fix: invalid handling of empty values in sqlcmd

[debarshibasak]

The built sqlcmd is throwing panic errors, for the empty values. For eg.

SQLCMDPASSWORD=<somepassword> ./sqlcmd -S <ip> -U 'sa' -d '' -Q "SELECT name FROM sys.databases WHERE name NOT IN ('tempdb','sys','msdb', 'model')" -b

Throws:

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

goroutine 1 [running]:
github.com/microsoft/go-sqlcmd/cmd/sqlcmd.checkDefaultValue({0xc000034150, 0x9, 0xefcf38?}, 0x4)
	/__w/1/s/go-sqlcmd/cmd/sqlcmd/sqlcmd.go:320 +0x2da
github.com/microsoft/go-sqlcmd/cmd/sqlcmd.convertOsArgs({0xc000034150, 0x9, 0x9})
	/__w/1/s/go-sqlcmd/cmd/sqlcmd/sqlcmd.go:302 +0x22a
github.com/microsoft/go-sqlcmd/cmd/sqlcmd.Execute({0x122eaac, 0x6})
	/__w/1/s/go-sqlcmd/cmd/sqlcmd/sqlcmd.go:274 +0x150
main.main()
	/__w/1/s/go-sqlcmd/cmd/modern/main.go:52 +0x209

After the fix:

name

pubs

I have validated for rest of the flags too.

[debarshibasak]

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[Copilot]

Pull request overview

Fixes a panic in the legacy cmd/sqlcmd argument-rewriting logic when a flag is followed by an empty string value (e.g., -d ""), ensuring sqlcmd can accept intentionally empty values without crashing.

Changes:

• Make flag detection safe for empty-string arguments by guarding index access and reusing isFlag in checkDefaultValue.
• Add a unit test case covering a flag with an explicit empty value (-d "") to prevent regression.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
cmd/sqlcmd/sqlcmd.go	Prevents panics by making isFlag safe on empty strings and using it in checkDefaultValue when checking the next arg.
cmd/sqlcmd/sqlcmd_test.go	Adds a regression test ensuring empty flag values (e.g., -d "") are preserved and don’t crash conversion.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[dlevy-msft-sql]

Fixes #750

[dlevy-msft-sql]

Thanks for the fix @debarshibasak and apologies for the long delay getting CI unblocked on this one! The root-cause analysis is spot on, and routing both call sites through isFlag instead of repeating args[i+1][0] == '-' is a nice cleanup. Tightening assert.ElementsMatch → assert.Equal in the test is also a real win, since arg order is the whole contract of convertOsArgs.

Before we merge, could you make a couple of small tweaks?

1. Rebase onto current main

The branch is a few months behind and main has since moved to Go 1.25.10 plus a few CI changes. A rebase + force-push will also re-trigger the workflows cleanly.

2. Add a test for the __complete "" panic

Issue #750 reports the same crash via a different path: sqlcmd __complete '' (empty arg that isn't preceded by a single-char flag). Your fix already covers it, but it would be great to lock that in with a regression test so it can't sneak back. Something like:

{
    "empty arg standalone (issue #750)",
    []string{"__complete", ""},
    []string{"__complete", ""},
},
{
    "minimal -d empty (issue #708)",
    []string{"-d", ""},
    []string{"-d", ""},
},

The minimal -d "" case is also worth having alongside the longer one. It's easier to read as "this is the exact panic from the issue."

3. Pin the behavior for -N "" and friends

Before this change, -N "" panicked. After it, isFlag("") returns false, so checkDefaultValue no longer injects "true" for -N "" (and similarly no default for -r "", -k "", -L "", -X ""). That's a reasonable choice, empty string isn't really "missing value", but it's a behavior change worth a test so a future refactor doesn't flip it accidentally:

{
    "-N with empty next arg",
    []string{"-N", ""},
    []string{"-N", ""}, // adjust if you'd prefer "true" to be appended
},

Whichever behavior you pick is fine with us; we just want it nailed down in the table.

Once those are in and CI is green, this is good to merge. Thanks again for tracking this down and for your patience on the review!