fix: Support parsing primitive values from single-key objects

[revidious]

Description

Fixes #1141

This PR adds support for parsing primitive values from single-key objects in unions. When an LLM responds with an object-wrapped primitive (e.g., {"status": 1}), we now correctly extract and validate the inner value.

Changes

• Add support for extracting primitive values (numbers, booleans, strings) from single-key objects
• Track the extracted key name using ImpliedKey flag
• Reject invalid cases:
  • Nested objects (e.g., {"status": {"code": 1}})
  • Arrays (e.g., {"values": [1]})
  • Multi-key objects

Test Plan

Added test cases covering:

• Basic object extraction: {"status": 1} → 1
• Multiple primitive types in union
• Invalid cases (nested objects, arrays)

All tests are passing.

---

Important

Adds support for parsing primitive values from single-key objects in unions, with tests for valid and invalid cases.

• Behavior:
  • Supports parsing primitive values from single-key objects in unions in coerce_literal.rs.
  • Extracts and validates inner values if they are numbers, booleans, or strings.
  • Rejects nested objects, arrays, and multi-key objects.
• Flags:
  • Uses ImpliedKey flag to track extracted key names.
• Tests:
  • Added tests in test_literals.rs for basic object extraction, multiple primitive types, and invalid cases (nested objects, arrays).

^{This description was created by for b4bf23f. It will automatically update as commits are pushed.}

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[ellipsis-dev]

👍 Looks good to me! Reviewed everything up to b4bf23f in 1 minute and 42 seconds

More details

• Looked at 178 lines of code in 2 files
• Skipped 0 files when reviewing.
• Skipped posting 2 drafted comments based on config settings.

1. engine/baml-lib/jsonish/src/deserializer/coercer/coerce_literal.rs:7

• Draft comment:
  The use std::vec; statement is unnecessary as the vec! macro is already included in the prelude.
• Reason this comment was not posted:
  Confidence changes required: 50%
  The comment should be placed on the first line of the diff, which is line 7.

2. engine/baml-lib/jsonish/src/deserializer/coercer/coerce_literal.rs:47

• Draft comment:
  Consider adding a log statement here to indicate that a single-key object is being processed. This can help in debugging and understanding the flow of data.
• Reason this comment was not posted:
  Confidence changes required: 33%
  The comment should be placed on the first line of the diff, which is line 7.

Workflow ID: wflow_dqxyZ8MpTJD0MMpq

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Name	Status	Preview	Comments	Updated (UTC)
baml	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Dec 11, 2024 0:21am

[hellovai]

LGTM!