Model intersection types directly

and use them to represent type variable bounds.

MOE_MIGRATED_REVID=220363183

11 files changed, 137 insertions, 103 deletions

diff --git a/java/com/google/turbine/binder/CanonicalTypeBinder.java b/java/com/google/turbine/binder/CanonicalTypeBinder.java
index e7fed05..caeda97 100644
--- a/java/com/google/turbine/binder/CanonicalTypeBinder.java
+++ b/java/com/google/turbine/binder/CanonicalTypeBinder.java
@@ -30,6 +30,7 @@ import com.google.turbine.binder.sym.TyVarSymbol;
 import com.google.turbine.diag.SourceFile;
 import com.google.turbine.type.Type;
 import com.google.turbine.type.Type.ClassTy;
+import com.google.turbine.type.Type.IntersectionTy;
 import com.google.turbine.types.Canonicalize;
 import java.util.Map;
 
@@ -153,14 +154,8 @@ public class CanonicalTypeBinder {
     ImmutableMap.Builder<TyVarSymbol, TyVarInfo> result = ImmutableMap.builder();
     for (Map.Entry<TyVarSymbol, TyVarInfo> e : tps.entrySet()) {
       TyVarInfo info = e.getValue();
-      Type superClassBound = null;
-      if (info.superClassBound() != null) {
-        superClassBound =
-            Canonicalize.canonicalize(source, position, env, sym, info.superClassBound());
-      }
-      ImmutableList<Type> interfaceBounds =
-          canonicalizeList(source, position, env, sym, info.interfaceBounds());
-      result.put(e.getKey(), new TyVarInfo(superClassBound, interfaceBounds, info.annotations()));
+      Type bound = Canonicalize.canonicalize(source, position, env, sym, info.bound());
+      result.put(e.getKey(), new TyVarInfo((IntersectionTy) bound, info.annotations()));
     }
     return result.build();
   }
diff --git a/java/com/google/turbine/binder/ConstBinder.java b/java/com/google/turbine/binder/ConstBinder.java
index 6852e23..0e81201 100644
--- a/java/com/google/turbine/binder/ConstBinder.java
+++ b/java/com/google/turbine/binder/ConstBinder.java
@@ -45,6 +45,7 @@ import com.google.turbine.type.Type;
 import com.google.turbine.type.Type.ArrayTy;
 import com.google.turbine.type.Type.ClassTy;
 import com.google.turbine.type.Type.ClassTy.SimpleClassTy;
+import com.google.turbine.type.Type.IntersectionTy;
 import com.google.turbine.type.Type.TyKind;
 import com.google.turbine.type.Type.TyVar;
 import com.google.turbine.type.Type.WildLowerBoundedTy;
@@ -293,8 +294,7 @@ public class ConstBinder {
       result.put(
           entry.getKey(),
           new TyVarInfo(
-              info.superClassBound() != null ? bindType(info.superClassBound()) : null,
-              bindTypes(info.interfaceBounds()),
+              (IntersectionTy) bindType(info.bound()),
               constEvaluator.evaluateAnnotations(info.annotations())));
     }
     return result.build();
@@ -333,6 +333,8 @@ public class ConstBinder {
       case PRIM_TY:
       case VOID_TY:
         return type;
+      case INTERSECTION_TY:
+        return IntersectionTy.create(bindTypes(((IntersectionTy) type).bounds()));
       default:
         throw new AssertionError(type.tyKind());
     }
diff --git a/java/com/google/turbine/binder/TypeBinder.java b/java/com/google/turbine/binder/TypeBinder.java
index 951a755..71c3f69 100644
--- a/java/com/google/turbine/binder/TypeBinder.java
+++ b/java/com/google/turbine/binder/TypeBinder.java
@@ -51,6 +51,7 @@ import com.google.turbine.tree.Tree.PrimTy;
 import com.google.turbine.tree.TurbineModifier;
 import com.google.turbine.type.AnnoInfo;
 import com.google.turbine.type.Type;
+import com.google.turbine.type.Type.IntersectionTy;
 import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.HashSet;
@@ -376,32 +377,20 @@ public class TypeBinder {
     ImmutableMap.Builder<TyVarSymbol, TyVarInfo> result = ImmutableMap.builder();
     for (Tree.TyParam tree : trees) {
       TyVarSymbol sym = symbols.get(tree.name().value());
-      Type classBound = null;
-      ImmutableList.Builder<Type> interfaceBounds = ImmutableList.builder();
-      boolean first = true;
-      for (Tree bound : tree.bounds()) {
-        Type ty = bindTy(scope, bound);
-        if (first && !isInterface(ty)) {
-          classBound = ty;
-        } else {
-          interfaceBounds.add(ty);
+      ImmutableList.Builder<Type> bounds = ImmutableList.builder();
+      if (tree.bounds().isEmpty()) {
+        bounds.add(Type.ClassTy.OBJECT);
+      } else {
+        for (Tree bound : tree.bounds()) {
+          bounds.add(bindTy(scope, bound));
         }
-        first = false;
       }
       ImmutableList<AnnoInfo> annotations = bindAnnotations(scope, tree.annos());
-      result.put(sym, new TyVarInfo(classBound, interfaceBounds.build(), annotations));
+      result.put(sym, new TyVarInfo(IntersectionTy.create(bounds.build()), annotations));
     }
     return result.build();
   }
 
-  private boolean isInterface(Type ty) {
-    if (ty.tyKind() != Type.TyKind.CLASS_TY) {
-      return false;
-    }
-    HeaderBoundClass hi = env.get(((Type.ClassTy) ty).sym());
-    return hi.kind() == TurbineTyKind.INTERFACE;
-  }
-
   private List<MethodInfo> bindMethods(CompoundScope scope, ImmutableList<Tree> members) {
     List<MethodInfo> methods = new ArrayList<>();
     for (Tree member : members) {
diff --git a/java/com/google/turbine/binder/bound/TypeBoundClass.java b/java/com/google/turbine/binder/bound/TypeBoundClass.java
index 8c36468..dc6bb43 100644
--- a/java/com/google/turbine/binder/bound/TypeBoundClass.java
+++ b/java/com/google/turbine/binder/bound/TypeBoundClass.java
@@ -27,6 +27,7 @@ import com.google.turbine.tree.Tree;
 import com.google.turbine.tree.Tree.MethDecl;
 import com.google.turbine.type.AnnoInfo;
 import com.google.turbine.type.Type;
+import com.google.turbine.type.Type.IntersectionTy;
 
 /** A bound node that augments {@link HeaderBoundClass} with type information. */
 public interface TypeBoundClass extends HeaderBoundClass {
@@ -56,27 +57,17 @@ public interface TypeBoundClass extends HeaderBoundClass {
 
   /** A type parameter declaration. */
   class TyVarInfo {
-    private final Type superClassBound;
-    private final ImmutableList<Type> interfaceBounds;
+    private final IntersectionTy bound;
     private final ImmutableList<AnnoInfo> annotations;
 
-    public TyVarInfo(
-        Type superClassBound,
-        ImmutableList<Type> interfaceBounds,
-        ImmutableList<AnnoInfo> annotations) {
-      this.superClassBound = superClassBound;
-      this.interfaceBounds = interfaceBounds;
+    public TyVarInfo(IntersectionTy bound, ImmutableList<AnnoInfo> annotations) {
+      this.bound = bound;
       this.annotations = annotations;
     }
 
-    /** A class bound, or {@code null}. */
-    public Type superClassBound() {
-      return superClassBound;
-    }
-
-    /** Interface type bounds. */
-    public ImmutableList<Type> interfaceBounds() {
-      return interfaceBounds;
+    /** The bound. */
+    public IntersectionTy bound() {
+      return bound;
     }
 
     /** Type parameter declaration annotations. */
diff --git a/java/com/google/turbine/binder/bytecode/BytecodeBoundClass.java b/java/com/google/turbine/binder/bytecode/BytecodeBoundClass.java
index f801a14..e500302 100644
--- a/java/com/google/turbine/binder/bytecode/BytecodeBoundClass.java
+++ b/java/com/google/turbine/binder/bytecode/BytecodeBoundClass.java
@@ -54,6 +54,7 @@ import com.google.turbine.model.TurbineTyKind;
 import com.google.turbine.type.AnnoInfo;
 import com.google.turbine.type.Type;
 import com.google.turbine.type.Type.ClassTy;
+import com.google.turbine.type.Type.IntersectionTy;
 import java.lang.annotation.RetentionPolicy;
 import java.util.Map;
 import java.util.function.Function;
@@ -324,15 +325,14 @@ public class BytecodeBoundClass implements BoundClass, HeaderBoundClass, TypeBou
           });
 
   private static TyVarInfo bindTyParam(Sig.TyParamSig sig, Function<String, TyVarSymbol> scope) {
-    Type superClassBound = null;
+    ImmutableList.Builder<Type> bounds = ImmutableList.builder();
     if (sig.classBound() != null) {
-      superClassBound = BytecodeBinder.bindTy(sig.classBound(), scope);
+      bounds.add(BytecodeBinder.bindTy(sig.classBound(), scope));
     }
-    ImmutableList.Builder<Type> interfaceBounds = ImmutableList.builder();
     for (Sig.TySig t : sig.interfaceBounds()) {
-      interfaceBounds.add(BytecodeBinder.bindTy(t, scope));
+      bounds.add(BytecodeBinder.bindTy(t, scope));
     }
-    return new TyVarInfo(superClassBound, interfaceBounds.build(), ImmutableList.of());
+    return new TyVarInfo(IntersectionTy.create(bounds.build()), ImmutableList.of());
   }
 
   @Override
diff --git a/java/com/google/turbine/lower/Lower.java b/java/com/google/turbine/lower/Lower.java
index 5ed646c..fe93a62 100644
--- a/java/com/google/turbine/lower/Lower.java
+++ b/java/com/google/turbine/lower/Lower.java
@@ -65,12 +65,14 @@ import com.google.turbine.diag.TurbineError;
 import com.google.turbine.diag.TurbineError.ErrorKind;
 import com.google.turbine.model.Const;
 import com.google.turbine.model.TurbineFlag;
+import com.google.turbine.model.TurbineTyKind;
 import com.google.turbine.model.TurbineVisibility;
 import com.google.turbine.type.AnnoInfo;
 import com.google.turbine.type.Type;
 import com.google.turbine.type.Type.ArrayTy;
 import com.google.turbine.type.Type.ClassTy;
 import com.google.turbine.type.Type.ClassTy.SimpleClassTy;
+import com.google.turbine.type.Type.TyKind;
 import com.google.turbine.type.Type.TyVar;
 import com.google.turbine.type.Type.WildTy;
 import com.google.turbine.types.Erasure;
@@ -236,7 +238,7 @@ public class Lower {
   private byte[] lower(SourceTypeBoundClass info, ClassSymbol sym, Set<ClassSymbol> symbols) {
     int access = classAccess(info);
     String name = sig.descriptor(sym);
-    String signature = sig.classSignature(info);
+    String signature = sig.classSignature(info, env);
     String superName = info.superclass() != null ? sig.descriptor(info.superclass()) : null;
     List<String> interfaces = new ArrayList<>();
     for (ClassSymbol i : info.interfaces()) {
@@ -672,15 +674,12 @@ public class Lower {
                 TypePath.root(),
                 info));
       }
-      if (p.superClassBound() != null) {
-        lowerTypeAnnotations(
-            result,
-            p.superClassBound(),
-            boundTargetType,
-            new TypeAnnotationInfo.TypeParameterBoundTarget(typeParameterIndex, 0));
-      }
-      int boundIndex = 1; // super class bound index is always 0; interface bounds start at 1
-      for (Type i : p.interfaceBounds()) {
+      int boundIndex = 0;
+      for (Type i : p.bound().bounds()) {
+        if (boundIndex == 0 && isInterface(i, env)) {
+          // super class bound index is always 0; interface bounds start at 1
+          boundIndex++;
+        }
         lowerTypeAnnotations(
             result,
             i,
@@ -691,6 +690,11 @@ public class Lower {
     }
   }
 
+  private boolean isInterface(Type type, Env<ClassSymbol, TypeBoundClass> env) {
+    return type.tyKind() == TyKind.CLASS_TY
+        && env.get(((ClassTy) type).sym()).kind() == TurbineTyKind.INTERFACE;
+  }
+
   private void lowerTypeAnnotations(
       Builder<TypeAnnotationInfo> result, Type type, TargetType targetType, Target target) {
     new LowerTypeAnnotations(result, targetType, target)
diff --git a/java/com/google/turbine/lower/LowerSignature.java b/java/com/google/turbine/lower/LowerSignature.java
index 99a6f3f..624cbf8 100644
--- a/java/com/google/turbine/lower/LowerSignature.java
+++ b/java/com/google/turbine/lower/LowerSignature.java
@@ -19,6 +19,7 @@ package com.google.turbine.lower;
 import com.google.common.collect.ImmutableList;
 import com.google.turbine.binder.bound.SourceTypeBoundClass;
 import com.google.turbine.binder.bound.TypeBoundClass;
+import com.google.turbine.binder.bound.TypeBoundClass.TyVarInfo;
 import com.google.turbine.binder.env.Env;
 import com.google.turbine.binder.sym.ClassSymbol;
 import com.google.turbine.binder.sym.TyVarSymbol;
@@ -32,11 +33,13 @@ import com.google.turbine.bytecode.sig.Sig.TySig;
 import com.google.turbine.bytecode.sig.Sig.UpperBoundTySig;
 import com.google.turbine.bytecode.sig.SigWriter;
 import com.google.turbine.model.TurbineFlag;
+import com.google.turbine.model.TurbineTyKind;
 import com.google.turbine.type.Type;
 import com.google.turbine.type.Type.ArrayTy;
 import com.google.turbine.type.Type.ClassTy;
 import com.google.turbine.type.Type.ClassTy.SimpleClassTy;
 import com.google.turbine.type.Type.PrimTy;
+import com.google.turbine.type.Type.TyKind;
 import com.google.turbine.type.Type.TyVar;
 import com.google.turbine.type.Type.WildTy;
 import java.util.Iterator;
@@ -141,7 +144,7 @@ public class LowerSignature {
     if (!needsMethodSig(sym, env, method)) {
       return null;
     }
-    ImmutableList<Sig.TyParamSig> typarams = tyParamSig(method.tyParams());
+    ImmutableList<Sig.TyParamSig> typarams = tyParamSig(method.tyParams(), env);
     ImmutableList.Builder<Sig.TySig> fparams = ImmutableList.builder();
     for (SourceTypeBoundClass.ParamInfo t : method.parameters()) {
       if (t.synthetic()) {
@@ -203,11 +206,11 @@ public class LowerSignature {
    * Produces a class signature attribute for a generic class, or {@code null} if the signature is
    * unnecessary.
    */
-  public String classSignature(SourceTypeBoundClass info) {
+  public String classSignature(SourceTypeBoundClass info, Env<ClassSymbol, TypeBoundClass> env) {
     if (!classNeedsSig(info)) {
       return null;
     }
-    ImmutableList<Sig.TyParamSig> typarams = tyParamSig(info.typeParameterTypes());
+    ImmutableList<Sig.TyParamSig> typarams = tyParamSig(info.typeParameterTypes(), env);
 
     ClassTySig xtnd = null;
     if (info.superClassType() != null) {
@@ -267,31 +270,46 @@ public class LowerSignature {
   }
 
   private ImmutableList<Sig.TyParamSig> tyParamSig(
-      Map<TyVarSymbol, SourceTypeBoundClass.TyVarInfo> px) {
+      Map<TyVarSymbol, TyVarInfo> px, Env<ClassSymbol, TypeBoundClass> env) {
     ImmutableList.Builder<Sig.TyParamSig> result = ImmutableList.builder();
     for (Map.Entry<TyVarSymbol, SourceTypeBoundClass.TyVarInfo> entry : px.entrySet()) {
-      result.add(tyParamSig(entry.getKey(), entry.getValue()));
+      result.add(tyParamSig(entry.getKey(), entry.getValue(), env));
     }
     return result.build();
   }
 
-  private Sig.TyParamSig tyParamSig(TyVarSymbol sym, SourceTypeBoundClass.TyVarInfo info) {
+  private Sig.TyParamSig tyParamSig(
+      TyVarSymbol sym, SourceTypeBoundClass.TyVarInfo info, Env<ClassSymbol, TypeBoundClass> env) {
+
     String identifier = sym.name();
     Sig.TySig cbound = null;
-    if (info.superClassBound() != null) {
-      cbound = signature(info.superClassBound());
-    } else if (info.interfaceBounds().isEmpty()) {
+    ImmutableList.Builder<Sig.TySig> ibounds = ImmutableList.builder();
+    if (info.bound().bounds().isEmpty()) {
       cbound =
           new ClassTySig(
               "java/lang", ImmutableList.of(new SimpleClassTySig("Object", ImmutableList.of())));
-    }
-    ImmutableList.Builder<Sig.TySig> ibounds = ImmutableList.builder();
-    for (Type i : info.interfaceBounds()) {
-      ibounds.add(signature(i));
+    } else {
+      boolean first = true;
+      for (Type bound : info.bound().bounds()) {
+        TySig sig = signature(bound);
+        if (first) {
+          if (!isInterface(bound, env)) {
+            cbound = sig;
+            continue;
+          }
+        }
+        ibounds.add(sig);
+        first = false;
+      }
     }
     return new Sig.TyParamSig(identifier, cbound, ibounds.build());
   }
 
+  private boolean isInterface(Type type, Env<ClassSymbol, TypeBoundClass> env) {
+    return type.tyKind() == TyKind.CLASS_TY
+        && env.get(((ClassTy) type).sym()).kind() == TurbineTyKind.INTERFACE;
+  }
+
   public String descriptor(ClassSymbol sym) {
     classes.add(sym);
     return sym.binaryName();
diff --git a/java/com/google/turbine/type/Type.java b/java/com/google/turbine/type/Type.java
index 018bbdf..e25eca5 100644
--- a/java/com/google/turbine/type/Type.java
+++ b/java/com/google/turbine/type/Type.java
@@ -44,7 +44,9 @@ public interface Type {
     /** A type variable type. */
     TY_VAR,
     /** A wildcard type. */
-    WILD_TY
+    WILD_TY,
+    /** An intersection type. */
+    INTERSECTION_TY
   }
 
   /** The type kind. */
@@ -100,7 +102,7 @@ public interface Type {
     }
 
     @Override
-    public String toString() {
+    public final String toString() {
       StringBuilder sb = new StringBuilder();
       boolean first = true;
       for (SimpleClassTy c : classes()) {
@@ -177,7 +179,7 @@ public interface Type {
     }
 
     @Override
-    public String toString() {
+    public final String toString() {
       return sym().owner() + "#" + sym().name();
     }
 
@@ -281,4 +283,20 @@ public interface Type {
       throw new IllegalStateException();
     }
   }
+
+  /** An intersection type. */
+  @AutoValue
+  abstract class IntersectionTy implements Type {
+
+    public abstract ImmutableList<Type> bounds();
+
+    public static IntersectionTy create(ImmutableList<Type> bounds) {
+      return new AutoValue_Type_IntersectionTy(bounds);
+    }
+
+    @Override
+    public TyKind tyKind() {
+      return TyKind.INTERSECTION_TY;
+    }
+  }
 }
diff --git a/java/com/google/turbine/types/Canonicalize.java b/java/com/google/turbine/types/Canonicalize.java
index 92553e1..0016011 100644
--- a/java/com/google/turbine/types/Canonicalize.java
+++ b/java/com/google/turbine/types/Canonicalize.java
@@ -30,6 +30,7 @@ import com.google.turbine.type.Type;
 import com.google.turbine.type.Type.ArrayTy;
 import com.google.turbine.type.Type.ClassTy;
 import com.google.turbine.type.Type.ClassTy.SimpleClassTy;
+import com.google.turbine.type.Type.IntersectionTy;
 import com.google.turbine.type.Type.TyKind;
 import com.google.turbine.type.Type.TyVar;
 import com.google.turbine.type.Type.WildTy;
@@ -109,6 +110,8 @@ public class Canonicalize {
         }
       case CLASS_TY:
         return canonicalizeClassTy(base, (ClassTy) type);
+      case INTERSECTION_TY:
+        return canonicalizeIntersectionTy(base, (IntersectionTy) type);
       default:
         throw new AssertionError(type.tyKind());
     }
@@ -370,6 +373,14 @@ public class Canonicalize {
     throw new AssertionError(type.boundKind());
   }
 
+  private Type canonicalizeIntersectionTy(ClassSymbol base, IntersectionTy type) {
+    ImmutableList.Builder<Type> bounds = ImmutableList.builder();
+    for (Type bound : type.bounds()) {
+      bounds.add(canonicalize(base, bound));
+    }
+    return IntersectionTy.create(bounds.build());
+  }
+
   private TypeBoundClass getInfo(ClassSymbol canonOwner) {
     TypeBoundClass info = env.get(canonOwner);
     if (info == null) {
diff --git a/java/com/google/turbine/types/Erasure.java b/java/com/google/turbine/types/Erasure.java
index 67aa69a..e2c7d8f 100644
--- a/java/com/google/turbine/types/Erasure.java
+++ b/java/com/google/turbine/types/Erasure.java
@@ -19,11 +19,13 @@ package com.google.turbine.types;
 import com.google.common.base.Function;
 import com.google.common.collect.ImmutableList;
 import com.google.turbine.binder.bound.SourceTypeBoundClass;
+import com.google.turbine.binder.bound.TypeBoundClass.TyVarInfo;
 import com.google.turbine.binder.sym.TyVarSymbol;
 import com.google.turbine.type.Type;
 import com.google.turbine.type.Type.ArrayTy;
 import com.google.turbine.type.Type.ClassTy;
 import com.google.turbine.type.Type.ClassTy.SimpleClassTy;
+import com.google.turbine.type.Type.IntersectionTy;
 import com.google.turbine.type.Type.TyVar;
 
 /** Generic type erasure. */
@@ -39,21 +41,22 @@ public class Erasure {
         return eraseArrayTy((Type.ArrayTy) ty, tenv);
       case TY_VAR:
         return eraseTyVar((TyVar) ty, tenv);
+      case INTERSECTION_TY:
+        return eraseIntersectionTy((Type.IntersectionTy) ty, tenv);
       default:
         throw new AssertionError(ty.tyKind());
     }
   }
 
+  private static Type eraseIntersectionTy(
+      IntersectionTy ty, Function<TyVarSymbol, TyVarInfo> tenv) {
+    return erase(ty.bounds().get(0), tenv);
+  }
+
   private static Type eraseTyVar(
       TyVar ty, Function<TyVarSymbol, SourceTypeBoundClass.TyVarInfo> tenv) {
     SourceTypeBoundClass.TyVarInfo info = tenv.apply(ty.sym());
-    if (info.superClassBound() != null) {
-      return erase(info.superClassBound(), tenv);
-    }
-    if (!info.interfaceBounds().isEmpty()) {
-      return erase(info.interfaceBounds().get(0), tenv);
-    }
-    return Type.ClassTy.OBJECT;
+    return erase(info.bound(), tenv);
   }
 
   private static Type.ArrayTy eraseArrayTy(
diff --git a/javatests/com/google/turbine/lower/LowerTest.java b/javatests/com/google/turbine/lower/LowerTest.java
index 7ea3d33..ec7d9f9 100644
--- a/javatests/com/google/turbine/lower/LowerTest.java
+++ b/javatests/com/google/turbine/lower/LowerTest.java
@@ -45,6 +45,7 @@ import com.google.turbine.testing.AsmUtils;
 import com.google.turbine.type.Type;
 import com.google.turbine.type.Type.ClassTy;
 import com.google.turbine.type.Type.ClassTy.SimpleClassTy;
+import com.google.turbine.type.Type.IntersectionTy;
 import com.google.turbine.type.Type.PrimTy;
 import com.google.turbine.type.Type.TyVar;
 import java.io.IOException;
@@ -95,13 +96,14 @@ public class LowerTest {
         ImmutableMap.of(
             new TyVarSymbol(new ClassSymbol("test/Test"), "V"),
             new SourceTypeBoundClass.TyVarInfo(
-                ClassTy.create(
+                IntersectionTy.create(
                     ImmutableList.of(
-                        SimpleClassTy.create(
-                            new ClassSymbol("test/Test$Inner"),
-                            ImmutableList.of(),
-                            ImmutableList.of()))),
-                ImmutableList.of(),
+                        ClassTy.create(
+                            ImmutableList.of(
+                                SimpleClassTy.create(
+                                    new ClassSymbol("test/Test$Inner"),
+                                    ImmutableList.of(),
+                                    ImmutableList.of()))))),
                 ImmutableList.of()));
     int access = TurbineFlag.ACC_SUPER | TurbineFlag.ACC_PUBLIC;
     ImmutableList<SourceTypeBoundClass.MethodInfo> methods =
@@ -122,24 +124,25 @@ public class LowerTest {
                 ImmutableMap.of(
                     new TyVarSymbol(new MethodSymbol(new ClassSymbol("test/Test"), "g"), "V"),
                     new SourceTypeBoundClass.TyVarInfo(
-                        null,
-                        ImmutableList.of(
-                            ClassTy.create(
-                                ImmutableList.of(
-                                    SimpleClassTy.create(
-                                        new ClassSymbol("java/lang/Runnable"),
-                                        ImmutableList.of(),
-                                        ImmutableList.of())))),
+                        IntersectionTy.create(
+                            ImmutableList.of(
+                                ClassTy.create(
+                                    ImmutableList.of(
+                                        SimpleClassTy.create(
+                                            new ClassSymbol("java/lang/Runnable"),
+                                            ImmutableList.of(),
+                                            ImmutableList.of()))))),
                         ImmutableList.of()),
                     new TyVarSymbol(new MethodSymbol(new ClassSymbol("test/Test"), "g"), "E"),
                     new SourceTypeBoundClass.TyVarInfo(
-                        ClassTy.create(
+                        IntersectionTy.create(
                             ImmutableList.of(
-                                SimpleClassTy.create(
-                                    new ClassSymbol("java/lang/Error"),
-                                    ImmutableList.of(),
-                                    ImmutableList.of()))),
-                        ImmutableList.of(),
+                                ClassTy.create(
+                                    ImmutableList.of(
+                                        SimpleClassTy.create(
+                                            new ClassSymbol("java/lang/Error"),
+                                            ImmutableList.of(),
+                                            ImmutableList.of()))))),
                         ImmutableList.of())),
                 Type.VOID,
                 ImmutableList.of(