s2 compression panic: index out of range [0] with length 0

[iamcalledrob]

I think this may be a separate issue to #902, so opening another one.

I'm encountering a panic when compressing a specific stream of data with s2. It looks like there may be a missing bounds check when emitting repeat chunks?

panic: runtime error: index out of range [0] with length 0

goroutine 251 [running]:
github.com/klauspost/compress/s2.emitRepeat({0x140009e400b?, 0x0?, 0x0?}, 0x140009e1f78?, 0x0?)
	/Users/rob/go/pkg/mod/github.com/klauspost/compress@v1.17.6/s2/encode_go.go:111 +0x1e0
github.com/klauspost/compress/s2.encodeBlockGo({0x140009e400b, 0x10004, 0x10004}, {0x140009d2008, 0x10000, 0x10007})
	/Users/rob/go/pkg/mod/github.com/klauspost/compress@v1.17.6/s2/encode_all.go:146 +0x938
github.com/klauspost/compress/s2.encodeBlock(...)
	/Users/rob/go/pkg/mod/github.com/klauspost/compress@v1.17.6/s2/encode_go.go:24
github.com/klauspost/compress/s2.(*Writer).encodeBlock(0x140009d2008?, {0x140009e400b?, 0x0?, 0x140003dcee0?}, {0x140009d2008?, 0x103bbf0f4?, 0x1400053e0a0?})
	/Users/rob/go/pkg/mod/github.com/klauspost/compress@v1.17.6/s2/writer.go:457 +0x178
github.com/klauspost/compress/s2.(*Writer).writeFull.func1()
	/Users/rob/go/pkg/mod/github.com/klauspost/compress@v1.17.6/s2/writer.go:599 +0x128
created by github.com/klauspost/compress/s2.(*Writer).writeFull in goroutine 235
	/Users/rob/go/pkg/mod/github.com/klauspost/compress@v1.17.6/s2/writer.go:590 +0x388

The stream in question is 185gb, but this crash occurs fairly early within it, and reproduces every time on arm64 (Darwin, M-series)

I'll look at following up with a more straightforward test case.

[klauspost]

Thanks. This should be enough for me to locate it.

[iamcalledrob]

Thank you so much for fixing this. Really appreciated.

[klauspost]

Thanks for the report! Published a new version.