While trying to construct a valid ast node programmatically, I have tried following: 

import ast

tree = ast.BinOp(left=ast.Num(n=2), right=ast.Num(n=2), op=ast.Add())
expr = ast.Expression(body=[tree])
ast.fix_missing_locations(expr)
exe = compile(expr, filename="", mode="eval")
print(eval(exe))

Unfortunately this gives unhelpful error message:

>>>    exe = compile(expr, filename="", mode="eval")
TypeError: required field "lineno" missing from expr

Turns out I need to make body of ast.Expression not a list, but a node:
expr = ast.Expression(body=tree)  # works

Confusion also comes from naming the field "body", which takes value of a list for ast.Module and some others.

with PR 17715 

>>> import ast
>>> expr_without_lineno_but_ok = ast.Expression(body=ast.BinOp(left=ast.Num(n=2), right=ast.Num(n=2), op=ast.Add()))
>>> expr_with_lineno_but_with_wrong_body = ast.Expression(body=[ast.BinOp(left=ast.Num(n=2), right=ast.Num(n=2), op=ast.Add())])
>>> ast.fix_missing_locations(expr_with_lineno_but_with_wrong_body)
>>> compile(expr_without_lineno_but_ok, "<temp>", "eval")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: required field "lineno" missing from expr
>>> compile(expr_with_lineno_but_with_wrong_body, "<temp>", "eval")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: expected some sort of expr, but got [<_ast.BinOp object at 0x7f3f57dc4c80>]

I've updated PR 17715 in order to point out exact field that error happened. Also it now only shows type

>>> import ast
>>> expr_without_lineno_but_ok = ast.Expression(body=ast.BinOp(left=ast.Num(n=2), right=ast.Num(n=2), op=ast.Add()))
>>> expr_with_lineno_but_with_wrong_body = ast.Expression(body=[ast.BinOp(left=ast.Num(n=2), right=ast.Num(n=2), op=ast.Add())])
>>> ast.fix_missing_locations(expr_with_lineno_but_with_wrong_body)
<ast.Expression object at 0x7f854123fbb0>
>>> compile(expr_without_lineno_but_ok, "<temp>", "eval")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: required field "lineno" missing from expr
>>> compile(expr_with_lineno_but_with_wrong_body, "<temp>", "eval")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: For field 'body'; expected expr type node, got list