impl(spanner): remove deprecated Admin classes

[mpeddada1]

Fixes #7356.
Removes deprecated admin classes for spanner and a few unused mocks. Also adds a migration guide.

[gemini-code-assist]

Summary of Changes

Hello @mpeddada1, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request performs a significant cleanup by eliminating previously deprecated admin classes and their related components from the Spanner client library. This action streamlines the codebase, removes obsolete interfaces, and ensures that the library adheres to its deprecation policy, making it easier to maintain and evolve.

Highlights

• Removal of Deprecated Admin Classes: The pull request completely removes the deprecated DatabaseAdminClient and InstanceAdminClient classes, along with their corresponding Connection interfaces, implementation files, and header definitions.
• Cleanup of Build System and Tests: All references to the removed deprecated admin classes have been purged from CMakeLists.txt files, Bazel build definitions (.bzl files), and associated unit and integration tests.

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[gemini-code-assist]

Code Review

This pull request correctly removes the deprecated DatabaseAdminClient and InstanceAdminClient classes, along with their associated connection classes, tests, and build file entries. The changes are clean and align with the goal of removing deprecated code.

I have a few suggestions for further cleanup: the mock files for the removed connection and stub classes appear to be unused now and could also be removed, along with their entries in the build files. I've left specific comments on the test files that used them.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.88%. Comparing base (a83d81f) to head (6d5a7d3).
⚠️ Report is 1 commits behind head on prepare-for-v3.0.0.

Additional details and impacted files

@@                  Coverage Diff                   @@
##           prepare-for-v3.0.0   #15862      +/-   ##
======================================================
+ Coverage               92.84%   92.88%   +0.03%     
======================================================
  Files                    2417     2398      -19     
  Lines                  222256   218492    -3764     
======================================================
- Hits                   206362   202948    -3414     
+ Misses                  15894    15544     -350     

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[devbww]

You should check that the edits/deletions in this PR match those made in the copybara rules used when importing google-cloud-cpp into google3. They should have the same effect.

I don't know whether the google3 import now uses the v3 branch or not (if not, I would suggest that you change it to do so ASAP), but don't forget to remove the copybara rules when this PR is merged into the import branch.

Aside: My recollection is that there are additional copybara rules that remove other deprecated code from google3. You should probably check on the status of those too.

[mpeddada1]

You should check that the edits/deletions in this PR match those made in the copybara rules used when importing google-cloud-cpp into google3. They should have the same effect.

I don't know whether the google3 import now uses the v3 branch or not (if not, I would suggest that you change it to do so ASAP), but don't forget to remove the copybara rules when this PR is merged into the import branch.

Aside: My recollection is that there are additional copybara rules that remove other deprecated code from google3. You should probably check on the status of those too.

hm that's a good point about copybara. I've created a ticket to track this change. cc/ @scotthart

[scotthart]

The ABI dump for spanner will need to be updated to reflect these changes.