Implement concat_ast utility

Closes #32.

Author: jhgg

graphql/core/utils/concat_ast.py

@@ -0,0 +1,9 @@
+import itertools
+
+from ..language.ast import Document
+
+
+def concat_ast(asts):
+    return Document(definitions=list(itertools.chain.from_iterable(
+        document.definitions for document in asts
+    )))

tests/core_utils/test_concat_ast.py

@@ -0,0 +1,28 @@
+from graphql.core import Source, parse
+
+from graphql.core.language.printer import print_ast
+from graphql.core.utils.concat_ast import concat_ast
+
+
+def test_it_concatenates_two_acts_together():
+    source_a = Source('{ a, b, ... Frag }')
+    source_b = Source('''
+        fragment Frag on T {
+            c
+        }
+    ''')
+
+    ast_a = parse(source_a)
+    ast_b = parse(source_b)
+    ast_c = concat_ast([ast_a, ast_b])
+
+    assert print_ast(ast_c) == '''{
+  a
+  b
+  ...Frag
+}
+
+fragment Frag on T {
+  c
+}
+'''