Connect-DbaInstance - Keep the tab completion cache of instance names an array

[andreasjordan]

Problem

The tab completion cache for -SqlInstance ([Dataplat.Dbatools.TabExpansion.TabExpansionHost]::Cache["sqlinstance"]) is a System.String instead of an array as soon as one instance is in it. From the second distinct instance on, every new name is concatenated onto that string, and because -notcontains then compares the whole string, every later connection to an already known instance appends its name again. In a long session the cache reads sql05\sql2025sql05\sql2019sql05\sql2019sql05\sql2019..., and the completer offers that blob instead of instance names. Both editions, reproduced with two Connect-DbaInstance calls: type System.String, value sql05\sql2019sql05\sql2022.

Surfaced in a full lab run: Add-DbaInstanceList.Tests.ps1 failed with Expected 'dbatoolsci_testinstance_...' to be found in collection sql05\sql2025sql05\sql2019sql05\sql2019.... The file passes alone because a fresh process has an empty cache and a one-name string still satisfies -contains.

Mechanism

The cache starts as $null. $null += "x" yields the string "x", not a one-element array, and every writer used +=: Connect-DbaInstance after each connection, Add-DbaInstanceList, and private/dynamicparams/sqlinstance.ps1 for the configured and environment instances. The @() initialisation in that script does not help, because the TEPP maintenance task that loads it runs later than the first connection in most sessions.

What changed

• New private function Add-DbaTeppInstanceName (in private/functions/tabcompletion, so the TEPP maintenance runspace has it too): rebuilds the cache as an array every time, lower cases the names as the completer expects, skips empty entries and duplicates.
• The three writers call it instead of +=. No behaviour change beyond the cache being an array of unique names.

Tests

• Add-DbaInstanceList.Tests.ps1: new test adds two instances and asserts the cache is an array containing both, with the first one exactly once. Red on old: Expected $true, but got $false on the array check (the cache is the string dbatoolsci_testinstance2_...dbatoolsci_testinstance_...).
• Connect-DbaInstance.Tests.ps1: new context connects to InstanceMulti1 and InstanceMulti2 and asserts both names are separate entries.
• Both files green through the testing-dbatools harness on PowerShell 7.6 and 5.1.

created by Claude and reviewed by Andreas Jordan

🤖 Generated with Claude Code