Restructures hashCode() on JSType and sub-types to prevent possib…

…le infinite recursions.

This change also centralizes some logic and vague comments about nominal type hashcodes.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=202002954

src/com/google/javascript/rhino/jstype/AllType.java

@@ -110,7 +110,7 @@ JSType resolveInternal(ErrorReporter reporter) {
   }
 
   @Override
-  public int hashCode() {
+  int recursionUnsafeHashCode() {
     return System.identityHashCode(this);
   }
 

src/com/google/javascript/rhino/jstype/ArrowType.java

@@ -220,7 +220,7 @@ boolean checkArrowEquivalenceHelper(
   }
 
   @Override
-  public int hashCode() {
+  int recursionUnsafeHashCode() {
     int hashCode = Objects.hashCode(returnType);
     if (parameters != null) {
       Node param = parameters.getFirstChild();

src/com/google/javascript/rhino/jstype/EnumElementType.java

@@ -39,7 +39,6 @@
 
 package com.google.javascript.rhino.jstype;
 
-import static com.google.common.base.Preconditions.checkState;
 
 import com.google.javascript.rhino.ErrorReporter;
 import com.google.javascript.rhino.Node;
@@ -142,14 +141,9 @@ public boolean isNominalType() {
     return hasReferenceName();
   }
 
-  /**
-   * If this is equal to a NamedType object, its hashCode must be equal
-   * to the hashCode of the NamedType object.
-   */
   @Override
-  public int hashCode() {
-    checkState(hasReferenceName());
-    return getReferenceName().hashCode();
+  int recursionUnsafeHashCode() {
+    return NamedType.nominalHashCode(this);
   }
 
   @Override

src/com/google/javascript/rhino/jstype/FunctionType.java

@@ -919,7 +919,7 @@ final boolean checkFunctionEquivalenceHelper(
   }
 
   @Override
-  public int hashCode() {
+  int recursionUnsafeHashCode() {
     int hc = kind.hashCode();
     switch (kind) {
       case CONSTRUCTOR:

src/com/google/javascript/rhino/jstype/InstanceObjectType.java

@@ -167,14 +167,10 @@ public boolean isNominalType() {
     return hasReferenceName();
   }
 
-  /**
-   * If this is equal to a NamedType object, its hashCode must be equal
-   * to the hashCode of the NamedType object.
-   */
   @Override
-  public int hashCode() {
+  int recursionUnsafeHashCode() {
     if (hasReferenceName()) {
-      return getReferenceName().hashCode();
+      return NamedType.nominalHashCode(this);
     } else {
       return super.hashCode();
     }

src/com/google/javascript/rhino/jstype/JSType.java

@@ -76,6 +76,8 @@ public abstract class JSType implements Serializable {
   private JSType resolveResult = null;
   protected TemplateTypeMap templateTypeMap;
 
+  private boolean hashCodeInProgress = false;
+
   private boolean inTemplatedCheckVisit = false;
   private static final CanCastToVisitor CAN_CAST_TO_VISITOR =
       new CanCastToVisitor();
@@ -765,12 +767,40 @@ public boolean equals(Object jsType) {
     return (jsType instanceof JSType) && isEquivalentTo((JSType) jsType);
   }
 
+  /**
+   * Calculates a hash of the object as per {@link Object#hashCode()}.
+   *
+   * <p>This method is <em>unsafe</em> for multi-threaded use. The implementation mutates instance
+   * state to prevent recursion and therefore expects sole access.
+   */
   @Override
-  public abstract int hashCode();
+  public final int hashCode() {
+    if (hashCodeInProgress) {
+      return -1; // Recursive base-case.
+    }
+
+    this.hashCodeInProgress = true;
+    int hashCode = recursionUnsafeHashCode();
+    this.hashCodeInProgress = false;
+    return hashCode;
+  }
 
   /**
-   * This predicate is used to test whether a given type can appear in a
-   * numeric context, such as an operand of a multiply operator.
+   * Calculates {@code #hashCode()} with the assumption that it will never be called recursively.
+   *
+   * <p>To work correctly this method should only called under the following conditions:
+   *
+   * <ul>
+   *   <li>by a subclass of {@link JSType};
+   *   <li>within the body of an override;
+   *   <li>when delegating to a superclass implementation.
+   * </ul>
+   */
+  abstract int recursionUnsafeHashCode();
+
+  /**
+   * This predicate is used to test whether a given type can appear in a numeric context, such as an
+   * operand of a multiply operator.
    */
   public boolean matchesNumberContext() {
     return false;

src/com/google/javascript/rhino/jstype/NamedType.java

@@ -40,6 +40,8 @@
 package com.google.javascript.rhino.jstype;
 
 import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.base.Preconditions.checkState;
+import static com.google.common.base.Strings.emptyToNull;
 
 import com.google.common.base.Predicate;
 import com.google.common.collect.ImmutableList;
@@ -84,6 +86,12 @@
 public final class NamedType extends ProxyObjectType {
   private static final long serialVersionUID = 1L;
 
+  static int nominalHashCode(ObjectType type) {
+    checkState(type.hasReferenceName());
+    String name = checkNotNull(emptyToNull(type.getReferenceName()));
+    return name.hashCode();
+  }
+
   private final String reference;
   private final String sourceName;
   private final int lineno;
@@ -209,13 +217,11 @@ public boolean isNominalType() {
   }
 
   @Override
-  public int hashCode() {
-    return reference.hashCode();
+  int recursionUnsafeHashCode() {
+    return nominalHashCode(this);
   }
 
-  /**
-   * Resolve the referenced type within the enclosing scope.
-   */
+  /** Resolve the referenced type within the enclosing scope. */
   @Override
   JSType resolveInternal(ErrorReporter reporter) {
 

src/com/google/javascript/rhino/jstype/NoObjectType.java

@@ -144,7 +144,7 @@ public final boolean matchesSymbolContext() {
   }
 
   @Override
-  public final int hashCode() {
+  int recursionUnsafeHashCode() {
     return System.identityHashCode(this);
   }
 

src/com/google/javascript/rhino/jstype/PrototypeObjectType.java

@@ -555,7 +555,7 @@ public void matchRecordTypeConstraint(ObjectType constraintObj) {
   }
 
   @Override
-  public int hashCode() {
+  int recursionUnsafeHashCode() {
     if (isStructuralType()) {
       return Objects.hash(className, properties);
     } else {

src/com/google/javascript/rhino/jstype/ProxyObjectType.java

@@ -290,7 +290,7 @@ public Iterable<ObjectType> getCtorExtendedInterfaces() {
   }
 
   @Override
-  public int hashCode() {
+  int recursionUnsafeHashCode() {
     return referencedType.hashCode();
   }
 

src/com/google/javascript/rhino/jstype/TemplatizedType.java

@@ -123,8 +123,8 @@ StringBuilder appendTo(StringBuilder sb, boolean forAnnotations) {
   }
 
   @Override
-  public int hashCode() {
-    int baseHash = super.hashCode();
+  int recursionUnsafeHashCode() {
+    int baseHash = super.recursionUnsafeHashCode();
 
     // TODO(b/110224889): This case can probably be removed if `equals()` is updated.
     if (isSpecializedOnlyWithUnknown) {

src/com/google/javascript/rhino/jstype/UnionType.java

@@ -508,7 +508,7 @@ public HasPropertyKind getPropertyKind(String pname, boolean autobox) {
   }
 
   @Override
-  public int hashCode() {
+  int recursionUnsafeHashCode() {
     return this.hashcode;
   }
 

src/com/google/javascript/rhino/jstype/UnknownType.java

@@ -176,7 +176,7 @@ JSType resolveInternal(ErrorReporter reporter) {
   }
 
   @Override
-  public int hashCode() {
+  int recursionUnsafeHashCode() {
     return System.identityHashCode(this);
   }
 }

src/com/google/javascript/rhino/jstype/ValueType.java

@@ -77,7 +77,8 @@ public HasPropertyKind getPropertyKind(String propertyName, boolean autobox) {
   }
 
   @Override
-  public final int hashCode() {
+  final int recursionUnsafeHashCode() {
+    // Subclasses of this type are unique within a JSTypeRegisty.
     return System.identityHashCode(this);
   }
 }