Improved comments on the new code.

FossilOrigin-Name: a38f0c1d7c1d7635732ac370d8fbc7e6a2005378e4621da7bc4f51a2f99912d1

manifest

@@ -1,5 +1,5 @@
-C Add\san\sALWAYS()\sto\san\sunreachable\sbranch.
-D 2021-01-30T16:16:42.507
+C Improved\scomments\son\sthe\snew\scode.
+D 2021-01-30T21:55:38.166
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -485,7 +485,7 @@ F src/btmutex.c 8acc2f464ee76324bf13310df5692a262b801808984c1b79defb2503bbafadb6
 F src/btree.c 47d9fe97d5c0d74506154e3597f8a23b81a00080751dc4d11fec91ee22796f4c
 F src/btree.h 285f8377aa1353185a32bf455faafa9ff9a0d40d074d60509534d14990c7829e
 F src/btreeInt.h 7614cae30f95b6aed0c7cac7718276a55cfe2c77058cbfd8bef5b75329757331
-F src/build.c ff2cdab3c86156c3c1808e282daaf04d298e532ef11478844964107496898cf9
+F src/build.c 118e1076282415229420d04f9cc25bb148a2c412d82ea3c319136d2122c842e5
 F src/callback.c d0b853dd413255d2e337b34545e54d888ea02f20da5ad0e63585b389624c4a6c
 F src/complete.c a3634ab1e687055cd002e11b8f43eb75c17da23e
 F src/ctime.c 2a322b9a3d75771fb4d99e0702851f4f68dda982507a0f798eefb0712969a410
@@ -607,7 +607,7 @@ F src/test_wsd.c 41cadfd9d97fe8e3e4e44f61a4a8ccd6f7ca8fe9
 F src/threads.c 4ae07fa022a3dc7c5beb373cf744a85d3c5c6c3c
 F src/tokenize.c c64c49d7c2ec4490c2fef1f24350167ba16b03b0c6cee58ad1a1d70a4325d4e9
 F src/treeview.c 4b92992176fb2caefbe06ba5bd06e0e0ebcde3d5564758da672631f17aa51cda
-F src/trigger.c ec5ba098328dccba9b5c2e5e9946df4dab1d551ae8b7d1b0bdaec65914bf2bfa
+F src/trigger.c 207168409c59f346df3a8b4556f0f35fdf721cd35e06fb3c75ea76b7ce95ed35
 F src/update.c 3dbc7189ffcf361c2149f1b1d0841a8a9689d27f15c5e72e6f14ebc447e6b0c0
 F src/upsert.c df8f1727d62b5987c4fd302cd4d7c0c84ae57cd65683c5a34a740dfe24039235
 F src/utf.c ee39565f0843775cc2c81135751ddd93eceb91a673ea2c57f61c76f288b041a0
@@ -1899,7 +1899,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P fea91e3a511b14dafcc4da92c59188f927ec60ed91441335183da6b4e7866c1b
-R 8cd82e0fb3b2559278f1acef6be93a28
+P 6bb6de42b62acd35ade6c95a11bb4c9b35e7e9a24620731ae36364c4d5c3bc31
+R 9e0cb8b9c72d2bfe4a3d882f4b872a05
 U drh
-Z 32c0d1eece5071f19ef4a6007df09364
+Z 296f4bf266bf4139fc832ba9efb3047c

manifest.uuid

@@ -1 +1 @@
-6bb6de42b62acd35ade6c95a11bb4c9b35e7e9a24620731ae36364c4d5c3bc31
+a38f0c1d7c1d7635732ac370d8fbc7e6a2005378e4621da7bc4f51a2f99912d1

src/build.c

@@ -1244,23 +1244,38 @@ void sqlite3ColumnPropertiesFromName(Table *pTab, Column *pCol){
 #endif
 
 /*
-** Name of the magic TEMP trigger used to implement RETURNING
+** Name of the special TEMP trigger used to implement RETURNING.  The
+** name begins with "sqlite_" so that it is guaranteed not to collide
+** with any application-generated triggers.
 */
-#define RETURNING_TRIGGER  "sqlite_returning"
+#define RETURNING_TRIGGER_NAME  "sqlite_returning"
 
 /*
-** Delete the data structures associated with the RETURNING clause.
+** Clean up the data structures associated with the RETURNING clause.
 */
 static void sqlite3DeleteReturning(sqlite3 *db, Returning *pRet){
   Hash *pHash;
   pHash = &(db->aDb[1].pSchema->trigHash);
-  sqlite3HashInsert(pHash, RETURNING_TRIGGER, 0);
+  sqlite3HashInsert(pHash, RETURNING_TRIGGER_NAME, 0);
   sqlite3ExprListDelete(db, pRet->pReturnEL);
   sqlite3DbFree(db, pRet);
 }
 
 /*
-** Add the RETURNING clause to the parser currently underway.
+** Add the RETURNING clause to the parse currently underway.
+**
+** This routine creates a special TEMP trigger that will fire for each row
+** of the DML statement.  That TEMP trigger contains a single SELECT
+** statement with a result set that is the argument of the RETURNING clause.
+** The trigger has the Trigger.bReturning flag and an opcode of
+** TK_RETURNING instead of TK_SELECT, so that the trigger code generator
+** knows to handle it specially.  The TEMP trigger is automatically
+** removed at the end of the parse.
+**
+** When this routine is called, we do not yet know if the RETURNING clause
+** is attached to a DELETE, INSERT, or UPDATE, so construct it as a
+** RETURNING trigger instead.  It will then be converted into the appropriate
+** type on the first call to sqlite3TriggersExist().
 */
 void sqlite3AddReturning(Parse *pParse, ExprList *pList){
   Returning *pRet;
@@ -1278,7 +1293,7 @@ void sqlite3AddReturning(Parse *pParse, ExprList *pList){
   sqlite3ParserAddCleanup(pParse,
      (void(*)(sqlite3*,void*))sqlite3DeleteReturning, pRet);
   if( db->mallocFailed ) return;
-  pRet->retTrig.zName = "sqlite_returning";
+  pRet->retTrig.zName = RETURNING_TRIGGER_NAME;
   pRet->retTrig.op = TK_RETURNING;
   pRet->retTrig.tr_tm = TRIGGER_AFTER;
   pRet->retTrig.bReturning = 1;
@@ -1291,8 +1306,8 @@ void sqlite3AddReturning(Parse *pParse, ExprList *pList){
   pRet->retSel.pEList = pList;
   pRet->retSel.pSrc = (SrcList*)&pRet->retSrcList;
   pHash = &(db->aDb[1].pSchema->trigHash);
-  assert( sqlite3HashFind(pHash, RETURNING_TRIGGER)==0 );
-  if( sqlite3HashInsert(pHash, "sqlite_returning", &pRet->retTrig)
+  assert( sqlite3HashFind(pHash, RETURNING_TRIGGER_NAME)==0 );
+  if( sqlite3HashInsert(pHash, RETURNING_TRIGGER_NAME, &pRet->retTrig)
           ==&pRet->retTrig ){
     sqlite3OomFault(db);
   }

src/trigger.c

@@ -739,10 +739,14 @@ Trigger *sqlite3TriggersExist(
   for(p=pList; p; p=p->pNext){
     if( p->op==op && checkColumnOverlap(p->pColumns, pChanges) ){
       mask |= p->tr_tm;
-    }else if( p->bReturning
-           && (p->op==TK_RETURNING || (p->op!=TK_DELETE && op!=TK_DELETE)) ){
+    }else if( p->op==TK_RETURNING ){
+      /* The first time a RETURNING trigger is seen, the "op" value tells
+      ** us what time of trigger it should be. */
       p->op = op;
       mask |= TRIGGER_AFTER;
+    }else if( p->bReturning && p->op==TK_INSERT && op==TK_UPDATE ){
+      /* Also fire a RETURNING trigger for INSERT on the UPDATE of an UPSERT */
+      mask |= TRIGGER_AFTER;
     }
   }
   if( pMask ){
@@ -1216,13 +1220,19 @@ void sqlite3CodeRowTrigger(
     assert( p->pSchema==p->pTabSchema 
          || p->pSchema==pParse->db->aDb[1].pSchema );
 
-    /* Determine whether we should code this trigger */
-    if( (p->op==op || (p->bReturning && p->op!=TK_DELETE))
+    /* Determine whether we should code this trigger.  One of two choices:
+    **   1. The trigger is an exact match to the current DML statement
+    **   2. This is a RETURNING trigger for INSERT but we are currently
+    **      doing the UPDATE part of an UPSERT.
+    */
+    if( (p->op==op || (p->bReturning && p->op==TK_INSERT && op==TK_UPDATE))
      && p->tr_tm==tr_tm 
      && checkColumnOverlap(p->pColumns, pChanges)
     ){
+      u8 origOp = p->op;
       p->op = op;
       sqlite3CodeRowTriggerDirect(pParse, p, pTab, reg, orconf, ignoreJump);
+      p->op = origOp;
     }
   }
 }