Fix parsing IPv6 remote URLs

[babakks]

This PR fixes the panic raised when there's a remote with an IPv6 URL.

Fixes #8703

Problem

I traced the problem, and as @williammartin suspected, the error ignored in the line below was masking the actual problem:

newURL, _ := url.Parse(u.String())

If we set the remotes as suggested by @jcgruenhage in #8703, the URL u (in the above code) will be "ssh:https://git@[/tmp/git-repo", which obviously, is not a valid URL (note the open bracket and the missing IPv6 address). When url.Parse receives this it expects a closing bracket to be there as well, and since it's not, it'll then return an error saying "missing ']' in host".

The malformed URL is created within the ParseURL function (in git/url.go) where the port number is removed from the host (by dropping everything after the first colon):

// (git/url.go:59)
if idx := strings.Index(u.Host, ":"); idx >= 0 {
	u.Host = u.Host[0:idx]
}

This works fine with IPv4 addresses since there's only one colon, if any, in the host part just before the port number. But, IPv6 addresses could have more than one colon. In our example case, u.Host is "[::1]:22" and after (incorrectly) stripping the port number it gets changed to "[", which would later cause the mentioned error in url.Parse.

To fix this, we can trim the port number from the end of the host like this:

// (git/url.go:59)
u.Host = strings.TrimSuffix(u.Host, ":"+u.Port())

This will also handle cases like ssh:https://host:/, where there's no port number after the colon.

With this change, the panic is avoided and we get the following legitimate response:

none of the git remotes configured for this repository point to a known GitHub host. To tell gh about a new GitHub host, please use `gh auth login`

[williammartin]

Setup

➜ git remote add ipv6 'ssh:https://git@[::1]:22/tmp/git-repo'
➜ git remote -v
ipv6    ssh:https://git@[::1]:22/tmp/git-repo (fetch)
ipv6    ssh:https://git@[::1]:22/tmp/git-repo (push)
origin  [email protected]:williammartin-test-org/test-repo.git (fetch)
origin  [email protected]:williammartin-test-org/test-repo.git (push)

Before

➜  gh pr create
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x30 pc=0x10065e64c]

goroutine 1 [running]:
github.com/cli/go-gh/v2/pkg/ssh.(*Translator).Translate(0x140005cc780, 0x14000888000)
        github.com/cli/go-gh/[email protected]/pkg/ssh/ssh.go:43 +0xbc
github.com/cli/cli/v2/context.TranslateRemotes({0x1400036c0d0, 0x2, 0x140006e3a40?}, {0x1022e8380, 0x140005cc780})
        github.com/cli/cli/v2/context/remote.go:109 +0x88
github.com/cli/cli/v2/pkg/cmd/factory.New.remotesFunc.(*remoteResolver).Resolver.func6()
        github.com/cli/cli/v2/pkg/cmd/factory/remote_resolver.go:49 +0xf4
github.com/cli/cli/v2/pkg/cmd/pr/create.getRemotes(0x1400024a900)
        github.com/cli/cli/v2/pkg/cmd/pr/create/create.go:695 +0x28
github.com/cli/cli/v2/pkg/cmd/pr/create.NewCreateContext(0x1400024a900)
        github.com/cli/cli/v2/pkg/cmd/pr/create/create.go:544 +0x78
github.com/cli/cli/v2/pkg/cmd/pr/create.createRun(0x1400024a900)
        github.com/cli/cli/v2/pkg/cmd/pr/create/create.go:243 +0x3c
github.com/cli/cli/v2/pkg/cmd/pr/create.NewCmdCreate.func1(0x140004a4008, {0x102c45880?, 0x4?, 0x10106ecd7?})
        github.com/cli/cli/v2/pkg/cmd/pr/create/create.go:204 +0x8e0
github.com/spf13/cobra.(*Command).execute(0x140004a4008, {0x102c45880, 0x0, 0x0})
        github.com/spf13/[email protected]/command.go:916 +0x654
github.com/spf13/cobra.(*Command).ExecuteC(0x140004ca308)
        github.com/spf13/[email protected]/command.go:1044 +0x320
github.com/spf13/cobra.(*Command).ExecuteContextC(...)
        github.com/spf13/[email protected]/command.go:977
main.mainRun()
        github.com/cli/cli/v2/cmd/gh/main.go:119 +0x4b0
main.main()
        github.com/cli/cli/v2/cmd/gh/main.go:46 +0x1c

After

➜ ~/workspace/cli/bin/gh pr create
must be on a branch named differently than "main"

LGTM thanks for the contribution!