Added scons tool to run black automatically during the build

.gitignore

@@ -390,3 +390,6 @@ gcov.css
 # https://clangd.llvm.org/ cache folder
 .clangd/
 .cache/
+
+# auto black format tool
+.black.out

SConstruct

@@ -149,6 +149,7 @@ opts.Add(BoolVariable("modules_enabled_by_default", "If no, disable all modules
 opts.Add(BoolVariable("no_editor_splash", "Don't use the custom splash screen for the editor", False))
 opts.Add("system_certs_path", "Use this path as SSL certificates default for editor (for package maintainers)", "")
 opts.Add(BoolVariable("use_precise_math_checks", "Math checks use very precise epsilon (debug option)", False))
+opts.Add(BoolVariable("auto_black", "Run black automatically every build.", True))
 
 # Thirdparty libraries
 opts.Add(BoolVariable("builtin_bullet", "Use the built-in Bullet library", True))
@@ -193,6 +194,9 @@ opts.Add("LINKFLAGS", "Custom flags for the linker")
 # in following code (especially platform and custom_modules).
 opts.Update(env_base)
 
+if env_base["auto_black"]:
+    env_base.Tool("black")
+
 # Platform selection: validate input, and add options.
 
 selected_platform = ""

site_scons/site_tools/black.py

@@ -0,0 +1,63 @@
+import os
+import subprocess
+from git import Repo
+import SCons
+from SCons.Script import *
+
+black_bin = None
+
+
+def run_changeset_black(env, target, source):
+    subprocess.getoutput("black -l 120 " + " ".join([s.path for s in source]) + " > " + target[0].path)
+    # because we have modified the files during a build, we should clear the nodes.
+    # this prevent unnecessary rebuids.
+    for s in source:
+        s.del_binfo()
+        s.clear_memoized_values()
+        s.ninfo = s.new_ninfo()
+        s.executor_cleanup()
+
+
+def exists(env):
+    global black_bin
+
+    black_bin = env.WhereIs("black")
+    if not black_bin:
+        black_bin = env.WhereIs("black", os.environ["PATH"])
+
+    return black_bin
+
+
+def generate(env):
+
+    if not exists(env):
+        print("black not found, not running black formatter.")
+        return
+
+    env["BLACK_OUTPUT"] = env.get("BLACK_OUTPUT", ".black.out")
+    repo = Repo(env.Dir("#").abspath)
+
+    files = [
+        file
+        for file in repo.git.diff("HEAD~1..HEAD", name_only=True).split("\n") + repo.untracked_files
+        if (
+            not file.startswith("thirdparty")
+            and (file.endswith("SConstruct") or file.endswith("SCsub") or file.endswith(".py"))
+        )
+    ]
+
+    if files:
+        changeset_black = env.Command(
+            target="$BLACK_OUTPUT",
+            source=files,
+            action=SCons.Action.Action(run_changeset_black, cmdstr="Formatting changeset with black..."),
+        )
+
+        # these next few lines for scons to always run the black formatter task
+        Default(changeset_black)
+        for target in COMMAND_LINE_TARGETS:
+            if target == "run-black":
+                continue
+            env.Depends(target, changeset_black)
+
+        env.Alias("run-black", changeset_black)