oras manifest fetch will panic if --platform flag is used on certain index/manifest list

[qweeah]

What happened in your environment?

If I baked an index containing a manifest without platform information and tried to use oras manifest fetch --platform, then the execution will painc.

What did you expect to happen?

The execution should fail with errors like

> oras manifest fetch --descriptor localhost:7000/command/images:multi1 --platform test/platform
Error: failed to find "localhost:7000/command/images:multi1": sha256:a75baa86dca530232c82eb68a5e97506aa85356e0ee5f1df852a01a9916fdca8: not found: no matching manifest was found in the manifest list

How can we reproduce it?

> cat test.platform.json
{"mediaType":"application/vnd.oci.image.index.v1+json","schemaVersion":2,"manifests":[{"mediaType":"application/vnd.oci.image.manifest.v1+json","digest":"sha256:9d84a5716c66a1d1b9c13f8ed157ba7d1edfe7f9b8766728b8a1f25c0d9c14c1","size":458},{"mediaType":"application/vnd.oci.image.manifest.v1+json","digest":"sha256:4f93460061882467e6fb3b772dc6ab72130d9ac1906aed2fc7589a5cd145433c","size":458,"platform":{"architecture":"arm64","os":"linux"}},{"mediaType":"application/vnd.oci.image.manifest.v1+json","digest":"sha256:58efe73e78fe043ca31b89007a025c594ce12aa7e6da27d21c7b14b50112e255","size":458,"platform":{"architecture":"arm","os":"linux","variant":"v7"}}]}
> oras manifest push localhost:7000/command/images:multi1 test.platform.json
Pushed [registry] localhost:7000/command/images:multi1
Digest: sha256:a75baa86dca530232c82eb68a5e97506aa85356e0ee5f1df852a01a9916fdca8
> oras manifest fetch --descriptor localhost:7000/command/images:multi1 --platform test/platform
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x5e308d]

goroutine 1 [running]:
oras.land/oras-go/v2/internal/platform.Match(0x0, 0xc00009c900)
        /home/runner/go/pkg/mod/oras.land/oras-go/[email protected]/internal/platform/platform.go:41 +0x2d
oras.land/oras-go/v2/internal/platform.SelectManifest({_, _}, {_, _}, {{0xc00002e0c0, 0x27}, {0xc000032050, 0x47}, 0x292, {0x0, ...}, ...}, ...)
        /home/runner/go/pkg/mod/oras.land/oras-go/[email protected]/internal/platform/platform.go:88 +0x66b
oras.land/oras-go/v2.resolve({0x9782c8, 0xc00020eab0}, {0x977600?, 0xc0000b4370?}, 0x0, {0x7ffd113505b6, 0x6}, {0xc00009c900?, 0xc0001df8c8?})
        /home/runner/go/pkg/mod/oras.land/oras-go/[email protected]/content.go:233 +0x5a6
oras.land/oras-go/v2.Resolve({0x9782c8?, 0xc00020eab0?}, {0x977600?, 0xc0000b4370?}, {0x7ffd113505b6?, 0x8?}, {0xc00009c900?, 0x49fdbc?})
        /home/runner/go/pkg/mod/oras.land/oras-go/[email protected]/content.go:196 +0xc9
oras.land/oras/cmd/oras/root/manifest.fetchManifest({_, _}, {{{0x0, 0x0}}, {0x0, 0x0}, {0x1}, {{0x7ffd113505c8, 0xd}, 0xc00009c900}, ...})
        /home/runner/work/oras/oras/cmd/oras/root/manifest/fetch.go:118 +0x27e
oras.land/oras/cmd/oras/root/manifest.fetchCmd.func2(0xc0000b1500?, {0xc0000a0b40?, 0x4?, 0x8b37c3?})
        /home/runner/work/oras/oras/cmd/oras/root/manifest/fetch.go:82 +0x5b
github.com/spf13/cobra.(*Command).execute(0xc0001fb500, {0xc0000a0b00, 0x4, 0x4})
        /home/runner/go/pkg/mod/github.com/spf13/[email protected]/command.go:940 +0x87c
github.com/spf13/cobra.(*Command).ExecuteC(0xc000128300)
        /home/runner/go/pkg/mod/github.com/spf13/[email protected]/command.go:1068 +0x3a5
github.com/spf13/cobra.(*Command).Execute(...)
        /home/runner/go/pkg/mod/github.com/spf13/[email protected]/command.go:992
github.com/spf13/cobra.(*Command).ExecuteContext(0x978290?, {0x978450?, 0xc0000a05c0?})
        /home/runner/go/pkg/mod/github.com/spf13/[email protected]/command.go:985 +0x47
main.main()
        /home/runner/work/oras/oras/cmd/oras/main.go:29 +0x96

What is the version of your ORAS CLI?

v1.1.0

What is your OS environment?

20.04

Are you willing to submit PRs to fix it?

• Yes, I am willing to fix it.

[qweeah]

Related to oras-project/oras-go#692