Parallelize syntax regression tests

The syntax highlighting regression tests can be trivially parallelized.
On my notebook (8 core), this results in a 3.9x speedup.

tests/syntax-tests/create_highlighted_versions.py

@@ -6,7 +6,7 @@ import sys
 import os.path as path
 import os
 import argparse
-
+from multiprocessing import Pool
 
 BAT_OPTIONS = [
     "--no-config",
@@ -38,68 +38,79 @@ def get_options(source):
     return options
 
 
+def create_highlighted_version(args):
+    output_basepath, source = args
+    env = os.environ.copy()
+    env.pop("BAT_CACHE_PATH", None)
+    env.pop("BAT_CONFIG_DIR", None)
+    env.pop("BAT_CONFIG_PATH", None)
+    env.pop("BAT_OPTS", None)
+    env.pop("BAT_PAGER", None)
+    env.pop("BAT_STYLE", None)
+    env.pop("BAT_TABS", None)
+    env.pop("BAT_THEME", None)
+    env.pop("NO_COLOR", None)
+    env.pop("PAGER", None)
+    env["COLORTERM"] = "truecolor"  # make sure to output 24bit colors
+
+    source_dirname = path.basename(path.dirname(source))
+    source_filename = path.basename(source)
+
+    if source_filename in SKIP_FILENAMES:
+        return
+
+    bat_output = subprocess.check_output(
+        ["bat"] + get_options(source) + [source],
+        stderr=subprocess.PIPE,
+        env=env,
+    )
+
+    output_dir = path.join(output_basepath, source_dirname)
+    output_path = path.join(output_dir, source_filename)
+
+    os.makedirs(output_dir, exist_ok=True)
+
+    with open(output_path, "wb") as output_file:
+        output_file.write(bat_output)
+
+    print("Created '{}'".format(output_path))
+
+
 def create_highlighted_versions(output_basepath):
     root = os.path.dirname(os.path.abspath(__file__))
-    sources = path.join(root, "source", "*")
+    source_paths = path.join(root, "source", "*")
 
-    for source in glob.glob(path.join(sources, "*")) + glob.glob(
-        path.join(sources, ".*")
+    sources = []
+    for source in glob.glob(path.join(source_paths, "*")) + glob.glob(
+        path.join(source_paths, ".*")
     ):
-        try:
-            env = os.environ.copy()
-            env.pop("BAT_CACHE_PATH", None)
-            env.pop("BAT_CONFIG_DIR", None)
-            env.pop("BAT_CONFIG_PATH", None)
-            env.pop("BAT_OPTS", None)
-            env.pop("BAT_PAGER", None)
-            env.pop("BAT_STYLE", None)
-            env.pop("BAT_TABS", None)
-            env.pop("BAT_THEME", None)
-            env.pop("NO_COLOR", None)
-            env.pop("PAGER", None)
-            env["COLORTERM"] = "truecolor"  # make sure to output 24bit colors
+        sources.append((output_basepath, source))
 
-            source_dirname = path.basename(path.dirname(source))
-            source_filename = path.basename(source)
+    try:
+        with Pool() as p:
+            p.map(create_highlighted_version, sources)
+    except subprocess.CalledProcessError as err:
+        print(
+            "=== Error: Could not highlight source file '{}".format(source),
+            file=sys.stderr,
+        )
+        print(
+            "=== bat stdout:\n{}".format(err.stdout.decode("utf-8")),
+            file=sys.stderr,
+        )
+        print(
+            "=== bat stderr:\n{}".format(err.stderr.decode("utf-8")),
+            file=sys.stderr,
+        )
+        return False
+    except FileNotFoundError:
+        print(
+            "Error: Could not execute 'bat'. Please make sure that the executable "
+            "is available on the PATH."
+        )
+        return False
 
-            if source_filename in SKIP_FILENAMES:
-                continue
-
-            bat_output = subprocess.check_output(
-                ["bat"] + get_options(source) + [source],
-                stderr=subprocess.PIPE,
-                env=env,
-            )
-
-            output_dir = path.join(output_basepath, source_dirname)
-            output_path = path.join(output_dir, source_filename)
-
-            os.makedirs(output_dir, exist_ok=True)
-
-            with open(output_path, "wb") as output_file:
-                output_file.write(bat_output)
-
-            print("Created '{}'".format(output_path))
-        except subprocess.CalledProcessError as err:
-            print(
-                "=== Error: Could not highlight source file '{}".format(source),
-                file=sys.stderr,
-            )
-            print(
-                "=== bat stdout:\n{}".format(err.stdout.decode("utf-8")),
-                file=sys.stderr,
-            )
-            print(
-                "=== bat stderr:\n{}".format(err.stderr.decode("utf-8")),
-                file=sys.stderr,
-            )
-            sys.exit(1)
-        except FileNotFoundError:
-            print(
-                "Error: Could not execute 'bat'. Please make sure that the executable "
-                "is available on the PATH."
-            )
-            sys.exit(1)
+    return True
 
 
 if __name__ == "__main__":
@@ -118,4 +129,5 @@ if __name__ == "__main__":
 
     args = parser.parse_args()
 
-    create_highlighted_versions(output_basepath=args.output)
+    if not create_highlighted_versions(output_basepath=args.output):
+        sys.exit(1)