Insert conditional SPI_push/SPI_pop calls into InputFunctionCall,

OutputFunctionCall, and friends.  This allows SPI-using functions to invoke
datatype I/O without concern for the possibility that a SPI-using function
will be called (which could be either the I/O function itself, or a function
used in a domain check constraint).  It's a tad ugly, but not nearly as ugly
as what'd be needed to make this work via retail insertion of push/pop
operations in all the PLs.

This reverts my patch of 2007-01-30 that inserted some retail SPI_push/pop
calls into plpgsql; that approach only fixed plpgsql, and not any other PLs.
But the other PLs have the issue too, as illustrated by a recent gripe from
Christian Schröder.

Back-patch to 8.2, which is as far back as this solution will work.  It's
also as far back as we need to worry about the domain-constraint case, since
earlier versions did not attempt to check domain constraints within datatype
input.  I'm not aware of any old I/O functions that use SPI themselves, so
this should be sufficient for a back-patch.

src/backend/utils/fmgr/fmgr.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/fmgr/fmgr.c,v 1.124 2009/01/01 17:23:51 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/fmgr/fmgr.c,v 1.125 2009/01/07 20:38:56 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -19,6 +19,7 @@
 #include "catalog/pg_language.h"
 #include "catalog/pg_proc.h"
 #include "executor/functions.h"
+#include "executor/spi.h"
 #include "lib/stringinfo.h"
 #include "miscadmin.h"
 #include "nodes/nodeFuncs.h"
@@ -1846,16 +1847,25 @@ OidFunctionCall9(Oid functionId, Datum arg1, Datum arg2,
  * the caller should assume the result is NULL, but we'll call the input
  * function anyway if it's not strict.  So this is almost but not quite
  * the same as FunctionCall3.
+ *
+ * One important difference from the bare function call is that we will
+ * push any active SPI context, allowing SPI-using I/O functions to be
+ * called from other SPI functions without extra notation.  This is a hack,
+ * but the alternative of expecting all SPI functions to do SPI_push/SPI_pop
+ * around I/O calls seems worse.
  */
 Datum
 InputFunctionCall(FmgrInfo *flinfo, char *str, Oid typioparam, int32 typmod)
 {
 	FunctionCallInfoData fcinfo;
 	Datum		result;
+	bool		pushed;
 
 	if (str == NULL && flinfo->fn_strict)
 		return (Datum) 0;		/* just return null result */
 
+	pushed = SPI_push_conditional();
+
 	InitFunctionCallInfoData(fcinfo, flinfo, 3, NULL, NULL);
 
 	fcinfo.arg[0] = CStringGetDatum(str);
@@ -1881,6 +1891,8 @@ InputFunctionCall(FmgrInfo *flinfo, char *str, Oid typioparam, int32 typmod)
 				 fcinfo.flinfo->fn_oid);
 	}
 
+	SPI_pop_conditional(pushed);
+
 	return result;
 }
 
@@ -1889,13 +1901,22 @@ InputFunctionCall(FmgrInfo *flinfo, char *str, Oid typioparam, int32 typmod)
  *
  * Do not call this on NULL datums.
  *
- * This is mere window dressing for FunctionCall1, but its use is recommended
- * anyway so that code invoking output functions can be identified easily.
+ * This is almost just window dressing for FunctionCall1, but it includes
+ * SPI context pushing for the same reasons as InputFunctionCall.
  */
 char *
 OutputFunctionCall(FmgrInfo *flinfo, Datum val)
 {
-	return DatumGetCString(FunctionCall1(flinfo, val));
+	char	   *result;
+	bool		pushed;
+
+	pushed = SPI_push_conditional();
+
+	result = DatumGetCString(FunctionCall1(flinfo, val));
+
+	SPI_pop_conditional(pushed);
+
+	return result;
 }
 
 /*
@@ -1904,7 +1925,8 @@ OutputFunctionCall(FmgrInfo *flinfo, Datum val)
  * "buf" may be NULL to indicate we are reading a NULL.  In this case
  * the caller should assume the result is NULL, but we'll call the receive
  * function anyway if it's not strict.  So this is almost but not quite
- * the same as FunctionCall3.
+ * the same as FunctionCall3.  Also, this includes SPI context pushing for
+ * the same reasons as InputFunctionCall.
  */
 Datum
 ReceiveFunctionCall(FmgrInfo *flinfo, StringInfo buf,
@@ -1912,10 +1934,13 @@ ReceiveFunctionCall(FmgrInfo *flinfo, StringInfo buf,
 {
 	FunctionCallInfoData fcinfo;
 	Datum		result;
+	bool		pushed;
 
 	if (buf == NULL && flinfo->fn_strict)
 		return (Datum) 0;		/* just return null result */
 
+	pushed = SPI_push_conditional();
+
 	InitFunctionCallInfoData(fcinfo, flinfo, 3, NULL, NULL);
 
 	fcinfo.arg[0] = PointerGetDatum(buf);
@@ -1941,6 +1966,8 @@ ReceiveFunctionCall(FmgrInfo *flinfo, StringInfo buf,
 				 fcinfo.flinfo->fn_oid);
 	}
 
+	SPI_pop_conditional(pushed);
+
 	return result;
 }
 
@@ -1949,14 +1976,24 @@ ReceiveFunctionCall(FmgrInfo *flinfo, StringInfo buf,
  *
  * Do not call this on NULL datums.
  *
- * This is little more than window dressing for FunctionCall1, but its use is
- * recommended anyway so that code invoking output functions can be identified
- * easily.	Note however that it does guarantee a non-toasted result.
+ * This is little more than window dressing for FunctionCall1, but it does
+ * guarantee a non-toasted result, which strictly speaking the underlying
+ * function doesn't.  Also, this includes SPI context pushing for the same
+ * reasons as InputFunctionCall.
  */
 bytea *
 SendFunctionCall(FmgrInfo *flinfo, Datum val)
 {
-	return DatumGetByteaP(FunctionCall1(flinfo, val));
+	bytea	   *result;
+	bool		pushed;
+
+	pushed = SPI_push_conditional();
+
+	result = DatumGetByteaP(FunctionCall1(flinfo, val));
+
+	SPI_pop_conditional(pushed);
+
+	return result;
 }
 
 /*