Google Summer of Code 2026 With the Kotlin Foundation: Recap

Summary

The Kotlin Foundation wrapped up its fourth Google Summer of Code program in 2026, supporting two projects by Ayako Hayasaka and Mark Seif Khalil. Ayako implemented tail-call support in the Kotlin/Wasm backend, using return_call and return_call_ref instructions to avoid stack growth in recursive programs, and then found and fixed a missing optimization for return_call in the V8 engine that caused a performance regression. Mark built a database and automated pipeline to collect and structure scattered information about where Kotlin is taught worldwide, covering courses, curricula, repositories, and learning platforms. In Ayako’s benchmarks, several recursive patterns achieved 1.7 to 4.3 times faster execution at a recursion depth of 10,000, and at a depth of one million, the same programs crashed without tail calls but completed successfully with them. The education landscape project now provides a reusable foundation for monitoring Kotlin’s presence in education and identifying trends and gaps.

Takeaways

1. 1

   Ayako Hayasaka added tail-call support to the Kotlin/Wasm backend by detecting tail-position calls and emitting return_call or return_call_ref WebAssembly instructions, enabling recursive programs to avoid call-stack growth.

2. 2

   In benchmarks, the tail-call optimization made recursive patterns 1.7-4.3x faster at a depth of 10,000 and prevented crashes at a depth of one million, where programs previously failed.

3. 3

   Mark Seif Khalil created a structured database and automated pipeline to gather scattered data from websites, curricula, repositories, and learning platforms, providing a reusable foundation for tracking Kotlin education globally.

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