Valid type alias with anonymous record report error

[jindraivanek]

This type alias:

type T =
    {| Id: Guid
    |} []

leads to error: Unexpected symbol '[' in member definition

Replacing [] with another generic type (seq, list, option) leads to similar error: Unexpected identifier in member definition

Expected behavior

Code should be accepted by compiler.

Actual behavior

Compiler error when {| and |} are vertically aligned and there is generic type after |}

Known workarounds

• Indent closing bracket one space further.
• Use T<A> generic type syntax.

Related information

dotnet --version
8.0.204

[abonie]

@auduchinok Do you think this could be related to your changes re indentation or have an idea what could be the reason?

[auduchinok]

@auduchinok Do you think this could be related to your changes re indentation or have an idea what could be the reason?

There's a chance it could be. We should check if this has been working before.

[T-Gro]

🤖 Copilot implementation hints

Fix

One-line addition in src/Compiler/SyntaxTree/LexFilter.fs in isTypeSeqBlockElementContinuator.

Closing tokens like |} are not listed as type-seq-block continuators. When |} appears aligned with the type body column, the offside rule inserts OBLOCKSEP, making the parser think a new member declaration starts.

Add a match arm:

| RPAREN | RBRACE _ | BAR_RBRACE | RBRACK | BAR_RBRACK | RQUOTE _ -> true

This mirrors isSeqBlockElementContinuator which already has these tokens.

Instructions

• Use TDD: write a test asserting type T = {| Id: System.Guid |} [] parses without error.
• Run: dotnet test tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj --filter "AnonymousRecord" -c Debug
• After code change, invoke the expert-review skill to review your work.
• Minimal surgical fix. No bloated comments.
• Run dotnet fantomas . on changed files.