Sebastian Sellmair
Senior Software Engineer at JetBrains
Munich, Bavaria, Germany
Summary
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RockstarSebastian Sellmair is a Senior Software Engineer at JetBrains with nine years of hands-on experience building and improving developer tooling for Kotlin and Android. He focuses on backend and automation engineering, contributing to flagship projects like the Kotlin compiler, Dokka documentation engine, and the IntelliJ Android plugin—work that spans compiler internals, multiplatform source-set handling, and robust build/dependency fixes. Sebastian is known for pragmatic problem-solving, from implementing fail-on-warning behaviors and fixing npm caching to refining expected/actual checks in the compiler to boost performance. Based in Munich, he combines deep language/tooling expertise with a practical eye for build reliability and cross-platform integration, often surfacing obscure edge-case fixes that improve everyday developer workflows.
9 years of coding experience
Github Skills (18)
kotlin10
multiplatform10
dokka10
plugin-development10
document-generation10
intellij-idea10
compiler-design10
android10
build-automation10
gradlew10
documents10
documentation10
test-automation10
gradle10
java9
Programming languages (10)
Github contributions (5)
Kotlin/dokka
Jun 2020 - Sep 2020
API documentation engine for Kotlin
Role in this project:
Back-end Developer & Automation Engineer
Back-end Developer & Automation EngineerContributions:76 reviews, 486 commits, 210 PRs in 3 months
Contributions summary:Sebastian contributed significantly to enhancing the Kotlin Dokka project by implementing various features and improvements related to documentation generation and plugin configuration. Their work includes the implementation of a project extension, the addition of options for reporting undocumented code, handling of failing `PsiMethod.findSuperMethods`, and improvements in source set matching within transformers. Additionally, they implemented the "failOnWarning" option, improved build process by addressing npm caching issues.
apidokkaapi-documentationkotlinjavadoc
JetBrains/kotlin
Nov 2019 - Jan 2023
The Kotlin Programming Language.
Role in this project:Backend Developer
Backend DeveloperContributions:46 reviews, 1505 commits, 32 PRs in 3 years 2 months
Contributions summary:Sebastian contributed to the Kotlin Programming Language compiler, specifically in the area of Multiplatform Project (MPP) support. Their work focused on improving the handling of expected/actual declarations, removing unnecessary code, and improving performance within the ExpectedActualDeclarationChecker. These changes involved modifications to core compiler components, including refactoring aspects related to class declarations and commonization of dependencies, with the aim of optimizing the compilation process.
maven-plugincompilerkotlinintellij-pluginprogramming-language
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