Fix access violation when using Express user instances

[emidah]

Fixes #1944

When SQL Server Express user instances are used, this constructor is called from a special code path at SQLConnectionFactory.cs#L98.

Because the _hostNameInCertificate option is not set in the constructor, the cloned connection at line 99 fails with an access violation somewhere on the native side.

Releases after PR #1608 (which initially added this option) are affected - Express user instances won't work at all in any of them.

[ErikEJ]

A test would be nice..

[emidah]

A test would be nice..

I would like to add some, but it seems difficult to do comprehensively. The local instances feature is currently completely untested, and it seems the closest public interface up the call stack is basically SqlConnection.Open()

If you think it's enough, I can add a test amounting to

Assert.Throws<SqlException>(() => connection.Open()); // hey, at least it doesn't throw an access violation anymore!

but that would not really add any guarantee of the feature working in the future - just that this one very specific issue doesn't occur.

As for integration tests, I am out of my depth there as to how they work in this project but I don't think any of the test pipelines run against Express, which is the only thing that supports this feature

[ErikEJ]

Yeah, anything is better than no test at all, IMHO.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.11 🎉

Comparison is base (a709006) 69.97% compared to head (a644dce) 70.08%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2101      +/-   ##
==========================================
+ Coverage   69.97%   70.08%   +0.11%     
==========================================
  Files         306      306              
  Lines       61975    61976       +1     
==========================================
+ Hits        43368    43437      +69     
+ Misses      18607    18539      -68     

Flag	Coverage Δ
addons	92.88% <ø> (ø)
netcore	73.59% <100.00%> (+0.17%)	⬆️
netfx	68.37% <100.00%> (+0.12%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...rc/Microsoft/Data/SqlClient/SqlConnectionString.cs	81.72% <100.00%> (+9.70%)	⬆️

... and 14 files with indirect coverage changes

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[emidah]

@dotnet-policy-service agree