Add safe cast for function cast

src/backend/parser/parse_coerce.c

@@ -1250,6 +1250,60 @@ build_coercion_expression(Node *node,
 		fexpr->location = location;
 		return (Node *) fexpr;
 	}
+	else if (pathtype == COERCION_PATH_FUNC_SAFE)
+	{
+		/* We build an ordinary FuncExpr with special arguments */
+		FuncExpr   *fexpr;
+		List	   *args;
+		Const	   *cons;
+
+		Assert(OidIsValid(funcId));
+
+		cons = makeConst(REGPROCEDUREOID,
+						 -1,
+						 InvalidOid,
+						 sizeof(regproc),
+						 funcId,
+						 false,
+						 true);
+
+		args = list_make2(node, cons);
+
+
+
+		if (nargs >= 2)
+		{
+			/* Pass target typmod as an int4 constant */
+			cons = makeConst(INT4OID,
+							 -1,
+							 InvalidOid,
+							 sizeof(int32),
+							 Int32GetDatum(targetTypMod),
+							 false,
+							 true);
+
+			args = lappend(args, cons);
+		}
+
+		if (nargs == 3)
+		{
+			/* Pass it a boolean isExplicit parameter, too */
+			cons = makeConst(BOOLOID,
+							 -1,
+							 InvalidOid,
+							 sizeof(bool),
+							 BoolGetDatum(isExplicit),
+							 false,
+							 true);
+
+			args = lappend(args, cons);
+		}
+
+		fexpr = makeFuncExpr(TRY_CAST_FUNCTION_OID, targetTypeId, args,
+							 InvalidOid, InvalidOid, cformat);
+		fexpr->location = location;
+		return (Node *) fexpr;
+	}
 	else if (pathtype == COERCION_PATH_ARRAYCOERCE)
 	{
 		/* We need to build an ArrayCoerceExpr */
@@ -2563,7 +2617,10 @@ find_coercion_pathway(Oid targetTypeId, Oid sourceTypeId,
 			switch (castForm->castmethod)
 			{
 				case COERCION_METHOD_FUNCTION:
-					result = COERCION_PATH_FUNC;
+					if (ccontext == COERCION_EXPLICIT_SAFE)
+						result = COERCION_PATH_FUNC_SAFE;
+					else
+						result = COERCION_PATH_FUNC;
 					*funcid = castForm->castfunc;
 					break;
 				case COERCION_METHOD_INOUT:

src/backend/parser/parse_expr.c

@@ -2467,9 +2467,13 @@ transformTypeCast(ParseState *pstate, TypeCast *tc)
 	if (location < 0)
 		location = tc->typeName->location;
 
+	CoercionContext ccontext = COERCION_EXPLICIT;
+	if (tc->is_trycast)
+		ccontext = COERCION_EXPLICIT_SAFE;
+
 	result = coerce_to_target_type(pstate, expr, inputType,
 								   targetType, targetTypmod,
-								   COERCION_EXPLICIT,
+								   ccontext,
 								   COERCE_EXPLICIT_CAST,
 								   location);
 	if (result == NULL)

src/backend/utils/misc/Makefile

@@ -21,7 +21,7 @@ OBJS = guc.o help_config.o pg_rusage.o ps_status.o rbtree.o \
        gpexpand.o \
        faultinjector.o uriparser.o \
        bitstream.o bitmap_compression.o guc_gp.o backend_cancel.o \
-       superuser.o timeout.o tzparser.o
+       superuser.o timeout.o try_cast.o tzparser.o
 
 # This location might depend on the installation directories. Therefore
 # we can't substitute it into pg_config.h.

src/backend/utils/misc/try_cast.c

@@ -0,0 +1,31 @@
+#include "postgres.h"
+
+#include <ctype.h>
+#include <limits.h>
+#include <math.h>
+
+#include "funcapi.h"
+#include "libpq/pqformat.h"
+#include "utils/try_cast.h"
+#include "utils/builtins.h"
+
+
+Datum
+try_cast(PG_FUNCTION_ARGS)
+{
+    Datum value = PG_GETARG_DATUM(0);
+
+    Datum funcId = PG_GETARG_DATUM(1);
+
+	PG_TRY();
+	{
+        Datum res = OidFunctionCall1(funcId, value);
+
+        PG_RETURN_DATUM(res);
+    }
+	PG_CATCH();
+	{
+		PG_RETURN_NULL();
+	}
+	PG_END_TRY();
+}

src/include/catalog/pg_proc.h

@@ -5234,6 +5234,10 @@ DESCR("import collations from operating system");
 DATA(insert OID = 3994 ( mdb_locale_enabled	PGNSP PGUID 12 1 0 0 0 f f f f t f v 0 0 16 "" _null_ _null_ _null_ _null_ mdb_locale_enabled _null_ _null_ _null_ ));
 DESCR("true if mdb locales enabled");
 
+DATA(insert OID = 3995 (  try_cast_func			   PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 2283 "2283 24" _null_ _null_ _null_ _null_ try_cast _null_ _null_ _null_ ));
+DESCR("try_cast function");
+#define TRY_CAST_FUNCTION_OID 3995
+
 /*
  * Include more definitions from pg_proc_gp.h, for GPDB-added functions. They
  * are kept in a separate file to make diffing and merging with upstream

src/include/nodes/primnodes.h

@@ -437,7 +437,8 @@ typedef enum CoercionContext
 {
 	COERCION_IMPLICIT,			/* coercion in context of expression */
 	COERCION_ASSIGNMENT,		/* coercion in context of assignment */
-	COERCION_EXPLICIT			/* explicit cast operation */
+	COERCION_EXPLICIT,			/* explicit cast operation */
+	COERCION_EXPLICIT_SAFE		/* explicit cast operation */
 } CoercionContext;
 
 /*

src/include/parser/parse_coerce.h

@@ -25,6 +25,7 @@ typedef enum CoercionPathType
 {
 	COERCION_PATH_NONE,			/* failed to find any coercion pathway */
 	COERCION_PATH_FUNC,			/* apply the specified coercion function */
+	COERCION_PATH_FUNC_SAFE,			/* apply the specified coercion function safe */
 	COERCION_PATH_RELABELTYPE,	/* binary-compatible cast, no function */
 	COERCION_PATH_ARRAYCOERCE,	/* need an ArrayCoerceExpr node */
 	COERCION_PATH_COERCEVIAIO	/* need a CoerceViaIO node */

src/include/utils/try_cast.h

@@ -0,0 +1,8 @@
+#ifndef TRY_CAST_H
+#define TRY_CAST_H
+
+#include "fmgr.h"
+
+extern Datum try_cast(PG_FUNCTION_ARGS);
+
+#endif