From 41d755c2891d80f8499d95dfc24f4e8e26dc8ce2 Mon Sep 17 00:00:00 2001 From: Fabian Meumertzheim Date: Wed, 5 Jul 2023 09:17:22 +0200 Subject: [PATCH] Add toolchain type or Java bootstrap runtime The `bootclasspath` rule in `rules_java` will soon use this toolchain type instead of the regular Java runtime toolchain type, which naturally carries a constraint on the target platform. Also adds more detailed explanations of the now three Java toolchain types. --- tools/jdk/BUILD.tools | 34 ++++++++++++++++++++++++++++++++-- 1 file changed, 32 insertions(+), 2 deletions(-) diff --git a/tools/jdk/BUILD.tools b/tools/jdk/BUILD.tools index 37171c677c39b6..1ab0cb8e600a0a 100644 --- a/tools/jdk/BUILD.tools +++ b/tools/jdk/BUILD.tools @@ -7,12 +7,42 @@ exports_files([ "java_stub_template.txt", ]) -# Used to distinguish toolchains used for Java development, ie the JavaToolchainProvider. +# A single binary distribution of a JDK (e.g., OpenJDK 17 for Windows arm64) provides three +# different types of toolchains from the perspective of Bazel: + +# The compilation toolchain, which provides the Java runtime used to execute the Java compiler, as +# well as various helper tools and settings. +# +# Toolchains of this type typically have constraints on the execution platform so that their Java +# runtime can run the compiler, but not on the target platform as Java compilation outputs are +# platform independent. +# +# Obtain the associated JavaToolchainInfo via: +# ctx.toolchains["@bazel_tools//tools/jdk:toolchain_type"].java toolchain_type(name = "toolchain_type") -# Used to distinguish toolchains used for Java execution, ie the JavaRuntimeInfo. +# The Java runtime that executable Java compilation outputs (e.g., java_binary with +# create_executable = True) will run on. +# +# Toolchains of this type typically have constraints on the target platform so that the runtime's +# native 'java' binary can be run there, but not on the execution platform as building an executable +# Java target only requires copying or symlinking the runtime, which can be done on any platform. +# +# Obtain the associated JavaRuntimeInfo via: +# ctx.toolchains["@bazel_tools//tools/jdk:runtime_toolchain_type"].java_runtime toolchain_type(name = "runtime_toolchain_type") +# The Java runtime to extract the bootclasspath from that is then used to compile Java sources. +# +# As the bootclasspath is platform independent, toolchains of this type may have no constraints. +# Purely as an optimization to prevent unnecessary fetches of remote runtimes for other +# architectures, toolchains of this type may have constraints on the execution platform that match +# those on the corresponding compilation toolchain. +# +# Toolchains of this type are only consumed internally by the bootclasspath rule and should not be +# accessed from Starlark. +toolchain_type(name = "bootstrap_runtime_toolchain_type") + # Aliases value of --plugins flag as a JavaPluginInfo java_plugins_flag_alias( name = "java_plugins_flag_alias",