sbt really wants tests to run in isolation with different classLoaders.
This complicates attempts to load JNI support as a singleton.

sbt uses multiple class loaders when running tests so we try to ensure a single class loader is used to load our singleton.

 - unload native code,
 - kill external processes.

Incorporate the backend name in the targetDirName to avoid collisions when sbt decides to run tests in parallel.

# Conflicts:
#	build.sbt
#	src/main/scala/chisel3/tester/FirrterpreterBackend.scala
#	src/main/scala/chisel3/tester/Testers2.scala
#	src/main/scala/chisel3/tester/ThreadedBackend.scala

# Conflicts:
#	build.sbt

option method.
Remove commented out Firrterpreter
Since TreadleBackend is new code (based on FirrterpreterBackend) I
have made it scalastyle clean

Add chisel options to select backend
Made treadle the default
Added necessary glue to hook in Treadle
Changed build.sbt to add Treadle dependency

If autoclonetype is unable to determine an outer class, this attempts to insert a null (and give a deprecation warning), preserving old behavior (in some cases) where the new behavior doesn't work.

This doesn't provide full compatibility with old autoclonetype: this does not attempt null insertion in the general first argument (if it's not an outer class reference). Reasoning is that inserting a null for an explicit argument is probably not the right thing to do, and will likely cause a difficult-to-debug NullPointerException (whereas that would be unlikely for an outer class, which is not always referenced in Bundle subclass code).

Revert to more of original design (reduce exception interception), but intercept at a higher level.
Remove waiting.acquire() in run() method in exception processing so we get to call threadFinished() and scheduler() after the thread's demise.
Synchronize access to allThreads.
Move thread manipulation code into ThreadedBackend - killAllTesterThreads().

Eliminate hang on failure.
Clear errors before test start and report them at test end.

Add JNITestAPI.java interface and cpp implementation.
We need to use System.load() to load the compiled (but fixed) cpp code,
but use dlopen/dlsym/dlclose in the fixed cpp code to load the shared library since Java doesn't provide an explicit unload (dlclose) mechanism.
Tease apart the pieces im sim_api.h so we can use them from both separate process ans shared library verilator implementations.
Remove unused imports.
Modify the generated verilator <Module>.mk to add rules to build shared library version of the simulator.
Use multiline string literal to compose the harness code.
Much cleanup and testing required.
TODO:
 - we hang un failed expects with some possibly JNI related semaphore.
 - break up finish/abort/unload so they're composable.

PiperOrigin-RevId: 187258707

Cache unadulterated signal names (don't add dut.name).
This will not work if we try to access signals for nested modules, but I don't think the current code supports that anyway. Add whatever prefix is required for the specific backend when we interrogate it for the actual signal.
Fix getDataNames() so it doesn't automatically add the top level name for an aggregate since these don't exist in some simulation environments (i.e., we need to synthesize them from their actual components).
Set the targetDirName something other than "."
Add scoping to resource names.
Support firrtl and verilator backends for BasicTest.scala.

Copy resources from chisel-testers.

Use TesterOptionsManager.
Use backendName to choose tester backend.
Rename VCS/Verilator tester backends.
Provide basic commend editing support.