Represent type-specific length coercion functions as pg_cast entries,

eliminating the former hard-wired convention about their names.  Allow
pg_cast entries to represent both type coercion and length coercion in
a single step --- this is represented by a function that takes an
extra typmod argument, just like a length coercion function.  This
nicely merges the type and length coercion mechanisms into something
at least a little cleaner than we had before.  Make use of the single-
coercion-step behavior to fix integer-to-bit coercion so that coercing
to bit(n) yields the rightmost n bits of the integer instead of the
leftmost n bits.  This should fix recurrent complaints about the odd
behavior of this coercion.  Clean up the documentation of the bit string
functions, and try to put it where people might actually find it.
Also, get rid of the unreliable heuristics in ruleutils.c about whether
to display nested coercion steps; instead require parse_coerce.c to
label them properly in the first place.

1 files changed, 23 insertions, 8 deletions

diff --git a/src/backend/commands/functioncmds.c b/src/backend/commands/functioncmds.c
index 757869a925a..7747eb1d776 100644
--- a/src/backend/commands/functioncmds.c
+++ b/src/backend/commands/functioncmds.c
@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/functioncmds.c,v 1.47 2004/05/26 04:41:11 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/functioncmds.c,v 1.48 2004/06/16 01:26:42 tgl Exp $
  *
  * DESCRIPTION
  *	  These routines take the parse tree and pick out the
@@ -809,6 +809,7 @@ CreateCast(CreateCastStmt *stmt)
 	Oid			sourcetypeid;
 	Oid			targettypeid;
 	Oid			funcid;
+	int			nargs;
 	char		castcontext;
 	Relation	relation;
 	HeapTuple	tuple;
@@ -831,11 +832,6 @@ CreateCast(CreateCastStmt *stmt)
 				 errmsg("target data type %s does not exist",
 						TypeNameToString(stmt->targettype))));
 
-	if (sourcetypeid == targettypeid)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-		  errmsg("source data type and target data type are the same")));
-
 	/* No shells, no pseudo-types allowed */
 	if (!get_typisdefined(sourcetypeid))
 		ereport(ERROR,
@@ -885,14 +881,23 @@ CreateCast(CreateCastStmt *stmt)
 			elog(ERROR, "cache lookup failed for function %u", funcid);
 
 		procstruct = (Form_pg_proc) GETSTRUCT(tuple);
-		if (procstruct->pronargs != 1)
+		nargs = procstruct->pronargs;
+		if (nargs < 1 || nargs > 3)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-					 errmsg("cast function must take one argument")));
+					 errmsg("cast function must take one to three arguments")));
 		if (procstruct->proargtypes[0] != sourcetypeid)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
 					 errmsg("argument of cast function must match source data type")));
+		if (nargs > 1 && procstruct->proargtypes[1] != INT4OID)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("second argument of cast function must be type integer")));
+		if (nargs > 2 && procstruct->proargtypes[2] != BOOLOID)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("third argument of cast function must be type boolean")));
 		if (procstruct->prorettype != targettypeid)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
@@ -931,6 +936,7 @@ CreateCast(CreateCastStmt *stmt)
 
 		/* indicates binary coercibility */
 		funcid = InvalidOid;
+		nargs = 0;
 
 		/*
 		 * Must be superuser to create binary-compatible casts, since
@@ -957,6 +963,15 @@ CreateCast(CreateCastStmt *stmt)
 					 errmsg("source and target data types are not physically compatible")));
 	}
 
+	/*
+	 * Allow source and target types to be same only for length coercion
+	 * functions.  We assume a multi-arg function does length coercion.
+	 */
+	if (sourcetypeid == targettypeid && nargs < 2)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+		  errmsg("source data type and target data type are the same")));
+
 	/* convert CoercionContext enum to char value for castcontext */
 	switch (stmt->context)
 	{