Add Kotlin Parcelize snippets

[erikrodriguez-se]

Snippets migration - Kotlin parcelize

Snippets for the Parcelize guide at developer.android.com/kotlin/parcelize, extracted into kotlin/src/main/kotlin/com/example/android/basics/ (Parcelize.kt and ParcelizeDataClass.kt) with region tags, plus the parcelize plugin in kotlin/build.gradle.kts. The multiplatform snippets are added to the kmp/shared module (package com.example.kmp.snippets).

Fifteen of the page's 24 code blocks are extracted. Most are verbatim; the differences that exist fall into three kinds, described below.

Region tag (android_kotlin_parcelize_*)	Page section	Verbatim	Deviation	Rendered / page
_basic	intro	no	import shown as a comment; colon spacing	4 / 4
_companion_parceler	intro	yes	—	12 / 12
_external_class_parceler	Custom Parcelers	yes	—	9 / 9
_type_parceler_class	Custom Parcelers	yes	—	4 / 4
_type_parceler_property	Custom Parcelers	yes	—	3 / 3
_type_parceler_type	Custom Parcelers	yes	—	3 / 3
_parcelable_creator	Create data from Parcel	no	import shown as a comment	5 / 5
_ignored_on_parcel	Skip properties from serialization	no	colon spacing	10 / 10
_raw_value	Parcel.writeValue	no	colon spacing	2 / 2
_sealed_class	Sealed classes and interfaces	no	colon spacing ×5	8 / 8
_data_class	Experimental / Data class serializer	no	@file:OptIn shown as a comment	6 / 6
_data_class_wrapper	Experimental / Data class serializer	no	colon spacing	8 / 8
_inheritance_base	Experimental / Non val or var params	no	colon spacing ×2	11 / 11
_multiplatform_common	Setup Parcelize for Kotlin multiplatform	no	package shown as a comment; colon spacing	19 / 19
_multiplatform_platform	Setup Parcelize for Kotlin multiplatform	no	package shown as a comment	6 / 6

The three kinds of deviation

Colon spacing. The page writes ): Parcelable; this repo's ktlint config rewrites it to ) : Parcelable. This is unavoidable — spotlessApply makes the change when run — and it accounts for most of the non-verbatim rows above.

File-top declarations shown as a comment. The _basic and _parcelable_creator blocks open with an import, _data_class opens with @file:OptIn(kotlinx.parcelize.Experimental::class), and the two _multiplatform_ blocks open with a package declaration. Kotlin requires those at the top of the file, above the package declaration and outside any snippet region. To keep them visible in the published snippet, the real line lives at the top of the file (uncommented, so it compiles) and a commented copy is placed inside the region. The published snippet therefore shows, for example, // import kotlinx.parcelize.Parcelize where the page shows a live import statement. The page's blocks would be updated to match.

One experimental block omitted. The page's "Non val or var parameters" section has two code blocks: _inheritance_base (the non-experimental approach, extracted) and an experimental variant that requires experimentalCodeGeneration=true. That flag is a parcelize compiler-plugin argument with module-level granularity — it cannot be scoped to a single snippet, and enabling it module-wide would compile the kotlin module's unrelated snippets (coroutines, flow testing) under experimental codegen. The experimental block is therefore not extracted, and the flag is not set. _inheritance_base alone still demonstrates the section's point.

Multiplatform snippets

The Kotlin 2.0+ multiplatform snippets are added to kmp/shared: _multiplatform_common in commonMain and _multiplatform_platform in androidMain. Two notes:

• iOS actuals. The common code declares expect interface MyParcelable and expect annotation class MyIgnoredOnParcel, so Kotlin requires an actual in every target — including iOS. The page says these "can be empty" but does not show them, so iosMain gets a small file with empty actuals. It is not a page snippet, so it carries no region tags.
• Gradle config. The additionalAnnotation compiler argument is applied in kmp/shared/build.gradle.kts but left untagged, matching how the page publishes build config (hand-maintained). The page's example package becomes com.example.kmp.snippets, so the additionalAnnotation value points at com.example.kmp.snippets.MyParcelize.

Code not extracted

• Gradle config — the Groovy plugins block (this repo is Kotlin DSL only), the Kotlin DSL plugins block, and the experimentalCodeGeneration block. Build-config blocks are published in their portable id("…") form on the page rather than this repo's version-catalog form, so they are left hand-maintained. (The additionalAnnotation block is applied but untagged — see "Multiplatform snippets" above.)
• Java — the UserCreator block under Create data from Parcel. Kotlin only.
• Multiplatform, pre-Kotlin 2.0 — the two expect/actual aliasing blocks under Setup Parcelize for Kotlin multiplatform. That approach is unsupported in Kotlin 2.0 and higher, which this project uses, so it will not compile. The Kotlin 2.0+ blocks from the same section are extracted — see "Multiplatform snippets" above.
• The experimental inheritance block and the // ERROR: not allowed example, both under Non val or var parameters in primary constructor. See "One experimental block omitted" above; the ERROR example cannot compile by design.

Deprecations

None. Ten imports, all current — android.os.Parcel, android.os.Parcelable and eight kotlinx.parcelize symbols. A forced full recompile produced zero warnings.

[snippet-bot]

Here is the summary of changes.

You are about to add 15 region tags.

• kmp/shared/src/androidMain/kotlin/com/example/kmp/snippets/Parcelize.kt:19, tag android_kotlin_parcelize_multiplatform_platform
• kmp/shared/src/commonMain/kotlin/com/example/kmp/snippets/Parcelize.kt:19, tag android_kotlin_parcelize_multiplatform_common
• kotlin/src/main/kotlin/com/example/android/basics/Parcelize.kt:31, tag android_kotlin_parcelize_basic
• kotlin/src/main/kotlin/com/example/android/basics/Parcelize.kt:40, tag android_kotlin_parcelize_companion_parceler
• kotlin/src/main/kotlin/com/example/android/basics/Parcelize.kt:60, tag android_kotlin_parcelize_external_class_parceler
• kotlin/src/main/kotlin/com/example/android/basics/Parcelize.kt:84, tag android_kotlin_parcelize_type_parceler_class
• kotlin/src/main/kotlin/com/example/android/basics/Parcelize.kt:103, tag android_kotlin_parcelize_type_parceler_property
• kotlin/src/main/kotlin/com/example/android/basics/Parcelize.kt:121, tag android_kotlin_parcelize_type_parceler_type
• kotlin/src/main/kotlin/com/example/android/basics/Parcelize.kt:132, tag android_kotlin_parcelize_parcelable_creator
• kotlin/src/main/kotlin/com/example/android/basics/Parcelize.kt:142, tag android_kotlin_parcelize_ignored_on_parcel
• kotlin/src/main/kotlin/com/example/android/basics/Parcelize.kt:159, tag android_kotlin_parcelize_raw_value
• kotlin/src/main/kotlin/com/example/android/basics/Parcelize.kt:166, tag android_kotlin_parcelize_sealed_class
• kotlin/src/main/kotlin/com/example/android/basics/Parcelize.kt:179, tag android_kotlin_parcelize_data_class_wrapper
• kotlin/src/main/kotlin/com/example/android/basics/Parcelize.kt:192, tag android_kotlin_parcelize_inheritance_base
• kotlin/src/main/kotlin/com/example/android/basics/ParcelizeDataClass.kt:26, tag android_kotlin_parcelize_data_class

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[francescoo22]

Multiplatform — all four expect/actual blocks under Setup Parcelize for Kotlin multiplatform. Will not compile in a plain Android module.

Wouldn't it be possible to put Parcelize snippets in a multiplatform module so that we can add them as well? Since we are currently working on improving support for KMP projects using Parcelize, it would be nice to include snippets showing multiplatform usage if that is not too complicated. (I saw that there's already a multiplatform module in the project)

[erikrodriguez-se]

Multiplatform — all four expect/actual blocks under Setup Parcelize for Kotlin multiplatform. Will not compile in a plain Android module.

Wouldn't it be possible to put Parcelize snippets in a multiplatform module so that we can add them as well? Since we are currently working on improving support for KMP projects using Parcelize, it would be nice to include snippets showing multiplatform usage if that is not too complicated. (I saw that there's already a multiplatform module in the project)

@francescoo22 I added the two migrate-able snippets into the KMP module as requested and updated the PR description. Thanks!

[francescoo22]

Thank you, looks good to me!

[kkuan2011]

Looks good, but it looks like the iOS build is failing? Would you know why?

[erikrodriguez-se]

Looks good, but it looks like the iOS build is failing? Would you know why?

Sorry, this built cleanly locally for me and I didn't see the CI fail. It looks like the build script is asking for an older version of Xcode that the runner doesn't have. I will see if I can update it.