Enhancement: DSLX: Create a tool to generate proc tests automatically

[mczyz-antmicro]

The process of creating proc unit tests is repetitive and requires rewriting boilerplate code. Take a look at:

• Proc https://github.com/google/xls/blob/main/xls/examples/delay_loopback_channel.x#L50
• Proc unit test https://github.com/google/xls/blob/main/xls/examples/delay_loopback_channel.x#L86

The steps to create a proc test are:

• Create new proc (config, init, next function)
• Declare the same channels as in Proc Under Test (PUT), but in reversed direction
• Add terminator channel
• In config function, create consumer/producer channel endpoints and attach them to PUT and test proc (this can be figured out based on the channel direction of the PUT)

Resulting code is predictable and could be done automatically with a tool, which parses the config function of the PUT. Ideally, the tool would be implemented in such a way, that it could be reused by code editors plugins, e.g. VSCode Plugin. Another solution would be to figure out how to change DSLX syntax to reduce the boilerplate.

[meheff]

FWIW we're kicking around an idea which would simplify the proc syntax. We hope to prioritize this in the coming months and will post more publicly. Here's an example test proc (syntax not at all finalized):

// Test proc using token-less sends and receives.
#[test_proc]
proc proc_test() {
  input: chan<u32>;
  result: chan<u32>;

  // Instantiation of proc under test.
  dut: instantiate my_proc(input.in, result.out);

  run {
    // Tokens are threaded implicitly. sends/recvs are serialized.
    send(input.out, u32:123);
    send(input.out, u32:42);

    assert_eq!(recv(result.in), u32:11);
    assert_eq!(recv(result.in), u32:12);

    // New builtin for terminating the test. This replaces the terminator channel.
    finish!();
  }
}