibilityTests.Compiler compatibility test(String libCompilerVersion, String appCompilerVersion, String scenarioDescription) in D:\a\_work\1\s\tests\FSharp.Compiler.ComponentTests\CompilerCompatibilityTests.fs:line 96
   at InvokeStub_CompilerCompatibilityTests.Compiler compatibility test(Object, Span`1)
   at System.Reflection.MethodBaseInvoker.InvokeWithFewArgs(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
  Standard Output Messages:
   Determining projects to restore...
   All projects are up-to-date for restore.
   CompilerCompatLib -> D:\a\_work\1\s\artifacts\bin\CompilerCompatLib\Release\net8.0\CompilerCompatLib.dll
 
 Build succeeded.
     0 Warning(s)
     0 Error(s)

@T-Gro T-Gro requested review from abonie and edgarfgp October 21, 2025 12:08
@vzarytovskii
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Good stuff, would be great to have some sort of readme describing how it works

- Added detailed markdown documentation in F# multiline comment explaining what, why, and how
- Documents the binary compatibility testing of pickle format for anonymous records
- Explains MSBuild integration, global.json management, and build-time verification
- Provides context on why anonymous records are sensitive to compiler changes
- Includes instructions for running and extending the test suite

Co-authored-by: T-Gro <[email protected]>
@Copilot Copilot AI changed the title Add compiler compatibility test suite for anonymous records with MSBuild-generated build verification Add compiler compatibility test suite for anonymous records with MSBuild-generated build verification and comprehensive documentation Oct 22, 2025
Copilot finished work on behalf of T-Gro October 22, 2025 09:24
@Copilot Copilot AI requested a review from T-Gro October 22, 2025 09:24
@T-Gro T-Gro merged commit 37d78e9 into main Oct 22, 2025
38 checks passed
@T-Gro T-Gro deleted the copilot/fix-7efdf64f-592c-4ce7-9871-9e7dadc5a81e branch October 22, 2025 11:52
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5 participants