**  (2)  Path is in argv[0] and dir is in argv[1]
*/
static int fsdirBestIndex(
  sqlite3_vtab *tab,
  sqlite3_index_info *pIdxInfo
){
  int i;                 /* Loop over constraints */
  int idx4 = -1;         /* Index in pIdxInfo->aConstraint of PATH= */
  int idx5 = -1;         /* Index in pIdxInfo->aConstraint of DIR= */


  const struct sqlite3_index_constraint *pConstraint;

  (void)tab;
  pConstraint = pIdxInfo->aConstraint;
  for(i=0; i<pIdxInfo->nConstraint; i++, pConstraint++){
    if( pConstraint->op!=SQLITE_INDEX_CONSTRAINT_EQ ) continue;


    if( pConstraint->iColumn==4 && pConstraint->usable ) idx4 = i;








    if( pConstraint->iColumn==5 ) idx5 = i;




  }


  if( idx4<0 || (idx5>=0 && pIdxInfo->aConstraint[idx5].usable==0) ){








    pIdxInfo->idxNum = 0;


    pIdxInfo->estimatedCost = (double)(((sqlite3_int64)1) << 60);
  }else{
    pIdxInfo->aConstraintUsage[idx4].omit = 1;
    pIdxInfo->aConstraintUsage[idx4].argvIndex = 1;
    if( idx5>=0 ){
      pIdxInfo->aConstraintUsage[idx5].omit = 1;
      pIdxInfo->aConstraintUsage[idx5].argvIndex = 2;
      pIdxInfo->idxNum = 2;
      pIdxInfo->estimatedCost = 10.0;
    }else{
      pIdxInfo->idxNum = 1;
      pIdxInfo->estimatedCost = 100.0;
    }
  }

**  (2)  Path is in argv[0] and dir is in argv[1]
*/
static int fsdirBestIndex(
  sqlite3_vtab *tab,
  sqlite3_index_info *pIdxInfo
){
  int i;                 /* Loop over constraints */
  int idxPath = -1;      /* Index in pIdxInfo->aConstraint of PATH= */
  int idxDir = -1;       /* Index in pIdxInfo->aConstraint of DIR= */
  int seenPath = 0;      /* True if an unusable PATH= constraint is seen */
  int seenDir = 0;       /* True if an unusable DIR= constraint is seen */
  const struct sqlite3_index_constraint *pConstraint;

  (void)tab;
  pConstraint = pIdxInfo->aConstraint;
  for(i=0; i<pIdxInfo->nConstraint; i++, pConstraint++){
    if( pConstraint->op!=SQLITE_INDEX_CONSTRAINT_EQ ) continue;
    switch( pConstraint->iColumn ){
      case FSDIR_COLUMN_PATH: {
        if( pConstraint->usable ){
          idxPath = i;
          seenPath = 0;
        }else if( idxPath<0 ){
          seenPath = 1;
        }
        break;
      }
      case FSDIR_COLUMN_DIR: {
        if( pConstraint->usable ){
          idxDir = i;
          seenDir = 0;
        }else if( idxDir<0 ){
          seenDir = 1;
        }
        break;
      }

    } 
  }
  if( seenPath || seenDir ){
    /* If input parameters are unusable, disallow this plan */
    return SQLITE_CONSTRAINT;
  }

  if( idxPath<0 ){
    pIdxInfo->idxNum = 0;
    /* The pIdxInfo->estimatedCost should have been initialized to a huge
    ** number.  Leave it unchanged. */
    pIdxInfo->estimatedRows = 0x7fffffff;
  }else{
    pIdxInfo->aConstraintUsage[idxPath].omit = 1;
    pIdxInfo->aConstraintUsage[idxPath].argvIndex = 1;
    if( idxDir>=0 ){
      pIdxInfo->aConstraintUsage[idxDir].omit = 1;
      pIdxInfo->aConstraintUsage[idxDir].argvIndex = 2;
      pIdxInfo->idxNum = 2;
      pIdxInfo->estimatedCost = 10.0;
    }else{
      pIdxInfo->idxNum = 1;
      pIdxInfo->estimatedCost = 100.0;
    }
  }

/*
** The table object reference passed as the second argument to this function
** must represent a virtual table. This function invokes the xBestIndex()
** method of the virtual table with the sqlite3_index_info object that
** comes in as the 3rd argument to this function.
**
** If an error occurs, pParse is populated with an error message and a
** non-zero value is returned. Otherwise, 0 is returned and the output
** part of the sqlite3_index_info structure is left populated.


**
** Whether or not an error is returned, it is the responsibility of the
** caller to eventually free p->idxStr if p->needToFreeIdxStr indicates
** that this is required.
*/
static int vtabBestIndex(Parse *pParse, Table *pTab, sqlite3_index_info *p){
  sqlite3_vtab *pVtab = sqlite3GetVTable(pParse->db, pTab)->pVtab;
  int rc;

  TRACE_IDX_INPUTS(p);
  rc = pVtab->pModule->xBestIndex(pVtab, p);
  TRACE_IDX_OUTPUTS(p);

  if( rc!=SQLITE_OK ){
    if( rc==SQLITE_NOMEM ){
      sqlite3OomFault(pParse->db);
    }else if( !pVtab->zErrMsg ){
      sqlite3ErrorMsg(pParse, "%s", sqlite3ErrStr(rc));
    }else{
      sqlite3ErrorMsg(pParse, "%s", pVtab->zErrMsg);
    }
  }
  sqlite3_free(pVtab->zErrMsg);
  pVtab->zErrMsg = 0;

#if 0
  /* This error is now caught by the caller.
  ** Search for "xBestIndex malfunction" below */
  for(i=0; i<p->nConstraint; i++){
    if( !p->aConstraint[i].usable && p->aConstraintUsage[i].argvIndex>0 ){
      sqlite3ErrorMsg(pParse, 
          "table %s: xBestIndex returned an invalid plan", pTab->zName);
    }
  }
#endif


  return pParse->nErr;
}
#endif /* !defined(SQLITE_OMIT_VIRTUALTABLE) */

#ifdef SQLITE_ENABLE_STAT3_OR_STAT4
/*
** Estimate the location of a particular key among all keys in an
** index.  Store the results in aStat as follows:
................................................................................
  pIdxInfo->estimatedCost = SQLITE_BIG_DBL / (double)2;
  pIdxInfo->estimatedRows = 25;
  pIdxInfo->idxFlags = 0;
  pIdxInfo->colUsed = (sqlite3_int64)pSrc->colUsed;

  /* Invoke the virtual table xBestIndex() method */
  rc = vtabBestIndex(pParse, pSrc->pTab, pIdxInfo);








  if( rc ) return rc;


  mxTerm = -1;
  assert( pNew->nLSlot>=nConstraint );
  for(i=0; i<nConstraint; i++) pNew->aLTerm[i] = 0;
  pNew->u.vtab.omitMask = 0;
  pIdxCons = *(struct sqlite3_index_constraint**)&pIdxInfo->aConstraint;
  for(i=0; i<nConstraint; i++, pIdxCons++){

/*
** The table object reference passed as the second argument to this function
** must represent a virtual table. This function invokes the xBestIndex()
** method of the virtual table with the sqlite3_index_info object that
** comes in as the 3rd argument to this function.
**
** If an error occurs, pParse is populated with an error message and an
** appropriate error code is returned.  A return of SQLITE_CONSTRAINT from
** xBestIndex is not considered an error.  SQLITE_CONSTRAINT indicates that
** the current configuration of "unusable" flags in sqlite3_index_info can
** not result in a valid plan.
**
** Whether or not an error is returned, it is the responsibility of the
** caller to eventually free p->idxStr if p->needToFreeIdxStr indicates
** that this is required.
*/
static int vtabBestIndex(Parse *pParse, Table *pTab, sqlite3_index_info *p){
  sqlite3_vtab *pVtab = sqlite3GetVTable(pParse->db, pTab)->pVtab;
  int rc;

  TRACE_IDX_INPUTS(p);
  rc = pVtab->pModule->xBestIndex(pVtab, p);
  TRACE_IDX_OUTPUTS(p);

  if( rc!=SQLITE_OK && rc!=SQLITE_CONSTRAINT ){
    if( rc==SQLITE_NOMEM ){
      sqlite3OomFault(pParse->db);
    }else if( !pVtab->zErrMsg ){
      sqlite3ErrorMsg(pParse, "%s", sqlite3ErrStr(rc));
    }else{
      sqlite3ErrorMsg(pParse, "%s", pVtab->zErrMsg);
    }
  }
  sqlite3_free(pVtab->zErrMsg);
  pVtab->zErrMsg = 0;












  // assert( pParse->nErr==0 || (rc!=SQLITE_OK && rc!=SQLITE_CONSTRAINT) );
  return rc;
}
#endif /* !defined(SQLITE_OMIT_VIRTUALTABLE) */

#ifdef SQLITE_ENABLE_STAT3_OR_STAT4
/*
** Estimate the location of a particular key among all keys in an
** index.  Store the results in aStat as follows:
................................................................................
  pIdxInfo->estimatedCost = SQLITE_BIG_DBL / (double)2;
  pIdxInfo->estimatedRows = 25;
  pIdxInfo->idxFlags = 0;
  pIdxInfo->colUsed = (sqlite3_int64)pSrc->colUsed;

  /* Invoke the virtual table xBestIndex() method */
  rc = vtabBestIndex(pParse, pSrc->pTab, pIdxInfo);
  if( rc ){
    if( rc==SQLITE_CONSTRAINT ){
      /* If the xBestIndex method returns SQLITE_CONSTRAINT, that means
      ** that the particular combination of parameters provided is unusable.
      ** Make no entries in the loop table.
      */
      return SQLITE_OK;
    }
    return rc;
  }

  mxTerm = -1;
  assert( pNew->nLSlot>=nConstraint );
  for(i=0; i<nConstraint; i++) pNew->aLTerm[i] = 0;
  pNew->u.vtab.omitMask = 0;
  pIdxCons = *(struct sqlite3_index_constraint**)&pIdxInfo->aConstraint;
  for(i=0; i<nConstraint; i++, pIdxCons++){

}

do_execsql_test 2.0 {
  CREATE VIRTUAL TABLE x1 USING tcl(vtab_command);
  CREATE TABLE t1 (x INT PRIMARY KEY);
} {}

do_execsql_test 2.1 {
  EXPLAIN QUERY PLAN SELECT * FROM t1, x1 WHERE x1.d=t1.x;
} {

  3 0 0 {SCAN TABLE x1 VIRTUAL TABLE INDEX 0:}
  7 0 0 {SEARCH TABLE t1 USING COVERING INDEX sqlite_autoindex_t1_1 (x=?)}
}

do_execsql_test 2.2 {
  EXPLAIN QUERY PLAN SELECT * FROM t1, x1(t1.x)
} {

  3 0 0 {SCAN TABLE t1} 
  5 0 0 {SCAN TABLE x1 VIRTUAL TABLE INDEX 555:}
}


finish_test

}

do_execsql_test 2.0 {
  CREATE VIRTUAL TABLE x1 USING tcl(vtab_command);
  CREATE TABLE t1 (x INT PRIMARY KEY);
} {}

do_eqp_test 2.1 {
  SELECT * FROM t1, x1 WHERE x1.d=t1.x;
} {
  QUERY PLAN
  |--SCAN TABLE x1 VIRTUAL TABLE INDEX 0:
  `--SEARCH TABLE t1 USING COVERING INDEX sqlite_autoindex_t1_1 (x=?)
}

do_eqp_test 2.2 {
  SELECT * FROM t1, x1(t1.x)
} {
  QUERY PLAN
  |--SCAN TABLE t1
  `--SCAN TABLE x1 VIRTUAL TABLE INDEX 555:
}


finish_test