Add --ts-undefined-for-optionals command line option (#8861)

* Add --ts-undefined-for-optionals command line option

# Details

- Fixes #7656
- Added a new `--ts-undefined-for-optionals` command line option for `flatc`.
- If enabled, generated TypeScript code uses `undefined` for optional fields rather than `null`.

* Also add TS generated test files

* Run `sh scripts/clang-format-git.sh`

* also add tests/ts/lalala-options.ts to the repo

* move new tests to tests/ts/optional_values dir

* add tests/ts/optional_values/optional_values_generated.cjs to the repo

* reuse existing optional_scalars.fbs and add new test

* add comma

* sh scripts/clang-format-git.sh

* remove comma

* sh scripts/clang-format-git.sh

* trying things

* sh scripts/clang-format-git.sh

* done

* address feedback

* sh scripts/clang-format-git.sh

* run `sh scripts/clang-format-git.sh`

* remove uneeded `eslint-disable @typescript-eslint/no-namespace` line

---------

Co-authored-by: José Luis Millán <jmillan@aliax.net>

ts/builder.ts

@@ -212,7 +212,7 @@ export class Builder {
   addFieldInt8(
     voffset: number,
     value: number,
-    defaultValue: number | null,
+    defaultValue: number | null | undefined,
   ): void {
     if (this.force_defaults || value != defaultValue) {
       this.addInt8(value);
@@ -223,7 +223,7 @@ export class Builder {
   addFieldInt16(
     voffset: number,
     value: number,
-    defaultValue: number | null,
+    defaultValue: number | null | undefined,
   ): void {
     if (this.force_defaults || value != defaultValue) {
       this.addInt16(value);
@@ -234,7 +234,7 @@ export class Builder {
   addFieldInt32(
     voffset: number,
     value: number,
-    defaultValue: number | null,
+    defaultValue: number | null | undefined,
   ): void {
     if (this.force_defaults || value != defaultValue) {
       this.addInt32(value);
@@ -245,7 +245,7 @@ export class Builder {
   addFieldInt64(
     voffset: number,
     value: bigint,
-    defaultValue: bigint | null,
+    defaultValue: bigint | null | undefined,
   ): void {
     if (this.force_defaults || value !== defaultValue) {
       this.addInt64(value);
@@ -256,7 +256,7 @@ export class Builder {
   addFieldFloat32(
     voffset: number,
     value: number,
-    defaultValue: number | null,
+    defaultValue: number | null | undefined,
   ): void {
     if (this.force_defaults || value != defaultValue) {
       this.addFloat32(value);
@@ -267,7 +267,7 @@ export class Builder {
   addFieldFloat64(
     voffset: number,
     value: number,
-    defaultValue: number | null,
+    defaultValue: number | null | undefined,
   ): void {
     if (this.force_defaults || value != defaultValue) {
       this.addFloat64(value);
@@ -614,8 +614,8 @@ export class Builder {
    *
    * @returns offset of obj
    */
-  createObjectOffset(obj: string | IGeneratedObject | null): Offset {
-    if (obj === null) {
+  createObjectOffset(obj: string | IGeneratedObject | null | undefined): Offset {
+    if (obj === null || obj === undefined) {
       return 0;
     }
 
@@ -629,7 +629,7 @@ export class Builder {
   /**
    * A helper function to pack a list of object
    *
-   * @returns list of offsets of each non null object
+   * @returns list of offsets of each non null/undefined object
    */
   createObjectOffsetList(list: (string | IGeneratedObject)[]): Offset[] {
     const ret: number[] = [];
@@ -637,11 +637,11 @@ export class Builder {
     for (let i = 0; i < list.length; ++i) {
       const val = list[i];
 
-      if (val !== null) {
+      if (val !== null && val !== undefined) {
         ret.push(this.createObjectOffset(val));
       } else {
         throw new TypeError(
-          'FlatBuffers: Argument for createObjectOffsetList cannot contain null.',
+          'FlatBuffers: Argument for createObjectOffsetList cannot contain null or undefined.',
         );
       }
     }

ts/flexbuffers.ts

@@ -1,4 +1,3 @@
-/* eslint-disable @typescript-eslint/no-namespace */
 import {Builder} from './flexbuffers/builder.js';
 import {toReference} from './flexbuffers/reference.js';
 export {toReference} from './flexbuffers/reference.js';