Adds container support to pymultic

Using the '-c' argument will - if possible - fetch and use a
container for each version of Python specified in the arguments
list.

scripts/pymultic

@@ -33,12 +33,17 @@ PYVERS = {
     '3.7': '3.7.10',
     '3.8': '3.8.9',
     '3.9': '3.9.4',
+    '3.10': '3.10.0',
 }
 
 OLD_PYTHONS = ('1.0', '1.1', '1.2', '1.3', '1.4', '1.5')
 OLD_PYURL = 'https://legacy.python.org/download/releases/src'
 PYURL = 'https://www.python.org/ftp/python'
 
+# Minimum version of Python with a pre-built container.
+PYVER_CONTAINER_MIN = '2.7'
+USE_CONTAINERS = False
+
 
 def fetch_python(snekdir, version):
     realver = PYVERS[version]
@@ -122,58 +127,19 @@ def acquire_python(snekdir, version):
     return pyexe
 
 
-if len(sys.argv) < 2:
-    print('Usage: {} [versions] input.py'.format(sys.argv[0]))
-    print('Compile input.py for one or more python versions')
-    print('Output is written to input.<version>.pyc for each version successfully compiled')
-    print()
-    print('Version is X.Y (e.g. 3.4), not including the patch version')
-    sys.exit(1)
-
-RE_PYVER = re.compile(r'\d\.\d')
-
-pythons = []
-infile = None
-for arg in sys.argv[1:]:
-    if RE_PYVER.match(arg):
-        if arg in PYVERS.keys():
-            pythons.append(arg)
-        else:
-            print('Unknown Python version: {}'.format(arg))
-            sys.exit(1)
-    elif arg.startswith('-'):
-        print("WARNING: Unrecognized argument '{}'".format(arg))
-    else:
-        infile = arg
-
-if infile is None:
-    print('No input file specified')
-    sys.exit(1)
-elif not os.path.exists(infile):
-    print('Error: Input file {} does not exist'.format(infile))
-    sys.exit(1)
-
-if len(pythons) == 0:
-    print('At least one Python version is required')
-    sys.exit(1)
-
-snekdir = os.path.dirname(os.path.realpath(__file__))
-result = 0
-for ver in pythons:
+def local_compile(snekdir, ver, infile):
     pyexe = acquire_python(snekdir, ver)
     proc = subprocess.Popen([pyexe, '-c', 'import sys; print(sys.version)'],
                             stdout=subprocess.PIPE)
     out, _ = proc.communicate()
     if proc.returncode != 0:
         print('Could not determine Python version for {}'.format(ver))
-        result = 1
-        continue
+        return None
 
     bcver = str(out, 'iso-8859-1').split(' ', 1)[0]
     if not bcver.startswith(ver):
         print('Python {} reported itself as version {}!'.format(ver, bcver))
-        result = 1
-        continue
+        return None
 
     if infile.endswith('.py'):
         outfile = os.path.basename(infile)[:-3]
@@ -210,7 +176,94 @@ for ver in pythons:
                     .format(infile, outfile)])
         proc.communicate()
 
-    if not os.path.exists(outfile):
+    return outfile
+
+
+def container_compile(snekdir, ver, infile):
+    if ver < PYVER_CONTAINER_MIN:
+        print('Container compilation requires a Python version >= {}'.format(PYVER_CONTAINER_MIN))
+        return None
+
+    if shutil.which('docker') is None:
+        print('Cannot find docker in $PATH')
+        return None
+
+    fullver = PYVERS[ver]
+
+    if infile.endswith('.py'):
+        outfile = os.path.basename(infile)[:-3]
+    else:
+        outfile = os.path.basename(infile)
+    outfile += '.{}.pyc'.format(ver)
+    if os.path.exists(outfile):
+        os.unlink(outfile)
+
+    print('*** Compiling for Python {}'.format(fullver))
+    # The easy way
+    proc = subprocess.Popen(['docker', 'run', '--privileged', '--rm', '--name', '{}-{}'.format(infile, ver),
+                             '-v', '{}:/src'.format(snekdir), '-w', '/src', 'python:{}'.format(fullver),
+                             'python', '-c', "import py_compile; py_compile.compile('{}', '{}')".format(infile, outfile)])
+    proc.communicate()
+
+    return outfile
+
+
+if len(sys.argv) < 2:
+    print('Usage: {} [-c] [versions] input.py'.format(sys.argv[0]))
+    print('Compile input.py for one or more python versions')
+    print()
+    print('-c\tuse prebuilt containers for running different versions of Python (only available for versions >= {})'
+          .format(PYVER_CONTAINER_MIN))
+    print()
+    print('Output is written to input.<version>.pyc for each version successfully compiled')
+    print()
+    print('Version is X.Y (e.g. 3.4), not including the patch version')
+    sys.exit(1)
+
+RE_PYVER = re.compile(r'\d\.\d')
+
+pythons = []
+infile = None
+for arg in sys.argv[1:]:
+    if RE_PYVER.match(arg):
+        if arg in PYVERS.keys():
+            pythons.append(arg)
+        else:
+            print('Unknown Python version: {}'.format(arg))
+            sys.exit(1)
+    elif arg == '-c':
+        USE_CONTAINERS = True
+    elif arg.startswith('-'):
+        print("WARNING: Unrecognized argument '{}'".format(arg))
+    else:
+        infile = arg
+
+if infile is None:
+    print('No input file specified')
+    sys.exit(1)
+elif not os.path.exists(infile):
+    print('Error: Input file {} does not exist'.format(infile))
+    sys.exit(1)
+
+if len(pythons) == 0:
+    print('At least one Python version is required')
+    sys.exit(1)
+
+snekdir = os.path.dirname(os.path.realpath(__file__))
+result = 0
+for ver in pythons:
+    compile_with_container = USE_CONTAINERS
+    if USE_CONTAINERS and ver < PYVER_CONTAINER_MIN:
+        print('Warning: No supported container for {} - using local build'.format(ver))
+        compile_with_container = False
+
+    outfile = None
+    if compile_with_container:
+        outfile = container_compile(snekdir, ver, infile)
+    else:
+        outfile = local_compile(snekdir, ver, infile)
+
+    if outfile is None or not os.path.exists(outfile):
         result = 1
 
 sys.exit(result)