Confusion on sqlite3 struct in sqlite3 source code - c

Question

In the function
static int sqlite3Prepare(
sqlite3 *db, /* Database handle. */
const char *zSql, /* UTF-8 encoded SQL statement. */
int nBytes, /* Length of zSql in bytes. */
int saveSqlFlag, /* True to copy SQL text into the sqlite3_stmt */
Vdbe *pReprepare, /* VM being reprepared */
sqlite3_stmt **ppStmt, /* OUT: A pointer to the prepared statement */
const char **pzTail /* OUT: End of parsed string */
) {
...
pParse = sqlite3StackAllocZero(db, sizeof(*pParse));
...
assert( !db->mallocFailed );
...
}
I know sqlite3 is just a fake struct declared as
typedef struct sqlite3 sqlite3;
without any body. I know sqlite3 * is usually is cast to a Vdbe*.
But here, db is of the type of sqlite3*, how can db->malloFailed exist? Why doesn't the compiler complain?
There is similar situation with sqlite3_stmt:
typedef struct sqlite3_stmt sqlite3_stmt;
with no body. I guess sqlite3_stmt is a syntax tree of parsed SQL statements. I would like to see the structure of it. However, the type is hidden so deeply using this weird pattern that I can't see what it is.
Even Vdbe is the same situation...
typedef struct Vdbe Vdbe;
Where on earth is the real struct?

Answer 1

sqlite3 is not a fake struct; the sqlite.h file just does not define its body.
Its definition is in the sqliteInt.h file (which is also part of the sqlite3.c amalgamation):
/*
** Each database connection is an instance of the following structure.
*/
struct sqlite3 {
sqlite3_vfs *pVfs; /* OS Interface */
struct Vdbe *pVdbe; /* List of active virtual machines */
CollSeq *pDfltColl; /* The default collating sequence (BINARY) */
...
u8 mallocFailed; /* True if we have seen a malloc failure */
...