Compiler Jl
Developmentcompiler-jlCompiler Jl is an Agent Skill for development published in the JuliaLang/julia repository on GitHub: a SKILL.md instruction file an AI agent can load to do this task.
Develop and test Julia's Compiler.jl. Use when modifying Compiler/, debugging compiler behavior, or activating stdlib Compiler for reflection/native-codegen experiments instead of using sysimage Base.Compiler.
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Compiler.jl development
Use this when modifying Compiler/ source, tests, or package metadata.
Compiler modules in Julia
During bootstrap, Compiler/ is built into the sysimage as Base.Compiler.
That in-sysimage compiler is what Julia normally uses for native compilation.
Because it is baked into the sysimage, changes made to Compiler/ after the
sysimage was built are not reflected in Base.Compiler unless Julia is rebuilt.
Compiler/ can also be loaded as a stdlib package, producing a separate
Compiler module from Base.Compiler. For day-to-day development, testing, and
debugging of post-sysimage source changes, prefer this stdlib Compiler module
over trying to replace Base.Compiler with Revise. It is usually reliable except
for failures caused by compatibility with the src/ runtime or other
sysimage/native-codegen integration issues.
When investigating a runtime compatibility issue, make -C src can update the
runtime faster than rebuilding the full Julia sysimage. Rebuild Julia when the
updated Compiler/ code needs to be baked into Base.Compiler or when checking
sysimage/native-codegen integration.
Experimenting with Compiler as a stdlib
Run the in-tree Julia runtime with the Compiler project:
./usr/bin/julia --project=Compiler
Reflection backend
For reflection-oriented debugging, activate the stdlib Compiler module:
using InteractiveUtils, Compiler
@activate Compiler
@activate Compiler is equivalent to @activate Compiler[:reflection]: Base and
InteractiveUtils reflection utilities such as code_typed, @code_typed, and
code_warntype will use the loaded stdlib Compiler module. This is useful for
trying compiler changes without rebuilding the sysimage.
Native compilation backend
If you specifically need to exercise the loaded stdlib Compiler as the native
compilation backend, use:
using InteractiveUtils, Compiler
@activate Compiler[:codegen]
This is broader than reflection activation: it makes the runtime invoke the loaded compiler for compilation requests. Use it only when debugging native compilation/codegen behavior, and expect failures here to involve sysimage, runtime, native-codegen, or compiler-cache interactions.
For ordinary debugging, prefer reflection activation. Use [:codegen] only when
you specifically need to test the native compilation backend; for final
integration checks, rebuild Julia and test the in-sysimage Base.Compiler.
Testing Compiler as a stdlib package
Run package tests from the repository root with the in-tree Julia runtime:
./usr/bin/julia --project=Compiler -e 'using Pkg; Pkg.test()'
To run a single test file, include it directly under a Test.@testset:
./usr/bin/julia --project=Compiler -e 'using Test; @testset "inline" include("Compiler/test/inline.jl")'
Most Compiler/test/ files include Compiler/test/setup_Compiler.jl, which
activates or imports the appropriate Compiler module for this workflow.
Testing Base.Compiler
Use the top-level test entry point when the goal is to test the Base.Compiler
that is baked into the sysimage:
./usr/bin/julia test/runtests.jl Compiler
If you changed Compiler/ and need those changes reflected in Base.Compiler,
rebuild Julia first so the sysimage contains the updated compiler code.