Johann Hemmann
Activist at Ferrous Systems GmbH
Berlin, Germany
Summary
🤩
Rockstar🎓
Top SchoolJohann Hemmann is a Rust-focused software engineer with eight years of experience building efficient, maintainable systems and a track record of contributions to flagship projects like rust-analyzer and the rust compiler itself. Based in Berlin, he combines backend and embedded expertise—ranging from refactoring complex IDE tooling to adding WebAssembly bindings for the high-performance AV1 encoder rav1e and optimizing logging for constrained devices with defmt. Currently at Ferrous Systems, Johann emphasizes code quality, compiler-friendly patterns, and cross-platform compatibility, often addressing Clippy warnings and improving test coverage. Outside of engineering he channels his commitment to a livable, sustainable future into active civic campaigns in Berlin, reflecting a rare blend of technical depth and social engagement. His background includes mentoring at CODE University and a successful GSoC/Mozilla internship porting rav1e to WASM, highlighting both teaching and open-source collaboration.
8 years of coding experience
5 years of employment as a software developer
Abitur, Abitur at Georg-Samuel-Dörffel-Gymnasium WeidaBachelor of Science - BS, Software Engineering, Bachelor of Science - BS, Software Engineering at CODE University of Applied Sciences
English, Russian, German
Stackoverflow
11reputation
6kreached
2answers
0questions
Github Skills (34)
compiler-compiler10
sys10
compiler10
embedded10
logging10
blazor-webassembly10
refactoring10
rust10
webassembly10
javascript9
clippy9
apidoc9
lang9
api9
video-encoder8
Programming languages (12)
Github contributions (5)
knurling-rs/defmt
Feb 2021 - Jan 2023
Efficient, deferred formatting for logging on embedded systems
Role in this project:
Embedded Systems Engineer / IoT Developer
Embedded Systems Engineer / IoT DeveloperContributions:21 releases, 332 reviews, 342 commits in 2 years
Contributions summary:Johann primarily contributed to the `defmt` project, a library for efficient logging on embedded systems, focusing on improving the codebase's quality and compatibility. Their work included fixing Clippy issues, which suggests an emphasis on code style and correctness. They also implemented compile-time checks and made changes to support specific target architectures (`armv6m`), indicating involvement in platform-specific development and integration. Finally, the user also worked on optimizing the codebase and making use of new features of the language.
deferredrustrust-toolstracingferrous-systems
rust-lang/rust-analyzer
Apr 2020 - Oct 2024
A Rust compiler front-end for IDEs
Role in this project:Back-end Developer
Back-end DeveloperContributions:23 reviews, 12 PRs, 42 comments in 4 years 6 months
Contributions summary:Johann primarily focused on refactoring and improving the `rust-analyzer` codebase. Their work involved restructuring code related to rename functionality, including the use of hashmaps and BTreeMaps for data structures. They also introduced iterators for code efficiency, refactored functions, and updated test cases, ensuring that the codebase remained maintainable and efficient.
rustlsp-servercompileridefront-end
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