[Repo Assist] Add ExceptionIfMissing static parameter to JsonProvider and XmlProvider

[github-actions]

🤖 This is an automated response from Repo Assist, an AI assistant.

Closes #1241

Summary

This PR implements opt-in strict mode for missing field handling in JsonProvider and XmlProvider.

Problem: When a field is missing from JSON/XML data, the type provider silently returns a default value ("" for string, NaN for float, etc.), which can hide data quality issues.

Solution: A new ExceptionIfMissing static parameter (default false) that, when true, raises an exception when a non-optional field is absent from the data.

Usage

// Strict mode - throws if 'Name' field is missing
type PersonStrict = JsonProvider<"""{"Name":"Alice","Age":30}""", ExceptionIfMissing=true>
let p = PersonStrict.Parse("""{"Age": 30}""")
p.Name  // raises System.Exception: 'Name' is missing

// Default mode (backward compatible) - returns "" for missing string
type Person = JsonProvider<"""{"Name":"Alice","Age":30}""">
let p = Person.Parse("""{"Age": 30}""")
p.Name  // returns ""

Same works for XmlProvider:

type ItemStrict = XmlProvider<"(item)(name)foo(/name)(/item)", ExceptionIfMissing=true>

Changes

• JsonRuntime.fs and TextRuntime.fs: Added GetNonOptionalValueStrict<'T> — like GetNonOptionalValue but without the string/float special cases that return "" / NaN.
• JsonConversionsGenerator.fs: Added exceptionIfMissing parameter; selects GetNonOptionalValueStrict vs GetNonOptionalValue at code generation time.
• ConversionsGenerator.fs: Added exceptionIfMissing parameter for XML/CSV/HTML string conversions.
• JsonGenerator.fs, XmlGenerator.fs: Added ExceptionIfMissing: bool to context records; propagated to code generation.
• JsonProvider.fs, XmlProvider.fs: Added ExceptionIfMissing static parameter (default false).
• CsvGenerator.fs, HtmlGenerator.fs: Always pass false — these providers don't expose the parameter.
• TypeProviderInstantiation.fs: Updated test helper to include new parameter.
• Tests added in tests/FSharp.Data.Tests/JsonProvider.fs and XmlProvider.fs.

Bug Fix (incidental)

Fixes a pre-existing bug in XmlProvider.fs where args.[14] was used for both UseSchemaTypeNames and PreferDateTimeOffset (correct: args.[14] = UseSchemaTypeNames, args.[15] = PreferDateTimeOffset, args.[16] = ExceptionIfMissing).

Test Status

✅ tests/FSharp.Data.Tests — 283 tests, all passed (includes 7 new ExceptionIfMissing tests)

⚠️ tests/FSharp.Data.DesignTime.Tests — 218 signature tests failing with pre-existing infrastructure error (CsvFile\1[RowType] not found in target reference assembly set). This is unrelated to these changes and present on main` as well.

Generated by Repo Assist for issue #1241

To install this agentic workflow, run

gh aw add githubnext/agentics/workflows/repo-assist.md@afb00b92a9514fee9a14c583f059a03d05738f70