Fix an action conflict from exec transitions + Starlark flags.

Specifically, if the same output is generated under two exec configurations
where the target configurations they came from are identical except for
different Starlark flags, we must guarantee the output paths are distinct.

PiperOrigin-RevId: 290743006

src/main/java/com/google/devtools/build/lib/analysis/config/CoreOptions.java

@@ -851,6 +851,7 @@ public FragmentOptions getHost() {
     CoreOptions host = (CoreOptions) getDefault();
 
     host.outputDirectoryName = "host";
+    host.transitionDirectoryNameFragment = transitionDirectoryNameFragment;
     host.compilationMode = hostCompilationMode;
     host.isHost = true;
     host.isExec = false;

src/test/java/com/google/devtools/build/lib/analysis/StarlarkAttrTransitionProviderTest.java

@@ -17,10 +17,12 @@
 import static com.google.common.truth.Truth.assertThat;
 
 import com.google.common.collect.ArrayListMultimap;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.ListMultimap;
 import com.google.common.collect.Maps;
+import com.google.common.eventbus.EventBus;
 import com.google.devtools.build.lib.analysis.StarlarkRuleTransitionProviderTest.DummyTestLoader;
 import com.google.devtools.build.lib.analysis.config.CoreOptions;
 import com.google.devtools.build.lib.analysis.util.BuildViewTestCase;
@@ -1605,6 +1607,80 @@ public void testTransitionOnBuildSetting_notABuildSetting() throws Exception {
             + "is not a build setting");
   }
 
+  /**
+   * Regression test for b/147245129.
+   *
+   * <p>This tests that when exec transitions are applied from target configurations that are
+   * identical except for different Starlark flags, outputs do not conflict.
+   */
+  @Test
+  public void testBuildSettingTransitionsWorkWithExecTransitions() throws Exception {
+    writeWhitelistFile();
+    // This setup creates an int_flag_reading_rule whose output is the value of an int_flag (which
+    // guarantees actions in configurations with different Starlark flag values are different). It
+    // then makes this a genrule exec tool (so it applies after an exec transition). And finally
+    // creates a build_setting_changing_rule that changes the int_flag's value and depends on the
+    // genrule. So building the genrule at both the top-level and under the
+    // build_setting_changing_rule triggers the test scenario.
+    scratch.file(
+        "test/skylark/rules.bzl",
+        "BuildSettingInfo = provider(fields = ['value'])",
+        "def _impl(ctx):",
+        "  return [BuildSettingInfo(value = ctx.build_setting_value)]",
+        "int_flag = rule(implementation = _impl, build_setting = config.int())",
+        "def _transition_impl(settings, attr):",
+        "  return {'//test/skylark:the-answer': 42}",
+        "my_transition = transition(",
+        "  implementation = _transition_impl,",
+        "  inputs = [],",
+        "  outputs = ['//test/skylark:the-answer'])",
+        "def _int_impl(ctx):",
+        "  value = ctx.attr._int_dep[BuildSettingInfo].value",
+        "  ctx.actions.write(ctx.outputs.out, str(value))",
+        "int_flag_reading_rule = rule(",
+        "  implementation = _int_impl,",
+        "  attrs = {",
+        "    '_int_dep': attr.label(default = '//test/skylark:the-answer'),",
+        "    'out': attr.output()",
+        "  })",
+        "def _rule_impl(ctx):",
+        "  pass",
+        "build_setting_changing_rule = rule(",
+        "  implementation = _rule_impl,",
+        "  attrs = {",
+        "    'dep': attr.label(cfg = my_transition, allow_single_file = True),",
+        "    '_whitelist_function_transition': attr.label(",
+        "      default = '//tools/whitelists/function_transition_whitelist'),",
+        "  })");
+    scratch.file(
+        "test/skylark/BUILD",
+        "load('//test/skylark:rules.bzl', 'build_setting_changing_rule', 'int_flag',",
+        "  'int_flag_reading_rule')",
+        "int_flag(",
+        "    name = 'the-answer',",
+        "    build_setting_default = 0)",
+        "genrule(",
+        "    name = 'with_exec_tool',",
+        "    srcs = [],",
+        "    outs = ['with_exec_tool.out'],",
+        "    cmd = 'echo hi > $@',",
+        "    exec_tools = [':int_reader'])",
+        "int_flag_reading_rule(",
+        "    name = 'int_reader',",
+        "    out = 'int_reader.out')",
+        "build_setting_changing_rule(",
+        "    name = 'transitioner',",
+        "    dep = ':with_exec_tool')");
+    // Note: calling getConfiguredTarget for each target doesn't activate conflict detection.
+    update(
+        ImmutableList.of("//test/skylark:transitioner", "//test/skylark:with_exec_tool.out"),
+        /*keepGoing=*/ false,
+        LOADING_PHASE_THREADS,
+        /*doAnalysis=*/ true,
+        new EventBus());
+    assertNoEvents();
+  }
+
   @Test
   public void testOptionConversionDynamicMode() throws Exception {
     // TODO(waltl): check that dynamic_mode is parsed properly.