Decoder — JSON to DecodedResult

Decoder is the layer below XanthamTree. It is responsible only for reading a Xantham JSON file off disk and applying the standard compression and sanitization passes before producing a DecodedResult.

You usually don't need to call into Decoder directly — XanthamTree does it for you — but it's exposed for tooling and tests.

The simple path

let result = Decoder.read "./schema.json"

match result with
| Ok decoded ->
    printfn
        "Loaded %i types and %i exported declarations."
        decoded.TypeMap.Count
        decoded.ExportTypeMap.Count
| Error e -> eprintfn "Decode failed: %s" e

Decoder.read is a proxy that constructs a default Settings and calls readWithSettings.

Settings

Decoder.Settings controls the three optional passes the decoder runs:

Construct settings with the Create static method:

let settings =
    Decoder.Settings.Create(
        inputFile = "./schema.json",
        performHealthCheck = true,
        compress = true,
        sanitize = false)

let decoded = Decoder.readWithSettings settings

DecodedResult

The shape returned on success:

• TypeMap : Map<TypeKey, TsType> — every structural type in the input.
• ExportTypeMap : Map<TypeKey, TsExportDeclaration> — every exported declaration.
• ExportMap : Map<string, Set<TypeKey>> — exports grouped by source module path.
• TopLevelExports : TypeKey list — exports declared at the top level of the input.
• LibEsExports : TypeKey list — exports that originate from the TS standard library files.

The wire format itself (Schema.EncodedResult) lives in Xantham.Common.

Health check

When enabled, the health check answers the question "are all referenced TypeKeys present in the type map?". It distinguishes:

• Missing keys — referenced but absent from TypeMap.
• Found-in-node-store — missing from TypeMap but present as an export declaration. Generation is still safe in this case.
• Unemitted keys — missing from both. Generation against this dataset is likely to fail.

The report is printed to stdout. The status emojis (✔️ / ❌) are part of the printed output, not the return value.