Play nicely with py3k for building docs

Previously, mkapiref.py required python2.6, as it used format strings,
but continued to use print as a keyword, not a function. But, since 2.6
is implicitly made a requirement, we can also count on print being
available as a function.

This change adds python2.6 as a soft requirement during ./configure,
and converts all print keywords to statements. There's no need to do
anything about the actual building of the doc since sphinx-build can
run under python2 and python3.

The net result is that it no longer matters whether 'python' points to
python2 or python3 (see PEP394), because both will be able to run
mkapiref.py successfully.

configure.ac

@@ -76,6 +76,7 @@ AC_PROG_LN_S
 AC_PROG_MAKE_SET
 AM_PROG_CC_C_O
 PKG_PROG_PKG_CONFIG([0.20])
+AM_PATH_PYTHON([2.6],, [:])
 
 AX_CXX_COMPILE_STDCXX_11([noext], [optional])
 

doc/Makefile.am

@@ -61,7 +61,7 @@ help:
 
 apiref.rst: $(top_builddir)/lib/includes/nghttp2/nghttp2ver.h \
 	$(top_builddir)/lib/includes/nghttp2/nghttp2.h
-	$(builddir)/mkapiref.py --header apiref-header.rst $^ > $@
+	$(PYTHON) $(builddir)/mkapiref.py --header apiref-header.rst $^ > $@
 
 clean:
 	-rm apiref.rst

doc/mkapiref.py

@@ -23,6 +23,7 @@
 # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 # Generates API reference from C source code.
+from __future__ import print_function # At least python 2.6 is required
 import re, sys, argparse
 
 class FunctionDoc:
@@ -32,10 +33,10 @@ class FunctionDoc:
         self.domain = domain
 
     def write(self, out):
-        print '''.. {}:: {}'''.format(self.domain, self.name)
-        print ''
+        print('''.. {}:: {}'''.format(self.domain, self.name))
+        print('')
         for line in self.content:
-            print '    {}'.format(line)
+            print('    {}'.format(line))
 
 class StructDoc:
     def __init__(self, name, content, members, member_domain):
@@ -46,17 +47,17 @@ class StructDoc:
 
     def write(self, out):
         if self.name:
-            print '''.. type:: {}'''.format(self.name)
-            print ''
+            print('''.. type:: {}'''.format(self.name))
+            print('')
             for line in self.content:
-                print '    {}'.format(line)
-            print ''
+                print('    {}'.format(line))
+            print('')
             for name, content in self.members:
-                print '''    .. {}:: {}'''.format(self.member_domain, name)
-                print ''
+                print('''    .. {}:: {}'''.format(self.member_domain, name))
+                print('')
                 for line in content:
-                    print '''        {}'''.format(line)
-            print ''
+                    print('''        {}'''.format(line))
+            print('')
 
 class MacroDoc:
     def __init__(self, name, content):
@@ -64,10 +65,10 @@ class MacroDoc:
         self.content = content
 
     def write(self, out):
-        print '''.. macro:: {}'''.format(self.name)
-        print ''
+        print('''.. macro:: {}'''.format(self.name))
+        print('')
         for line in self.content:
-            print '    {}'.format(line)
+            print('    {}'.format(line))
 
 def make_api_ref(infiles):
     macros = []
@@ -99,12 +100,12 @@ def make_api_ref(infiles):
     for title, docs in alldocs:
         if not docs:
             continue
-        print title
-        print '-'*len(title)
+        print(title)
+        print('-'*len(title))
         for doc in docs:
             doc.write(sys.stdout)
-            print ''
-        print ''
+            print('')
+        print('')
 
 def process_macro(infile):
     content = read_content(infile)
@@ -204,6 +205,6 @@ if __name__ == '__main__':
                         help='source file')
     args = parser.parse_args()
     if args.header:
-        print args.header.read()
+        print(args.header.read())
     for infile in args.files:
         make_api_ref(args.files)