jetbrains / kotlin

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Code

How jetbrains/kotlin is laid out, and where to start for common changes.

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Where to start reading

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Find files for a task

Add a new compiler diagnostic

Define diagnostic in FIR diagnostic generator configuration
Implement diagnostic check in FIR checker rules
Register diagnostic message in compiler messages bundle

Add support for a new target backend (e.g., WebAssembly)

Implement IR-to-target lowering in new backend module
Wire target selection into compiler CLI argument parsing
Add backend-specific code generation tests

Add IDE analysis capability (symbol queries, hover info)

Define new query interface in platform API
Implement FIR-based resolver in Analysis API
Expose via public Analysis API contract
Add IDE test case in analysis test framework

Add a new compiler plugin hook

Invoke plugin hook at appropriate compilation phase
Document hook contract and provide example plugin

Add or update tests

Change build or automation

RepoPilot lists up to 500 files, so a file missing here may still exist.

No public API or start-up file could be picked out from the file names.

Code quality and hotspots

Largest source files

Branch points39 per file on average
Code issues0 errors, 9 warnings
Largest file1,729 lines
Hotspot load0 high-risk files

Static checks on the 15 largest source files.

Tests, CI and tooling

CIGitHub Actions1 workflow
Tests950 test files0.37 test files per source file (file count, not coverage)
Dependency updatesNo config detected

Test folders: analysis/analysis-api-fir/testFixtures/org/jetbrains/kotlin/analysis/api/impl/base/test/cases/annotations · analysis/analysis-api-fir/testFixtures/org/jetbrains/kotlin/analysis/api/impl/base/test/cases/components/containingDeclarationProvider · analysis/analysis-api-fir/testFixtures/org/jetbrains/kotlin/analysis/api/impl/base/test/cases/components/diagnosticProvider

Hotspots

compiler/config.jvm/gen/org/jetbrains/kotlin/config/JVMConfigurationKeys.kt13 commits in 180 days · 16 branch points
compiler/java-direct/src/org/jetbrains/kotlin/java/direct/JavaClassFinderOverAstImpl.kt6 commits in 180 days · 19 branch points
compiler/multiplatform-parsing/common/src/gen/KDocFlexLexer.kt3 commits in 180 days · 92 branch points
compiler/multiplatform-parsing/common/src/gen/KotlinFlexLexer.kt2 commits in 180 days · 66 branch points
compiler/daemon/daemon-client/src/main/kotlin/KotlinCompilerClient.kt2 commits in 180 days · 80 branch points
analysis/light-classes-base/src/org/jetbrains/kotlin/asJava/LightClassUtil.kt2 commits in 180 days · 72 branch points
build-common/testFixtures/org/jetbrains/kotlin/incremental/testingUtils/classFilesComparison.kt3 commits in 180 days · 16 branch points
compiler/resolution.common/src/org/jetbrains/kotlin/resolve/calls/NewCommonSuperTypeCalculator.kt1 commit in 180 days · 86 branch points

Files that change often and branch heavily, highest first. Branch points count if, loop, case, catch, ternary, && and || in the file.