Remove gen_node_support.pl's special treatment of EquivalenceClasses.

It seems better to deal with this by explicit annotations on the
fields in question, instead of magic knowledge embedded in the
script.  While that creates a risk-of-omission from failing to
annotate fields, the preceding commit should catch any such
oversights.

Discussion: https://postgr.es/m/263413.1669513145@sss.pgh.pa.us

src/backend/nodes/gen_node_support.pl

@@ -171,9 +171,6 @@ my @custom_read_write;
 # Track node types with manually assigned NodeTag numbers.
 my %manual_nodetag_number;
 
-# EquivalenceClasses are never moved, so just shallow-copy the pointer
-push @scalar_types, qw(EquivalenceClass* EquivalenceMember*);
-
 # This is a struct, so we can copy it by assignment.  Equal support is
 # currently not required.
 push @scalar_types, qw(QualCost);
@@ -454,9 +451,14 @@ foreach my $infile (@ARGV)
 								&& $attr !~ /^copy_as\(\w+\)$/
 								&& $attr !~ /^read_as\(\w+\)$/
 								&& !elem $attr,
-								qw(equal_ignore equal_ignore_if_zero read_write_ignore
+								qw(copy_as_scalar
-								write_only_relids write_only_nondefault_pathtarget write_only_req_outer)
+								equal_as_scalar
-							  )
+								equal_ignore
+								equal_ignore_if_zero
+								read_write_ignore
+								write_only_relids
+								write_only_nondefault_pathtarget
+								write_only_req_outer))
 							{
 								die
 								  "$infile:$lineno: unrecognized attribute \"$attr\"\n";
@@ -691,6 +693,8 @@ _equal${n}(const $n *a, const $n *b)
 		# extract per-field attributes
 		my $array_size_field;
 		my $copy_as_field;
+		my $copy_as_scalar  = 0;
+		my $equal_as_scalar = 0;
 		foreach my $a (@a)
 		{
 			if ($a =~ /^array_size\(([\w.]+)\)$/)
@@ -705,19 +709,41 @@ _equal${n}(const $n *a, const $n *b)
 			{
 				$copy_as_field = $1;
 			}
+			elsif ($a eq 'copy_as_scalar')
+			{
+				$copy_as_scalar = 1;
+			}
+			elsif ($a eq 'equal_as_scalar')
+			{
+				$equal_as_scalar = 1;
+			}
 			elsif ($a eq 'equal_ignore')
 			{
 				$equal_ignore = 1;
 			}
 		}
 
-		# override type-specific copy method if copy_as is specified
+		# override type-specific copy method if requested
 		if (defined $copy_as_field)
 		{
 			print $cff "\tnewnode->$f = $copy_as_field;\n"
 			  unless $copy_ignore;
 			$copy_ignore = 1;
 		}
+		elsif ($copy_as_scalar)
+		{
+			print $cff "\tCOPY_SCALAR_FIELD($f);\n"
+			  unless $copy_ignore;
+			$copy_ignore = 1;
+		}
+
+		# override type-specific equal method if requested
+		if ($equal_as_scalar)
+		{
+			print $eff "\tCOMPARE_SCALAR_FIELD($f);\n"
+			  unless $equal_ignore;
+			$equal_ignore = 1;
+		}
 
 		# select instructions by field type
 		if ($t eq 'char*')

src/include/nodes/nodes.h

@@ -86,6 +86,12 @@ typedef enum NodeTag
  *
  * - copy_as(VALUE): In copyObject(), replace the field's value with VALUE.
  *
+ * - copy_as_scalar: In copyObject(), copy the field as a scalar value
+ *   (e.g. a pointer) even if it is a node-type pointer.
+ *
+ * - equal_as_scalar: In equal(), compare the field as a scalar value
+ *   even if it is a node-type pointer.
+ *
  * - equal_ignore: Ignore the field for equality.
  *
  * - equal_ignore_if_zero: Ignore the field for equality if it is zero.

src/include/nodes/pathnodes.h

@@ -1279,7 +1279,9 @@ typedef struct StatisticExtInfo
  *
  * NB: EquivalenceClasses are never copied after creation.  Therefore,
  * copyObject() copies pointers to them as pointers, and equal() compares
- * pointers to EquivalenceClasses via pointer equality.
+ * pointers to EquivalenceClasses via pointer equality.  This is implemented
+ * by putting copy_as_scalar and equal_as_scalar attributes on fields that
+ * are pointers to EquivalenceClasses.  The same goes for EquivalenceMembers.
  */
 typedef struct EquivalenceClass
 {
@@ -1370,7 +1372,8 @@ typedef struct PathKey
 
 	NodeTag		type;
 
-	EquivalenceClass *pk_eclass;	/* the value that is ordered */
+	/* the value that is ordered */
+	EquivalenceClass *pk_eclass pg_node_attr(copy_as_scalar, equal_as_scalar);
 	Oid			pk_opfamily;	/* btree opfamily defining the ordering */
 	int			pk_strategy;	/* sort direction (ASC or DESC) */
 	bool		pk_nulls_first; /* do NULLs come before normal values? */
@@ -2478,7 +2481,7 @@ typedef struct RestrictInfo
 	 * Generating EquivalenceClass.  This field is NULL unless clause is
 	 * potentially redundant.
 	 */
-	EquivalenceClass *parent_ec pg_node_attr(equal_ignore, read_write_ignore);
+	EquivalenceClass *parent_ec pg_node_attr(copy_as_scalar, equal_ignore, read_write_ignore);
 
 	/*
 	 * cache space for cost and selectivity
@@ -2506,13 +2509,13 @@ typedef struct RestrictInfo
 	 */
 
 	/* EquivalenceClass containing lefthand */
-	EquivalenceClass *left_ec pg_node_attr(equal_ignore, read_write_ignore);
+	EquivalenceClass *left_ec pg_node_attr(copy_as_scalar, equal_ignore, read_write_ignore);
 	/* EquivalenceClass containing righthand */
-	EquivalenceClass *right_ec pg_node_attr(equal_ignore, read_write_ignore);
+	EquivalenceClass *right_ec pg_node_attr(copy_as_scalar, equal_ignore, read_write_ignore);
 	/* EquivalenceMember for lefthand */
-	EquivalenceMember *left_em pg_node_attr(equal_ignore);
+	EquivalenceMember *left_em pg_node_attr(copy_as_scalar, equal_ignore);
 	/* EquivalenceMember for righthand */
-	EquivalenceMember *right_em pg_node_attr(equal_ignore);
+	EquivalenceMember *right_em pg_node_attr(copy_as_scalar, equal_ignore);
 
 	/*
 	 * List of MergeScanSelCache structs.  Those aren't Nodes, so hard to