Index: src/btree.c
==================================================================
--- src/btree.c
+++ src/btree.c
@@ -1784,11 +1784,11 @@
       mutexShared = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
       sqlite3_mutex_enter(mutexShared);
 #endif
       for(pBt=GLOBAL(BtShared*,sqlite3SharedCacheList); pBt; pBt=pBt->pNext){
         assert( pBt->nRef>0 );
-        if( 0==strcmp(zFullPathname, sqlite3PagerFilename(pBt->pPager))
+        if( 0==strcmp(zFullPathname, sqlite3PagerFilename(pBt->pPager, 0))
                  && sqlite3PagerVfs(pBt->pPager)==pVfs ){
           int iDb;
           for(iDb=db->nDb-1; iDb>=0; iDb--){
             Btree *pExisting = db->aDb[iDb].pBt;
             if( pExisting && pExisting->pBt==pBt ){
@@ -8049,18 +8049,19 @@
   return sqlite3StrAccumFinish(&sCheck.errMsg);
 }
 #endif /* SQLITE_OMIT_INTEGRITY_CHECK */
 
 /*
-** Return the full pathname of the underlying database file.
+** Return the full pathname of the underlying database file.  Return
+** an empty string if the database is in-memory or a TEMP database.
 **
 ** The pager filename is invariant as long as the pager is
 ** open so it is safe to access without the BtShared mutex.
 */
 const char *sqlite3BtreeGetFilename(Btree *p){
   assert( p->pBt->pPager!=0 );
-  return sqlite3PagerFilename(p->pBt->pPager);
+  return sqlite3PagerFilename(p->pBt->pPager, 1);
 }
 
 /*
 ** Return the pathname of the journal file for this database. The return
 ** value of this routine is the same regardless of whether the journal file

Index: src/pager.c
==================================================================
--- src/pager.c
+++ src/pager.c
@@ -4358,11 +4358,11 @@
   *ppPager = 0;
 
 #ifndef SQLITE_OMIT_MEMORYDB
   if( flags & PAGER_MEMORY ){
     memDb = 1;
-    if( zFilename ){
+    if( zFilename && zFilename[0] ){
       zPathname = sqlite3DbStrDup(0, zFilename);
       if( zPathname==0  ) return SQLITE_NOMEM;
       nPathname = sqlite3Strlen30(zPathname);
       zFilename = 0;
     }
@@ -6299,13 +6299,20 @@
   return rc;
 }
 
 /*
 ** Return the full pathname of the database file.
+**
+** Except, if the pager is in-memory only, then return an empty string if
+** nullIfMemDb is true.  This routine is called with nullIfMemDb==1 when
+** used to report the filename to the user, for compatibility with legacy
+** behavior.  But when the Btree needs to know the filename for matching to
+** shared cache, it uses nullIfMemDb==0 so that in-memory databases can
+** participate in shared-cache.
 */
-const char *sqlite3PagerFilename(Pager *pPager){
-  return pPager->zFilename;
+const char *sqlite3PagerFilename(Pager *pPager, int nullIfMemDb){
+  return (nullIfMemDb && pPager->memDb) ? "" : pPager->zFilename;
 }
 
 /*
 ** Return the VFS structure for the pager.
 */
@@ -6746,12 +6753,11 @@
 ** Return true if the underlying VFS for the given pager supports the
 ** primitives necessary for write-ahead logging.
 */
 int sqlite3PagerWalSupported(Pager *pPager){
   const sqlite3_io_methods *pMethods = pPager->fd->pMethods;
-  return pPager->memDb==0 && 
-        (pPager->exclusiveMode || (pMethods->iVersion>=2 && pMethods->xShmMap));
+  return pPager->exclusiveMode || (pMethods->iVersion>=2 && pMethods->xShmMap);
 }
 
 /*
 ** Attempt to take an exclusive lock on the database file. If a PENDING lock
 ** is obtained instead, immediately release it.

Index: src/pager.h
==================================================================
--- src/pager.h
+++ src/pager.h
@@ -149,11 +149,11 @@
 
 /* Functions used to query pager state and configuration. */
 u8 sqlite3PagerIsreadonly(Pager*);
 int sqlite3PagerRefcount(Pager*);
 int sqlite3PagerMemUsed(Pager*);
-const char *sqlite3PagerFilename(Pager*);
+const char *sqlite3PagerFilename(Pager*, int);
 const sqlite3_vfs *sqlite3PagerVfs(Pager*);
 sqlite3_file *sqlite3PagerFile(Pager*);
 const char *sqlite3PagerJournalname(Pager*);
 int sqlite3PagerNosync(Pager*);
 void *sqlite3PagerTempSpace(Pager*);

Index: src/test_btree.c
==================================================================
--- src/test_btree.c
+++ src/test_btree.c
@@ -31,11 +31,11 @@
 #ifndef SQLITE_OMIT_SHARED_CACHE
   extern BtShared *sqlite3SharedCacheList;
   BtShared *pBt;
   Tcl_Obj *pRet = Tcl_NewObj();
   for(pBt=GLOBAL(BtShared*,sqlite3SharedCacheList); pBt; pBt=pBt->pNext){
-    const char *zFile = sqlite3PagerFilename(pBt->pPager);
+    const char *zFile = sqlite3PagerFilename(pBt->pPager, 1);
     Tcl_ListObjAppendElement(interp, pRet, Tcl_NewStringObj(zFile, -1));
     Tcl_ListObjAppendElement(interp, pRet, Tcl_NewIntObj(pBt->nRef));
   }
   Tcl_SetObjResult(interp, pRet);
 #endif

Index: src/vdbe.c
==================================================================
--- src/vdbe.c
+++ src/vdbe.c
@@ -5509,11 +5509,11 @@
   eOld = sqlite3PagerGetJournalMode(pPager);
   if( eNew==PAGER_JOURNALMODE_QUERY ) eNew = eOld;
   if( !sqlite3PagerOkToChangeJournalMode(pPager) ) eNew = eOld;
 
 #ifndef SQLITE_OMIT_WAL
-  zFilename = sqlite3PagerFilename(pPager);
+  zFilename = sqlite3PagerFilename(pPager, 1);
 
   /* Do not allow a transition to journal_mode=WAL for a database
   ** in temporary storage or if the VFS does not support shared memory 
   */
   if( eNew==PAGER_JOURNALMODE_WAL

Index: test/attach.test
==================================================================
--- test/attach.test
+++ test/attach.test
@@ -855,8 +855,8 @@
 } {noname inmem}
 do_test attach-10.2 {
   lrange [execsql {
     PRAGMA database_list;
   }] 9 end
-} {4 noname {} 5 inmem :memory:}
+} {4 noname {} 5 inmem {}}
 
 finish_test