feat: Add fixed-size array support to the Go code generator

[statxc]

Summary

Add fixed-size array support to the Go code generator, resolving a long-standing gap where Go was the only major language without support for the [type:length] struct field syntax (fixes #8417).

Changes

• src/idl_parser.cpp: Add IDLOptions::kGo to the SupportsAdvancedArrayFeatures() allowlist.
• src/idl_gen_go.cpp: Implement array-aware code generation for Go, including:
  • Indexed accessors and length methods for scalar and struct array fields
  • Scalar array mutators with bounds-checked index access
  • Builder body logic with correct reverse-order writing and nested struct flattening
  • Object API (Pack/UnPack) support using Go fixed-size arrays ([N]Type)
• tests/go_arrays_test_test.go: Comprehensive test covering read, mutate, object API round-trip, and standalone struct creation against the arrays_test.fbs schema.
• tests/GoArraysTest.sh: Test runner script following the same pattern as GoTest.sh.

Design

The implementation follows the same flattening strategy used by the Java and C# generators: nested struct array fields are expanded into per-sub-field slices in the Create function signature. For example, d:[NestedStruct:2] becomes d_a [][]int32, d_b []TestEnum, d_c [][]TestEnum, d_d [][]int64. Field offsets were verified against the Java reference output.

Test plan

• go vet clean on generated code
• All 4 new tests pass (TestArrayStructRead, TestArrayStructMutate, TestArrayStructObjectAPI, TestNestedStructStandalone)
• Existing Go tests (GoTest.sh) still pass
• flatc builds with no warnings

[statxc]

@jtdavis777 would you review this PR
thank you

[jtdavis777]

this is also a language I am not familiar with, and that I think we do not have an active maintainer of. so will take me some time

[statxc]

@jtdavis777 could you give me any updates for me?

[jtdavis777]

this looks like another chunky feature that will take me a little bit to digest -- what I can say is there is a SupportsAdvancedArrayFeatures feature in the idl_parser I think you will need to enable -- it isn't a well documented area of the code but we will need to make sure Go conforms to all the features under this umbrella.

[statxc]

this looks like another chunky feature that will take me a little bit to digest -- what I can say is there is a SupportsAdvancedArrayFeatures feature in the idl_parser I think you will need to enable -- it isn't a well documented area of the code but we will need to make sure Go conforms to all the features under this umbrella.

Good call on SupportsAdvancedArrayFeatures - that's already enabled in this PR(kGo added to the whitelist in idl_parser.cpp).
I checked Go's coverage against the other backends. Read, mutate, create, and full object API round-trip all work and are tested against arrays_test.fbs. Two small gaps vs C++/Rust:

1. No dedicated struct array mutator - though it still works because D(nil, 0) returns a pointer into the buffer, so you can mutate fields on the returned struct directly.
2. No full-array slice getter (same as TypeScript).

Happy to close either gap if you want full parity.

[jtdavis777]

thanks for the explanation -- I didn't catch in my quick scan of your PR that you had already enabled. I don't think absolute parity is necessary out of the gate as long as basic functionality is present. I will do my best to review this (with some of my free time next week most likely) but I would also love to see if I can ping someone else familiar with flatbuffers Go to chime in

[jtdavis777]

@mustiikhalil do you have any Go experience? :)

[jtdavis777]

I am pretty sure there are some example FBS files that ensure that flatc can generate code for them and at least one of them is a dedicated arrays test. can you poke around and see if we can make sure Go is one of the languages tested with that?

[statxc]

@jtdavis777 Good catch. I looked into it and there are two things I need to hook up:

1. scripts/generate_code.py - this is the central script that generates code from arrays_test.fbs for C++, C#, Java, Rust, Python, and Swift. Go is already included there for monster_test.fbs but not for arrays_test.fbs. I'll add --go to the arrays_test generation call.
2. tests/TestAll.sh - GoArraysTest.sh exists but isn't called here. I'll add it next to GoTest.sh.

I'll get both of those wired up.

[statxc]

@jtdavis777 Good catch. I looked into it and there are two things I need to hook up:

1. scripts/generate_code.py - this is the central script that generates code from arrays_test.fbs for C++, C#, Java, Rust, Python, and Swift. Go is already included there for monster_test.fbs but not for arrays_test.fbs. I'll add --go to the arrays_test generation call.
2. tests/TestAll.sh - GoArraysTest.sh exists but isn't called here. I'll add it next to GoTest.sh.

I'll get both of those wired up.

Updated! please review again @jtdavis777
thanks

[jtdavis777]

test side LGTM - would still love to find another golang person to look this over