Make TagMap a facade over an id store and a name store (dense store - part 6)

gradle/forbiddenApiFilters/instrumentation.txt

@@ -7,3 +7,14 @@ datadog.trace.bootstrap.instrumentation.api.AgentSpan#setServiceName(java.lang.S
 # (see datadog.apicontract.Restricted). Instrumentation uses TagMap's checked methods.
 @defaultMessage TagMap.internals() is restricted to the tracer core; use TagMap's checked methods instead.
 datadog.trace.api.TagMap#internals()
+
+# A span's tag stores, how it gets them from a parent, and the span's view of them skip checks the tracer
+# core has already made; they are @Restricted to the core (see datadog.apicontract.Restricted).
+# Instrumentation uses TagMap's checked methods.
+@defaultMessage Tag stores are restricted to the tracer core; use TagMap's checked methods instead.
+datadog.trace.api.HashStore
+datadog.trace.api.IdStore
+datadog.trace.api.TagMap#readThroughParent(datadog.trace.api.TagMap)
+datadog.trace.api.TagMap#viewOf(datadog.trace.api.IdStore,datadog.trace.api.HashStore,boolean)
+datadog.trace.api.TagMap#customStore()
+datadog.trace.api.TagMap#isCustomStoreBorrowed()

internal-api/src/main/java/datadog/trace/api/HashStore.java

@@ -38,6 +38,14 @@ public final class HashStore {
    */
   private Set<String> removedFromParent;
 
+  /**
+   * {@code parent}'s custom store, for an owner to borrow read-only until its first custom write,
+   * or null.
+   */
+  public static HashStore inheritedFrom(TagMap parent) {
+    return parent == null ? null : parent.nameStore;
+  }
+
   /**
    * A fresh custom store for an owner's first custom write, reading through to {@code borrowed},
    * the store it borrowed until now (may be null).

internal-api/src/main/java/datadog/trace/api/HashSupport.java

@@ -414,24 +414,6 @@ static String toInternalString(Object[] buckets) {
     return ledger.toString();
   }
 
-  /** Whether {@code buckets} holds no entry, checked bucket by bucket. */
-  static boolean isEmpty(Object[] buckets) {
-    Object[] thisBuckets = buckets;
-
-    for (int i = 0; i < thisBuckets.length; ++i) {
-      Object curBucket = thisBuckets[i];
-
-      if (curBucket instanceof Entry) {
-        return false;
-      } else if (curBucket instanceof BucketGroup) {
-        BucketGroup curGroup = (BucketGroup) curBucket;
-        if (!curGroup.isEmptyChain()) return false;
-      }
-    }
-
-    return true;
-  }
-
   /** Walks a bucket array's raw entries, tombstones included, for an iterator. */
   static final class BucketWalker {
     private Object[] buckets;

internal-api/src/main/java/datadog/trace/api/IdStore.java

@@ -27,6 +27,11 @@ interface Cursor {
     EntryReader next();
   }
 
+  /** A fresh id store reading through to {@code parent}'s known tags (parent may be null). */
+  public static IdStore create(TagMap parent) {
+    return IdStoreFactory.Default.INSTANCE.create(parent == null ? null : parent.knownStore);
+  }
+
   /** Throws for an id that names no known tag. */
   static IllegalArgumentException notKnown(long tagId) {
     return new IllegalArgumentException("not a known tag id: " + Long.toHexString(tagId));