Add rudimentary support for cross-compilation

Not really tested, actual cross compilers, feel free to send patches.
Fixes #6354

Makefile

@@ -61,3 +61,13 @@ docs: man html
 
 develop-docs:
 	$(MAKE) -C docs develop-docs
+
+
+prepare-for-cross-compile:
+	$(MAKE) clean
+	$(MAKE) build
+	python3 setup.py $(VVAL) clean --clean-for-cross-compile
+
+cross-compile:
+	python3 setup.py linux-package --skip-code-generation
+	

docs/build.rst

@@ -204,3 +204,19 @@ the kitty program expects to find them there.
 
 This applies to creating packages for |kitty| for macOS package managers such as
 Homebrew or MacPorts as well.
+
+Cross-compilation
+-------------------
+
+While cross compilation is neither officially supported, nor recommended, as it
+means the test suite cannot be run for the cross-compiled build, there is some
+support for cross-compilation. Basically, run::
+
+    make prepare-for-cross-compile
+
+Then setup the cross compile environment (CC, CFLAGS, etc.) and run::
+
+    make cross-compile
+
+This will create the cross compiled build in the :file:`linux-package`
+directory.

setup.py

@@ -62,6 +62,8 @@ class Options(argparse.Namespace):
     sanitize: bool = False
     prefix: str = './linux-package'
     dir_for_static_binaries: str = 'build/static'
+    skip_code_generation: bool = False
+    clean_for_cross_compile: bool = False
     incremental: bool = True
     profile: bool = False
     libdir_name: str = 'lib'
@@ -841,10 +843,11 @@ def extract_rst_targets() -> Dict[str, Dict[str, str]]:
     return cast(Dict[str, Dict[str, str]], m['main']())
 
 
-def build_ref_map() -> str:
+def build_ref_map(skip_generation: bool = False) -> str:
+    dest = 'kitty/docs_ref_map_generated.h'
+    if not skip_generation:
         d = extract_rst_targets()
         h = 'static const char docs_ref_map[] = {\n' + textwrap.fill(', '.join(map(str, bytearray(json.dumps(d).encode('utf-8'))))) + '\n};\n'
-    dest = 'kitty/docs_ref_map_generated.h'
         q = ''
         with suppress(FileNotFoundError), open(dest) as f:
             q = f.read()
@@ -868,7 +871,7 @@ def build(args: Options, native_optimizations: bool = True, call_init: bool = Tr
     if call_init:
         init_env_from_args(args, native_optimizations)
     sources, headers = find_c_files()
-    headers.append(build_ref_map())
+    headers.append(build_ref_map(args.skip_code_generation))
     compile_c_extension(
         kitty_env(), 'kitty/fast_data_types', args.compilation_database, sources, headers
     )
@@ -881,6 +884,9 @@ def safe_makedirs(path: str) -> None:
 
 
 def update_go_generated_files(args: Options, kitty_exe: str) -> None:
+    if args.skip_code_generation:
+        print('Skipping generation of Go files due to command line option', flush=True)
+        return
     # update all the various auto-generated go files, if needed
     if args.verbose:
         print('Updating Go generated files...', flush=True)
@@ -1493,7 +1499,7 @@ def clean_launcher_dir(launcher_dir: str) -> None:
             os.remove(x)
 
 
-def clean() -> None:
+def clean(for_cross_compile: bool = False) -> None:
 
     def safe_remove(*entries: str) -> None:
         for x in entries:
@@ -1506,7 +1512,9 @@ def clean() -> None:
     safe_remove(
         'build', 'compile_commands.json', 'link_commands.json',
         'linux-package', 'kitty.app', 'asan-launcher',
-        'kitty-profile', 'docs/generated')
+        'kitty-profile')
+    if not for_cross_compile:
+        safe_remove('docs/generated')
     clean_launcher_dir('kitty/launcher')
 
     def excluded(root: str, d: str) -> bool:
@@ -1521,7 +1529,9 @@ def clean() -> None:
             dirs.remove(d)
         for f in files:
             ext = f.rpartition('.')[-1]
-            if ext in ('so', 'dylib', 'pyc', 'pyo') or f.endswith('_generated.h') or f.endswith('_generated.go') or f.endswith('_generated.bin'):
+            if ext in ('so', 'dylib', 'pyc', 'pyo') or (not for_cross_compile and (
+                    f.endswith('_generated.h') or f.endswith('_generated.go') or f.endswith('_generated.bin'))
+            ):
                 os.unlink(os.path.join(root, f))
     for x in glob.glob('glfw/wayland-*-protocol.[ch]'):
         os.unlink(x)
@@ -1581,6 +1591,19 @@ def option_parser() -> argparse.ArgumentParser:  # {{{
         default=Options.dir_for_static_binaries,
         help='Where to create the static kitten binary'
     )
+    p.add_argument(
+        '--skip-code-generation',
+        default=Options.skip_code_generation,
+        action='store_true',
+        help='Do not create the *_generated.* source files. This is useful if they'
+        ' have already been generated by a previous build, for example during a two-stage cross compilation.'
+    )
+    p.add_argument(
+        '--clean-for-cross-compile',
+        default=Options.clean_for_cross_compile,
+        action='store_true',
+        help='Do not clean generated Go source files. Useful for cross-compilation.'
+    )
     p.add_argument(
         '--full',
         dest='incremental',
@@ -1743,7 +1766,7 @@ def main() -> None:
         texe = os.path.abspath(os.path.join(launcher_dir, 'kitty'))
         os.execl(texe, texe, '+launch', 'test.py')
     if args.action == 'clean':
-        clean()
+        clean(for_cross_compile=args.clean_for_cross_compile)
         return
 
     with CompilationDatabase(args.incremental) as cdb: