Release 17.8

[YuliiaKovalova]

(adapted from #8896)

Preparation for the release:

• When VS main snaps to 17.9, create vs17.8 branch
• Create darc channel for VS 17.9 if it doesn't already exist
  darc add-channel --name "VS 17.9"
• Ping internal "First Responders" Teams channel to get the new channel made available as a promotion target (e.g. Make "VS 17.6" darc channel promotionable arcade#12150): Make VS 17.7 and 17.8 promotable arcade#12989
• Remove the main to old release channel default channel
  darc delete-default-channel --repo https://github.com/dotnet/msbuild --branch main --channel "VS 17.8"
• Associate the main branch with the next release channel
  darc add-default-channel --channel "VS 17.9" --branch main --repo https://github.com/dotnet/msbuild
• Check subscriptions for the current channel VS 17.8 and update as necessary (for instance, SDK's main branch should usually be updated, whereas release branches often should not be
  darc get-subscriptions --exact --source-repo https://github.com/dotnet/msbuild --channel "VS 17.8"
  Update channel VS 17.8 to VS 17.9 for the sdk main subscription
  `darc update-subscription --id sdk_main_branch_id
• Ensure that the current release channel VS 17.8 is associated with the correct release branch
  darc get-default-channels --source-repo https://github.com/dotnet/msbuild --branch vs17.8
  if it is not, darc add-default-channel --channel "VS 17.8" --branch vs17.8 --repo https://github.com/dotnet/msbuild
• Fast-forward merge the correct commit (the one that is currently inserted to VS main) to the vs17.8 branch
  git push upstream 797fd829a374a880f63fd4eea4ea6990404c48f4:refs/heads/vs17.8 Note the commit for future steps
  The branch should point to a good, recent spot, so the final-branding PR goes in on top of the right set of commits.
• Update the branch merge flow in dotnet/versions to have the currently-in-servicing branches (extend Automate MSBuild's merge chain versions#867): MSBuild 17.7 -> 17.8 versions#911
• Fix OptProf data flow for the new vs17.8 branch
  • Run manually OptProf pipeline for vs17.8 ('Run pipeline' in upper right)
  • Run the MSBuild pipeline for vs17.8 without OptProf (set SkipApplyOptimizationData variable in 'Advanced options' section of the 'Run pipeline' menu to true)
  • Run the MSBuild pipeline for vs17.8 with no extra vustomization - OptProf should succeed now
• Update the release-branch insertion release definition to have InsertTargetBranch rel/d17.8.
• Prepare final branding PR for vs17.8 but ⚠️ DO NOT MERGE IT YET ⚠️:
• Create 17.9 branding PR, including public API baseline package version change (see Public api analyzer change #8116 (comment)): Version 17.8 #8949
• Merge 17.9 branding PR
• Prepare QB-mode bug for final branding insertion in internal VS repo
• Merge final branding to vs17.8 branch
• Note down the build (will be helpful for requesting nuget packages publishing): (https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=8436672&view=results)
• Get QB approval
• Merge to VS (babysit the automatically generated VS insertion PR https://devdiv.visualstudio.com/DevDiv/_git/VS/pullrequests for the MSBuild commit noted in above step): https://dev.azure.com/devdiv/DevDiv/_git/VS/pullrequest/499661
• Update the PackageValidationBaselineVersion to the latest released version (17.8.0) - this might require temporary addition of build artifacts feed as the new version is not yet added to the official feeds (this is post release). This can trigger a high severity CG error (https://eng.ms/docs/cloud-ai-platform/devdiv/one-engineering-system-1es/1es-docs/secure-supply-chain/how-to-securely-configure-package-source-files) - however it should be fine to keep this temporary feed untill the release.
• Create 17.8 localization ticket: https://aka.ms/ceChangeLocConfig (requesting to flip localization from 17.7 to 17.8)
  https://ceapex.visualstudio.com/CEINTL/_workitems/edit/907751
• Disable the 17.7 localization - by setting EnableReleaseOneLocBuild to false
• Enable 17.8 localization - by setting EnableReleaseOneLocBuild to true

ASAP On/After GA (based on release schedule (internal) https://dev.azure.com/devdiv/DevDiv/_wiki/wikis/DevDiv.wiki/10097/Dev17-Release):

• Push packages to nuget.org (not currently automated, contact dnceng - search "Publish MSBuild 17.6 to NuGet.org" email subject for template).
• Remove the temporarily added build feed from nuget.config if it was added in the Update the PackageValidationBaselineVersion step
• Update main subscriptions to the new channel (this can be done before or after release - depending on when the source repos from our previous - VS 17.8 - channle start to publish in the next - VS 17.9 - channel)
  darc get-subscriptions --exact --target-repo https://github.com/dotnet/msbuild --target-branch main
• Create the 17.8 release
  • Create tag (can be done upfront)

  git checkout <commit noted above>
  git tag v17.8.3
  git push upstream v17.8.3
  

  • Create Release in Github with Create Release from Tag GH option (https://github.com/JanKrivanek/msbuild/releases/new?tag=v17.8.3) - the release notes can be prepopulated (Generate Release Notes)

[f-alizada]

Closing since every step that planned was completed.
Thank you @YuliiaKovalova, @rainersigwald