NullnessAnalysis improvements

Visit field initializers in nullness analysis if available to improve precision.

Also:
- handle array initializers and conditional expressions
- add some more built-in knowledge of non-null methods and fields

RELNOTES: improved NullnessAnalysis precision using field initializers and other improvements
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=108300064

core/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/AbstractNullnessPropagationTransfer.java

@@ -717,14 +717,14 @@ Nullness visitGreaterThanOrEqual() {
   @Override
   public final TransferResult<Nullness, LocalStore<Nullness>> visitTernaryExpression(
       TernaryExpressionNode node, TransferInput<Nullness, LocalStore<Nullness>> input) {
-    ReadableLocalVariableUpdates updates = new ReadableLocalVariableUpdates();
-    Nullness result = visitTernaryExpression(node, values(input), updates);
-    return updateRegularStore(result, input, updates);
+    Nullness result = visitTernaryExpression(node, values(input));
+    // TODO(kmb): Return conditional result if node itself is of boolean type, as for method calls
+    return noStoreChanges(result, input);
   }
 
-  Nullness visitTernaryExpression(TernaryExpressionNode node, SubNodeValues inputs,
-      LocalVariableUpdates updates) {
-    return NULLABLE;
+  Nullness visitTernaryExpression(TernaryExpressionNode node, SubNodeValues inputs) {
+    return inputs.valueOfSubNode(node.getThenOperand())
+        .leastUpperBound(inputs.valueOfSubNode(node.getElseOperand()));
   }
 
   @Override

core/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/NullnessAnalysis.java

@@ -68,6 +68,11 @@ public NullnessAnalysis(Predicate<MethodInfo> additionalNonNullReturningMethods)
    * that, in those cases, it will always return {@code NONNULL}.
    */
   public Nullness getNullness(TreePath exprPath, Context context) {
-    return DataFlow.expressionDataflow(exprPath, context, nullnessPropagation);
+    try {
+      nullnessPropagation.setContext(context).setCompilationUnit(exprPath.getCompilationUnit());
+      return DataFlow.expressionDataflow(exprPath, context, nullnessPropagation);
+    } finally {
+      nullnessPropagation.setContext(null).setCompilationUnit(null);
+    }
   }
 }