gistfile1.txt

diff --git a/packages/firestore/src/api/user_data_converter.ts b/packages/firestore/src/api/user_data_converter.ts
index a37f1be1..9544dbef 100644
--- a/packages/firestore/src/api/user_data_converter.ts
+++ b/packages/firestore/src/api/user_data_converter.ts
@@ -173,6 +173,7 @@ class ParseContext {
   constructor(
     readonly dataSource: UserDataSource,
     readonly methodName: string,
+    readonly localWriteTime: Timestamp,
     readonly path: FieldPath | null,
     readonly arrayElement?: boolean,
     fieldTransforms?: FieldTransform[],
@@ -193,6 +194,7 @@ class ParseContext {
     const context = new ParseContext(
       this.dataSource,
       this.methodName,
+      this.localWriteTime,
       childPath,
       /*arrayElement=*/ false,
       this.fieldTransforms,
@@ -207,6 +209,7 @@ class ParseContext {
     const context = new ParseContext(
       this.dataSource,
       this.methodName,
+      this.localWriteTime,
       childPath,
       /*arrayElement=*/ false,
       this.fieldTransforms,
@@ -222,6 +225,7 @@ class ParseContext {
     return new ParseContext(
       this.dataSource,
       this.methodName,
+      this.localWriteTime,
       /*path=*/ null,
       /*arrayElement=*/ true,
       this.fieldTransforms,
@@ -295,6 +299,7 @@ export class UserDataConverter {
     const context = new ParseContext(
       UserDataSource.Set,
       methodName,
+      Timestamp.now(),
       FieldPath.EMPTY_PATH
     );
     validatePlainObject('Data must be an object, but it was:', context, input);
@@ -317,6 +322,7 @@ export class UserDataConverter {
     const context = new ParseContext(
       UserDataSource.MergeSet,
       methodName,
+      Timestamp.now(),
       FieldPath.EMPTY_PATH
     );
     validatePlainObject('Data must be an object, but it was:', context, input);
@@ -371,6 +377,7 @@ export class UserDataConverter {
     const context = new ParseContext(
       UserDataSource.Update,
       methodName,
+      Timestamp.now(),
       FieldPath.EMPTY_PATH
     );
     validatePlainObject('Data must be an object, but it was:', context, input);
@@ -408,6 +415,7 @@ export class UserDataConverter {
     const context = new ParseContext(
       UserDataSource.Update,
       methodName,
+      Timestamp.now(),
       FieldPath.EMPTY_PATH
     );
     const keys = [fieldPathFromArgument(methodName, field)];
@@ -461,6 +469,7 @@ export class UserDataConverter {
     const context = new ParseContext(
       UserDataSource.Argument,
       methodName,
+      Timestamp.now(),
       FieldPath.EMPTY_PATH
     );
     const parsed = this.parseData(input, context);
@@ -601,12 +610,16 @@ export class UserDataConverter {
       }
     } else if (value instanceof ServerTimestampFieldValueImpl) {
       context.fieldTransforms.push(
-        new FieldTransform(context.path, ServerTimestampTransform.instance)
+        new FieldTransform(
+          context.path,
+          new ServerTimestampTransform(context.localWriteTime)
+        )
       );
     } else if (value instanceof ArrayUnionFieldValueImpl) {
       const parsedElements = this.parseArrayTransformElements(
         value.methodName,
-        value._elements
+        value._elements,
+        context
       );
       const arrayUnion = new ArrayUnionTransformOperation(parsedElements);
       context.fieldTransforms.push(
@@ -615,7 +628,8 @@ export class UserDataConverter {
     } else if (value instanceof ArrayRemoveFieldValueImpl) {
       const parsedElements = this.parseArrayTransformElements(
         value.methodName,
-        value._elements
+        value._elements,
+        context
       );
       const arrayRemove = new ArrayRemoveTransformOperation(parsedElements);
       context.fieldTransforms.push(
@@ -671,17 +685,22 @@ export class UserDataConverter {
 
   private parseArrayTransformElements(
     methodName: string,
-    elements: AnyJs[]
+    elements: AnyJs[],
+    oldcontext: ParseContext
   ): FieldValue[] {
     return elements.map((element, i) => {
       // Although array transforms are used with writes, the actual elements
       // being unioned or removed are not considered writes since they cannot
       // contain any FieldValue sentinels, etc.
+
+      // This should be .childContextForArgument or something along those lines
       const context = new ParseContext(
         UserDataSource.Argument,
         methodName,
+        oldcontext.localWriteTime,
         FieldPath.EMPTY_PATH
       );
+
       return this.parseData(element, context.childContextForArray(i));
     });
   }
diff --git a/packages/firestore/src/local/local_serializer.ts b/packages/firestore/src/local/local_serializer.ts
index 5fa4d850..e1d8476e 100644
--- a/packages/firestore/src/local/local_serializer.ts
+++ b/packages/firestore/src/local/local_serializer.ts
@@ -83,10 +83,10 @@ export class LocalSerializer {
 
   /** Decodes a DbMutationBatch into a MutationBatch */
   fromDbMutationBatch(dbBatch: DbMutationBatch): MutationBatch {
+    const timestamp = Timestamp.fromMillis(dbBatch.localWriteTimeMs);
     const mutations = dbBatch.mutations.map(m =>
-      this.remoteSerializer.fromMutation(m)
+      this.remoteSerializer.fromMutation(m, timestamp)
     );
-    const timestamp = Timestamp.fromMillis(dbBatch.localWriteTimeMs);
     return new MutationBatch(dbBatch.batchId, timestamp, mutations);
   }
 
diff --git a/packages/firestore/src/model/mutation.ts b/packages/firestore/src/model/mutation.ts
index 4d6e4d42..da2f41df 100644
--- a/packages/firestore/src/model/mutation.ts
+++ b/packages/firestore/src/model/mutation.ts
@@ -243,8 +243,7 @@ export abstract class Mutation {
    */
   abstract applyToLocalView(
     maybeDoc: MaybeDocument | null,
-    baseDoc: MaybeDocument | null,
-    localWriteTime: Timestamp
+    baseDoc: MaybeDocument | null
   ): MaybeDocument | null;
 
   abstract isEqual(other: Mutation): boolean;
@@ -313,8 +312,7 @@ export class SetMutation extends Mutation {
 
   applyToLocalView(
     maybeDoc: MaybeDocument | null,
-    baseDoc: MaybeDocument | null,
-    localWriteTime: Timestamp
+    baseDoc: MaybeDocument | null
   ): MaybeDocument | null {
     this.verifyKeyMatches(maybeDoc);
 
@@ -393,8 +391,7 @@ export class PatchMutation extends Mutation {
 
   applyToLocalView(
     maybeDoc: MaybeDocument | null,
-    baseDoc: MaybeDocument | null,
-    localWriteTime: Timestamp
+    baseDoc: MaybeDocument | null
   ): MaybeDocument | null {
     this.verifyKeyMatches(maybeDoc);
 
@@ -504,8 +501,7 @@ export class TransformMutation extends Mutation {
 
   applyToLocalView(
     maybeDoc: MaybeDocument | null,
-    baseDoc: MaybeDocument | null,
-    localWriteTime: Timestamp
+    baseDoc: MaybeDocument | null
   ): MaybeDocument | null {
     this.verifyKeyMatches(maybeDoc);
 
@@ -514,10 +510,7 @@ export class TransformMutation extends Mutation {
     }
 
     const doc = this.requireDocument(maybeDoc);
-    const transformResults = this.localTransformResults(
-      localWriteTime,
-      baseDoc
-    );
+    const transformResults = this.localTransformResults(baseDoc);
     const newData = this.transformObject(doc.data, transformResults);
     return new Document(this.key, doc.version, newData, {
       hasLocalMutations: true
@@ -606,10 +599,7 @@ export class TransformMutation extends Mutation {
    * @param baseDoc The document prior to applying this mutation batch.
    * @return The transform results list.
    */
-  private localTransformResults(
-    localWriteTime: Timestamp,
-    baseDoc: MaybeDocument | null
-  ): FieldValue[] {
+  private localTransformResults(baseDoc: MaybeDocument | null): FieldValue[] {
     const transformResults = [] as FieldValue[];
     for (const fieldTransform of this.fieldTransforms) {
       const transform = fieldTransform.transform;
@@ -619,7 +609,7 @@ export class TransformMutation extends Mutation {
         previousValue = baseDoc.field(fieldTransform.field) || null;
       }
 
-      transformResults.push(transform.transform(previousValue, localWriteTime));
+      transformResults.push(transform.transform(previousValue));
     }
     return transformResults;
   }
@@ -670,8 +660,7 @@ export class DeleteMutation extends Mutation {
 
   applyToLocalView(
     maybeDoc: MaybeDocument | null,
-    baseDoc: MaybeDocument | null,
-    localWriteTime: Timestamp
+    baseDoc: MaybeDocument | null
   ): MaybeDocument | null {
     this.verifyKeyMatches(maybeDoc);
 
diff --git a/packages/firestore/src/model/mutation_batch.ts b/packages/firestore/src/model/mutation_batch.ts
index c5fc7661..69bc449a 100644
--- a/packages/firestore/src/model/mutation_batch.ts
+++ b/packages/firestore/src/model/mutation_batch.ts
@@ -104,11 +104,7 @@ export class MutationBatch {
     for (let i = 0; i < this.mutations.length; i++) {
       const mutation = this.mutations[i];
       if (mutation.key.isEqual(docKey)) {
-        maybeDoc = mutation.applyToLocalView(
-          maybeDoc,
-          baseDoc,
-          this.localWriteTime
-        );
+        maybeDoc = mutation.applyToLocalView(maybeDoc, baseDoc);
       }
     }
     return maybeDoc;
diff --git a/packages/firestore/src/model/transform_operation.ts b/packages/firestore/src/model/transform_operation.ts
index 14f009ba..ab1e2034 100644
--- a/packages/firestore/src/model/transform_operation.ts
+++ b/packages/firestore/src/model/transform_operation.ts
@@ -22,22 +22,17 @@ import { assert } from '../util/assert';
 /** Represents a transform within a TransformMutation. */
 export interface TransformOperation {
   /** Transforms the provided `previousValue`. */
-  transform(previousValue: FieldValue, localWriteTime?: Timestamp): FieldValue;
+  transform(previousValue: FieldValue): FieldValue;
 
   isEqual(other: TransformOperation): boolean;
 }
 
 /** Transforms a value into a server-generated timestamp. */
 export class ServerTimestampTransform implements TransformOperation {
-  private constructor() {}
-  static instance = new ServerTimestampTransform();
+  constructor(private localWriteTime: Timestamp) {}
 
-  transform(previousValue: FieldValue, localWriteTime?: Timestamp): FieldValue {
-    assert(
-      localWriteTime !== undefined,
-      'ServerTimestampTransform.transform() requires localWriteTime.'
-    );
-    return new ServerTimestampValue(localWriteTime!, previousValue);
+  transform(previousValue: FieldValue): FieldValue {
+    return new ServerTimestampValue(this.localWriteTime, previousValue);
   }
 
   isEqual(other: TransformOperation): boolean {
@@ -49,7 +44,7 @@ export class ServerTimestampTransform implements TransformOperation {
 export class ArrayUnionTransformOperation implements TransformOperation {
   constructor(readonly elements: FieldValue[]) {}
 
-  transform(previousValue: FieldValue, localWriteTime?: Timestamp): FieldValue {
+  transform(previousValue: FieldValue): FieldValue {
     const result = coercedFieldValuesArray(previousValue);
     for (const toUnion of this.elements) {
       if (!result.find(element => element.isEqual(toUnion))) {
@@ -71,7 +66,7 @@ export class ArrayUnionTransformOperation implements TransformOperation {
 export class ArrayRemoveTransformOperation implements TransformOperation {
   constructor(readonly elements: FieldValue[]) {}
 
-  transform(previousValue: FieldValue, localWriteTime?: Timestamp): FieldValue {
+  transform(previousValue: FieldValue): FieldValue {
     let result = coercedFieldValuesArray(previousValue);
     for (const toRemove of this.elements) {
       result = result.filter(element => !element.isEqual(toRemove));
diff --git a/packages/firestore/src/remote/serializer.ts b/packages/firestore/src/remote/serializer.ts
index 42915e45..eab52f38 100644
--- a/packages/firestore/src/remote/serializer.ts
+++ b/packages/firestore/src/remote/serializer.ts
@@ -836,7 +836,7 @@ export class JsonProtoSerializer {
     return result;
   }
 
-  fromMutation(proto: api.Write): Mutation {
+  fromMutation(proto: api.Write, writeTime: Timestamp): Mutation {
     const precondition = proto.currentDocument
       ? this.fromPrecondition(proto.currentDocument)
       : Precondition.NONE;
@@ -857,7 +857,7 @@ export class JsonProtoSerializer {
     } else if (proto.transform) {
       const key = this.fromName(proto.transform.document!);
       const fieldTransforms = proto.transform.fieldTransforms!.map(transform =>
-        this.fromFieldTransform(transform)
+        this.fromFieldTransform(transform, writeTime)
       );
       assert(
         precondition.exists === true,
@@ -936,7 +936,10 @@ export class JsonProtoSerializer {
     }
   }
 
-  private fromFieldTransform(proto: api.FieldTransform): FieldTransform {
+  private fromFieldTransform(
+    proto: api.FieldTransform,
+    writeTime: Timestamp
+  ): FieldTransform {
     // tslint:disable-next-line:no-any We need to match generated Proto types.
     const type = (proto as any)['transform_type'];
     let transform: TransformOperation | null = null;
@@ -945,7 +948,7 @@ export class JsonProtoSerializer {
         proto.setToServerValue === 'REQUEST_TIME',
         'Unknown server value transform proto: ' + JSON.stringify(proto)
       );
-      transform = ServerTimestampTransform.instance;
+      transform = new ServerTimestampTransform(writeTime);
     } else if (hasTag(proto, type, 'appendMissingElements')) {
       const values = proto.appendMissingElements!.values || [];
       transform = new ArrayUnionTransformOperation(