Exclude //external targets from //...

Fixes bazelbuild#3307 and bazelbuild#1606. The problem was that TargetPatternResolver was
trying to figure out if repositories were tagged as "manual," but
repository rules don't have a "tags" field.  Repository rules shouldn't
be included by //... generally. TargetPatternResolver was just ls-ing
// to find all the "packages," so this removes external/ from consideration.

PiperOrigin-RevId: 161134437

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

@@ -16,6 +16,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.devtools.build.lib.analysis.BlazeDirectories;
+import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
 import com.google.devtools.build.lib.events.Event;
@@ -197,6 +198,10 @@ private Iterable<SkyKey> getSubdirDeps(
           && PathPackageLocator.DEFAULT_TOP_LEVEL_EXCLUDES.contains(basename)) {
         continue;
       }
+      if (basename.equals(Label.EXTERNAL_PACKAGE_NAME.getPathString())) {
+        // Not a real package.
+        continue;
+      }
       PathFragment subdirectory = rootRelativePath.getRelative(basename);
 
       // If this subdirectory is one of the excluded paths, don't recurse into it.

src/test/shell/bazel/empty_package.sh

@@ -44,4 +44,17 @@ EOF
   expect_log "SCREEEECH"
 }
 
+function test_empty_external() {
+  mkdir foo
+  cd foo
+  touch WORKSPACE
+  # Create a dummy BUILD file, otherwise `bazel build` will complain that there
+  # were no targets to build.
+  cat > BUILD <<EOF
+exports_files(["BUILD"])
+EOF
+  mkdir external
+  bazel build ... &> $TEST_log || fail "Failed to build ..."
+}
+
 run_suite "empty package tests"