本節繼續介紹PostgreSQL的語法分析定義檔案gram.y的第四部分User subroutines(使用者自定義例程).
Bison輸入檔案的組成:
```
%{
Declarations
%}
Definitions
%%
Productions
%%
User subroutines
```

### 一、User subroutines
使用者自定義例程會原封不動的複製到gram.c檔案中,詳細請參考gram.c檔案.

### 二、原始碼
下面是gram.y使用者自定義部分的原始碼
```

/*
 * The signature of this function is required by bison.  However, we
 * ignore the passed yylloc and instead use the last token position
 * available from the scanner.
 */
static void
base_yyerror(YYLTYPE *yylloc, core_yyscan_t yyscanner, const char *msg)
{
	parser_yyerror(msg);
}

static RawStmt *
makeRawStmt(Node *stmt, int stmt_location)
{
	RawStmt    *rs = makeNode(RawStmt);

rs->stmt = stmt;
	rs->stmt_location = stmt_location;
	rs->stmt_len = 0;			/* might get changed later */
	return rs;
}

/* Adjust a RawStmt to reflect that it doesn't run to the end of the string */
static void
updateRawStmtEnd(RawStmt *rs, int end_location)
{
	/*
	 * If we already set the length, don't change it.  This is for situations
	 * like "select foo ;; select bar" where the same statement will be last
	 * in the string for more than one semicolon.
	 */
	if (rs->stmt_len > 0)
		return;

/* OK, update length of RawStmt */
	rs->stmt_len = end_location - rs->stmt_location;
}

static Node *
makeColumnRef(char *colname, List *indirection,
			  int location, core_yyscan_t yyscanner)
{
	/*
	 * Generate a ColumnRef node, with an A_Indirection node added if there
	 * is any subscripting in the specified indirection list.  However,
	 * any field selection at the start of the indirection list must be
	 * transposed into the "fields" part of the ColumnRef node.
	 */
	ColumnRef  *c = makeNode(ColumnRef);
	int		nfields = 0;
	ListCell *l;

c->location = location;
	foreach(l, indirection)
	{
		if (IsA(lfirst(l), A_Indices))
		{
			A_Indirection *i = makeNode(A_Indirection);

if (nfields == 0)
			{
				/* easy case - all indirection goes to A_Indirection */
				c->fields = list_make1(makeString(colname));
				i->indirection = check_indirection(indirection, yyscanner);
			}
			else
			{
				/* got to split the list in two */
				i->indirection = check_indirection(list_copy_tail(indirection,
																  nfields),
												   yyscanner);
				indirection = list_truncate(indirection, nfields);
				c->fields = lcons(makeString(colname), indirection);
			}
			i->arg = (Node *) c;
			return (Node *) i;
		}
		else if (IsA(lfirst(l), A_Star))
		{
			/* We only allow '*' at the end of a ColumnRef */
			if (lnext(l) != NULL)
				parser_yyerror("improper use of \"*\"");
		}
		nfields++;
	}
	/* No subscripting, so all indirection gets added to field list */
	c->fields = lcons(makeString(colname), indirection);
	return (Node *) c;
}

static Node *
makeTypeCast(Node *arg, TypeName *typename, int location)
{
	TypeCast *n = makeNode(TypeCast);
	n->arg = arg;
	n->typeName = typename;
	n->location = location;
	return (Node *) n;
}

static Node *
makeStringConst(char *str, int location)
{
	A_Const *n = makeNode(A_Const);

n->val.type = T_String;
	n->val.val.str = str;
	n->location = location;

return (Node *)n;
}

static Node *
makeStringConstCast(char *str, int location, TypeName *typename)
{
	Node *s = makeStringConst(str, location);

return makeTypeCast(s, typename, -1);
}

static Node *
makeIntConst(int val, int location)
{
	A_Const *n = makeNode(A_Const);

n->val.type = T_Integer;
	n->val.val.ival = val;
	n->location = location;

return (Node *)n;
}

static Node *
makeFloatConst(char *str, int location)
{
	A_Const *n = makeNode(A_Const);

n->val.type = T_Float;
	n->val.val.str = str;
	n->location = location;

return (Node *)n;
}

static Node *
makeBitStringConst(char *str, int location)
{
	A_Const *n = makeNode(A_Const);

n->val.type = T_BitString;
	n->val.val.str = str;
	n->location = location;

return (Node *)n;
}

static Node *
makeNullAConst(int location)
{
	A_Const *n = makeNode(A_Const);

n->val.type = T_Null;
	n->location = location;

return (Node *)n;
}

static Node *
makeAConst(Value *v, int location)
{
	Node *n;

switch (v->type)
	{
		case T_Float:
			n = makeFloatConst(v->val.str, location);
			break;

case T_Integer:
			n = makeIntConst(v->val.ival, location);
			break;

case T_String:
		default:
			n = makeStringConst(v->val.str, location);
			break;
	}

return n;
}

/* makeBoolAConst()
 * Create an A_Const string node and put it inside a boolean cast.
 */
static Node *
makeBoolAConst(bool state, int location)
{
	A_Const *n = makeNode(A_Const);

n->val.type = T_String;
	n->val.val.str = (state ? "t" : "f");
	n->location = location;

return makeTypeCast((Node *)n, SystemTypeName("bool"), -1);
}

/* makeRoleSpec
 * Create a RoleSpec with the given type
 */
static RoleSpec *
makeRoleSpec(RoleSpecType type, int location)
{
	RoleSpec *spec = makeNode(RoleSpec);

spec->roletype = type;
	spec->location = location;

return spec;
}

/* check_qualified_name --- check the result of qualified_name production
 *
 * It's easiest to let the grammar production for qualified_name allow
 * subscripts and '*', which we then must reject here.
 */
static void
check_qualified_name(List *names, core_yyscan_t yyscanner)
{
	ListCell   *i;

foreach(i, names)
	{
		if (!IsA(lfirst(i), String))
			parser_yyerror("syntax error");
	}
}

/* check_func_name --- check the result of func_name production
 *
 * It's easiest to let the grammar production for func_name allow subscripts
 * and '*', which we then must reject here.
 */
static List *
check_func_name(List *names, core_yyscan_t yyscanner)
{
	ListCell   *i;

foreach(i, names)
	{
		if (!IsA(lfirst(i), String))
			parser_yyerror("syntax error");
	}
	return names;
}

/* check_indirection --- check the result of indirection production
 *
 * We only allow '*' at the end of the list, but it's hard to enforce that
 * in the grammar, so do it here.
 */
static List *
check_indirection(List *indirection, core_yyscan_t yyscanner)
{
	ListCell *l;

foreach(l, indirection)
	{
		if (IsA(lfirst(l), A_Star))
		{
			if (lnext(l) != NULL)
				parser_yyerror("improper use of \"*\"");
		}
	}
	return indirection;
}

/* extractArgTypes()
 * Given a list of FunctionParameter nodes, extract a list of just the
 * argument types (TypeNames) for input parameters only.  This is what
 * is needed to look up an existing function, which is what is wanted by
 * the productions that use this call.
 */
static List *
extractArgTypes(List *parameters)
{
	List	   *result = NIL;
	ListCell   *i;

foreach(i, parameters)
	{
		FunctionParameter *p = (FunctionParameter *) lfirst(i);

if (p->mode != FUNC_PARAM_OUT && p->mode != FUNC_PARAM_TABLE)
			result = lappend(result, p->argType);
	}
	return result;
}

/* extractAggrArgTypes()
 * As above, but work from the output of the aggr_args production.
 */
static List *
extractAggrArgTypes(List *aggrargs)
{
	Assert(list_length(aggrargs) == 2);
	return extractArgTypes((List *) linitial(aggrargs));
}

/* makeOrderedSetArgs()
 * Build the result of the aggr_args production (which see the comments for).
 * This handles only the case where both given lists are nonempty, so that
 * we have to deal with multiple VARIADIC arguments.
 */
static List *
makeOrderedSetArgs(List *directargs, List *orderedargs,
				   core_yyscan_t yyscanner)
{
	FunctionParameter *lastd = (FunctionParameter *) llast(directargs);
	int			ndirectargs;

/* No restriction unless last direct arg is VARIADIC */
	if (lastd->mode == FUNC_PARAM_VARIADIC)
	{
		FunctionParameter *firsto = (FunctionParameter *) linitial(orderedargs);

/*
		 * We ignore the names, though the aggr_arg production allows them;
		 * it doesn't allow default values, so those need not be checked.
		 */
		if (list_length(orderedargs) != 1 ||
			firsto->mode != FUNC_PARAM_VARIADIC ||
			!equal(lastd->argType, firsto->argType))
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 errmsg("an ordered-set aggregate with a VARIADIC direct argument must have one VARIADIC aggregated argument of the same data type"),
					 parser_errposition(exprLocation((Node *) firsto))));

/* OK, drop the duplicate VARIADIC argument from the internal form */
		orderedargs = NIL;
	}

/* don't merge into the next line, as list_concat changes directargs */
	ndirectargs = list_length(directargs);

return list_make2(list_concat(directargs, orderedargs),
					  makeInteger(ndirectargs));
}

/* insertSelectOptions()
 * Insert ORDER BY, etc into an already-constructed SelectStmt.
 *
 * This routine is just to avoid duplicating code in SelectStmt productions.
 */
static void
insertSelectOptions(SelectStmt *stmt,
					List *sortClause, List *lockingClause,
					Node *limitOffset, Node *limitCount,
					WithClause *withClause,
					core_yyscan_t yyscanner)
{
	Assert(IsA(stmt, SelectStmt));

/*
	 * Tests here are to reject constructs like
	 *	(SELECT foo ORDER BY bar) ORDER BY baz
	 */
	if (sortClause)
	{
		if (stmt->sortClause)
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("multiple ORDER BY clauses not allowed"),
					 parser_errposition(exprLocation((Node *) sortClause))));
		stmt->sortClause = sortClause;
	}
	/* We can handle multiple locking clauses, though */
	stmt->lockingClause = list_concat(stmt->lockingClause, lockingClause);
	if (limitOffset)
	{
		if (stmt->limitOffset)
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("multiple OFFSET clauses not allowed"),
					 parser_errposition(exprLocation(limitOffset))));
		stmt->limitOffset = limitOffset;
	}
	if (limitCount)
	{
		if (stmt->limitCount)
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("multiple LIMIT clauses not allowed"),
					 parser_errposition(exprLocation(limitCount))));
		stmt->limitCount = limitCount;
	}
	if (withClause)
	{
		if (stmt->withClause)
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("multiple WITH clauses not allowed"),
					 parser_errposition(exprLocation((Node *) withClause))));
		stmt->withClause = withClause;
	}
}

static Node *
makeSetOp(SetOperation op, bool all, Node *larg, Node *rarg)
{
	SelectStmt *n = makeNode(SelectStmt);

n->op = op;
	n->all = all;
	n->larg = (SelectStmt *) larg;
	n->rarg = (SelectStmt *) rarg;
	return (Node *) n;
}

/* SystemFuncName()
 * Build a properly-qualified reference to a built-in function.
 */
List *
SystemFuncName(char *name)
{
	return list_make2(makeString("pg_catalog"), makeString(name));
}

/* SystemTypeName()
 * Build a properly-qualified reference to a built-in type.
 *
 * typmod is defaulted, but may be changed afterwards by caller.
 * Likewise for the location.
 */
TypeName *
SystemTypeName(char *name)
{
	return makeTypeNameFromNameList(list_make2(makeString("pg_catalog"),
											   makeString(name)));
}

/* doNegate()
 * Handle negation of a numeric constant.
 *
 * Formerly, we did this here because the optimizer couldn't cope with
 * indexquals that looked like "var = -4" --- it wants "var = const"
 * and a unary minus operator applied to a constant didn't qualify.
 * As of Postgres 7.0, that problem doesn't exist anymore because there
 * is a constant-subexpression simplifier in the optimizer.  However,
 * there's still a good reason for doing this here, which is that we can
 * postpone committing to a particular internal representation for simple
 * negative constants.	It's better to leave "-123.456" in string form
 * until we know what the desired type is.
 */
static Node *
doNegate(Node *n, int location)
{
	if (IsA(n, A_Const))
	{
		A_Const *con = (A_Const *)n;

/* report the constant's location as that of the '-' sign */
		con->location = location;

if (con->val.type == T_Integer)
		{
			con->val.val.ival = -con->val.val.ival;
			return n;
		}
		if (con->val.type == T_Float)
		{
			doNegateFloat(&con->val);
			return n;
		}
	}

return (Node *) makeSimpleA_Expr(AEXPR_OP, "-", NULL, n, location);
}

static void
doNegateFloat(Value *v)
{
	char   *oldval = v->val.str;

Assert(IsA(v, Float));
	if (*oldval == '+')
		oldval++;
	if (*oldval == '-')
		v->val.str = oldval+1;	/* just strip the '-' */
	else
		v->val.str = psprintf("-%s", oldval);
}

static Node *
makeAndExpr(Node *lexpr, Node *rexpr, int location)
{
	Node	   *lexp = lexpr;

/* Look through AEXPR_PAREN nodes so they don't affect flattening */
	while (IsA(lexp, A_Expr) &&
		   ((A_Expr *) lexp)->kind == AEXPR_PAREN)
		lexp = ((A_Expr *) lexp)->lexpr;
	/* Flatten "a AND b AND c ..." to a single BoolExpr on sight */
	if (IsA(lexp, BoolExpr))
	{
		BoolExpr *blexpr = (BoolExpr *) lexp;

if (blexpr->boolop == AND_EXPR)
		{
			blexpr->args = lappend(blexpr->args, rexpr);
			return (Node *) blexpr;
		}
	}
	return (Node *) makeBoolExpr(AND_EXPR, list_make2(lexpr, rexpr), location);
}

static Node *
makeOrExpr(Node *lexpr, Node *rexpr, int location)
{
	Node	   *lexp = lexpr;

/* Look through AEXPR_PAREN nodes so they don't affect flattening */
	while (IsA(lexp, A_Expr) &&
		   ((A_Expr *) lexp)->kind == AEXPR_PAREN)
		lexp = ((A_Expr *) lexp)->lexpr;
	/* Flatten "a OR b OR c ..." to a single BoolExpr on sight */
	if (IsA(lexp, BoolExpr))
	{
		BoolExpr *blexpr = (BoolExpr *) lexp;

if (blexpr->boolop == OR_EXPR)
		{
			blexpr->args = lappend(blexpr->args, rexpr);
			return (Node *) blexpr;
		}
	}
	return (Node *) makeBoolExpr(OR_EXPR, list_make2(lexpr, rexpr), location);
}

static Node *
makeNotExpr(Node *expr, int location)
{
	return (Node *) makeBoolExpr(NOT_EXPR, list_make1(expr), location);
}

static Node *
makeAArrayExpr(List *elements, int location)
{
	A_ArrayExpr *n = makeNode(A_ArrayExpr);

n->elements = elements;
	n->location = location;
	return (Node *) n;
}

static Node *
makeSQLValueFunction(SQLValueFunctionOp op, int32 typmod, int location)
{
	SQLValueFunction *svf = makeNode(SQLValueFunction);

svf->op = op;
	/* svf->type will be filled during parse anaXXXis */
	svf->typmod = typmod;
	svf->location = location;
	return (Node *) svf;
}

static Node *
makeXmlExpr(XmlExprOp op, char *name, List *named_args, List *args,
			int location)
{
	XmlExpr		*x = makeNode(XmlExpr);

x->op = op;
	x->name = name;
	/*
	 * named_args is a list of ResTarget; it'll be split apart into separate
	 * expression and name lists in transformXmlExpr().
	 */
	x->named_args = named_args;
	x->arg_names = NIL;
	x->args = args;
	/* xmloption, if relevant, must be filled in by caller */
	/* type and typmod will be filled in during parse anaXXXis */
	x->type = InvalidOid;			/* marks the node as not analyzed */
	x->location = location;
	return (Node *) x;
}

/*
 * Merge the input and output parameters of a table function.
 */
static List *
mergeTableFuncParameters(List *func_args, List *columns)
{
	ListCell   *lc;

/* Explicit OUT and INOUT parameters shouldn't be used in this syntax */
	foreach(lc, func_args)
	{
		FunctionParameter *p = (FunctionParameter *) lfirst(lc);

if (p->mode != FUNC_PARAM_IN && p->mode != FUNC_PARAM_VARIADIC)
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("OUT and INOUT arguments aren't allowed in TABLE functions")));
	}

return list_concat(func_args, columns);
}

/*
 * Determine return type of a TABLE function.  A single result column
 * returns setof that column's type; otherwise return setof record.
 */
static TypeName *
TableFuncTypeName(List *columns)
{
	TypeName *result;

if (list_length(columns) == 1)
	{
		FunctionParameter *p = (FunctionParameter *) linitial(columns);

result = copyObject(p->argType);
	}
	else
		result = SystemTypeName("record");

result->setof = true;

return result;
}

/*
 * Convert a list of (dotted) names to a RangeVar (like
 * makeRangeVarFromNameList, but with position support).  The
 * "AnyName" refers to the any_name production in the grammar.
 */
static RangeVar *
makeRangeVarFromAnyName(List *names, int position, core_yyscan_t yyscanner)
{
	RangeVar *r = makeNode(RangeVar);

switch (list_length(names))
	{
		case 1:
			r->catalogname = NULL;
			r->schemaname = NULL;
			r->relname = strVal(linitial(names));
			break;
		case 2:
			r->catalogname = NULL;
			r->schemaname = strVal(linitial(names));
			r->relname = strVal(lsecond(names));
			break;
		case 3:
			r->catalogname = strVal(linitial(names));
			r->schemaname = strVal(lsecond(names));
			r->relname = strVal(lthird(names));
			break;
		default:
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("improper qualified name (too many dotted names): %s",
							NameListToString(names)),
					 parser_errposition(position)));
			break;
	}

r->relpersistence = RELPERSISTENCE_PERMANENT;
	r->location = position;

return r;
}

/* Separate Constraint nodes from COLLATE clauses in a ColQualList */
static void
SplitColQualList(List *qualList,
				 List **constraintList, CollateClause **collClause,
				 core_yyscan_t yyscanner)
{
	ListCell   *cell;
	ListCell   *prev;
	ListCell   *next;

*collClause = NULL;
	prev = NULL;
	for (cell = list_head(qualList); cell; cell = next)
	{
		Node   *n = (Node *) lfirst(cell);

next = lnext(cell);
		if (IsA(n, Constraint))
		{
			/* keep it in list */
			prev = cell;
			continue;
		}
		if (IsA(n, CollateClause))
		{
			CollateClause *c = (CollateClause *) n;

if (*collClause)
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("multiple COLLATE clauses not allowed"),
						 parser_errposition(c->location)));
			*collClause = c;
		}
		else
			elog(ERROR, "unexpected node type %d", (int) n->type);
		/* remove non-Constraint nodes from qualList */
		qualList = list_delete_cell(qualList, cell, prev);
	}
	*constraintList = qualList;
}

/*
 * Process result of ConstraintAttributeSpec, and set appropriate bool flags
 * in the output command node.  Pass NULL for any flags the particular
 * command doesn't support.
 */
static void
processCASbits(int cas_bits, int location, const char *constrType,
			   bool *deferrable, bool *initdeferred, bool *not_valid,
			   bool *no_inherit, core_yyscan_t yyscanner)
{
	/* defaults */
	if (deferrable)
		*deferrable = false;
	if (initdeferred)
		*initdeferred = false;
	if (not_valid)
		*not_valid = false;

if (cas_bits & (CAS_DEFERRABLE | CAS_INITIALLY_DEFERRED))
	{
		if (deferrable)
			*deferrable = true;
		else
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 /* translator: %s is CHECK, UNIQUE, or similar */
					 errmsg("%s constraints cannot be marked DEFERRABLE",
							constrType),
					 parser_errposition(location)));
	}

if (cas_bits & CAS_INITIALLY_DEFERRED)
	{
		if (initdeferred)
			*initdeferred = true;
		else
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 /* translator: %s is CHECK, UNIQUE, or similar */
					 errmsg("%s constraints cannot be marked DEFERRABLE",
							constrType),
					 parser_errposition(location)));
	}

if (cas_bits & CAS_NOT_VALID)
	{
		if (not_valid)
			*not_valid = true;
		else
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 /* translator: %s is CHECK, UNIQUE, or similar */
					 errmsg("%s constraints cannot be marked NOT VALID",
							constrType),
					 parser_errposition(location)));
	}

if (cas_bits & CAS_NO_INHERIT)
	{
		if (no_inherit)
			*no_inherit = true;
		else
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 /* translator: %s is CHECK, UNIQUE, or similar */
					 errmsg("%s constraints cannot be marked NO INHERIT",
							constrType),
					 parser_errposition(location)));
	}
}

/*----------
 * Recursive view transformation
 *
 * Convert
 *
 *     CREATE RECURSIVE VIEW relname (aliases) AS query
 *
 * to
 *
 *     CREATE VIEW relname (aliases) AS
 *         WITH RECURSIVE relname (aliases) AS (query)
 *         SELECT aliases FROM relname
 *
 * Actually, just the WITH ... part, which is then inserted into the original
 * view definition as the query.
 * ----------
 */
static Node *
makeRecursiveViewSelect(char *relname, List *aliases, Node *query)
{
	SelectStmt *s = makeNode(SelectStmt);
	WithClause *w = makeNode(WithClause);
	CommonTableExpr *cte = makeNode(CommonTableExpr);
	List	   *tl = NIL;
	ListCell   *lc;

/* create common table expression */
	cte->ctename = relname;
	cte->aliascolnames = aliases;
	cte->ctequery = query;
	cte->location = -1;

/* create WITH clause and attach CTE */
	w->recursive = true;
	w->ctes = list_make1(cte);
	w->location = -1;

/* create target list for the new SELECT from the alias list of the
	 * recursive view specification */
	foreach (lc, aliases)
	{
		ResTarget *rt = makeNode(ResTarget);

rt->name = NULL;
		rt->indirection = NIL;
		rt->val = makeColumnRef(strVal(lfirst(lc)), NIL, -1, 0);
		rt->location = -1;

tl = lappend(tl, rt);
	}

/* create new SELECT combining WITH clause, target list, and fake FROM
	 * clause */
	s->withClause = w;
	s->targetList = tl;
	s->fromClause = list_make1(makeRangeVar(NULL, relname, -1));

return (Node *) s;
}

/* parser_init()
 * Initialize to parse one query string
 */
void
parser_init(base_yy_extra_type *yyext)
{
	yyext->parsetree = NIL;		/* in case grammar forgets to set it */
}

```

### 三、參考資料
[Flex&Bison](http://web.iitd.ac.in/~sumeet/flex__bison.pdf)

PostgreSQL 原始碼解讀（179）- 查詢#96(語法分析：gram.y)#4

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