From: drh <drh@noemail.net>
Date: Sat, 20 Aug 2016 01:06:22 +0000 (+0000)
Subject: Improvements to comments.  No code changes.
X-Git-Tag: version-3.15.0~110^2~62
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=8762ec19356cced5e3f3d3647912ed9f7507ae64;p=thirdparty%2Fsqlite.git

Improvements to comments.  No code changes.

FossilOrigin-Name: 4165d20f64d778a4e48f511a37cfced8579d4dbe
---

diff --git a/manifest b/manifest
index 122bc50e37..c056b2c63e 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Add\ssupport\sfor\svector\sassignments\sin\sthe\sSET\sclause\sof\san\sUPDATE\sstatement.
-D 2016-08-20T00:51:37.333
+C Improvements\sto\scomments.\s\sNo\scode\schanges.
+D 2016-08-20T01:06:22.412
 F Makefile.in cfd8fb987cd7a6af046daa87daa146d5aad0e088
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc d66d0395c38571aab3804f8db0fa20707ae4609a
@@ -338,7 +338,7 @@ F src/ctime.c e77f3dc297b4b65c96da78b4ae4272fdfae863d7
 F src/date.c 95c9a8d00767e7221a8e9a31f4e913fc8029bf6b
 F src/dbstat.c 19ee7a4e89979d4df8e44cfac7a8f905ec89b77d
 F src/delete.c 76c084f0265f4a3cd1ecf17eee112a94f1ccbc05
-F src/expr.c bdc98d3301358bac9b19e23a22375f5220a77274
+F src/expr.c d5cffb307d4e812c41a6fb1f6bc94e6b0801e3e8
 F src/fault.c 160a0c015b6c2629d3899ed2daf63d75754a32bb
 F src/fkey.c e2be0968c1adc679c87e467aa5b4f167588f38a8
 F src/func.c 29cc9acb170ec1387b9f63eb52cd85f8de96c771
@@ -1519,7 +1519,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P d8feea7dcde83179bff303072426561cfe825e58
-R d0cc8110f72472ebd6ad961310b5fb0d
+P f320d47d6b7b08d9552c8444004bc256348bda90
+R d44ef1061d1c50d06d327d2ef8a626d9
 U drh
-Z 375b2bf2a6add0d9f506b37662f21e95
+Z fa86522a92bb8bcf293bd50750ba2b7b
diff --git a/manifest.uuid b/manifest.uuid
index 653a21c0af..f9c4d10372 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-f320d47d6b7b08d9552c8444004bc256348bda90
\ No newline at end of file
+4165d20f64d778a4e48f511a37cfced8579d4dbe
\ No newline at end of file
diff --git a/src/expr.c b/src/expr.c
index d8737c075e..5a5afe5ff3 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -367,11 +367,21 @@ Expr *sqlite3VectorFieldSubexpr(Expr *pVector, int i){
 ** sqlite3ExprCode() will generate all necessary code to compute
 ** the iField-th column of the vector expression pVector.
 **
+** It is ok for pVector to be a scalar (as long as iField==0).  
+** In that case, this routine works like sqlite3ExprDup().
+**
 ** The caller owns the returned Expr object and is responsible for
 ** ensuring that the returned value eventually gets freed.
 **
-** The caller retains ownership of pVector and must ensure that pVector
-** remains valid as long as the returned value is in use.
+** The caller retains ownership of pVector.  If pVector is a TK_SELECT,
+** then the return value will reference pVector and so pVector must remain
+** valid for the life of the returned object.  If pVector is a TK_VECTOR
+** or a scalar expression, then it can be deleted as soon as this routine
+** routines.
+**
+** A trick to cause a TK_SELECT pVector to be deleted together with
+** the returned Expr object is to attach the pVector to the pRight field
+** of the returned TK_SELECT_COLUMN Expr object.
 */
 Expr *sqlite3ExprForVectorField(
   Parse *pParse,       /* Parsing context */
@@ -384,16 +394,17 @@ Expr *sqlite3ExprForVectorField(
     /* The TK_SELECT_COLUMN Expr node:
     **
     ** pLeft:           pVector containing TK_SELECT
-    ** pRight:          pVector if ownership taken
+    ** pRight:          not used.  But recursively deleted.
     ** iColumn:         Index of a column in pVector
     ** pLeft->iTable:   First in an array of register holding result, or 0
     **                  if the result is not yet computed.
     **
     ** sqlite3ExprDelete() specifically skips the recursive delete of
     ** pLeft on TK_SELECT_COLUMN nodes.  But pRight is followed, so pVector
-    ** is included on pRight if ownership is taken.  Typically there will
-    ** be multiple TK_SELECT_COLUMN nodes with the same pLeft pointer to 
-    ** the pVector, but only one of them will own the pVector.
+    ** can be attached to pRight to cause this node to take ownership of
+    ** pVector.  Typically there will be multiple TK_SELECT_COLUMN nodes
+    ** with the same pLeft pointer to the pVector, but only one of them
+    ** will own the pVector.
     */
     pRet = sqlite3PExpr(pParse, TK_SELECT_COLUMN, pVector, 0, 0);
     if( pRet ) pRet->iColumn = iField;
@@ -1436,13 +1447,14 @@ no_mem:
 }
 
 /*
-** pColumns and pExpr for a vector assignment, like this:
+** pColumns and pExpr form a vector assignment which is part of the SET
+** clause of an UPDATE statement.  Like this:
 **
 **        (a,b,c) = (expr1,expr2,expr3)
 ** Or:    (a,b,c) = (SELECT x,y,z FROM ....)
 **
 ** For each term of the vector assignment, append new entries to the
-** expression list.  In the case of a subquery on the LHS, append
+** expression list pList.  In the case of a subquery on the LHS, append
 ** TK_SELECT_COLUMN expressions.
 */
 ExprList *sqlite3ExprListAppendVector(