The ultimate goal is to allow Clang-Tidy to reap the benefits of our BugReporter while also not being entirely dependent on the Static Analyzer (eg., be able to get compiled with CLANG_ENABLE_STATIC_ANALYZER=OFF). This would involve eventually moving the basic BugReporter and BugReport/BasicBugReport classes into libAnalysis.
This is the minimal patch that separates the BugReport class into BasicBugReport and PathSensitiveBugReport in a sensible manner and compiles. I looked through all their APIs and made a quick guess on whether they do or do not require path-sensitive reasoning and put them into the respective class based on that.
There's no common base class for the two BugReporters yet.
Checker API breakage was fairly bearable, in most cases i just had to specify whether i want a basic report or a path-sensitive report. Most path-insensitive checkers were already using the EmitBasicReport() wrapper so they are unaffected.