WIP: codegen: add B-ASIC commit hash in VHDL preamble

This adds the (short) Git commit ID of HEAD to the VHDL codegen preamble. Useful when debugging generated code.

Ex:

--
-- This code was automatically generated by the B-ASIC toolbox.
-- Code generation timestamp: (2023-03-15 14:47:44.405842)
-- B-ASIC short commit hash: fa55492
-- URL: https://gitlab.liu.se/da/B-ASIC
--

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

b_asic/codegen/vhdl/common.py

@@ -4,6 +4,7 @@ Generation of common VHDL constructs
 
 from datetime import datetime
 from io import TextIOWrapper
+from subprocess import PIPE, Popen
 from typing import Any, Optional, Set, Tuple
 
 from b_asic.codegen.vhdl import VHDL_TAB
@@ -18,9 +19,18 @@ def write_b_asic_vhdl_preamble(f: TextIOWrapper):
     f : :class:`io.TextIOWrapper`
         The file object to write the header to.
     """
+    # Try to acquire the current git commit hash
+    git_commit_id = None
+    try:
+        process = Popen(['git', 'rev-parse', '--short', 'HEAD'], stdout=PIPE)
+        git_commit_id = process.communicate()[0].decode('utf-8').strip()
+    except:
+        pass
     f.write(f'--\n')
     f.write(f'-- This code was automatically generated by the B-ASIC toolbox.\n')
     f.write(f'-- Code generation timestamp: ({datetime.now()})\n')
+    if git_commit_id:
+        f.write(f'-- B-ASIC short commit hash: {git_commit_id}\n')
     f.write(f'-- URL: https://gitlab.liu.se/da/B-ASIC\n')
     f.write(f'--\n\n')