New pool scaffolding

[mdaigle]

This is the first PR targeting #3356. The goal of this PR is to be non-disruptive and create a separate workspace for the new connection pool implementation.

• Introduces an app context switch to control pool version used
• Adds a shim class for the new connection pool implementation.
• Marks DbConnectionPool methods that are only called from within the class as private to simplify the API.
• Renames PutObject to ReturnInternalConnection for clarity.

To see the POC implementation, take a look at #3211

[Copilot]

Pull Request Overview

Adds scaffolding for a new V2 connection pool implementation, introduces an app-context switch, and simplifies the existing pool API by privatizing and renaming methods.

• Introduce UseConnectionPoolV2 switch in LocalAppContextSwitches
• Rename PutObject to ReturnInternalConnection and mark methods private where appropriate
• Add ChannelDbConnectionPool stub and switch selection logic in DbConnectionPoolGroup

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
LocalAppContextSwitches.cs	Added UseConnectionPoolV2 switch constant, backing field, and property
WaitHandleDbConnectionPool.cs	Privatized pool internals, renamed PutObject calls to ReturnInternalConnection, updated argument names
DbConnectionPoolGroup.cs	Switched instantiation between WaitHandleDbConnectionPool and ChannelDbConnectionPool based on the new switch
DbConnectionPool.cs	Renamed abstract PutObject to ReturnInternalConnection, removed obsolete methods
ChannelDbConnectionPool.cs	Added new stub class with unimplemented methods
DbConnectionInternal.cs	Updated internal call from PutObject to ReturnInternalConnection
*.csproj (netfx/netcore)	Added ChannelDbConnectionPool to project files, relocated WaitHandleDbConnectionPool entries

Comments suppressed due to low confidence (1)

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/ConnectionPool/ChannelDbConnectionPool.cs:22

• All methods in ChannelDbConnectionPool are currently stubs throwing NotImplementedException. Without implementations and corresponding tests, switching to V2 will break at runtime. Add implementations (or at least safe fallbacks) and unit tests before enabling this path.

internal override int Count => throw new NotImplementedException();

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 17 lines in your changes missing coverage. Please review.

Project coverage is 58.65%. Comparing base (dc1298a) to head (831dc5b).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
...lient/ConnectionPool/WaitHandleDbConnectionPool.cs	75.86%	14 Missing ⚠️
...icrosoft/Data/ProviderBase/DbConnectionInternal.cs	80.00%	1 Missing ⚠️
.../SqlClient/ConnectionPool/DbConnectionPoolGroup.cs	91.66%	1 Missing ⚠️
...icrosoft/Data/SqlClient/LocalAppContextSwitches.cs	80.00%	1 Missing ⚠️

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HEAD has 1 upload less than BASE

Flag	BASE (dc1298a)	HEAD (831dc5b)
addons	1	0

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3352      +/-   ##
==========================================
- Coverage   65.16%   58.65%   -6.52%     
==========================================
  Files         300      293       -7     
  Lines       65379    65073     -306     
==========================================
- Hits        42606    38169    -4437     
- Misses      22773    26904    +4131     

Flag	Coverage Δ
addons	?
netcore	62.75% <80.00%> (-5.67%)	⬇️
netfx	59.60% <80.00%> (-6.73%)	⬇️

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[paulmedynski]

Some simple doc fixes, and a philosophical question.

[mdaigle]

@imasud00 @paulmedynski I've addressed your comments if you can take another look, please

[benrr101]

Some comments I'd like addressed, some comments don't matter that much.

[benrr101]

Looks good, thanks for addressing the comments

[imasud00]

[paulmedynski]

We're also missing some switches in :

src/Microsoft.Data.SqlClient/tests/FunctionalTests/LocalAppContextSwitchesTests.cs

Can you add the currently missing ones and your new switch?

[benrr101]

Sure, removing the test is acceptable too 😅