The record generator for anonymous records.

[Krzysztof-Cieslak]

Sample code:

let x () : {| A: int; B: string  |} = 
    {| A = 123 |}

The error message on the second line: Two anonymous record types have mismatched sets of field names '["A"; "B"]' and '["A"]'.
Having info present in error message we should be able to generate stub for missing fields just like in case of normal records

[Angr1st]

I would like to tackle this. Do you know where the stub for the missing fields for regular records is created?

[baronfel]

The current record stub generation code is found src/FsAutoComplete.Core/RecordStubGenerator.fs, and the place it's called is the GetRecordStub member in src/FsAutoComplete.Core/Commands.fs. My guess is that shouldGenerateRecordStub needs to be updated to apply to anon records with 'missing' fields, and formatRecord would need to be updated as well.

[Angr1st]

Is there a Tool or Documentation to visualize the AST of F# Source Code to improve my understanding of the differences between a RecordExpression and an AnonRecordExpression?

[baronfel]

Yep! There's a good one over at https://jindraivanek.gitlab.io/ast-viewer, and a slightly-less good one at sharplab.io.

[github-actions]

🤖 This is an automated response from Repo Assist.

This request is still relevant and feasible! A lot has changed in the codebase since 2019, so here's an updated map of where an implementation should live.

Current architecture (post-refactor):

• All code fixes are in src/FsAutoComplete/CodeFixes/
• The regular record stub generator is a great model: CodeFixes/GenerateRecordStub.fs
• The underlying logic lives in src/FsAutoComplete.Core/RecordStubGenerator.fs
• Anonymous record support does not yet exist in either file

Implementation approach

The simplest path is a diagnostic-driven code fix. The F# compiler emits:

FS3578: Two anonymous record types have mismatched sets of field names ["A"; "B"] and ["A"]

You can detect this error in a CodeFix by matching on SourceDiagnostic whose code is 3578 and whose message matches the pattern. From the error text you can extract:

• The expected field set (["A"; "B"])
• The actual field set (["A"])

Then compute the missing fields and insert them into the anonymous record expression at the cursor position.

Key files to look at:

• CodeFixes/GenerateRecordStub.fs — shows how a record stub fix is wired up
• src/FsAutoComplete.Core/RecordStubGenerator.fs — shouldGenerateRecordStub and formatRecord for naming inspiration
• CodeFixes/AddMissingRecordFields.fs — another record-field fix you might find useful

Good first issue candidate? Yes — if you can parse the error message and determine the insert position (after the last = in the anonymous record expression), the rest is straightforward text insertion. The main complexity is finding the right source range within the {| ... |} literal.

Happy to help with more details if someone picks this up!

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[github-actions]

🤖 This is an automated response from Repo Assist.

Good news — PR #1510 implements this fix! It adds a GenerateAnonRecordStub code fix that triggers on the FS3578 diagnostic and inserts fieldName = failwith "Not Implemented" stubs for each missing field.

For example:

let f (x: {| A: int; B: string |}) = x
let y = f {| A = 1 |}   // FS3578 — B is missing
// → fix inserts: {| A = 1; B = failwith "Not Implemented" |}

The PR is currently a draft awaiting review. See #1510 for full details.

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