A positive way of saying "Grammar Nazi" [duplicate]

Grammar Nazi is usually how they describe someone who corrects other people's grammar (or spelling, or other errors).

Is there any expression that shows such a person in a positive light?

I ask because the person being corrected might actually be grateful about it and want to show this Grammar Nazi in a positive light.

For example:

John Doe is a real ____ . If he hadn't pointed out all the mistakes in my résumé , everyone would think I was a fool and I'd still be looking for a job.

I'm not looking for terms implying generic smartness. This term should specifically imply John Doe is good at English (or any other language).

EDIT: This question asks for an "alternative expression" which should be "funny, slightly reproachful, but not really offensive". It accepts the answer 'Grammar police', and other top answers include 'pedant' and 'fascist'.

I'm looking for a positive term. And those answers aren't applicable here.

Solution 1:

We grammar nazis refer to ourselves as "educated", "meticulous", and "amazing".

I'm assuming you're looking for an idiom; unfortunately none is in common use. I suggest the use of the word "savvy".

John Doe is really grammar savvy.

Solution 2:

I'd vote for something like stickler for accuracy. In fact ODO even uses that as an example:

stickler noun
A person who insists on a certain quality or type of behaviour:
he’s a stickler for accuracy
I’m a stickler when it comes to timekeeping

Solution 3:

If you wanted to peg such a person in a positive light, refer to them as a grammarian:

A person who studies and writes about grammar.

So: "John Doe is a real grammarian."

Much more flattering than Grammar Nazi.