Replace Guava VisibleForTesting in opencensus-api (issue #1081).

This commit adds two annotations to replace the uses of Guava's
VisibleForTesting annotation in opencensus-api.  Each annotation has a more
specific meaning than VisibleForTesting, to make the uses of the annotations
more informative.

DefaultVisibilityForTesting - This annotation replaces the main use of
@VisibleForTesting, indicating that an element was changed from private to
package-private for testing.

PublicForTesting - This annotation is temporary and should be removed as part
of issue #977.

10 files changed, 91 insertions, 16 deletions

diff --git a/api/src/main/java/io/opencensus/internal/DefaultVisibilityForTesting.java b/api/src/main/java/io/opencensus/internal/DefaultVisibilityForTesting.java
new file mode 100644
index 00000000..e90a6573
--- /dev/null
+++ b/api/src/main/java/io/opencensus/internal/DefaultVisibilityForTesting.java
@@ -0,0 +1,37 @@
+/*
+ * Copyright 2018, OpenCensus Authors
+ *
+ * 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 io.opencensus.internal;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Indicates that an element is package-private instead of private only for the purpose of testing.
+ * This annotation is only meant to be used as documentation in the source code.
+ */
+@Retention(RetentionPolicy.SOURCE)
+@Target({
+  ElementType.ANNOTATION_TYPE,
+  ElementType.CONSTRUCTOR,
+  ElementType.FIELD,
+  ElementType.METHOD,
+  ElementType.PACKAGE,
+  ElementType.TYPE
+})
+public @interface DefaultVisibilityForTesting {}
diff --git a/api/src/main/java/io/opencensus/internal/PublicForTesting.java b/api/src/main/java/io/opencensus/internal/PublicForTesting.java
new file mode 100644
index 00000000..cfd37ff2
--- /dev/null
+++ b/api/src/main/java/io/opencensus/internal/PublicForTesting.java
@@ -0,0 +1,38 @@
+/*
+ * Copyright 2018, OpenCensus Authors
+ *
+ * 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 io.opencensus.internal;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Indicates that an element is public instead of package-private only for the purpose of testing.
+ * This annotation is only meant to be used as documentation in the source code.
+ */
+// TODO(#977): All uses of this annotation should be removed or replaced with @Internal.
+@Retention(RetentionPolicy.SOURCE)
+@Target({
+  ElementType.ANNOTATION_TYPE,
+  ElementType.CONSTRUCTOR,
+  ElementType.FIELD,
+  ElementType.METHOD,
+  ElementType.PACKAGE,
+  ElementType.TYPE
+})
+public @interface PublicForTesting {}
diff --git a/api/src/main/java/io/opencensus/stats/Measure.java b/api/src/main/java/io/opencensus/stats/Measure.java
index ddd25763..4b47cd79 100644
--- a/api/src/main/java/io/opencensus/stats/Measure.java
+++ b/api/src/main/java/io/opencensus/stats/Measure.java
@@ -17,8 +17,8 @@
 package io.opencensus.stats;
 
 import com.google.auto.value.AutoValue;
-import com.google.common.annotations.VisibleForTesting;
 import io.opencensus.common.Function;
+import io.opencensus.internal.DefaultVisibilityForTesting;
 import io.opencensus.internal.StringUtils;
 import io.opencensus.internal.Utils;
 import javax.annotation.concurrent.Immutable;
@@ -31,7 +31,7 @@ import javax.annotation.concurrent.Immutable;
 @Immutable
 public abstract class Measure {
 
-  @VisibleForTesting static final int NAME_MAX_LENGTH = 255;
+  @DefaultVisibilityForTesting static final int NAME_MAX_LENGTH = 255;
 
   /**
    * Applies the given match function to the underlying data type.
diff --git a/api/src/main/java/io/opencensus/stats/Stats.java b/api/src/main/java/io/opencensus/stats/Stats.java
index d7f77e34..8393f631 100644
--- a/api/src/main/java/io/opencensus/stats/Stats.java
+++ b/api/src/main/java/io/opencensus/stats/Stats.java
@@ -16,7 +16,7 @@
 
 package io.opencensus.stats;
 
-import com.google.common.annotations.VisibleForTesting;
+import io.opencensus.internal.DefaultVisibilityForTesting;
 import io.opencensus.internal.Provider;
 import java.util.logging.Level;
 import java.util.logging.Logger;
@@ -89,7 +89,7 @@ public final class Stats {
   }
 
   // Any provider that may be used for StatsComponent can be added here.
-  @VisibleForTesting
+  @DefaultVisibilityForTesting
   static StatsComponent loadStatsComponent(@Nullable ClassLoader classLoader) {
     try {
       // Call Class.forName with literal string name of the class to help shading tools.
diff --git a/api/src/main/java/io/opencensus/stats/View.java b/api/src/main/java/io/opencensus/stats/View.java
index 42179d58..f563ff9a 100644
--- a/api/src/main/java/io/opencensus/stats/View.java
+++ b/api/src/main/java/io/opencensus/stats/View.java
@@ -17,9 +17,9 @@
 package io.opencensus.stats;
 
 import com.google.auto.value.AutoValue;
-import com.google.common.annotations.VisibleForTesting;
 import io.opencensus.common.Duration;
 import io.opencensus.common.Function;
+import io.opencensus.internal.DefaultVisibilityForTesting;
 import io.opencensus.internal.StringUtils;
 import io.opencensus.internal.Utils;
 import io.opencensus.tags.TagKey;
@@ -42,7 +42,7 @@ import javax.annotation.concurrent.Immutable;
 @SuppressWarnings("deprecation")
 public abstract class View {
 
-  @VisibleForTesting static final int NAME_MAX_LENGTH = 255;
+  @DefaultVisibilityForTesting static final int NAME_MAX_LENGTH = 255;
 
   private static final Comparator<TagKey> TAG_KEY_COMPARATOR =
       new Comparator<TagKey>() {
diff --git a/api/src/main/java/io/opencensus/tags/Tags.java b/api/src/main/java/io/opencensus/tags/Tags.java
index e4c6a579..07123647 100644
--- a/api/src/main/java/io/opencensus/tags/Tags.java
+++ b/api/src/main/java/io/opencensus/tags/Tags.java
@@ -16,7 +16,7 @@
 
 package io.opencensus.tags;
 
-import com.google.common.annotations.VisibleForTesting;
+import io.opencensus.internal.DefaultVisibilityForTesting;
 import io.opencensus.internal.Provider;
 import io.opencensus.tags.propagation.TagPropagationComponent;
 import java.util.logging.Level;
@@ -91,7 +91,7 @@ public final class Tags {
   }
 
   // Any provider that may be used for TagsComponent can be added here.
-  @VisibleForTesting
+  @DefaultVisibilityForTesting
   static TagsComponent loadTagsComponent(@Nullable ClassLoader classLoader) {
     try {
       // Call Class.forName with literal string name of the class to help shading tools.
diff --git a/api/src/main/java/io/opencensus/trace/Status.java b/api/src/main/java/io/opencensus/trace/Status.java
index 0a0e45ce..5296541c 100644
--- a/api/src/main/java/io/opencensus/trace/Status.java
+++ b/api/src/main/java/io/opencensus/trace/Status.java
@@ -16,9 +16,9 @@
 
 package io.opencensus.trace;
 
-import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Objects;
+import io.opencensus.internal.PublicForTesting;
 import io.opencensus.internal.Utils;
 import java.util.ArrayList;
 import java.util.Collections;
@@ -229,7 +229,7 @@ public final class Status {
      * @return the status that has the current {@code CanonicalCode}.
      * @since 0.5
      */
-    @VisibleForTesting
+    @PublicForTesting
     public Status toStatus() {
       return STATUS_LIST.get(value);
     }
diff --git a/api/src/main/java/io/opencensus/trace/TraceOptions.java b/api/src/main/java/io/opencensus/trace/TraceOptions.java
index ee09376f..c5d44f45 100644
--- a/api/src/main/java/io/opencensus/trace/TraceOptions.java
+++ b/api/src/main/java/io/opencensus/trace/TraceOptions.java
@@ -16,9 +16,9 @@
 
 package io.opencensus.trace;
 
-import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Objects;
+import io.opencensus.internal.DefaultVisibilityForTesting;
 import io.opencensus.internal.Utils;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
@@ -241,7 +241,7 @@ public final class TraceOptions {
   }
 
   // Returns the current set of options bitmask.
-  @VisibleForTesting
+  @DefaultVisibilityForTesting
   byte getOptions() {
     return options;
   }
diff --git a/api/src/main/java/io/opencensus/trace/Tracing.java b/api/src/main/java/io/opencensus/trace/Tracing.java
index e67eb008..f55cd775 100644
--- a/api/src/main/java/io/opencensus/trace/Tracing.java
+++ b/api/src/main/java/io/opencensus/trace/Tracing.java
@@ -16,8 +16,8 @@
 
 package io.opencensus.trace;
 
-import com.google.common.annotations.VisibleForTesting;
 import io.opencensus.common.Clock;
+import io.opencensus.internal.DefaultVisibilityForTesting;
 import io.opencensus.internal.Provider;
 import io.opencensus.trace.config.TraceConfig;
 import io.opencensus.trace.export.ExportComponent;
@@ -87,7 +87,7 @@ public final class Tracing {
   }
 
   // Any provider that may be used for TraceComponent can be added here.
-  @VisibleForTesting
+  @DefaultVisibilityForTesting
   static TraceComponent loadTraceComponent(@Nullable ClassLoader classLoader) {
     try {
       // Call Class.forName with literal string name of the class to help shading tools.
diff --git a/api/src/main/java/io/opencensus/trace/export/SampledSpanStore.java b/api/src/main/java/io/opencensus/trace/export/SampledSpanStore.java
index 3ee80ce2..99bc5288 100644
--- a/api/src/main/java/io/opencensus/trace/export/SampledSpanStore.java
+++ b/api/src/main/java/io/opencensus/trace/export/SampledSpanStore.java
@@ -17,7 +17,7 @@
 package io.opencensus.trace.export;
 
 import com.google.auto.value.AutoValue;
-import com.google.common.annotations.VisibleForTesting;
+import io.opencensus.internal.PublicForTesting;
 import io.opencensus.internal.Utils;
 import io.opencensus.trace.Span;
 import io.opencensus.trace.Status;
@@ -129,7 +129,7 @@ public abstract class SampledSpanStore {
    * @return the set of unique span names registered to the library.
    * @since 0.7
    */
-  @VisibleForTesting
+  @PublicForTesting
   public abstract Set<String> getRegisteredSpanNamesForCollection();
 
   /**