Bzlmod: change main repo runfiles/execpath prefix to "_main"

See code comment for more explanation.

PiperOrigin-RevId: 480917215
Change-Id: I3a86d2bf45aeaa964cc8b101a6ecef0aab7238d7

src/main/java/com/google/devtools/build/lib/skyframe/BUILD

@@ -2898,11 +2898,14 @@ java_library(
     srcs = ["WorkspaceNameFunction.java"],
     deps = [
         ":package_value",
+        ":precomputed_value",
         ":workspace_name_value",
         "//src/main/java/com/google/devtools/build/lib/cmdline",
         "//src/main/java/com/google/devtools/build/lib/packages",
+        "//src/main/java/com/google/devtools/build/lib/packages/semantics",
         "//src/main/java/com/google/devtools/build/skyframe",
         "//src/main/java/com/google/devtools/build/skyframe:skyframe-objects",
+        "//src/main/java/net/starlark/java/eval",
         "//third_party:jsr305",
     ],
 )

src/main/java/com/google/devtools/build/lib/skyframe/WorkspaceNameFunction.java

@@ -16,11 +16,13 @@
 import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.packages.BuildFileContainsErrorsException;
 import com.google.devtools.build.lib.packages.Package;
+import com.google.devtools.build.lib.packages.semantics.BuildLanguageOptions;
 import com.google.devtools.build.skyframe.SkyFunction;
 import com.google.devtools.build.skyframe.SkyFunctionException;
 import com.google.devtools.build.skyframe.SkyKey;
 import com.google.devtools.build.skyframe.SkyValue;
 import javax.annotation.Nullable;
+import net.starlark.java.eval.StarlarkSemantics;
 
 /**
  * {@link SkyFunction} for {@link WorkspaceNameValue}s.
@@ -33,6 +35,23 @@ public class WorkspaceNameFunction implements SkyFunction {
   @Nullable
   public SkyValue compute(SkyKey skyKey, Environment env)
       throws InterruptedException, WorkspaceNameFunctionException {
+    StarlarkSemantics starlarkSemantics = PrecomputedValue.STARLARK_SEMANTICS.get(env);
+    if (starlarkSemantics == null) {
+      return null;
+    }
+    if (starlarkSemantics.getBool(BuildLanguageOptions.ENABLE_BZLMOD)) {
+      // When Bzlmod is enabled, we don't care what the "workspace name" specified in the WORKSPACE
+      // file is, and always use the static string "_main" instead. The workspace name returned by
+      // this SkyFunction is only used as the runfiles/execpath prefix for the main repo; for other
+      // repos, the canonical repo name is used. The canonical name of the main repo is the empty
+      // string, so we can't use that; instead, we just use a static string.
+      //
+      // "_main" was chosen because it's not a valid apparent repo name, which, coupled with the
+      // fact that no Bzlmod-generated canonical repo names are valid apparent repo names, means
+      // that a path passed to rlocation can go through repo mapping multiple times without any
+      // danger (i.e. going through repo mapping is idempotent).
+      return WorkspaceNameValue.withName("_main");
+    }
     SkyKey externalPackageKey = PackageValue.key(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER);
     PackageValue externalPackageValue = (PackageValue) env.getValue(externalPackageKey);
     if (externalPackageValue == null) {

src/test/java/com/google/devtools/build/lib/skyframe/WorkspaceNameFunctionTest.java

@@ -54,6 +54,15 @@ public void testNormal() throws Exception {
         .isEqualTo(WorkspaceNameValue.withName("good"));
   }
 
+  @Test
+  public void bzlmod() throws Exception {
+    setBuildLanguageOptions("--enable_bzlmod");
+    scratch.overwriteFile("WORKSPACE", "workspace(name = 'good')");
+    assertThatEvaluationResult(eval())
+        .hasEntryThat(key)
+        .isEqualTo(WorkspaceNameValue.withName("_main"));
+  }
+
   @Test
   public void testErrorInExternalPkg() throws Exception {
     reporter.removeHandler(failFastHandler);

src/test/shell/bazel/BUILD

@@ -832,7 +832,10 @@ sh_test(
     size = "medium",
     srcs = ["runfiles_test.sh"],
     data = [":test-deps"],
-    tags = ["no_windows"],
+    tags = [
+        "no_windows",
+        "requires-network",
+    ],
 )
 
 sh_test(
@@ -1013,7 +1016,10 @@ sh_test(
     size = "medium",
     srcs = ["execroot_test.sh"],
     data = [":test-deps"],
-    tags = ["no_windows"],
+    tags = [
+        "no_windows",
+        "requires-network",
+    ],
 )
 
 sh_test(

src/test/shell/bazel/execroot_test.sh

@@ -44,6 +44,32 @@ EOF
   assert_contains "$(dirname $execroot)/${ws_name}/bazel-out" out
 }
 
+function test_execroot_structure_with_bzlmod() {
+  cat > WORKSPACE <<EOF
+workspace(name = "whatever_doesnt_matter")
+EOF
+  cat > MODULE.bazel <<EOF
+module(name="this_also_doesnt_matter")
+EOF
+
+  mkdir dir
+  cat > dir/BUILD <<'EOF'
+genrule(
+  name = "use-srcs",
+  srcs = ["BUILD"],
+  cmd = "cp $< $@",
+  outs = ["used-srcs"],
+)
+EOF
+
+  bazel build --enable_bzlmod -s //dir:use-srcs &> $TEST_log \
+      || fail "expected success"
+  execroot="$(bazel info --enable_bzlmod execution_root)"
+  test -e "$execroot/../_main"
+  ls -l bazel-out | tee out
+  assert_contains "$(dirname $execroot)/_main/bazel-out" out
+}
+
 function test_sibling_repository_layout() {
     touch WORKSPACE
 

src/test/shell/bazel/runfiles_test.sh

@@ -50,6 +50,34 @@ EOF
   [[ -x bazel-bin/foo/foo.runfiles/$name/foo/foo ]] || fail "No foo executable under $name"
 }
 
+function test_runfiles_bzlmod() {
+  create_workspace_with_default_repos WORKSPACE "blorp_malorp"
+  cat > MODULE.bazel <<EOF
+module(name="blep")
+EOF
+
+  mkdir foo
+  cat > foo/BUILD <<EOF
+java_test(
+    name = "foo",
+    srcs = ["Noise.java"],
+    test_class = "Noise",
+)
+EOF
+  cat > foo/Noise.java <<EOF
+public class Noise {
+  public static void main(String[] args) {
+    System.err.println(System.getenv("I'm a test."));
+  }
+}
+EOF
+
+  bazel build --enable_bzlmod //foo:foo >& $TEST_log || fail "Build failed"
+  [[ -d bazel-bin/foo/foo.runfiles/_main ]] || fail "_main runfiles directory not created"
+  [[ -d bazel-bin/foo/foo.runfiles/_main/foo ]] || fail "No foo subdirectory under _main"
+  [[ -x bazel-bin/foo/foo.runfiles/_main/foo/foo ]] || fail "No foo executable under _main"
+}
+
 function test_legacy_runfiles_change() {
   create_workspace_with_default_repos WORKSPACE foo
   cat >> WORKSPACE <<EOF