Support Python 3's keyword-only arguments.

Previously, they would parse correctly in Python 3, but any keyword-only
arguments would be quietly lost, and the user would either get
`TypeError: foo() got an unexpected keyword argument...` or the
confusing behavior of having the keyword argument overwritten with
whatever's in the context with the same name.

5 files changed, 74 insertions, 34 deletions

diff --git a/mako/ast.py b/mako/ast.py
index 24ef1b4..3713cc3 100644
--- a/mako/ast.py
+++ b/mako/ast.py
@@ -112,38 +112,65 @@ class FunctionDecl(object):
         if not allow_kwargs and self.kwargs:
             raise exceptions.CompileException(
                                 "'**%s' keyword argument not allowed here" %
-                                self.argnames[-1], **exception_kwargs)
+                                self.kwargnames[-1], **exception_kwargs)
 
-    def get_argument_expressions(self, include_defaults=True):
-        """return the argument declarations of this FunctionDecl as a printable
-        list."""
+    def get_argument_expressions(self, as_call=False):
+        """Return the argument declarations of this FunctionDecl as a printable
+        list.
+
+        By default the return value is appropriate for writing in a ``def``;
+        set `as_call` to true to build arguments to be passed to the function
+        instead (assuming locals with the same names as the arguments exist).
+        """
 
         namedecls = []
-        defaults = [d for d in self.defaults]
-        kwargs = self.kwargs
-        varargs = self.varargs
-        argnames = [f for f in self.argnames]
-        argnames.reverse()
-        for arg in argnames:
-            default = None
-            if kwargs:
-                arg = "**" + arg_stringname(arg)
-                kwargs = False
-            elif varargs:
-                arg = "*" + arg_stringname(arg)
-                varargs = False
+
+        # Build in reverse order, since defaults and slurpy args come last
+        argnames = self.argnames[::-1]
+        kwargnames = self.kwargnames[::-1]
+        defaults = self.defaults[::-1]
+        kwdefaults = self.kwdefaults[::-1]
+
+        # Named arguments
+        if self.kwargs:
+            namedecls.append("**" + kwargnames.pop(0))
+
+        for name in kwargnames:
+            # Keyword-only arguments must always be used by name, so even if
+            # this is a call, print out `foo=foo`
+            if as_call:
+                namedecls.append("%s=%s" % (name, name))
+            elif kwdefaults:
+                default = kwdefaults.pop(0)
+                if default is None:
+                    # The AST always gives kwargs a default, since you can do
+                    # `def foo(*, a=1, b, c=3)`
+                    namedecls.append(name)
+                else:
+                    namedecls.append("%s=%s" % (
+                        name, pyparser.ExpressionGenerator(default).value()))
             else:
-                default = len(defaults) and defaults.pop() or None
-            if include_defaults and default:
-                namedecls.insert(0, "%s=%s" %
-                            (arg,
-                            pyparser.ExpressionGenerator(default).value()
-                            )
-                        )
+                namedecls.append(name)
+
+        # Positional arguments
+        if self.varargs:
+            namedecls.append("*" + argnames.pop(0))
+
+        for name in argnames:
+            if as_call or not defaults:
+                namedecls.append(name)
             else:
-                namedecls.insert(0, arg)
+                default = defaults.pop(0)
+                namedecls.append("%s=%s" % (
+                    name, pyparser.ExpressionGenerator(default).value()))
+
+        namedecls.reverse()
         return namedecls
 
+    @property
+    def allargnames(self):
+        return self.argnames + self.kwargnames
+
 class FunctionArgs(FunctionDecl):
     """the argument portion of a function declaration"""
 
diff --git a/mako/codegen.py b/mako/codegen.py
index 769e0c6..045d03c 100644
--- a/mako/codegen.py
+++ b/mako/codegen.py
@@ -543,7 +543,7 @@ class _GenerateRenderMethod(object):
         """write a locally-available callable referencing a top-level def"""
         funcname = node.funcname
         namedecls = node.get_argument_expressions()
-        nameargs = node.get_argument_expressions(include_defaults=False)
+        nameargs = node.get_argument_expressions(as_call=True)
 
         if not self.in_def and (
                                 len(self.identifiers.locally_assigned) > 0 or
@@ -864,7 +864,7 @@ class _GenerateRenderMethod(object):
         if node.is_anonymous:
             self.printer.writeline("%s()" % node.funcname)
         else:
-            nameargs = node.get_argument_expressions(include_defaults=False)
+            nameargs = node.get_argument_expressions(as_call=True)
             nameargs += ['**pageargs']
             self.printer.writeline("if 'parent' not in context._data or "
                                   "not hasattr(context._data['parent'], '%s'):"
diff --git a/mako/compat.py b/mako/compat.py
index 31da8bd..c5ef84b 100644
--- a/mako/compat.py
+++ b/mako/compat.py
@@ -3,6 +3,7 @@ import time
 
 py3k = sys.version_info >= (3, 0)
 py33 = sys.version_info >= (3, 3)
+py2k = sys.version_info < (3,)
 py26 = sys.version_info >= (2, 6)
 py25 = sys.version_info >= (2, 5)
 jython = sys.platform.startswith('java')
diff --git a/mako/parsetree.py b/mako/parsetree.py
index ab83c5c..0612070 100644
--- a/mako/parsetree.py
+++ b/mako/parsetree.py
@@ -437,7 +437,7 @@ class DefTag(Tag):
         return self.function_decl.get_argument_expressions(**kw)
 
     def declared_identifiers(self):
-        return self.function_decl.argnames
+        return self.function_decl.allargnames
 
     def undeclared_identifiers(self):
         res = []
@@ -451,7 +451,7 @@ class DefTag(Tag):
         ).union(
             self.expression_undeclared_identifiers
         ).difference(
-            self.function_decl.argnames
+            self.function_decl.allargnames
         )
 
 class BlockTag(Tag):
@@ -502,7 +502,7 @@ class BlockTag(Tag):
         return self.body_decl.get_argument_expressions(**kw)
 
     def declared_identifiers(self):
-        return self.body_decl.argnames
+        return self.body_decl.allargnames
 
     def undeclared_identifiers(self):
         return (self.filter_args.\
@@ -524,7 +524,7 @@ class CallTag(Tag):
                                             **self.exception_kwargs)
 
     def declared_identifiers(self):
-        return self.code.declared_identifiers.union(self.body_decl.argnames)
+        return self.code.declared_identifiers.union(self.body_decl.allargnames)
 
     def undeclared_identifiers(self):
         return self.code.undeclared_identifiers.\
@@ -554,7 +554,7 @@ class CallNamespaceTag(Tag):
                                     **self.exception_kwargs)
 
     def declared_identifiers(self):
-        return self.code.declared_identifiers.union(self.body_decl.argnames)
+        return self.code.declared_identifiers.union(self.body_decl.allargnames)
 
     def undeclared_identifiers(self):
         return self.code.undeclared_identifiers.\
@@ -589,6 +589,6 @@ class PageTag(Tag):
                                 **self.exception_kwargs)
 
     def declared_identifiers(self):
-        return self.body_decl.argnames
+        return self.body_decl.allargnames
 
 
diff --git a/mako/pyparser.py b/mako/pyparser.py
index fc4db9d..2744022 100644
--- a/mako/pyparser.py
+++ b/mako/pyparser.py
@@ -214,13 +214,25 @@ if _ast:
 
         def visit_FunctionDef(self, node):
             self.listener.funcname = node.name
+
             argnames = [arg_id(arg) for arg in node.args.args]
             if node.args.vararg:
                 argnames.append(arg_stringname(node.args.vararg))
+
+            if compat.py2k:
+                # kw-only args don't exist in Python 2
+                kwargnames = []
+            else:
+                kwargnames = [arg_id(arg) for arg in node.args.kwonlyargs]
             if node.args.kwarg:
-                argnames.append(arg_stringname(node.args.kwarg))
+                kwargnames.append(arg_stringname(node.args.kwarg))
             self.listener.argnames = argnames
             self.listener.defaults = node.args.defaults  # ast
+            self.listener.kwargnames = kwargnames
+            if compat.py2k:
+                self.listener.kwdefaults = []
+            else:
+                self.listener.kwdefaults = node.args.kw_defaults
             self.listener.varargs = node.args.vararg
             self.listener.kwargs = node.args.kwarg