Baselining new rules (aka. grandfathering in debt) on a large repo is quite difficult

[bichuga]

Version Used:
2.9

Steps to Reproduce:
With the goal of bringing Roslyn Analyzers as a build-breaking code hygiene tool to your large, many-sln codebase....

1. Wire up Roslyn to run a default set of analyzers as part of every project. This will likely require .targets changes and build.props edits.
2. Run a build. As expected, the build is broken in potentially thousands of places.
3. Grandfather in all existing debt.

Expected Behavior:
Feature exists to baseline the entire repo.

Actual Behavior:
No such feature exists.

Since the feature does not yet exist, we built a custom ScopeIdentifier analyzer which generates all of the missing information needed to be able to crunch a Roslyn SARIF file into a LocalSuppressions.cs. We include this scopeidentifier like a normal analyzer <Analyzer Include="…ScopeIdentifier.dll" /> and drop an <errorlog>foo.Sarif</errorlog> during a build. From there we have a Roslyn suppressor tool combine these two files into LocalSuppressions.cs.

[bichuga]

Suggestions:

1. Output the missing scope and target information into the SARIF file.
2. Build a feature by which Roslyn will generate the suppressions file and update the csproj to include this file. The functionality already exists in VS to do essentially this (via right click -> suppress all in suppressions file). We need this functionality to be available natively in msbuild.

[mavasani]

Extracted out (1) to #42489