Fix and improve description of locktag types in lock.h

The description of the lock type for speculative insertions was
incorrect, being copy-pasted from another one.

As discussed, also move the description for all the fields of lock tag
types from the structure listing lock tag types to the set of macros
setting each LOCKTAG.

Author: John Naylor
Discussion: https://postgr.es/m/CACPNZCtA0-ybaC4fFfaDq_8p_TUOLvGxZH9Dm-=TMHZJarBa7Q@mail.gmail.com

Author: michaelpq

src/include/storage/lock.h

@@ -138,27 +138,13 @@ typedef uint16 LOCKMETHODID;
 typedef enum LockTagType
 {
 	LOCKTAG_RELATION,			/* whole relation */
-	/* ID info for a relation is DB OID + REL OID; DB OID = 0 if shared */
 	LOCKTAG_RELATION_EXTEND,	/* the right to extend a relation */
-	/* same ID info as RELATION */
 	LOCKTAG_PAGE,				/* one page of a relation */
-	/* ID info for a page is RELATION info + BlockNumber */
 	LOCKTAG_TUPLE,				/* one physical tuple */
-	/* ID info for a tuple is PAGE info + OffsetNumber */
 	LOCKTAG_TRANSACTION,		/* transaction (for waiting for xact done) */
-	/* ID info for a transaction is its TransactionId */
 	LOCKTAG_VIRTUALTRANSACTION, /* virtual transaction (ditto) */
-	/* ID info for a virtual transaction is its VirtualTransactionId */
 	LOCKTAG_SPECULATIVE_TOKEN,	/* speculative insertion Xid and token */
-	/* ID info for a transaction is its TransactionId */
 	LOCKTAG_OBJECT,				/* non-relation database object */
-	/* ID info for an object is DB OID + CLASS OID + OBJECT OID + SUBID */
-
-	/*
-	 * Note: object ID has same representation as in pg_depend and
-	 * pg_description, but notice that we are constraining SUBID to 16 bits.
-	 * Also, we use DB OID = 0 for shared objects such as tablespaces.
-	 */
 	LOCKTAG_USERLOCK,			/* reserved for old contrib/userlock code */
 	LOCKTAG_ADVISORY			/* advisory user locks */
 } LockTagType;
@@ -190,6 +176,8 @@ typedef struct LOCKTAG
  * the physical fields of LOCKTAG.  Use these to set up LOCKTAG values,
  * rather than accessing the fields directly.  Note multiple eval of target!
  */
+
+/* ID info for a relation is DB OID + REL OID; DB OID = 0 if shared */
 #define SET_LOCKTAG_RELATION(locktag,dboid,reloid) \
 	((locktag).locktag_field1 = (dboid), \
 	 (locktag).locktag_field2 = (reloid), \
@@ -198,6 +186,7 @@ typedef struct LOCKTAG
 	 (locktag).locktag_type = LOCKTAG_RELATION, \
 	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)
 
+/* same ID info as RELATION */
 #define SET_LOCKTAG_RELATION_EXTEND(locktag,dboid,reloid) \
 	((locktag).locktag_field1 = (dboid), \
 	 (locktag).locktag_field2 = (reloid), \
@@ -206,6 +195,7 @@ typedef struct LOCKTAG
 	 (locktag).locktag_type = LOCKTAG_RELATION_EXTEND, \
 	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)
 
+/* ID info for a page is RELATION info + BlockNumber */
 #define SET_LOCKTAG_PAGE(locktag,dboid,reloid,blocknum) \
 	((locktag).locktag_field1 = (dboid), \
 	 (locktag).locktag_field2 = (reloid), \
@@ -214,6 +204,7 @@ typedef struct LOCKTAG
 	 (locktag).locktag_type = LOCKTAG_PAGE, \
 	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)
 
+/* ID info for a tuple is PAGE info + OffsetNumber */
 #define SET_LOCKTAG_TUPLE(locktag,dboid,reloid,blocknum,offnum) \
 	((locktag).locktag_field1 = (dboid), \
 	 (locktag).locktag_field2 = (reloid), \
@@ -222,6 +213,7 @@ typedef struct LOCKTAG
 	 (locktag).locktag_type = LOCKTAG_TUPLE, \
 	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)
 
+/* ID info for a transaction is its TransactionId */
 #define SET_LOCKTAG_TRANSACTION(locktag,xid) \
 	((locktag).locktag_field1 = (xid), \
 	 (locktag).locktag_field2 = 0, \
@@ -230,6 +222,7 @@ typedef struct LOCKTAG
 	 (locktag).locktag_type = LOCKTAG_TRANSACTION, \
 	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)
 
+/* ID info for a virtual transaction is its VirtualTransactionId */
 #define SET_LOCKTAG_VIRTUALTRANSACTION(locktag,vxid) \
 	((locktag).locktag_field1 = (vxid).backendId, \
 	 (locktag).locktag_field2 = (vxid).localTransactionId, \
@@ -238,6 +231,10 @@ typedef struct LOCKTAG
 	 (locktag).locktag_type = LOCKTAG_VIRTUALTRANSACTION, \
 	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)
 
+/*
+ * ID info for a speculative insert is TRANSACTION info +
+ * its speculative insert counter.
+ */
 #define SET_LOCKTAG_SPECULATIVE_INSERTION(locktag,xid,token) \
 	((locktag).locktag_field1 = (xid), \
 	 (locktag).locktag_field2 = (token),		\
@@ -246,6 +243,13 @@ typedef struct LOCKTAG
 	 (locktag).locktag_type = LOCKTAG_SPECULATIVE_TOKEN, \
 	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)
 
+/*
+ * ID info for an object is DB OID + CLASS OID + OBJECT OID + SUBID
+ *
+ * Note: object ID has same representation as in pg_depend and
+ * pg_description, but notice that we are constraining SUBID to 16 bits.
+ * Also, we use DB OID = 0 for shared objects such as tablespaces.
+ */
 #define SET_LOCKTAG_OBJECT(locktag,dboid,classoid,objoid,objsubid) \
 	((locktag).locktag_field1 = (dboid), \
 	 (locktag).locktag_field2 = (classoid), \