Idempotency problem when adding members to a single case union without a pipe

[joprice]

Issue created from fantomas-online

Formatted code

module Test


type X = X
    with

        // a newline is added boave this line on each frmat if the union does not begin with a pipe
        static member x = 1

type Y =
    | Y

    static member x = 1

Reformatted code

module Test


type X = X
    with


        // a newline is added boave this line on each frmat if the union does not begin with a pipe
        static member x = 1

type Y =
    | Y

    static member x = 1

Problem description

Fantomas was not able to produce the same code after reformatting the result.

Extra information

• The formatted result breaks my code.
• The formatted result gives compiler warnings.
• I or my company would be willing to help fix this.
• I would like a release if this problem is solved.

[nojaf]

Hello, thanks for reporting this issue.

I believe the problem may be around:

fantomas/src/Fantomas.Core/CodePrinter.fs

Line 3585 in e2aa020

+> onlyIfCtx (fun ctx -> ctx.Config.NewlineBetweenTypeDefinitionAndMembers) sepNln

Something along the lines of

onlyIfCtx
    (fun ctx -> ctx.Config.NewlineBetweenTypeDefinitionAndMembers)
    (sepNlnUnlessContentBefore (MemberDefn.Node members.[0]))

probably avoid the problem.

Are you interested in sending a PR for this?

[joprice]

Not yet familiar with the codebase but I can try it out and let you know if I don't get make progress.

[nojaf]

We have some documentation about how the project is structured: https://fsprojects.github.io/fantomas/docs/contributors/Solution%20Structure.html

Let me know if you have any questions.

[joprice]

Nice. I checked out the project to make sure I can at least built it and get the test to success, but this test failed:

 Failed code that was invalid should be still be written [837 ms]
 Error Message:
    Assert.That(, )
 Expected: 0
 But was:  134

 Stack Trace:
    at FsUnit.TopLevelOperators.should[a,a](FSharpFunc`2 f, a x, Object actual)
  at Fantomas.Tests.Integration.ForceTests.code that was invalid should be still be written() in fantomas/src/Fantomas.Tests/Integration/ForceTests.fs:line 29

1)    at FsUnit.TopLevelOperators.should[a,a](FSharpFunc`2 f, a x, Object actual)
  at Fantomas.Tests.Integration.ForceTests.code that was invalid should be still be written() in fantomas/src/Fantomas.Tests/Integration/ForceTests.fs:line 29

Unrelated, but nice to start with a clean slate when modifying things. Is this one expected?

[joprice]

actually I missed an error above that that might be the cause

The active test run was aborted. Reason: Test host process crashed : Stack overflow.
Repeat 2 times:
--------------------------------
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
--------------------------------
   at [email protected](LinkExpr)
   at Microsoft.FSharp.Primitives.Basics.List.mapToFreshConsTail[[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](Microsoft.FSharp.Collections.FSharpList`1<System.__Canon>, Microsoft.FSharp.Core.FSharpFunc`2<System.__Canon,System.__Canon>, Microsoft.FSharp.Collections.FSharpList`1<System.__Canon>)
   at Microsoft.FSharp.Primitives.Basics.List.map[[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](Microsoft.FSharp.Core.FSharpFunc`2<System.__Canon,System.__Canon>, Microsoft.FSharp.Collections.FSharpList`1<System.__Canon>)
   at Microsoft.FSharp.Collections.ListModule.Map[[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](Microsoft.FSharp.Core.FSharpFunc`2<System.__Canon,System.__Canon>, Microsoft.FSharp.Collections.FSharpList`1<System.__Canon>)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at [email protected](System.Tuple`2<Fantomas.FCS.Text.Range,Fantomas.FCS.Syntax.SynExpr>)
   at Fantomas.Core.ASTTransformer.mkTuple(CreationAide, Microsoft.FSharp.Collections.FSharpList`1<Fantomas.FCS.Syntax.SynExpr>, Microsoft.FSharp.Collections.FSharpList`1<Fantomas.FCS.Text.Range>, Fantomas.FCS.Text.Range)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at Fantomas.Core.ASTTransformer.mkParenExpr(CreationAide, Fantomas.FCS.Text.Range, Fantomas.FCS.Syntax.SynExpr, Fantomas.FCS.Text.Range, Fantomas.FCS.Text.Range)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at Fantomas.Core.ASTTransformer.mkParenExpr(CreationAide, Fantomas.FCS.Text.Range, Fantomas.FCS.Syntax.SynExpr, Fantomas.FCS.Text.Range, Fantomas.FCS.Text.Range)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at [email protected](System.Tuple`4<Microsoft.FSharp.Core.FSharpChoice`2<SingleTextNode,System.Tuple`2<Fantomas.FCS.Text.Range,Fantomas.FCS.Text.Range>>,Fantomas.FCS.Syntax.SynExpr,SingleTextNode,Fantomas.FCS.Syntax.SynExpr>)
   at Microsoft.FSharp.Primitives.Basics.List.map[[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](Microsoft.FSharp.Core.FSharpFunc`2<System.__Canon,System.__Canon>, Microsoft.FSharp.Collections.FSharpList`1<System.__Canon>)
   at Microsoft.FSharp.Collections.ListModule.Map[[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](Microsoft.FSharp.Core.FSharpFunc`2<System.__Canon,System.__Canon>, Microsoft.FSharp.Collections.FSharpList`1<System.__Canon>)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at Fantomas.Core.ASTTransformer.collectComputationExpressionStatements(CreationAide, Fantomas.FCS.Syntax.SynExpr, Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Collections.FSharpList`1<ComputationExpressionStatement>,Microsoft.FSharp.Collections.FSharpList`1<ComputationExpressionStatement>>)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at Fantomas.Core.ASTTransformer.collectComputationExpressionStatements(CreationAide, Fantomas.FCS.Syntax.SynExpr, Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Collections.FSharpList`1<ComputationExpressionStatement>,Microsoft.FSharp.Collections.FSharpList`1<ComputationExpressionStatement>>)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)
   at Fantomas.Core.ASTTransformer.mkExpr(CreationAide, Fantomas.FCS.Syntax.SynExpr)

[nojaf]

Ok, this is interesting. Are you on Mac? And does running dotnet test ./src/Fantomas.Core.Tests/Fantomas.Core.Tests.fsproj work for you?

If it does, you could try and ignore this integration test. It did work for me locally. Not quite sure what went wrong.

[joprice]

I get the same error when running just the Fantomas.Core.Tests, so seems like something more general is wrong with my local env.

[joprice]

To narrow it down a little more,

• Fantomas.Tests run but the integration test ForceTests fails
• Fantomas.Client.Tests run fine,
• Fantomas.Core.Tests stack overflow

Unfortunately, the last one seems to be where a test for this type of change is meant to go.

[nojaf]

Please tell me again what you SDK version is? What operating system?
Can you use the dev container maybe?

[joprice]

I'm on arm mac with osx 14.5, dotnet version 8.0.303. I can try the devcontainer out.

[joprice]

It passes when run via a container with npx @devcontainers/cli up --workspace-folder . and npx @devcontainers/cli exec --workspace-folder . dotnet test.

[joprice]

I just tried running the build via dotnet fsi build.fsx -p Build and it passed without requiring the container. I noticed that it's running the tests under Release configuration. Running with Release: dotnet test src/Fantomas.Core.Tests -c Release does not stack overflow for me. I assume that the parser relies on some optimizations like tco that is only kicking in release mode. That allows me to run them locally without a container.

[nojaf]

I'm not sure what is wrong with your environment but it feels like something is overriding <Tailcalls>true</Tailcalls> for you.

[nojaf]

NuGet is acting weird,

[nojaf]

@joprice available now in https://www.nuget.org/packages/fantomas/6.3.13