Fix AST handling of docstrings and __future__ ordering

This closes hylang#1367 and closes hylang#1540

hy/compiler.py

@@ -19,6 +19,7 @@
 from hy.macros import require, macroexpand, tag_macroexpand
 import hy.importer
 
+import functools
 import traceback
 import importlib
 import ast
@@ -279,6 +280,17 @@ def is_unpack(kind, x):
             and x[0] == "unpack-" + kind)
 
 
+def import_order(a, b):
+    """Put __future__ imports ahead of others"""
+    if (isinstance(a, ast.ImportFrom) and
+        isinstance(b, (ast.Import, ast.ImportFrom)) and
+        a.module == '__future__'):
+        return -1
+    else:
+        return 0
+
+import_order_key = functools.cmp_to_key(import_order)
+
 _stdlib = {}
 
 
@@ -318,6 +330,7 @@ def update_imports(self, result):
     def imports_as_stmts(self, expr):
         """Convert the Result's imports to statements"""
         ret = Result()
+
         for module, names in self.imports.items():
             if None in names:
                 e = HyExpression([
@@ -1719,7 +1732,18 @@ def hy_compile(tree, module_name, root=ast.Module, get_expr=False):
     if not get_expr:
         result += result.expr_as_stmt()
 
-    body = compiler.imports_as_stmts(tree) + result.stmts
+    body = []
+
+    # Pull out a single docstring and prepend to the resulting body.
+    if (len(result.stmts) > 0 and
+        issubclass(root, ast.Module) and
+        isinstance(result.stmts[0], ast.Expr) and
+        isinstance(result.stmts[0].value, ast.Str)):
+
+        body += [result.stmts.pop(0)]
+
+    body += sorted(compiler.imports_as_stmts(tree) + result.stmts,
+                   key=import_order_key)
 
     ret = root(body=body)
 

tests/compilers/test_ast.py

@@ -664,3 +664,31 @@ def test_ast_bad_yield_from():
 def test_eval_generator_with_return():
     """Ensure generators with a return statement works."""
     can_eval("(fn [] (yield 1) (yield 2) (return))")
+
+
+def test_docsting_imports():
+    """Confirm that docstrings come before import statements in AST output."""
+    hy_tree = import_buffer_to_hst('"hello world"\n(print (first [1 2]))')
+    hy_ast = hy_compile(hy_tree, 'test')
+    assert hy_ast.body[0].value.s == 'hello world'
+
+
+def test_futures_imports():
+    """Make sure __future__ imports go first."""
+    hy_tree = import_buffer_to_hst((
+        '(import [__future__ [print_function]])\n'
+        '(import sys)\n'
+        '(setv name 10)'))
+
+    hy_ast = hy_compile(hy_tree, 'test')
+    assert hy_ast.body[0].module == '__future__'
+    assert hy_ast.body[1].module == 'hy.core.language'
+
+    hy_tree = import_buffer_to_hst((
+        '(import sys)\n'
+        '(import [__future__ [print_function]])\n'
+        '(setv name 10)'))
+
+    hy_ast = hy_compile(hy_tree, 'test')
+    assert hy_ast.body[0].module == '__future__'
+    assert hy_ast.body[1].module == 'hy.core.language'