Support arrays over domains.

Allowing arrays with a domain type as their element type was left un-done
in the original domain patch, but not for any very good reason.  This
omission leads to such surprising results as array_agg() not working on
a domain column, because the parser can't identify a suitable output type
for the polymorphic aggregate.

In order to fix this, first clean up the APIs of coerce_to_domain() and
some internal functions in parse_coerce.c so that we consistently pass
around a CoercionContext along with CoercionForm.  Previously, we sometimes
passed an "isExplicit" boolean flag instead, which is strictly less
information; and coerce_to_domain() didn't even get that, but instead had
to reverse-engineer isExplicit from CoercionForm.  That's contrary to the
documentation in primnodes.h that says that CoercionForm only affects
display and not semantics.  I don't think this change fixes any live bugs,
but it makes things more consistent.  The main reason for doing it though
is that now build_coercion_expression() receives ccontext, which it needs
in order to be able to recursively invoke coerce_to_target_type().

Next, reimplement ArrayCoerceExpr so that the node does not directly know
any details of what has to be done to the individual array elements while
performing the array coercion.  Instead, the per-element processing is
represented by a sub-expression whose input is a source array element and
whose output is a target array element.  This simplifies life in
parse_coerce.c, because it can build that sub-expression by a recursive
invocation of coerce_to_target_type().  The executor now handles the
per-element processing as a compiled expression instead of hard-wired code.
The main advantage of this is that we can use a single ArrayCoerceExpr to
handle as many as three successive steps per element: base type conversion,
typmod coercion, and domain constraint checking.  The old code used two
stacked ArrayCoerceExprs to handle type + typmod coercion, which was pretty
inefficient, and adding yet another array deconstruction to do domain
constraint checking seemed very unappetizing.

In the case where we just need a single, very simple coercion function,
doing this straightforwardly leads to a noticeable increase in the
per-array-element runtime cost.  Hence, add an additional shortcut evalfunc
in execExprInterp.c that skips unnecessary overhead for that specific form
of expression.  The runtime speed of simple cases is within 1% or so of
where it was before, while cases that previously required two levels of
array processing are significantly faster.

Finally, create an implicit array type for every domain type, as we do for
base types, enums, etc.  Everything except the array-coercion case seems
to just work without further effort.

Tom Lane, reviewed by Andrew Dunstan

Discussion: https://postgr.es/m/9852.1499791473@sss.pgh.pa.us

4 files changed, 39 insertions, 28 deletions

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 0baf9785c98..f76da490447 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -3632,11 +3632,14 @@ cost_qual_eval_walker(Node *node, cost_qual_eval_context *context)
 	else if (IsA(node, ArrayCoerceExpr))
 	{
 		ArrayCoerceExpr *acoerce = (ArrayCoerceExpr *) node;
-		Node	   *arraynode = (Node *) acoerce->arg;
-
-		if (OidIsValid(acoerce->elemfuncid))
-			context->total.per_tuple += get_func_cost(acoerce->elemfuncid) *
-				cpu_operator_cost * estimate_array_length(arraynode);
+		QualCost	perelemcost;
+
+		cost_qual_eval_node(&perelemcost, (Node *) acoerce->elemexpr,
+							context->root);
+		context->total.startup += perelemcost.startup;
+		if (perelemcost.per_tuple > 0)
+			context->total.per_tuple += perelemcost.per_tuple *
+				estimate_array_length((Node *) acoerce->arg);
 	}
 	else if (IsA(node, RowCompareExpr))
 	{
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index b0c9e944597..dee4414cec2 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -1395,12 +1395,6 @@ fix_expr_common(PlannerInfo *root, Node *node)
 		record_plan_function_dependency(root,
 										((ScalarArrayOpExpr *) node)->opfuncid);
 	}
-	else if (IsA(node, ArrayCoerceExpr))
-	{
-		if (OidIsValid(((ArrayCoerceExpr *) node)->elemfuncid))
-			record_plan_function_dependency(root,
-											((ArrayCoerceExpr *) node)->elemfuncid);
-	}
 	else if (IsA(node, Const))
 	{
 		Const	   *con = (Const *) node;
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
index 9d75e8612ae..d7db32ebf5e 100644
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -306,9 +306,9 @@ expand_targetlist(List *tlist, int command_type,
 						new_expr = coerce_to_domain(new_expr,
 													InvalidOid, -1,
 													atttype,
+													COERCION_IMPLICIT,
 													COERCE_IMPLICIT_CAST,
 													-1,
-													false,
 													false);
 					}
 					else
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 93add27dbe2..79613622805 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -1361,6 +1361,17 @@ contain_nonstrict_functions_walker(Node *node, void *context)
 		return true;
 	if (IsA(node, FieldStore))
 		return true;
+	if (IsA(node, ArrayCoerceExpr))
+	{
+		/*
+		 * ArrayCoerceExpr is strict at the array level, regardless of what
+		 * the per-element expression is; so we should ignore elemexpr and
+		 * recurse only into the arg.
+		 */
+		return expression_tree_walker((Node *) ((ArrayCoerceExpr *) node)->arg,
+									  contain_nonstrict_functions_walker,
+									  context);
+	}
 	if (IsA(node, CaseExpr))
 		return true;
 	if (IsA(node, ArrayExpr))
@@ -1380,14 +1391,11 @@ contain_nonstrict_functions_walker(Node *node, void *context)
 	if (IsA(node, BooleanTest))
 		return true;
 
-	/*
-	 * Check other function-containing nodes; but ArrayCoerceExpr is strict at
-	 * the array level, regardless of elemfunc.
-	 */
-	if (!IsA(node, ArrayCoerceExpr) &&
-		check_functions_in_node(node, contain_nonstrict_functions_checker,
+	/* Check other function-containing nodes */
+	if (check_functions_in_node(node, contain_nonstrict_functions_checker,
 								context))
 		return true;
+
 	return expression_tree_walker(node, contain_nonstrict_functions_walker,
 								  context);
 }
@@ -1757,7 +1765,7 @@ find_nonnullable_rels_walker(Node *node, bool top_level)
 	}
 	else if (IsA(node, ArrayCoerceExpr))
 	{
-		/* ArrayCoerceExpr is strict at the array level */
+		/* ArrayCoerceExpr is strict at the array level; ignore elemexpr */
 		ArrayCoerceExpr *expr = (ArrayCoerceExpr *) node;
 
 		result = find_nonnullable_rels_walker((Node *) expr->arg, top_level);
@@ -1965,7 +1973,7 @@ find_nonnullable_vars_walker(Node *node, bool top_level)
 	}
 	else if (IsA(node, ArrayCoerceExpr))
 	{
-		/* ArrayCoerceExpr is strict at the array level */
+		/* ArrayCoerceExpr is strict at the array level; ignore elemexpr */
 		ArrayCoerceExpr *expr = (ArrayCoerceExpr *) node;
 
 		result = find_nonnullable_vars_walker((Node *) expr->arg, top_level);
@@ -3005,32 +3013,38 @@ eval_const_expressions_mutator(Node *node,
 			{
 				ArrayCoerceExpr *expr = (ArrayCoerceExpr *) node;
 				Expr	   *arg;
+				Expr	   *elemexpr;
 				ArrayCoerceExpr *newexpr;
 
 				/*
-				 * Reduce constants in the ArrayCoerceExpr's argument, then
-				 * build a new ArrayCoerceExpr.
+				 * Reduce constants in the ArrayCoerceExpr's argument and
+				 * per-element expressions, then build a new ArrayCoerceExpr.
 				 */
 				arg = (Expr *) eval_const_expressions_mutator((Node *) expr->arg,
 															  context);
+				elemexpr = (Expr *) eval_const_expressions_mutator((Node *) expr->elemexpr,
+																   context);
 
 				newexpr = makeNode(ArrayCoerceExpr);
 				newexpr->arg = arg;
-				newexpr->elemfuncid = expr->elemfuncid;
+				newexpr->elemexpr = elemexpr;
 				newexpr->resulttype = expr->resulttype;
 				newexpr->resulttypmod = expr->resulttypmod;
 				newexpr->resultcollid = expr->resultcollid;
-				newexpr->isExplicit = expr->isExplicit;
 				newexpr->coerceformat = expr->coerceformat;
 				newexpr->location = expr->location;
 
 				/*
-				 * If constant argument and it's a binary-coercible or
-				 * immutable conversion, we can simplify it to a constant.
+				 * If constant argument and per-element expression is
+				 * immutable, we can simplify the whole thing to a constant.
+				 * Exception: although contain_mutable_functions considers
+				 * CoerceToDomain immutable for historical reasons, let's not
+				 * do so here; this ensures coercion to an array-over-domain
+				 * does not apply the domain's constraints until runtime.
 				 */
 				if (arg && IsA(arg, Const) &&
-					(!OidIsValid(newexpr->elemfuncid) ||
-					 func_volatile(newexpr->elemfuncid) == PROVOLATILE_IMMUTABLE))
+					elemexpr && !IsA(elemexpr, CoerceToDomain) &&
+					!contain_mutable_functions((Node *) elemexpr))
 					return (Node *) evaluate_expr((Expr *) newexpr,
 												  newexpr->resulttype,
 												  newexpr->resulttypmod,