SCons: unify code generations routine and minimize timestamp changes

Previously, all of the code generation routines would just needlessly
write the same files over and over, even when not needed.

This became a problem with the advent of the experimental ninja backend
for SCons, which can be trivially enabled with a few lines of code and
relies on timestamp changes, making it thus impractical.

core/SCsub

@@ -3,6 +3,7 @@
 Import("env")
 
 import core_builders
+import methods
 
 env.core_sources = []
 
@@ -35,10 +36,12 @@ if "SCRIPT_AES256_ENCRYPTION_KEY" in os.environ:
         )
         Exit(255)
 
-# NOTE: It is safe to generate this file here, since this is still executed serially
-with open("script_encryption_key.gen.cpp", "w", encoding="utf-8", newline="\n") as f:
-    f.write('#include "core/config/project_settings.h"\nuint8_t script_encryption_key[32]={' + txt + "};\n")
 
+script_encryption_key_contents = (
+    '#include "core/config/project_settings.h"\nuint8_t script_encryption_key[32]={' + txt + "};\n"
+)
+
+methods.write_file_if_needed("script_encryption_key.gen.cpp", script_encryption_key_contents)
 
 # Add required thirdparty code.
 

editor/SCsub

@@ -7,19 +7,24 @@ env.editor_sources = []
 import os
 import glob
 import editor_builders
+import methods
 
 
 def _make_doc_data_class_path(to_path):
-    # NOTE: It is safe to generate this file here, since this is still executed serially
-    with open(os.path.join(to_path, "doc_data_class_path.gen.h"), "w", encoding="utf-8", newline="\n") as g:
-        g.write("static const int _doc_data_class_path_count = " + str(len(env.doc_class_path)) + ";\n")
-        g.write("struct _DocDataClassPath { const char* name; const char* path; };\n")
+    file_path = os.path.join(to_path, "doc_data_class_path.gen.h")
 
-        g.write("static const _DocDataClassPath _doc_data_class_paths[" + str(len(env.doc_class_path) + 1) + "] = {\n")
-        for c in sorted(env.doc_class_path):
-            g.write('\t{"' + c + '", "' + env.doc_class_path[c] + '"},\n')
-        g.write("\t{nullptr, nullptr}\n")
-        g.write("};\n")
+    class_path_data = ""
+    class_path_data += "static const int _doc_data_class_path_count = " + str(len(env.doc_class_path)) + ";\n"
+    class_path_data += "struct _DocDataClassPath { const char* name; const char* path; };\n"
+    class_path_data += (
+        "static const _DocDataClassPath _doc_data_class_paths[" + str(len(env.doc_class_path) + 1) + "] = {\n"
+    )
+    for c in sorted(env.doc_class_path):
+        class_path_data += '\t{"' + c + '", "' + env.doc_class_path[c] + '"},\n'
+    class_path_data += "\t{nullptr, nullptr}\n"
+    class_path_data += "};\n"
+
+    methods.write_file_if_needed(file_path, class_path_data)
 
 
 if env.editor_build:
@@ -38,10 +43,7 @@ if env.editor_build:
         reg_exporters += "\tregister_" + e + "_exporter_types();\n"
     reg_exporters += "}\n"
 
-    # NOTE: It is safe to generate this file here, since this is still executed serially
-    with open("register_exporters.gen.cpp", "w", encoding="utf-8", newline="\n") as f:
-        f.write(reg_exporters_inc)
-        f.write(reg_exporters)
+    methods.write_file_if_needed("register_exporters.gen.cpp", reg_exporters_inc + reg_exporters)
 
     # Core API documentation.
     docs = []

methods.py

@@ -228,14 +228,22 @@ def get_version_info(module_version_string="", silent=False):
     return version_info
 
 
+def write_file_if_needed(path, string):
+    try:
+        with open(path, "r", encoding="utf-8", newline="\n") as f:
+            if f.read() == string:
+                return
+    except FileNotFoundError:
+        pass
+
+    with open(path, "w", encoding="utf-8", newline="\n") as f:
+        f.write(string)
+
+
 def generate_version_header(module_version_string=""):
     version_info = get_version_info(module_version_string)
 
-    # NOTE: It is safe to generate these files here, since this is still executed serially.
-
-    with open("core/version_generated.gen.h", "w", encoding="utf-8", newline="\n") as f:
-        f.write(
-            """\
+    version_info_header = """\
 /* THIS FILE IS GENERATED DO NOT EDIT */
 #ifndef VERSION_GENERATED_GEN_H
 #define VERSION_GENERATED_GEN_H
@@ -252,21 +260,20 @@ def generate_version_header(module_version_string=""):
 #define VERSION_DOCS_URL "https://docs.godotengine.org/en/" VERSION_DOCS_BRANCH
 #endif // VERSION_GENERATED_GEN_H
 """.format(
-                **version_info
-            )
-        )
+        **version_info
+    )
 
-    with open("core/version_hash.gen.cpp", "w", encoding="utf-8", newline="\n") as fhash:
-        fhash.write(
-            """\
+    version_hash_data = """\
 /* THIS FILE IS GENERATED DO NOT EDIT */
 #include "core/version.h"
 const char *const VERSION_HASH = "{git_hash}";
 const uint64_t VERSION_TIMESTAMP = {git_timestamp};
 """.format(
-                **version_info
-            )
-        )
+        **version_info
+    )
+
+    write_file_if_needed("core/version_generated.gen.h", version_info_header)
+    write_file_if_needed("core/version_hash.gen.cpp", version_hash_data)
 
 
 def parse_cg_file(fname, uniforms, sizes, conditionals):
@@ -385,15 +392,18 @@ def is_module(path):
 
 
 def write_disabled_classes(class_list):
-    with open("core/disabled_classes.gen.h", "w", encoding="utf-8", newline="\n") as f:
-        f.write("/* THIS FILE IS GENERATED DO NOT EDIT */\n")
-        f.write("#ifndef DISABLED_CLASSES_GEN_H\n")
-        f.write("#define DISABLED_CLASSES_GEN_H\n\n")
-        for c in class_list:
-            cs = c.strip()
-            if cs != "":
-                f.write("#define ClassDB_Disable_" + cs + " 1\n")
-        f.write("\n#endif\n")
+    file_contents = ""
+
+    file_contents += "/* THIS FILE IS GENERATED DO NOT EDIT */\n"
+    file_contents += "#ifndef DISABLED_CLASSES_GEN_H\n"
+    file_contents += "#define DISABLED_CLASSES_GEN_H\n\n"
+    for c in class_list:
+        cs = c.strip()
+        if cs != "":
+            file_contents += "#define ClassDB_Disable_" + cs + " 1\n"
+    file_contents += "\n#endif\n"
+
+    write_file_if_needed("core/disabled_classes.gen.h", file_contents)
 
 
 def write_modules(modules):
@@ -435,9 +445,7 @@ void uninitialize_modules(ModuleInitializationLevel p_level) {
         uninitialize_cpp,
     )
 
-    # NOTE: It is safe to generate this file here, since this is still executed serially
-    with open("modules/register_module_types.gen.cpp", "w", encoding="utf-8", newline="\n") as f:
-        f.write(modules_cpp)
+    write_file_if_needed("modules/register_module_types.gen.cpp", modules_cpp)
 
 
 def convert_custom_modules_path(path):

platform/SCsub

@@ -1,5 +1,7 @@
 #!/usr/bin/env python
 
+import methods
+
 Import("env")
 
 env.platform_sources = []
@@ -18,12 +20,7 @@ reg_apis_inc += "\n"
 reg_apis += "}\n\n"
 unreg_apis += "}\n"
 
-# NOTE: It is safe to generate this file here, since this is still execute serially
-with open("register_platform_apis.gen.cpp", "w", encoding="utf-8", newline="\n") as f:
-    f.write(reg_apis_inc)
-    f.write(reg_apis)
-    f.write(unreg_apis)
-
+methods.write_file_if_needed("register_platform_apis.gen.cpp", reg_apis_inc + reg_apis + unreg_apis)
 env.add_source_files(env.platform_sources, "register_platform_apis.gen.cpp")
 
 lib = env.add_library("platform", env.platform_sources)

platform_methods.py

@@ -5,6 +5,7 @@ import platform
 import uuid
 import functools
 import subprocess
+import methods
 
 # NOTE: The multiprocessing module is not compatible with SCons due to conflict on cPickle
 
@@ -67,8 +68,8 @@ def generate_export_icons(platform_path, platform_name):
 
         # NOTE: It is safe to generate this file here, since this is still executed serially.
         wf = export_path + "/" + name + "_svg.gen.h"
-        with open(wf, "w", encoding="utf-8", newline="\n") as svgw:
-            svgw.write(svg_str)
+
+        methods.write_file_if_needed(wf, svg_str)
 
 
 def get_build_version(short):

scu_builders.py

@@ -13,9 +13,9 @@ _scu_folders = set()
 _max_includes_per_scu = 1024
 
 
-def clear_out_existing_files(output_folder, extension):
+def clear_out_stale_files(output_folder, extension, fresh_files):
     output_folder = os.path.abspath(output_folder)
-    # print("clear_out_existing_files from folder: " + output_folder)
+    # print("clear_out_stale_files from folder: " + output_folder)
 
     if not os.path.isdir(output_folder):
         # folder does not exist or has not been created yet,
@@ -23,8 +23,9 @@ def clear_out_existing_files(output_folder, extension):
         return
 
     for file in glob.glob(output_folder + "/*." + extension):
-        # print("removed pre-existing file: " + file)
-        os.remove(file)
+        if not file in fresh_files:
+            # print("removed stale file: " + file)
+            os.remove(file)
 
 
 def folder_not_found(folder):
@@ -87,11 +88,16 @@ def write_output_file(file_count, include_list, start_line, end_line, output_fol
 
     short_filename = output_filename_prefix + num_string + ".gen." + extension
     output_filename = output_folder + "/" + short_filename
-    if _verbose:
-        print("SCU: Generating: %s" % short_filename)
-
     output_path = Path(output_filename)
-    output_path.write_text(file_text, encoding="utf8")
+
+    if not output_path.exists() or output_path.read_text() != file_text:
+        if _verbose:
+            print("SCU: Generating: %s" % short_filename)
+        output_path.write_text(file_text, encoding="utf8")
+    elif _verbose:
+        print("SCU: Generation not needed for: " + short_filename)
+
+    return output_filename
 
 
 def write_exception_output_file(file_count, exception_string, output_folder, output_filename_prefix, extension):
@@ -109,11 +115,16 @@ def write_exception_output_file(file_count, exception_string, output_folder, out
     short_filename = output_filename_prefix + "_exception" + num_string + ".gen." + extension
     output_filename = output_folder + "/" + short_filename
 
-    if _verbose:
-        print("SCU: Generating: " + short_filename)
-
     output_path = Path(output_filename)
-    output_path.write_text(file_text, encoding="utf8")
+
+    if not output_path.exists() or output_path.read_text() != file_text:
+        if _verbose:
+            print("SCU: Generating: " + short_filename)
+        output_path.write_text(file_text, encoding="utf8")
+    elif _verbose:
+        print("SCU: Generation not needed for: " + short_filename)
+
+    return output_filename
 
 
 def find_section_name(sub_folder):
@@ -214,10 +225,7 @@ def process_folder(folders, sought_exceptions=[], includes_per_scu=0, extension=
     output_folder = abs_main_folder + "/scu/"
     output_filename_prefix = "scu_" + out_filename
 
-    # Clear out any existing files (usually we will be overwriting,
-    # but we want to remove any that are pre-existing that will not be
-    # overwritten, so as to not compile anything stale)
-    clear_out_existing_files(output_folder, extension)
+    fresh_files = set()
 
     for file_count in range(0, num_output_files):
         end_line = start_line + lines_per_file
@@ -226,19 +234,28 @@ def process_folder(folders, sought_exceptions=[], includes_per_scu=0, extension=
         if file_count == (num_output_files - 1):
             end_line = len(found_includes)
 
-        write_output_file(
+        fresh_file = write_output_file(
             file_count, found_includes, start_line, end_line, output_folder, output_filename_prefix, extension
         )
 
+        fresh_files.add(fresh_file)
+
         start_line = end_line
 
     # Write the exceptions each in their own scu gen file,
     # so they can effectively compile in "old style / normal build".
     for exception_count in range(len(found_exceptions)):
-        write_exception_output_file(
+        fresh_file = write_exception_output_file(
             exception_count, found_exceptions[exception_count], output_folder, output_filename_prefix, extension
         )
 
+        fresh_files.add(fresh_file)
+
+    # Clear out any stale file (usually we will be overwriting if necessary,
+    # but we want to remove any that are pre-existing that will not be
+    # overwritten, so as to not compile anything stale).
+    clear_out_stale_files(output_folder, extension, fresh_files)
+
 
 def generate_scu_files(max_includes_per_scu):
     print("=============================")