Add support for configuring --system using java_package_configuration

Also use `cfg = "target"` for `java_toolchain.package_configuration` to ensure `java_package_configuration.system` is built in the target config, and do the exec transition later for `java_package_configuration.data` (which we do want in the exec config). The system needs to match the target Java language configuration, the data is an exec dependency used at built-time.

PiperOrigin-RevId: 684478368
Change-Id: Iaa2020525b204cf9eabc0cd1830cb3bdc40da683

Author: cushon

java/common/rules/java_package_configuration.bzl

@@ -21,13 +21,16 @@ load("//java/common/rules/impl:java_helper.bzl", "helper")
 
 _java_common_internal = java_common.internal_DO_NOT_USE()
 
+BootClassPathInfo = java_common.BootClassPathInfo
+
 JavaPackageConfigurationInfo = provider(
     "A provider for Java per-package configuration",
     fields = [
         "data",
         "javac_opts",
         "matches",
         "package_specs",
+        "system",
     ],
 )
 
@@ -41,13 +44,15 @@ def _rule_impl(ctx):
     javacopts = _java_common_internal.expand_java_opts(ctx, "javacopts", tokenize = True)
     javacopts_depset = helper.detokenize_javacopts(javacopts)
     package_specs = [package[PackageSpecificationInfo] for package in ctx.attr.packages]
+    system = ctx.attr.system[BootClassPathInfo] if ctx.attr.system else None
     return [
         DefaultInfo(),
         JavaPackageConfigurationInfo(
             data = depset(ctx.files.data),
             javac_opts = javacopts_depset,
             matches = lambda label: _matches(package_specs, label),
             package_specs = package_specs,
+            system = system,
         ),
     ]
 
@@ -104,11 +109,18 @@ Java compiler flags.
             """,
         ),
         "data": attr.label_list(
+            cfg = "exec",
             allow_files = True,
             doc = """
 The list of files needed by this configuration at runtime.
             """,
         ),
+        "system": attr.label(
+            providers = [BootClassPathInfo],
+            doc = """
+Corresponds to javac's --system flag.
+""",
+        ),
         # buildifier: disable=attr-licenses
         "output_licenses": attr.license() if hasattr(attr, "license") else attr.string_list(),
     },

java/common/rules/java_toolchain.bzl

@@ -522,7 +522,7 @@ Label of the one-version allowlist for tests.
             """,
         ),
         "package_configuration": attr.label_list(
-            cfg = "exec",
+            cfg = "target",
             providers = [JavaPackageConfigurationInfo],
             doc = """
 Configuration that should be applied to the specified package groups.

java/docs/rules.md

@@ -247,7 +247,7 @@ java_library(<a href="#java_library-name">name</a>, <a href="#java_library-deps"
 ## java_package_configuration
 
 <pre>
-java_package_configuration(<a href="#java_package_configuration-name">name</a>, <a href="#java_package_configuration-data">data</a>, <a href="#java_package_configuration-javacopts">javacopts</a>, <a href="#java_package_configuration-output_licenses">output_licenses</a>, <a href="#java_package_configuration-packages">packages</a>)
+java_package_configuration(<a href="#java_package_configuration-name">name</a>, <a href="#java_package_configuration-data">data</a>, <a href="#java_package_configuration-javacopts">javacopts</a>, <a href="#java_package_configuration-output_licenses">output_licenses</a>, <a href="#java_package_configuration-packages">packages</a>, <a href="#java_package_configuration-system">system</a>)
 </pre>
 
 <p>
@@ -295,6 +295,7 @@ java_toolchain(
 | <a id="java_package_configuration-javacopts"></a>javacopts |  Java compiler flags.   | List of strings | optional |  `[]`  |
 | <a id="java_package_configuration-output_licenses"></a>output_licenses |  -   | List of strings | optional |  `[]`  |
 | <a id="java_package_configuration-packages"></a>packages |  The set of <code><a href="${link package_group}">package_group</a></code>s the configuration should be applied to.   | <a href="https://bazel.build/concepts/labels">List of labels</a> | optional |  `[]`  |
+| <a id="java_package_configuration-system"></a>system |  Corresponds to javac's --system flag.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional |  `None`  |
 
 
 <a id="java_plugin"></a>