draft of abbreviation expansion tab completion

1-Draft/RFC0030-Abbreviation-Expansion-TabComplete.md

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+---
+RFC: RFC0030
+Author: Steve Lee
+Status: Experimental-Accepted
+SupercededBy: N/A
+Version: 1.0
+Area: Engine-CommandCompleter
+Comments Due: 12/4/2018
+Plan to implement: Yes
+---
+
+# Abbreviation expansion based tab completion
+
+PowerShell rules for cmdlet naming is to be descriptive.
+Cloud services cmdlets tend to be granular and vast.
+
+Azure PowerShell, for example, has a cmdlet called `New-AzSqlServerDisasterRecoveryConfiguration`.
+If you start with `New-Az` and hit tab, you'll get 334 matches.
+Then you continue typing `New-AzSql` and hit tab, you still get 19 matches.
+
+These cmdlets typically do not have aliases since the aliases would be very long.
+
+## Motivation
+
+    As a PowerShell user,
+    I can tab complete long cmdlet names easily and predictably,
+    so that I can be more efficient using PowerShell interactively.
+
+## Specification
+
+Since PowerShell rule for cmdlet naming relies on Pascal Casing,
+you can consistently predict a long cmdlet name used often by simply specifying
+the uppercase letters:
+
+```none
+PS /Users/steve> n-assdrc<tab>
+
+becomes
+
+PS /Users/steve> New-AzSqlServerDisasterRecoveryConfiguration
+```
+
+The dash is still required to avoid short abbreviations from conflicting with aliases.
+The abbreviation is not an alias as it does not work if specified on the command
+line or script:
+
+```none
+PS /Users/steve> n-assdrc
+n-assdrc : The term 'n-assdrc' is not recognized as the name of a cmdlet, function, script file, or operable program.
+Check the spelling of the name, or if a path was included, verify that the path is correct and try again.
+At line:1 char:1
++ n-assdrc
++ ~~~~~~~~
++ CategoryInfo          : ObjectNotFound: (n-assdrc:String) [], CommandNotFoundException
++ FullyQualifiedErrorId : CommandNotFoundException
+```
+
+This feature is intended only to be used interactively with tab completion.
+
+Even shorter commands can benefit:
+
+```none
+PS /Users/steve> ct-j<tab>
+
+becomes
+
+PS /Users/steve> ConvertTo-Json
+```
+
+## Alternate Proposals and Considerations
+
+PowerShell convention is for 2 letter abbreviations to entirely be in uppercase.
+So you have cmdlets like `Set-AzVM`.
+The abbreviated form is `s-avm`, not `s-av` which might be expected.
+
+This feature is not dynamic aliases as readability of scripts would be significantly
+impacted if `n-assdrc` was allowed in scripts.
+
+Partial support where just verb or noun is abbreviated is not supported.
+This could be added in the future based on customer feedback.
+
+Fuzzy matching is not in scope of this RFC.
+Fuzzy matching for [suggestions on CommandNotFoundException](https://github.com/PowerShell/PowerShell/pull/8458)
+was implemented and could be used as a base for supporting tab completion.
+
+If more variants/algorithms are supported, we may need a way to allow the user
+to pick which ones they want to use.
+
+---------------
+## PowerShell Committee Decision
+
+### Voting Results
+
+Joey Aiello: Accept
+
+Bruce Payette: Accept
+
+Steve Lee: Accept
+
+Hemant Mahawar: Accept
+
+Jim Truher: Accept
+
+### Majority Decision
+
+Committee agrees that the RFC is complete for the targeted scenario and additional enhancement requires are out of scope and should be separate RFCs.
+
+### Minority Decision
+
+N/A