Support subscripting of arbitrary types, not only arrays.

This patch generalizes the subscripting infrastructure so that any
data type can be subscripted, if it provides a handler function to
define what that means.  Traditional variable-length (varlena) arrays
all use array_subscript_handler(), while the existing fixed-length
types that support subscripting use raw_array_subscript_handler().
It's expected that other types that want to use subscripting notation
will define their own handlers.  (This patch provides no such new
features, though; it only lays the foundation for them.)

To do this, move the parser's semantic processing of subscripts
(including coercion to whatever data type is required) into a
method callback supplied by the handler.  On the execution side,
replace the ExecEvalSubscriptingRef* layer of functions with direct
calls to callback-supplied execution routines.  (Thus, essentially
no new run-time overhead should be caused by this patch.  Indeed,
there is room to remove some overhead by supplying specialized
execution routines.  This patch does a little bit in that line,
but more could be done.)

Additional work is required here and there to remove formerly
hard-wired assumptions about the result type, collation, etc
of a SubscriptingRef expression node; and to remove assumptions
that the subscript values must be integers.

One useful side-effect of this is that we now have a less squishy
mechanism for identifying whether a data type is a "true" array:
instead of wiring in weird rules about typlen, we can look to see
if pg_type.typsubscript == F_ARRAY_SUBSCRIPT_HANDLER.  For this
to be bulletproof, we have to forbid user-defined types from using
that handler directly; but there seems no good reason for them to
do so.

This patch also removes assumptions that the number of subscripts
is limited to MAXDIM (6), or indeed has any hard-wired limit.
That limit still applies to types handled by array_subscript_handler
or raw_array_subscript_handler, but to discourage other dependencies
on this constant, I've moved it from c.h to utils/array.h.

Dmitry Dolgov, reviewed at various times by Tom Lane, Arthur Zakirov,
Peter Eisentraut, Pavel Stehule

Discussion: https://postgr.es/m/CA+q6zcVDuGBv=M0FqBYX8DPebS3F_0KQ6OVFobGJPM507_SZ_w@mail.gmail.com
Discussion: https://postgr.es/m/CA+q6zcVovR+XY4mfk-7oNk-rF91gH0PebnNfuUjuuDsyHjOcVA@mail.gmail.com

1 files changed, 31 insertions, 25 deletions

diff --git a/src/include/executor/execExpr.h b/src/include/executor/execExpr.h
index abb489e2062..b4e0a9b7d3d 100644
--- a/src/include/executor/execExpr.h
+++ b/src/include/executor/execExpr.h
@@ -32,6 +32,11 @@ typedef void (*ExecEvalSubroutine) (ExprState *state,
 									struct ExprEvalStep *op,
 									ExprContext *econtext);
 
+/* API for out-of-line evaluation subroutines returning bool */
+typedef bool (*ExecEvalBoolSubroutine) (ExprState *state,
+										struct ExprEvalStep *op,
+										ExprContext *econtext);
+
 /*
  * Discriminator for ExprEvalSteps.
  *
@@ -185,8 +190,8 @@ typedef enum ExprEvalOp
 	 */
 	EEOP_FIELDSTORE_FORM,
 
-	/* Process a container subscript; short-circuit expression to NULL if NULL */
-	EEOP_SBSREF_SUBSCRIPT,
+	/* Process container subscripts; possibly short-circuit result to NULL */
+	EEOP_SBSREF_SUBSCRIPTS,
 
 	/*
 	 * Compute old container element/slice when a SubscriptingRef assignment
@@ -494,19 +499,19 @@ typedef struct ExprEvalStep
 			int			ncolumns;
 		}			fieldstore;
 
-		/* for EEOP_SBSREF_SUBSCRIPT */
+		/* for EEOP_SBSREF_SUBSCRIPTS */
 		struct
 		{
+			ExecEvalBoolSubroutine subscriptfunc;	/* evaluation subroutine */
 			/* too big to have inline */
 			struct SubscriptingRefState *state;
-			int			off;	/* 0-based index of this subscript */
-			bool		isupper;	/* is it upper or lower subscript? */
 			int			jumpdone;	/* jump here on null */
 		}			sbsref_subscript;
 
 		/* for EEOP_SBSREF_OLD / ASSIGN / FETCH */
 		struct
 		{
+			ExecEvalSubroutine subscriptfunc;	/* evaluation subroutine */
 			/* too big to have inline */
 			struct SubscriptingRefState *state;
 		}			sbsref;
@@ -640,36 +645,41 @@ typedef struct SubscriptingRefState
 {
 	bool		isassignment;	/* is it assignment, or just fetch? */
 
-	Oid			refelemtype;	/* OID of the container element type */
-	int16		refattrlength;	/* typlen of container type */
-	int16		refelemlength;	/* typlen of the container element type */
-	bool		refelembyval;	/* is the element type pass-by-value? */
-	char		refelemalign;	/* typalign of the element type */
+	/* workspace for type-specific subscripting code */
+	void	   *workspace;
 
-	/* numupper and upperprovided[] are filled at compile time */
-	/* at runtime, extracted subscript datums get stored in upperindex[] */
+	/* numupper and upperprovided[] are filled at expression compile time */
+	/* at runtime, subscripts are computed in upperindex[]/upperindexnull[] */
 	int			numupper;
-	bool		upperprovided[MAXDIM];
-	int			upperindex[MAXDIM];
+	bool	   *upperprovided;	/* indicates if this position is supplied */
+	Datum	   *upperindex;
+	bool	   *upperindexnull;
 
 	/* similarly for lower indexes, if any */
 	int			numlower;
-	bool		lowerprovided[MAXDIM];
-	int			lowerindex[MAXDIM];
-
-	/* subscript expressions get evaluated into here */
-	Datum		subscriptvalue;
-	bool		subscriptnull;
+	bool	   *lowerprovided;
+	Datum	   *lowerindex;
+	bool	   *lowerindexnull;
 
 	/* for assignment, new value to assign is evaluated into here */
 	Datum		replacevalue;
 	bool		replacenull;
 
-	/* if we have a nested assignment, SBSREF_OLD puts old value here */
+	/* if we have a nested assignment, sbs_fetch_old puts old value here */
 	Datum		prevvalue;
 	bool		prevnull;
 } SubscriptingRefState;
 
+/* Execution step methods used for SubscriptingRef */
+typedef struct SubscriptExecSteps
+{
+	/* See nodes/subscripting.h for more detail about these */
+	ExecEvalBoolSubroutine sbs_check_subscripts;	/* process subscripts */
+	ExecEvalSubroutine sbs_fetch;	/* fetch an element */
+	ExecEvalSubroutine sbs_assign;	/* assign to an element */
+	ExecEvalSubroutine sbs_fetch_old;	/* fetch old value for assignment */
+} SubscriptExecSteps;
+
 
 /* functions in execExpr.c */
 extern void ExprEvalPushStep(ExprState *es, const ExprEvalStep *s);
@@ -712,10 +722,6 @@ extern void ExecEvalFieldStoreDeForm(ExprState *state, ExprEvalStep *op,
 									 ExprContext *econtext);
 extern void ExecEvalFieldStoreForm(ExprState *state, ExprEvalStep *op,
 								   ExprContext *econtext);
-extern bool ExecEvalSubscriptingRef(ExprState *state, ExprEvalStep *op);
-extern void ExecEvalSubscriptingRefFetch(ExprState *state, ExprEvalStep *op);
-extern void ExecEvalSubscriptingRefOld(ExprState *state, ExprEvalStep *op);
-extern void ExecEvalSubscriptingRefAssign(ExprState *state, ExprEvalStep *op);
 extern void ExecEvalConvertRowtype(ExprState *state, ExprEvalStep *op,
 								   ExprContext *econtext);
 extern void ExecEvalScalarArrayOp(ExprState *state, ExprEvalStep *op);