c - extern declaration, T* v/s T[]

Question

I saw following piece of code in a legacy project.

/* token.c */
struct token id_tokens[MAX_TOKENS];

/* analyse.c (v1) */
extern struct token *id_tokens; /* Raised my eyebrow, id_token declares a pointer */

I insisted on changing analyse.c to contain the declaration as below:

/* analyse.c (v2) */
extern struct token id_tokens[]; /* I am happy with this. id_tokens declares array of unspecified size. */

I want v2 because pointer to T is not same as array of T. My friend's counter argumented that behaviour of both are same, so it doesn't matter whether I use v1 and v2.

Question 1: Does array of incomplete type deplete to a pointer?

Question 2: Is my friend right that both versions are behaviorally guaranteed to be equivalent?

Answer 1

The first version is wrong. Arrays are NOT pointers, the declaration extern struct token *id_tokens; doesn't match the definition type struct token id_tokens[MAX_TOKENS];.

Reference: C FAQ: I had the definition char a[6] in one source file, and in another I declared extern char *a. Why didn't it work?. Also, see this.