a Pure LLVM Lit test framework

[sequencer]

I wanna use #3596 to subsume #3410, see this simple test:

//> RUN: scala-cli $THIS | firtool -format=fir
import chisel3._
import circt.stage.ChiselStage
class EmptyModule extends Module
println(ChiselStage.emitCHIRRTL(new EmptyModule))

In the build system, it will be processed into:

//>using scala "2.13.12"
//> using jars /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.12/scala-library-2.13.12.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-reflect/2.13.12/scala-reflect-2.13.12.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/lihaoyi/os-lib_2.13/0.9.1/os-lib_2.13-0.9.1.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/lihaoyi/upickle_2.13/3.1.0/upickle_2.13-3.1.0.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/json4s/json4s-native_2.13/4.0.6/json4s-native_2.13-4.0.6.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/io/github/alexarchambault/data-class_2.13/0.2.5/data-class_2.13-0.2.5.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/apache/commons/commons-text/1.10.0/commons-text-1.10.0.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/github/scopt/scopt_2.13/3.7.1/scopt_2.13-3.7.1.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/lihaoyi/geny_2.13/1.0.0/geny_2.13-1.0.0.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/lihaoyi/ujson_2.13/3.1.0/ujson_2.13-3.1.0.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/lihaoyi/upack_2.13/3.1.0/upack_2.13-3.1.0.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/lihaoyi/upickle-implicits_2.13/3.1.0/upickle-implicits_2.13-3.1.0.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/json4s/json4s-core_2.13/4.0.6/json4s-core_2.13-4.0.6.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/json4s/json4s-native-core_2.13/4.0.6/json4s-native-core_2.13-4.0.6.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/apache/commons/commons-lang3/3.12.0/commons-lang3-3.12.0.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/lihaoyi/upickle-core_2.13/3.1.0/upickle-core_2.13-3.1.0.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/json4s/json4s-ast_2.13/4.0.6/json4s-ast_2.13-4.0.6.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/json4s/json4s-scalap_2.13/4.0.6/json4s-scalap_2.13-4.0.6.jar /home/sequencer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/thoughtworks/paranamer/paranamer/2.8/paranamer-2.8.jar /home/sequencer/projects/chisel/compile-resources /home/sequencer/projects/chisel/src/main/resources /home/sequencer/projects/chisel/out/chisel/2.13.12/compile.dest/classes /home/sequencer/projects/chisel/svsim/compile-resources /home/sequencer/projects/chisel/svsim/src/main/resources /home/sequencer/projects/chisel/out/svsim/2.13.12/compile.dest/classes /home/sequencer/projects/chisel/firrtl/compile-resources /home/sequencer/projects/chisel/firrtl/src/main/resources /home/sequencer/projects/chisel/out/firrtl/2.13.12/compile.dest/classes /home/sequencer/projects/chisel/macros/compile-resources /home/sequencer/projects/chisel/macros/src/main/resources /home/sequencer/projects/chisel/out/macros/2.13.12/compile.dest/classes /home/sequencer/projects/chisel/core/compile-resources /home/sequencer/projects/chisel/core/src/main/resources /home/sequencer/projects/chisel/out/core/2.13.12/compile.dest/classes /home/sequencer/projects/chisel/binder/compile-resources /home/sequencer/projects/chisel/binder/src/main/resources /home/sequencer/projects/chisel/out/circtpanamabinder/2.13.12/compile.dest/classes /home/sequencer/projects/chisel/filecheck/utility/compile-resources /home/sequencer/projects/chisel/filecheck/utility/resources /home/sequencer/projects/chisel/out/filecheckutility/2.13.12/compile.dest/classes

import chisel3._
import circt.stage.ChiselStage
class EmptyModule extends Module
println(ChiselStage.emitCHIRRTL(new EmptyModule))

I know this is magic...
But I think this maybe the simplest way to add test and being able to migrate most of tests to this framework to share test for firtool and binding frameworks.

Farewell ScalaTest.

One possible test speed downgrade is for each RUN, it will spwan and JVM, but we have no other way to avoid this. but one of the benefit is we can control each javac and scalac option in a fine-grand way, providing a better way to increase the coverage and flexibility.

I'm thinking using LLVM LIT to replace mill execution, but not quite sure if this is a good approach, since mill can provide a prefect run cache(we can cache out folder in the future)

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• Did you add appropriate documentation in docs/src?
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• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• Feature (or new API)
• API modification
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• Rebase: You will rebase the PR onto master and it will be merged with a merge commit.

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• Did you add the appropriate labels? (Select the most appropriate one based on the "Type of Improvement")
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[sequencer]

This PR is blocked by the scala-cli bug: VirtusLab/scala-cli#2621

[sequencer]

After NixOS/nixpkgs#281556 merged, I can remove the vended nix/scala-cli.nix.
This PR finally rocks!!!

❯ mill "lit[2.13.12].run"
[345/345] lit[2.13.12].run
[lit] -- Testing: 2 tests, 2 workers --
[lit] PASS: CHISEL :: CompilerPlugin/WithCompilerPlugin.sc (1 of 2)
[lit] PASS: CHISEL :: CompilerPlugin/WithoutCompilerPlugin.sc (2 of 2)
[lit]
[lit] Testing Time: 6.99s
[lit]   Passed: 2

I'm going to slip this PR into the main branch and skip review, since it only affect the test code. The panama binding framework will use this as its test infrastructure and CI can use https://github.com/jackkoenig/FileCheck in the future.