Fix unboxing of lists and messages in java auto impls. Add missing go…

java/src/com/google/template/soy/jbcsrc/ExternCompiler.java

@@ -572,7 +572,7 @@ private static Expression adaptImplicitParameter(ConstantVariables vars, TypeInf
   }
 
   private SoyExpression adaptReturnExpression(SoyExpression raw, SoyRuntimeType type) {
-    return raw.coerceTo(type.runtimeType());
+    return raw.coerceTo(type);
   }
 
   /**

java/src/com/google/template/soy/jbcsrc/SoyNodeCompiler.java

@@ -2149,7 +2149,7 @@ protected Statement visitAssignmentNode(AssignmentNode node) {
     // ASM has no common type for object v. primitive representations. So we need to coerce the
     // new value to fix within the bounds of the old value. This is mostly boxed v. unboxed and
     // numeric conversions among primitives.
-    newValue = newValue.coerceTo(letOrParam.accessor().resultType());
+    newValue = newValue.coerceToTypeOf(letOrParam.accessor());
 
     if (letOrParam instanceof Variable) {
       // This is assignment on a let.

java/src/com/google/template/soy/jbcsrc/restricted/SoyExpression.java

@@ -1026,12 +1026,34 @@ public SoyExpression coerceTo(Type runtimeType) {
           // Field may be a subclass of SoyValue, so need to perform a cast.
           return SoyExpression.forSoyValue(
               boxed.soyType(), boxed.delegate.checkedCast(runtimeType));
-        } else if (BytecodeUtils.STRING_TYPE.equals(runtimeType)) {
+        } else if (runtimeType.equals(BytecodeUtils.STRING_TYPE)) {
           return this.unboxAsStringOrJavaNull();
         }
         // Unhandled cases where we have a boxed value (list, message) but require an
         // unboxed value.
     }
     return this;
   }
+
+  public SoyExpression coerceTo(SoyRuntimeType soyRuntimeType) {
+    if (soyRuntimeType.runtimeType().equals(BytecodeUtils.LIST_TYPE)) {
+      Expression unboxed = unboxAsListOrJavaNull();
+      return (unboxed instanceof SoyExpression)
+          ? (SoyExpression) unboxed
+          : SoyExpression.forList(soyRuntimeType.asListType(), unboxed);
+    } else if (!soyRuntimeType.isBoxed() && soyRuntimeType.isKnownProtoOrUnionOfProtos()) {
+      Expression unboxed = unboxAsMessageOrJavaNull(soyRuntimeType.runtimeType());
+      return (unboxed instanceof SoyExpression)
+          ? (SoyExpression) unboxed
+          : SoyExpression.forProto(soyRuntimeType, unboxed);
+    }
+    return coerceTo(soyRuntimeType.runtimeType());
+  }
+
+  public SoyExpression coerceToTypeOf(Expression expression) {
+    if (expression instanceof SoyExpression) {
+      return coerceTo(((SoyExpression) expression).soyRuntimeType());
+    }
+    return coerceTo(expression.resultType());
+  }
 }

java/src/com/google/template/soy/jssrc/internal/GenJsCodeVisitor.java

@@ -1631,10 +1631,12 @@ protected void visitExternNode(ExternNode node) {
       JsDoc.Builder jsDocBuilder = JsDoc.builder();
       for (FunctionType.Parameter param : node.getType().getParameters()) {
         JsType jsType = getJsTypeForParamForDeclaration(param.getType());
-        jsDocBuilder.addParam("p$" + param.getName(), jsType.typeExpr());
+        jsDocBuilder.addParam("p$" + param.getName(), jsType.typeExpr()).addGoogRequires(jsType);
       }
-      jsDocBuilder.addParameterizedAnnotation(
-          "return", getJsTypeForParamForDeclaration(node.getType().getReturnType()).typeExpr());
+      JsType returnType = getJsTypeForParamForDeclaration(node.getType().getReturnType());
+      jsDocBuilder
+          .addParameterizedAnnotation("return", returnType.typeExpr())
+          .addGoogRequires(returnType);
 
       Statement body = generateAutoExtern(auto);
       Expression function = Expressions.function(jsDocBuilder.build(), body);