Fix common prefix for instrumentation filter

In case that two path share a prefix, the instrumentation filter is
not computed proper.
bazelbuild#10949
This PR takes as a base the one that was created by @caiyulun and
adds some tests.
Original PR: bazelbuild#10949

src/main/java/com/google/devtools/build/lib/buildtool/InstrumentationFilterSupport.java

@@ -25,6 +25,7 @@
 import com.google.devtools.build.lib.packages.Rule;
 import com.google.devtools.build.lib.packages.Target;
 import com.google.devtools.build.lib.packages.TargetUtils;
+import com.google.devtools.build.lib.vfs.PathFragment;
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.Set;
@@ -124,9 +125,9 @@ private static void optimizeFilterSet(SortedSet<String> packageFilters) {
     if (iterator.hasNext()) {
       // Optimize away nested filters.
       iterator = packageFilters.iterator();
-      String prev = iterator.next();
+      PathFragment prev = PathFragment.create(iterator.next());
       while (iterator.hasNext()) {
-        String current = iterator.next();
+        PathFragment current = PathFragment.create(iterator.next());
         if (current.startsWith(prev)) {
           iterator.remove();
         } else {

src/test/java/com/google/devtools/build/lib/buildtool/BUILD

@@ -311,6 +311,21 @@ java_test(
     ],
 )
 
+java_test(
+    name = "InstrumentationFilterSupportTest",
+    srcs = [
+        "InstrumentationFilterSupportTest.java",
+    ],
+    deps = [
+        "//src/main/java/com/google/devtools/build/lib:runtime",
+        "//src/main/java/com/google/devtools/build/lib/events",
+        "//src/main/java/com/google/devtools/build/lib/packages",
+        "//src/test/java/com/google/devtools/build/lib/analysis/util",
+        "//third_party:junit4",
+        "//third_party:truth",
+    ],
+)
+
 java_test(
     name = "LabelCrossesPackageBoundaryTest",
     srcs = ["LabelCrossesPackageBoundaryTest.java"],

src/test/java/com/google/devtools/build/lib/buildtool/InstrumentationFilterSupportTest.java

@@ -0,0 +1,47 @@
+// Copyright 2020 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.buildtool;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.devtools.build.lib.analysis.util.BuildViewTestCase;
+import com.google.devtools.build.lib.events.EventCollector;
+import com.google.devtools.build.lib.events.EventKind;
+import com.google.devtools.build.lib.packages.Target;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.io.IOException;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Tests {@link com.google.devtools.build.lib.buildtool.InstrumentationFilterSupport}. */
+@RunWith(JUnit4.class)
+public class InstrumentationFilterSupportTest extends BuildViewTestCase{
+
+  @Test
+  public void testComputeInstrumentationFilter() throws Exception {
+    EventCollector events = new EventCollector(EventKind.INFO);
+    scratch.file("foo/BUILD", "sh_test(name='t', srcs=['t.sh'])");
+    scratch.file("foobar/BUILD", "sh_test(name='t', srcs=['t.sh'])");
+    List<Target> listOfTargets = new ArrayList<Target>();
+    listOfTargets.add(getTarget("//foo:t"));
+    listOfTargets.add(getTarget("//foobar:t"));
+    Collection<Target> targets = Collections.unmodifiableCollection(listOfTargets);
+    String expectedFilter = "^//foo[/:],^//foobar[/:]";
+    assertThat(InstrumentationFilterSupport.computeInstrumentationFilter(events, targets)).isEqualTo(expectedFilter);
+  }
+}