bpo-46541: Generate the global objects initializer. (gh-30941)

This change is a prerequisite for generating code for other global objects (like strings in gh-30928).

(We borrowed some code from Tools/scripts/deepfreeze.py.)

https://bugs.python.org/issue46541

Tools/scripts/generate_global_objects.py

@@ -0,0 +1,124 @@
+import argparse
+import ast
+import builtins
+import collections
+import contextlib
+import os.path
+import sys
+
+
+assert os.path.isabs(__file__), __file__
+ROOT = os.path.dirname(os.path.dirname(os.path.dirname(__file__)))
+INTERNAL = os.path.join(ROOT, 'Include', 'internal')
+
+
+#######################################
+# helpers
+
+def iter_to_marker(lines, marker):
+    for line in lines:
+        if line.rstrip() == marker:
+            break
+        yield line
+
+
+class Printer:
+
+    def __init__(self, file):
+        self.level = 0
+        self.file = file
+        self.continuation = [False]
+
+    @contextlib.contextmanager
+    def indent(self):
+        save_level = self.level
+        try:
+            self.level += 1
+            yield
+        finally:
+            self.level = save_level
+
+    def write(self, arg):
+        eol = '\n'
+        if self.continuation[-1]:
+            eol = f' \\{eol}' if arg else f'\\{eol}'
+        self.file.writelines(("    "*self.level, arg, eol))
+
+    @contextlib.contextmanager
+    def block(self, prefix, suffix="", *, continuation=None):
+        if continuation is None:
+            continuation = self.continuation[-1]
+        self.continuation.append(continuation)
+
+        self.write(prefix + " {")
+        with self.indent():
+            yield
+        self.continuation.pop()
+        self.write("}" + suffix)
+
+
+#######################################
+# the global objects
+
+START = '/* The following is auto-generated by Tools/scripts/generate_global_objects.py. */'
+END = '/* End auto-generated code */'
+
+
+def generate_runtime_init():
+    # First get some info from the declarations.
+    nsmallposints = None
+    nsmallnegints = None
+    with open(os.path.join(INTERNAL, 'pycore_global_objects.h')) as infile:
+        for line in infile:
+            if line.startswith('#define _PY_NSMALLPOSINTS'):
+                nsmallposints = int(line.split()[-1])
+            elif line.startswith('#define _PY_NSMALLNEGINTS'):
+                nsmallnegints = int(line.split()[-1])
+                break
+        else:
+            raise NotImplementedError
+    assert nsmallposints and nsmallnegints
+
+    # Then target the runtime initializer.
+    filename = os.path.join(INTERNAL, 'pycore_runtime_init.h')
+
+    # Read the non-generated part of the file.
+    with open(filename) as infile:
+        before = ''.join(iter_to_marker(infile, START))[:-1]
+        for _ in iter_to_marker(infile, END):
+            pass
+        after = infile.read()[:-1]
+
+    # Generate the file.
+    with open(filename, 'w', encoding='utf-8') as outfile:
+        printer = Printer(outfile)
+        printer.write(before)
+        printer.write(START)
+        with printer.block('#define _Py_global_objects_INIT', continuation=True):
+            with printer.block('.singletons =', ','):
+                # Global int objects.
+                with printer.block('.small_ints =', ','):
+                    for i in range(-nsmallnegints, nsmallposints):
+                        printer.write(f'_PyLong_DIGIT_INIT({i}),')
+                printer.write('')
+                # Global bytes objects.
+                printer.write('.bytes_empty = _PyBytes_SIMPLE_INIT(0, 0),')
+                with printer.block('.bytes_characters =', ','):
+                    for i in range(256):
+                        printer.write(f'_PyBytes_CHAR_INIT({i}),')
+        printer.write(END)
+        printer.write(after)
+
+
+#######################################
+# the script
+
+def main() -> None:
+    generate_runtime_init()
+
+
+if __name__ == '__main__':
+    argv = sys.argv[1:]
+    if argv:
+        sys.exit(f'ERROR: got unexpected args {argv}')
+    main()