Fix the backup API so that a backup from an empty database to a non-empty

database works.  Ticket [0bf974bdf9].  The only changes are in assert()
statements.

FossilOrigin-Name: ddb71cd9ed395804a13dc136bb7688a7627c798f

manifest

@@ -1,5 +1,8 @@
-C Merged\saccidental\sfork.
+-----BEGIN PGP SIGNED MESSAGE-----
-D 2009-11-06T03:33:02
+Hash: SHA1
+
+C Fix\sthe\sbackup\sAPI\sso\sthat\sa\sbackup\sfrom\san\sempty\sdatabase\sto\sa\snon-empty\ndatabase\sworks.\s\sTicket\s[0bf974bdf9].\s\sThe\sonly\schanges\sare\sin\sassert()\nstatements.
+D 2009-11-06T04:13:18
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 F Makefile.in a77dfde96ad86aafd3f71651a4333a104debe86a
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -146,9 +149,9 @@ F src/os.c 8d62d8d98ad7909cb0dd294c1e5f3835c887ccb6
 F src/os.h 00a1334a4eecee7f7bef79ac606b88d325119f21
 F src/os_common.h 8c61457df58f1a4bd5f5adc3e90e01b37bf7afbc
 F src/os_os2.c bed77dc26e3a95ce4a204936b9a1ca6fe612fcc5
-F src/os_unix.c a4b4ea928ce31ed34cb8f90ed36a35df19312fad
+F src/os_unix.c bdd6ca0932dcb51c344081aff430bcc71c14db7f
 F src/os_win.c 5ffab20249a61e0625f869efe157fa009747039b
-F src/pager.c 36e29a1056457305d3afc5a8f81f7d9bf27dd70d
+F src/pager.c 5b5a980aec52a3864bba8600c003b6ad6f4112c2
 F src/pager.h 11852d044c86cf5a9d6e34171fb0c4fcf1f6265f
 F src/parse.y 0204f0dfe8974dc2a0d46eb9ab98a433a1f963d6
 F src/pcache.c c92ffd4f3e1279b3766854c6d18b5bf4aac0d1fa
@@ -762,7 +765,14 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
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manifest.uuid

@@ -1 +1 @@
-d410cd4e42ecf50a849f49cf3395ec169350e7cf
+ddb71cd9ed395804a13dc136bb7688a7627c798f

src/os_unix.c

@@ -3113,6 +3113,19 @@ static int unixTruncate(sqlite3_file *id, i64 nByte){
     ((unixFile*)id)->lastErrno = errno;
     return SQLITE_IOERR_TRUNCATE;
   }else{
+#ifndef NDEBUG
+    /* If we are doing a normal write to a database file (as opposed to
+    ** doing a hot-journal rollback or a write to some file other than a
+    ** normal database file) and we truncate the file to zero length,
+    ** that effectively updates the change counter.  This might happen
+    ** when restoring a database using the backup API from a zero-length
+    ** source.
+    */
+    if( ((unixFile*)id)->inNormalWrite && nByte==0 ){
+      ((unixFile*)id)->transCntrChng = 1;
+    }
+#endif
+
     return SQLITE_OK;
   }
 }

src/pager.c

@@ -4446,7 +4446,7 @@ static int pager_incr_changecounter(Pager *pPager, int isDirectMode){
 #endif
 
   assert( pPager->state>=PAGER_RESERVED );
-  if( !pPager->changeCountDone && ALWAYS(pPager->dbSize>0) ){
+  if( !pPager->changeCountDone && pPager->dbSize>0 ){
     PgHdr *pPgHdr;                /* Reference to page 1 */
     u32 change_counter;           /* Initial value of change-counter field */