Use templates for generating wasm2c source (#712)

This uses a very simple template syntax, without any advanced features:

```
%%top
...
%%bottom
...
```

This template will generate output with two C strings:

```
const char SECTION_NAME(top)[] = ...
...
const char SECTION_NAME(bottom)[] = ...
...
```

To update the generated files, run `make update-wasm2c`.

1 files changed, 80 insertions, 0 deletions

diff --git a/src/wasm2c_tmpl.py b/src/wasm2c_tmpl.py
new file mode 100755
index 00000000..d43c2065
--- /dev/null
+++ b/src/wasm2c_tmpl.py
@@ -0,0 +1,80 @@
+#!/usr/bin/env python
+#
+# Copyright 2018 WebAssembly Community Group participants
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+from __future__ import print_function
+import argparse
+try:
+  from cStringIO import StringIO
+except ImportError:
+  from io import StringIO
+import os
+import sys
+
+def EscapeCString(s):
+  out = ''
+  for b in bytearray(s.encode('utf-8')):
+    if b in (34, 92):
+      # " or \
+      out += '\\' + chr(b)
+    elif b == 10:
+      # newline
+      out += '\\n'
+    elif 32 <= b <= 127:
+      # printable char
+      out += chr(b)
+    else:
+      # non-printable; write as \xab
+      out += '\\x%02x' % b
+
+  return out
+
+
+def main(args):
+  arg_parser = argparse.ArgumentParser()
+  arg_parser.add_argument('-o', '--output', metavar='PATH',
+                          help='output file.')
+  arg_parser.add_argument('file', help='input file.')
+  options = arg_parser.parse_args(args)
+
+  section_name = None
+  output = StringIO()
+
+  output.write('/* Generated from \'%s\' by wasm2c_tmpl.py, do not edit! */\n' %
+               os.path.basename(options.file))
+
+  with open(options.file) as f:
+    for line in f.readlines():
+      if line.startswith('%%'):
+        if section_name is not None:
+          output.write(';\n\n');
+        section_name = line[2:-1]
+        output.write('const char SECTION_NAME(%s)[] =\n' % section_name)
+      else:
+        output.write('"%s"\n' % EscapeCString(line))
+
+  output.write(';\n');
+  if options.output:
+    with open(options.output, 'w') as outf:
+      outf.write(output.getvalue())
+  else:
+    sys.stdout.write(output.getvalue())
+
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv[1:]))