Always collect FileProvider's filesToBuild as data runfiles

Guidelines for Starlark rules suggest that `data`-like attributes on
rules should always merge the default outputs of rule targets into the
transitive runfiles. See:
https://docs.bazel.build/versions/main/skylark/rules.html#runfiles-features-to-avoid

As a result, Starlark rules generally don't (and shouldn't) explicitly
include their default outputs into their runfiles. Before this commit,
native rules did not merge these outputs in the same way as idiomatic
Starlark rules, which led to unexpectedly absent runfiles.

src/main/java/com/google/devtools/build/lib/analysis/Runfiles.java

@@ -980,6 +980,13 @@ private Builder addTargetIncludingFileTargets(TransitiveInfoCollection target,
         return this;
       }
 
+      if (mapping == RunfilesProvider.DATA_RUNFILES) {
+        FileProvider fileProvider = target.getProvider(FileProvider.class);
+        if (fileProvider != null) {
+          addTransitiveArtifacts(fileProvider.getFilesToBuild());
+        }
+      }
+
       return addTargetExceptFileTargets(target, mapping);
     }
 

src/test/java/com/google/devtools/build/lib/starlark/StarlarkIntegrationTest.java

@@ -714,6 +714,134 @@ public void testDefaultInfoWithRunfilesConstructor() throws Exception {
     assertThat(getConfiguredTarget("//src:r_tools")).isNotNull();
   }
 
+  @Test
+  public void testDefaultInfoFilesAddedToCcBinaryTargetRunfiles() throws Exception {
+    scratch.file(
+        "test/starlark/extension.bzl",
+        "def custom_rule_impl(ctx):",
+        "  out = ctx.actions.declare_file(ctx.attr.name + '.out')",
+        "  ctx.actions.write(out, 'foobar')",
+        "  return [DefaultInfo(files = depset([out]))]",
+        "",
+        "custom_rule = rule(implementation = custom_rule_impl)");
+
+    scratch.file(
+        "test/starlark/BUILD",
+        "load('//test/starlark:extension.bzl', 'custom_rule')",
+        "",
+        "custom_rule(name = 'cr')",
+        "cc_binary(name = 'binary', data = [':cr'])"
+    );
+
+    ConfiguredTarget target = getConfiguredTarget("//test/starlark:binary");
+
+    assertThat(target.getLabel().toString()).isEqualTo("//test/starlark:binary");
+    assertThat(
+        ActionsTestUtil.baseArtifactNames(
+            target.getProvider(RunfilesProvider.class).getDefaultRunfiles().getAllArtifacts()))
+        .contains("cr.out");
+    assertThat(
+        ActionsTestUtil.baseArtifactNames(
+            target.getProvider(RunfilesProvider.class).getDataRunfiles().getAllArtifacts()))
+        .contains("cr.out");
+  }
+
+  @Test
+  public void testDefaultInfoFilesAddedToJavaBinaryTargetRunfiles() throws Exception {
+    scratch.file(
+        "test/starlark/extension.bzl",
+        "def custom_rule_impl(ctx):",
+        "  out = ctx.actions.declare_file(ctx.attr.name + '.out')",
+        "  ctx.actions.write(out, 'foobar')",
+        "  return [DefaultInfo(files = depset([out]))]",
+        "",
+        "custom_rule = rule(implementation = custom_rule_impl)");
+
+    scratch.file(
+        "test/starlark/BUILD",
+        "load('//test/starlark:extension.bzl', 'custom_rule')",
+        "",
+        "custom_rule(name = 'cr')",
+        "java_binary(name = 'binary', data = [':cr'], srcs = ['Foo.java'], main_class = 'Foo')"
+    );
+
+    ConfiguredTarget target = getConfiguredTarget("//test/starlark:binary");
+
+    assertThat(target.getLabel().toString()).isEqualTo("//test/starlark:binary");
+    assertThat(
+        ActionsTestUtil.baseArtifactNames(
+            target.getProvider(RunfilesProvider.class).getDefaultRunfiles().getAllArtifacts()))
+        .contains("cr.out");
+    assertThat(
+        ActionsTestUtil.baseArtifactNames(
+            target.getProvider(RunfilesProvider.class).getDataRunfiles().getAllArtifacts()))
+        .contains("cr.out");
+  }
+
+  @Test
+  public void testDefaultInfoFilesAddedToPyBinaryTargetRunfiles() throws Exception {
+    scratch.file(
+        "test/starlark/extension.bzl",
+        "def custom_rule_impl(ctx):",
+        "  out = ctx.actions.declare_file(ctx.attr.name + '.out')",
+        "  ctx.actions.write(out, 'foobar')",
+        "  return [DefaultInfo(files = depset([out]))]",
+        "",
+        "custom_rule = rule(implementation = custom_rule_impl)");
+
+    scratch.file(
+        "test/starlark/BUILD",
+        "load('//test/starlark:extension.bzl', 'custom_rule')",
+        "",
+        "custom_rule(name = 'cr')",
+        "py_binary(name = 'binary', data = [':cr'], srcs = ['binary.py'])"
+    );
+
+    ConfiguredTarget target = getConfiguredTarget("//test/starlark:binary");
+
+    assertThat(target.getLabel().toString()).isEqualTo("//test/starlark:binary");
+    assertThat(
+        ActionsTestUtil.baseArtifactNames(
+            target.getProvider(RunfilesProvider.class).getDefaultRunfiles().getAllArtifacts()))
+        .contains("cr.out");
+    assertThat(
+        ActionsTestUtil.baseArtifactNames(
+            target.getProvider(RunfilesProvider.class).getDataRunfiles().getAllArtifacts()))
+        .contains("cr.out");
+  }
+
+  @Test
+  public void testDefaultInfoFilesAddedToShBinaryTargetRunfiles() throws Exception {
+    scratch.file(
+        "test/starlark/extension.bzl",
+        "def custom_rule_impl(ctx):",
+        "  out = ctx.actions.declare_file(ctx.attr.name + '.out')",
+        "  ctx.actions.write(out, 'foobar')",
+        "  return [DefaultInfo(files = depset([out]))]",
+        "",
+        "custom_rule = rule(implementation = custom_rule_impl)");
+
+    scratch.file(
+        "test/starlark/BUILD",
+        "load('//test/starlark:extension.bzl', 'custom_rule')",
+        "",
+        "custom_rule(name = 'cr')",
+        "sh_binary(name = 'binary', data = [':cr'], srcs = ['script.sh'])"
+    );
+
+    ConfiguredTarget target = getConfiguredTarget("//test/starlark:binary");
+
+    assertThat(target.getLabel().toString()).isEqualTo("//test/starlark:binary");
+    assertThat(
+        ActionsTestUtil.baseArtifactNames(
+            target.getProvider(RunfilesProvider.class).getDefaultRunfiles().getAllArtifacts()))
+        .contains("cr.out");
+    assertThat(
+        ActionsTestUtil.baseArtifactNames(
+            target.getProvider(RunfilesProvider.class).getDataRunfiles().getAllArtifacts()))
+        .contains("cr.out");
+  }
+
   @Test
   public void testInstrumentedFilesProviderWithCodeCoverageDisabled() throws Exception {
     setBuildLanguageOptions("--incompatible_disallow_struct_provider_syntax=false");