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+/*-------------------------------------------------------------------------
+ *
+ * supportnodes.h
+ *	  Definitions for planner support functions.
+ *
+ * This file defines the API for "planner support functions", which
+ * are SQL functions (normally written in C) that can be attached to
+ * another "target" function to give the system additional knowledge
+ * about the target function.  All the current capabilities have to do
+ * with planning queries that use the target function, though it is
+ * possible that future extensions will add functionality to be invoked
+ * by the parser or executor.
+ *
+ * A support function must have the SQL signature
+ *		supportfn(internal) returns internal
+ * The argument is a pointer to one of the Node types defined in this file.
+ * The result is usually also a Node pointer, though its type depends on
+ * which capability is being invoked.  In all cases, a NULL pointer result
+ * (that's PG_RETURN_POINTER(NULL), not PG_RETURN_NULL()) indicates that
+ * the support function cannot do anything useful for the given request.
+ * Support functions must return a NULL pointer, not fail, if they do not
+ * recognize the request node type or cannot handle the given case; this
+ * allows for future extensions of the set of request cases.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/nodes/supportnodes.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef SUPPORTNODES_H
+#define SUPPORTNODES_H
+
+#include "nodes/primnodes.h"
+
+struct PlannerInfo;				/* avoid including pathnodes.h here */
+struct IndexOptInfo;
+struct SpecialJoinInfo;
+
+
+/*
+ * The Simplify request allows the support function to perform plan-time
+ * simplification of a call to its target function.  For example, a varchar
+ * length coercion that does not decrease the allowed length of its argument
+ * could be replaced by a RelabelType node, or "x + 0" could be replaced by
+ * "x".  This is invoked during the planner's constant-folding pass, so the
+ * function's arguments can be presumed already simplified.
+ *
+ * The planner's PlannerInfo "root" is typically not needed, but can be
+ * consulted if it's necessary to obtain info about Vars present in
+ * the given node tree.  Beware that root could be NULL in some usages.
+ *
+ * "fcall" will be a FuncExpr invoking the support function's target
+ * function.  (This is true even if the original parsetree node was an
+ * operator call; a FuncExpr is synthesized for this purpose.)
+ *
+ * The result should be a semantically-equivalent transformed node tree,
+ * or NULL if no simplification could be performed.  Do *not* return or
+ * modify *fcall, as it isn't really a separately allocated Node.  But
+ * it's okay to use fcall->args, or parts of it, in the result tree.
+ */
+typedef struct SupportRequestSimplify
+{
+	NodeTag		type;
+
+	struct PlannerInfo *root;	/* Planner's infrastructure */
+	FuncExpr   *fcall;			/* Function call to be simplified */
+} SupportRequestSimplify;
+
+/*
+ * The Selectivity request allows the support function to provide a
+ * selectivity estimate for a function appearing at top level of a WHERE
+ * clause (so it applies only to functions returning boolean).
+ *
+ * The input arguments are the same as are supplied to operator restriction
+ * and join estimators, except that we unify those two APIs into just one
+ * request type.  See clause_selectivity() for the details.
+ *
+ * If an estimate can be made, store it into the "selectivity" field and
+ * return the address of the SupportRequestSelectivity node; the estimate
+ * must be between 0 and 1 inclusive.  Return NULL if no estimate can be
+ * made (in which case the planner will fall back to a default estimate,
+ * traditionally 1/3).
+ *
+ * If the target function is being used as the implementation of an operator,
+ * the support function will not be used for this purpose; the operator's
+ * restriction or join estimator is consulted instead.
+ */
+typedef struct SupportRequestSelectivity
+{
+	NodeTag		type;
+
+	/* Input fields: */
+	struct PlannerInfo *root;	/* Planner's infrastructure */
+	Oid			funcid;			/* function we are inquiring about */
+	List	   *args;			/* pre-simplified arguments to function */
+	Oid			inputcollid;	/* function's input collation */
+	bool		is_join;		/* is this a join or restriction case? */
+	int			varRelid;		/* if restriction, RTI of target relation */
+	JoinType	jointype;		/* if join, outer join type */
+	struct SpecialJoinInfo *sjinfo; /* if outer join, info about join */
+
+	/* Output fields: */
+	Selectivity selectivity;	/* returned selectivity estimate */
+} SupportRequestSelectivity;
+
+/*
+ * The Cost request allows the support function to provide an execution
+ * cost estimate for its target function.  The cost estimate can include
+ * both a one-time (query startup) component and a per-execution component.
+ * The estimate should *not* include the costs of evaluating the target
+ * function's arguments, only the target function itself.
+ *
+ * The "node" argument is normally the parse node that is invoking the
+ * target function.  This is a FuncExpr in the simplest case, but it could
+ * also be an OpExpr, DistinctExpr, NullIfExpr, or WindowFunc, or possibly
+ * other cases in future.  NULL is passed if the function cannot presume
+ * its arguments to be equivalent to what the calling node presents as
+ * arguments; that happens for, e.g., aggregate support functions and
+ * per-column comparison operators used by RowExprs.
+ *
+ * If an estimate can be made, store it into the cost fields and return the
+ * address of the SupportRequestCost node.  Return NULL if no estimate can be
+ * made, in which case the planner will rely on the target function's procost
+ * field.  (Note: while procost is automatically scaled by cpu_operator_cost,
+ * this is not the case for the outputs of the Cost request; the support
+ * function must scale its results appropriately on its own.)
+ */
+typedef struct SupportRequestCost
+{
+	NodeTag		type;
+
+	/* Input fields: */
+	struct PlannerInfo *root;	/* Planner's infrastructure (could be NULL) */
+	Oid			funcid;			/* function we are inquiring about */
+	Node	   *node;			/* parse node invoking function, or NULL */
+
+	/* Output fields: */
+	Cost		startup;		/* one-time cost */
+	Cost		per_tuple;		/* per-evaluation cost */
+} SupportRequestCost;
+
+/*
+ * The Rows request allows the support function to provide an output rowcount
+ * estimate for its target function (so it applies only to set-returning
+ * functions).
+ *
+ * The "node" argument is the parse node that is invoking the target function;
+ * currently this will always be a FuncExpr or OpExpr.
+ *
+ * If an estimate can be made, store it into the rows field and return the
+ * address of the SupportRequestRows node.  Return NULL if no estimate can be
+ * made, in which case the planner will rely on the target function's prorows
+ * field.
+ */
+typedef struct SupportRequestRows
+{
+	NodeTag		type;
+
+	/* Input fields: */
+	struct PlannerInfo *root;	/* Planner's infrastructure (could be NULL) */
+	Oid			funcid;			/* function we are inquiring about */
+	Node	   *node;			/* parse node invoking function */
+
+	/* Output fields: */
+	double		rows;			/* number of rows expected to be returned */
+} SupportRequestRows;
+
+/*
+ * The IndexCondition request allows the support function to generate
+ * a directly-indexable condition based on a target function call that is
+ * not itself indexable.  The target function call must appear at the top
+ * level of WHERE or JOIN/ON, so this applies only to functions returning
+ * boolean.
+ *
+ * The "node" argument is the parse node that is invoking the target function;
+ * currently this will always be a FuncExpr or OpExpr.  The call is made
+ * only if at least one function argument matches an index column's variable
+ * or expression.  "indexarg" identifies the matching argument (it's the
+ * argument's zero-based index in the node's args list).
+ *
+ * If the transformation is possible, return a List of directly-indexable
+ * condition expressions, else return NULL.  (A List is used because it's
+ * sometimes useful to generate more than one indexable condition, such as
+ * when a LIKE with constant prefix gives rise to both >= and < conditions.)
+ *
+ * "Directly indexable" means that the condition must be directly executable
+ * by the index machinery.  Typically this means that it is a binary OpExpr
+ * with the index column value on the left, a pseudo-constant on the right,
+ * and an operator that is in the index column's operator family.  Other
+ * possibilities include RowCompareExpr, ScalarArrayOpExpr, and NullTest,
+ * depending on the index type; but those seem less likely to be useful for
+ * derived index conditions.  "Pseudo-constant" means that the right-hand
+ * expression must not contain any volatile functions, nor any Vars of the
+ * table the index is for; use is_pseudo_constant_for_index() to check this.
+ * (Note: if the passed "node" is an OpExpr, the core planner already verified
+ * that the non-indexkey operand is pseudo-constant; but when the "node"
+ * is a FuncExpr, it does not check, since it doesn't know which of the
+ * function's arguments you might need to use in an index comparison value.)
+ *
+ * In many cases, an index condition can be generated but it is weaker than
+ * the function condition itself; for example, a LIKE with a constant prefix
+ * can produce an index range check based on the prefix, but we still need
+ * to execute the LIKE operator to verify the rest of the pattern.  We say
+ * that such an index condition is "lossy".  When returning an index condition,
+ * you should set the "lossy" request field to true if the condition is lossy,
+ * or false if it is an exact equivalent of the function's result.  The core
+ * code will initialize that field to true, which is the common case.
+ *
+ * It is important to verify that the index operator family is the correct
+ * one for the condition you want to generate.  Core support functions tend
+ * to use the known OID of a built-in opfamily for this, but extensions need
+ * to work harder, since their OIDs aren't fixed.  A possibly workable
+ * answer for an index on an extension datatype is to verify the index AM's
+ * OID instead, and then assume that there's only one relevant opclass for
+ * your datatype so the opfamily must be the right one.  Generating OpExpr
+ * nodes may also require knowing extension datatype OIDs (often you can
+ * find these out by applying exprType() to a function argument) and
+ * operator OIDs (which you can look up using get_opfamily_member).
+ */
+typedef struct SupportRequestIndexCondition
+{
+	NodeTag		type;
+
+	/* Input fields: */
+	struct PlannerInfo *root;	/* Planner's infrastructure */
+	Oid			funcid;			/* function we are inquiring about */
+	Node	   *node;			/* parse node invoking function */
+	int			indexarg;		/* index of function arg matching indexcol */
+	struct IndexOptInfo *index; /* planner's info about target index */
+	int			indexcol;		/* index of target index column (0-based) */
+	Oid			opfamily;		/* index column's operator family */
+	Oid			indexcollation; /* index column's collation */
+
+	/* Output fields: */
+	bool		lossy;			/* set to false if index condition is an exact
+								 * equivalent of the function call */
+} SupportRequestIndexCondition;
+
+#endif							/* SUPPORTNODES_H */