parse_coerce.c

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/*-------------------------------------------------------------------------
 *
 * parse_coerce.c
 *		handle type coercions/conversions for parser
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_coerce.c,v 2.111.2.1 2003/12/17 19:49:52 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/pg_cast.h"
#include "catalog/pg_proc.h"
#include "nodes/makefuncs.h"
#include "nodes/params.h"
#include "optimizer/clauses.h"
#include "parser/parse_coerce.h"
#include "parser/parse_expr.h"
#include "parser/parse_func.h"
#include "parser/parse_type.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"


static Node *coerce_type_typmod(Node *node,
				   Oid targetTypeId, int32 targetTypMod,
				   CoercionForm cformat, bool isExplicit);


/*
 * coerce_to_target_type()
 *		Convert an expression to a target type and typmod.
 *
 * This is the general-purpose entry point for arbitrary type coercion
 * operations.	Direct use of the component operations can_coerce_type,
 * coerce_type, and coerce_type_typmod should be restricted to special
 * cases (eg, when the conversion is expected to succeed).
 *
 * Returns the possibly-transformed expression tree, or NULL if the type
 * conversion is not possible.	(We do this, rather than ereport'ing directly,
 * so that callers can generate custom error messages indicating context.)
 *
 * pstate - parse state (can be NULL, see coerce_type)
 * expr - input expression tree (already transformed by transformExpr)
 * exprtype - result type of expr
 * targettype - desired result type
 * targettypmod - desired result typmod
 * ccontext, cformat - context indicators to control coercions
 */
Node *
coerce_to_target_type(ParseState *pstate, Node *expr, Oid exprtype,
					  Oid targettype, int32 targettypmod,
					  CoercionContext ccontext,
					  CoercionForm cformat)
{
	if (can_coerce_type(1, &exprtype, &targettype, ccontext))
		expr = coerce_type(pstate, expr, exprtype, targettype,
						   ccontext, cformat);
	else if (ccontext >= COERCION_ASSIGNMENT)
	{
		/*
		 * String hacks to get transparent conversions for char and
		 * varchar: if a coercion to text is available, use it for forced
		 * coercions to char(n) or varchar(n) or domains thereof.
		 *
		 * This is pretty grotty, but seems easier to maintain than providing
		 * entries in pg_cast that parallel all the ones for text.
		 */
		Oid			targetbasetype = getBaseType(targettype);

		if (targetbasetype == BPCHAROID || targetbasetype == VARCHAROID)
		{
			Oid			text_id = TEXTOID;

			if (can_coerce_type(1, &exprtype, &text_id, ccontext))
			{
				expr = coerce_type(pstate, expr, exprtype, text_id,
								   ccontext, cformat);
				if (targetbasetype != targettype)
				{
					/* need to coerce to domain over char or varchar */
					expr = coerce_to_domain(expr, targetbasetype, targettype,
											cformat);
				}
				else
				{
					/*
					 * need a RelabelType if no typmod coercion will be
					 * performed
					 */
					if (targettypmod < 0)
						expr = (Node *) makeRelabelType((Expr *) expr,
														targettype, -1,
														cformat);
				}
			}
			else
				expr = NULL;
		}
		else
			expr = NULL;
	}
	else
		expr = NULL;

	/*
	 * If the target is a fixed-length type, it may need a length coercion
	 * as well as a type coercion.
	 */
	if (expr != NULL)
		expr = coerce_type_typmod(expr, targettype, targettypmod,
								  cformat,
								  (cformat != COERCE_IMPLICIT_CAST));

	return expr;
}


/*
 * coerce_type()
 *		Convert an expression to a different type.
 *
 * The caller should already have determined that the coercion is possible;
 * see can_coerce_type.
 *
 * No coercion to a typmod (length) is performed here.	The caller must
 * call coerce_type_typmod as well, if a typmod constraint is wanted.
 * (But if the target type is a domain, it may internally contain a
 * typmod constraint, which will be applied inside coerce_to_domain.)
 *
 * pstate is only used in the case that we are able to resolve the type of
 * a previously UNKNOWN Param.	It is okay to pass pstate = NULL if the
 * caller does not want type information updated for Params.
 */
Node *
coerce_type(ParseState *pstate, Node *node,
			Oid inputTypeId, Oid targetTypeId,
			CoercionContext ccontext, CoercionForm cformat)
{
	Node	   *result;
	Oid			funcId;

	if (targetTypeId == inputTypeId ||
		node == NULL)
	{
		/* no conversion needed */
		return node;
	}
	if (targetTypeId == ANYOID ||
		targetTypeId == ANYARRAYOID ||
		targetTypeId == ANYELEMENTOID)
	{
		/* assume can_coerce_type verified that implicit coercion is okay */
		/* NB: we do NOT want a RelabelType here */
		return node;
	}
	if (inputTypeId == UNKNOWNOID && IsA(node, Const))
	{
		/*
		 * Input is a string constant with previously undetermined type.
		 * Apply the target type's typinput function to it to produce a
		 * constant of the target type.
		 *
		 * NOTE: this case cannot be folded together with the other
		 * constant-input case, since the typinput function does not
		 * necessarily behave the same as a type conversion function. For
		 * example, int4's typinput function will reject "1.2", whereas
		 * float-to-int type conversion will round to integer.
		 *
		 * XXX if the typinput function is not immutable, we really ought to
		 * postpone evaluation of the function call until runtime. But
		 * there is no way to represent a typinput function call as an
		 * expression tree, because C-string values are not Datums. (XXX
		 * This *is* possible as of 7.3, do we want to do it?)
		 */
		Const	   *con = (Const *) node;
		Const	   *newcon = makeNode(Const);
		Type		targetType = typeidType(targetTypeId);
		char		targetTyptype = typeTypType(targetType);

		newcon->consttype = targetTypeId;
		newcon->constlen = typeLen(targetType);
		newcon->constbyval = typeByVal(targetType);
		newcon->constisnull = con->constisnull;

		if (!con->constisnull)
		{
			char	   *val = DatumGetCString(DirectFunctionCall1(unknownout,
													   con->constvalue));

			/*
			 * We pass typmod -1 to the input routine, primarily because
			 * existing input routines follow implicit-coercion semantics
			 * for length checks, which is not always what we want here.
			 * Any length constraint will be applied later by our caller.
			 *
			 * Note that we call stringTypeDatum using the domain's pg_type
			 * row, if it's a domain.  This works because the domain row
			 * has the same typinput and typelem as the base type ---
			 * ugly...
			 */
			newcon->constvalue = stringTypeDatum(targetType, val, -1);
			pfree(val);
		}

		result = (Node *) newcon;

		/* If target is a domain, apply constraints. */
		if (targetTyptype == 'd')
			result = coerce_to_domain(result, InvalidOid, targetTypeId,
									  cformat);

		ReleaseSysCache(targetType);

		return result;
	}
	if (inputTypeId == UNKNOWNOID && IsA(node, Param) &&
		((Param *) node)->paramkind == PARAM_NUM &&
		pstate != NULL && pstate->p_variableparams)
	{
		/*
		 * Input is a Param of previously undetermined type, and we want
		 * to update our knowledge of the Param's type.  Find the topmost
		 * ParseState and update the state.
		 */
		Param	   *param = (Param *) node;
		int			paramno = param->paramid;
		ParseState *toppstate;

		toppstate = pstate;
		while (toppstate->parentParseState != NULL)
			toppstate = toppstate->parentParseState;

		if (paramno <= 0 ||		/* shouldn't happen, but... */
			paramno > toppstate->p_numparams)
			ereport(ERROR,
					(errcode(ERRCODE_UNDEFINED_PARAMETER),
					 errmsg("there is no parameter $%d", paramno)));

		if (toppstate->p_paramtypes[paramno - 1] == UNKNOWNOID)
		{
			/* We've successfully resolved the type */
			toppstate->p_paramtypes[paramno - 1] = targetTypeId;
		}
		else if (toppstate->p_paramtypes[paramno - 1] == targetTypeId)
		{
			/* We previously resolved the type, and it matches */
		}
		else
		{
			/* Ooops */
			ereport(ERROR,
					(errcode(ERRCODE_AMBIGUOUS_PARAMETER),
				   errmsg("inconsistent types deduced for parameter $%d",
						  paramno),
					 errdetail("%s versus %s",
					format_type_be(toppstate->p_paramtypes[paramno - 1]),
							   format_type_be(targetTypeId))));
		}

		param->paramtype = targetTypeId;
		return (Node *) param;
	}
	if (find_coercion_pathway(targetTypeId, inputTypeId, ccontext,
							  &funcId))
	{
		if (OidIsValid(funcId))
		{
			/*
			 * Generate an expression tree representing run-time
			 * application of the conversion function.	If we are dealing
			 * with a domain target type, the conversion function will
			 * yield the base type.
			 */
			Oid			baseTypeId = getBaseType(targetTypeId);

			result = (Node *) makeFuncExpr(funcId, baseTypeId,
										   makeList1(node),
										   cformat);

			/*
			 * If domain, coerce to the domain type and relabel with
			 * domain type ID
			 */
			if (targetTypeId != baseTypeId)
				result = coerce_to_domain(result, baseTypeId, targetTypeId,
										  cformat);
		}
		else
		{
			/*
			 * We don't need to do a physical conversion, but we do need
			 * to attach a RelabelType node so that the expression will be
			 * seen to have the intended type when inspected by
			 * higher-level code.
			 *
			 * Also, domains may have value restrictions beyond the base type
			 * that must be accounted for.	If the destination is a domain
			 * then we won't need a RelabelType node.
			 */
			result = coerce_to_domain(node, InvalidOid, targetTypeId,
									  cformat);
			if (result == node)
			{
				/*
				 * XXX could we label result with exprTypmod(node) instead
				 * of default -1 typmod, to save a possible
				 * length-coercion later? Would work if both types have
				 * same interpretation of typmod, which is likely but not
				 * certain.
				 */
				result = (Node *) makeRelabelType((Expr *) result,
												  targetTypeId, -1,
												  cformat);
			}
		}
		return result;
	}
	if (typeInheritsFrom(inputTypeId, targetTypeId))
	{
		/*
		 * Input class type is a subclass of target, so nothing to do ---
		 * except relabel the type.  This is binary compatibility for
		 * complex types.
		 */
		return (Node *) makeRelabelType((Expr *) node,
										targetTypeId, -1,
										cformat);
	}
	/* If we get here, caller blew it */
	elog(ERROR, "failed to find conversion function from %s to %s",
		 format_type_be(inputTypeId), format_type_be(targetTypeId));
	return NULL;				/* keep compiler quiet */
}


/*
 * can_coerce_type()
 *		Can input_typeids be coerced to target_typeids?
 *
 * We must be told the context (CAST construct, assignment, implicit coercion)
 * as this determines the set of available casts.
 */
bool
can_coerce_type(int nargs, Oid *input_typeids, Oid *target_typeids,
				CoercionContext ccontext)
{
	bool		have_generics = false;
	int			i;

	/* run through argument list... */
	for (i = 0; i < nargs; i++)
	{
		Oid			inputTypeId = input_typeids[i];
		Oid			targetTypeId = target_typeids[i];
		Oid			funcId;

		/* no problem if same type */
		if (inputTypeId == targetTypeId)
			continue;

		/* don't choke on references to no-longer-existing types */
		if (!typeidIsValid(inputTypeId))
			return false;
		if (!typeidIsValid(targetTypeId))
			return false;

		/* accept if target is ANY */
		if (targetTypeId == ANYOID)
			continue;

		/* accept if target is ANYARRAY or ANYELEMENT, for now */
		if (targetTypeId == ANYARRAYOID ||
			targetTypeId == ANYELEMENTOID)
		{
			have_generics = true;		/* do more checking later */
			continue;
		}

		/*
		 * If input is an untyped string constant, assume we can convert
		 * it to anything except a class type.
		 */
		if (inputTypeId == UNKNOWNOID)
		{
			if (ISCOMPLEX(targetTypeId))
				return false;
			continue;
		}

		/*
		 * If pg_cast shows that we can coerce, accept.  This test now
		 * covers both binary-compatible and coercion-function cases.
		 */
		if (find_coercion_pathway(targetTypeId, inputTypeId, ccontext,
								  &funcId))
			continue;

		/*
		 * If input is a class type that inherits from target, accept
		 */
		if (typeInheritsFrom(inputTypeId, targetTypeId))
			continue;

		/*
		 * Else, cannot coerce at this argument position
		 */
		return false;
	}

	/* If we found any generic argument types, cross-check them */
	if (have_generics)
	{
		if (!check_generic_type_consistency(input_typeids, target_typeids,
											nargs))
			return false;
	}

	return true;
}


/*
 * Create an expression tree to represent coercion to a domain type.
 *
 * 'arg': input expression
 * 'baseTypeId': base type of domain, if known (pass InvalidOid if caller
 *		has not bothered to look this up)
 * 'typeId': target type to coerce to
 * 'cformat': coercion format
 *
 * If the target type isn't a domain, the given 'arg' is returned as-is.
 */
Node *
coerce_to_domain(Node *arg, Oid baseTypeId, Oid typeId, CoercionForm cformat)
{
	CoerceToDomain *result;
	int32		typmod;

	/* Get the base type if it hasn't been supplied */
	if (baseTypeId == InvalidOid)
		baseTypeId = getBaseType(typeId);

	/* If it isn't a domain, return the node as it was passed in */
	if (baseTypeId == typeId)
		return arg;

	/*
	 * If the domain applies a typmod to its base type, build the
	 * appropriate coercion step.  Mark it implicit for display purposes,
	 * because we don't want it shown separately by ruleutils.c; but the
	 * isExplicit flag passed to the conversion function depends on the
	 * manner in which the domain coercion is invoked, so that the
	 * semantics of implicit and explicit coercion differ.	(Is that
	 * really the behavior we want?)
	 *
	 * NOTE: because we apply this as part of the fixed expression structure,
	 * ALTER DOMAIN cannot alter the typtypmod.  But it's unclear that
	 * that would be safe to do anyway, without lots of knowledge about
	 * what the base type thinks the typmod means.
	 */
	typmod = get_typtypmod(typeId);
	if (typmod >= 0)
		arg = coerce_type_typmod(arg, baseTypeId, typmod,
								 COERCE_IMPLICIT_CAST,
								 (cformat != COERCE_IMPLICIT_CAST));

	/*
	 * Now build the domain coercion node.	This represents run-time
	 * checking of any constraints currently attached to the domain.  This
	 * also ensures that the expression is properly labeled as to result
	 * type.
	 */
	result = makeNode(CoerceToDomain);
	result->arg = (Expr *) arg;
	result->resulttype = typeId;
	result->resulttypmod = -1;	/* currently, always -1 for domains */
	result->coercionformat = cformat;

	return (Node *) result;
}


/*
 * coerce_type_typmod()
 *		Force a value to a particular typmod, if meaningful and possible.
 *
 * This is applied to values that are going to be stored in a relation
 * (where we have an atttypmod for the column) as well as values being
 * explicitly CASTed (where the typmod comes from the target type spec).
 *
 * The caller must have already ensured that the value is of the correct
 * type, typically by applying coerce_type.
 *
 * NOTE: this does not need to work on domain types, because any typmod
 * coercion for a domain is considered to be part of the type coercion
 * needed to produce the domain value in the first place.  So, no getBaseType.
 */
static Node *
coerce_type_typmod(Node *node, Oid targetTypeId, int32 targetTypMod,
				   CoercionForm cformat, bool isExplicit)
{
	Oid			funcId;
	int			nargs;

	/*
	 * A negative typmod is assumed to mean that no coercion is wanted.
	 */
	if (targetTypMod < 0 || targetTypMod == exprTypmod(node))
		return node;

	funcId = find_typmod_coercion_function(targetTypeId, &nargs);

	if (OidIsValid(funcId))
	{
		List	   *args;
		Const	   *cons;

		/* Pass given value, plus target typmod as an int4 constant */
		cons = makeConst(INT4OID,
						 sizeof(int32),
						 Int32GetDatum(targetTypMod),
						 false,
						 true);

		args = makeList2(node, cons);

		if (nargs == 3)