Add support for configuring --system using `java_package_configurat…

…ion`

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: Ia546c9bc84cc726c985b15e7785af390a02b0349

src/main/starlark/builtins_bzl/common/java/java_common_internal_for_builtins.bzl

@@ -134,9 +134,15 @@ def compile(
             ["-Abazel.repository=" + ctx.label.workspace_name],
             order = "preorder",
         ))
+    system_override = False
     for package_config in java_toolchain._package_configuration:
         if package_config.matches(ctx.label):
             all_javac_opts.append(package_config.javac_opts)
+            if package_config.system:
+                if system_override:
+                    fail("Multiple system package configurations found for %s" % ctx.label)
+                bootclasspath = package_config.system
+                system_override = True
 
     all_javac_opts.append(depset(
         ["--add-exports=%s=ALL-UNNAMED" % x for x in add_exports],

src/main/starlark/builtins_bzl/common/java/java_package_configuration.bzl

@@ -14,6 +14,7 @@
 
 """Implementation for the java_package_configuration rule"""
 
+load(":common/java/boot_class_path_info.bzl", "BootClassPathInfo")
 load(":common/java/java_helper.bzl", "helper")
 
 _java_common_internal = _builtins.internal.java_common_internal_do_not_use
@@ -27,6 +28,7 @@ JavaPackageConfigurationInfo = provider(
         "javac_opts",
         "matches",
         "package_specs",
+        "system",
     ],
 )
 
@@ -40,13 +42,15 @@ 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,
         ),
     ]
 
@@ -103,11 +107,18 @@ 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.
+""",
+        ),
         "output_licenses": attr.license() if hasattr(attr, "license") else attr.string_list(),
     },
 )

src/main/starlark/builtins_bzl/common/java/java_toolchain.bzl

@@ -520,7 +520,7 @@ 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.