Fix PartiallyGenerated for array properties

[ethanhuang13]

Summary

• Generate partial types for arrays as [Element.PartiallyGenerated] instead of [Element].
• Decode partial array properties using element partial types.
• Add GenerableMacro test coverage for array partials.

Problem

When a @Generable struct has an array property (e.g. [CatProfile]), the AnyLanguageModel macro previously synthesized the partially generated property as [CatProfile], not a partially generated array. This breaks SwiftUI usage and diverges from FoundationModels’ macro output.

FoundationModels’ GenerableMacro produces a partially generated property of type [CatProfile.PartiallyGenerated]?, and AnyLanguageModel needed to align with that output.

Example

@Generable
struct CatProfiles {
  @Guide(description: "Cats", .count(5))
  var catProfiles: [CatProfile]
}

extension CatProfiles.PartiallyGenerated: View {
  var body: some View {
    if let catProfiles {
      // Previously needed a workaround: `ForEach(catProfiles.asPartiallyGenerated())`.
      // Now aligned with FoundationModels.
      ForEach(catProfiles) { catProfile in
        // ...
      }
    }
  }
}

Before

• Generated property type: public var catProfiles: [CatProfile] (not partially generated)
• Forces ForEach(catProfiles.asPartiallyGenerated()) to get the correct shape for SwiftUI.

After

• Generated property type: public var catProfiles: [CatProfile.PartiallyGenerated]?
• Correct SwiftUI usage becomes ForEach(catProfiles) with no extra conversion.

Testing

• swift test (new GenerableMacro test passes).

[mattt]

Thank you, @ethanhuang13! Taking a look now...

[mattt]

Thanks for pushing this through, @ethanhuang13! The array partial type fix is great.

One short‑term issue I noticed: the new PartiallyGenerated property declarations now use .PartiallyGenerated for all types, which inadvertently breaks primitives and dictionaries (e.g. String.PartiallyGenerated doesn’t exist). I made a minimal follow‑up adjustment (13589db) to keep primitives/dicts as‑is, preserve optional element types, and make array/dictionary detection a bit more robust. I also added a couple of focused tests so we don’t regress.

Looking at topLevelColonIndex, I suspect this is all due for a rethink, as this all seems to be reimplementing aspects of SwiftSyntax albeit poorly. Let's push these incremental changes and take that on in a follow-up PR.

[Copilot]

Pull request overview

This PR fixes the @Generable macro to generate correct partial types for array properties, aligning with FoundationModels' macro behavior. Previously, arrays like [CatProfile] were synthesized as [CatProfile] in the PartiallyGenerated struct, but now they correctly become [CatProfile.PartiallyGenerated]? for non-primitive element types.

Changes:

• Added type analysis utilities to distinguish arrays, dictionaries, and primitives
• Modified partial type generation to recursively handle array elements
• Updated property decoding to initialize arrays with partially generated element types

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
Tests/AnyLanguageModelTests/GenerableMacroTests.swift	Adds test coverage for array properties with both complex and primitive element types
Sources/AnyLanguageModelMacros/GenerableMacro.swift	Implements type analysis helpers and updates partial type generation logic for arrays

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 9 comments.

Comments suppressed due to low confidence (1)

Sources/AnyLanguageModelMacros/GenerableMacro.swift:1

• The depth check at line 194 occurs inside the loop but after the switch statement, which means negative depth from mismatched brackets won't be caught until after processing the current character. For example, with input ]:[String], the function would decrement depth to -1 but continue processing. The check should occur after each depth modification to catch structural errors earlier. Move the depth check inside each case that modifies totalDepth.

import SwiftCompilerPlugin

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

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[mattt]

@ethanhuang13 Thanks again for your help. Merging this PR now.