Support [NO] INDENT option in XMLSERIALIZE().

This adds the ability to pretty-print XML documents ... according to
libxml's somewhat idiosyncratic notions of what's pretty, anyway.
One notable divergence from a strict reading of the spec is that
libxml is willing to collapse empty nodes "<node></node>" to just
"<node/>", whereas SQL and the underlying XML spec say that this
option should only result in whitespace tweaks.  Nonetheless,
it seems close enough to justify using the SQL-standard syntax.

Jim Jones, reviewed by Peter Smith and myself

Discussion: https://postgr.es/m/2f5df461-dad8-6d7d-4568-08e10608a69b@uni-muenster.de

Author: tglsfdc

doc/src/sgml/datatype.sgml

@@ -4460,7 +4460,7 @@ xml '<foo>bar</foo>'
     <type>xml</type>, uses the function
     <function>xmlserialize</function>:<indexterm><primary>xmlserialize</primary></indexterm>
 <synopsis>
-XMLSERIALIZE ( { DOCUMENT | CONTENT } <replaceable>value</replaceable> AS <replaceable>type</replaceable> )
+XMLSERIALIZE ( { DOCUMENT | CONTENT } <replaceable>value</replaceable> AS <replaceable>type</replaceable> [ [ NO ] INDENT ] )
 </synopsis>
     <replaceable>type</replaceable> can be
     <type>character</type>, <type>character varying</type>, or
@@ -4470,6 +4470,13 @@ XMLSERIALIZE ( { DOCUMENT | CONTENT } <replaceable>value</replaceable> AS <repla
     you to simply cast the value.
    </para>
 
+   <para>
+    The <literal>INDENT</literal> option causes the result to be
+    pretty-printed, while <literal>NO INDENT</literal> (which is the
+    default) just emits the original input string.  Casting to a character
+    type likewise produces the original string.
+   </para>
+
    <para>
     When a character string value is cast to or from type
     <type>xml</type> without going through <type>XMLPARSE</type> or

src/backend/catalog/sql_features.txt

@@ -621,7 +621,7 @@ X061	XMLParse: character string input and DOCUMENT option			YES
 X065	XMLParse: binary string input and CONTENT option			NO	
 X066	XMLParse: binary string input and DOCUMENT option			NO	
 X068	XMLSerialize: BOM			NO	
-X069	XMLSerialize: INDENT			NO	
+X069	XMLSerialize: INDENT			YES	
 X070	XMLSerialize: character string serialization and CONTENT option			YES	
 X071	XMLSerialize: character string serialization and DOCUMENT option			YES	
 X072	XMLSerialize: character string serialization			YES	

src/backend/executor/execExprInterp.c

@@ -3837,8 +3837,10 @@ ExecEvalXmlExpr(ExprState *state, ExprEvalStep *op)
 					return;
 				value = argvalue[0];
 
-				*op->resvalue = PointerGetDatum(xmltotext_with_xmloption(DatumGetXmlP(value),
-																		 xexpr->xmloption));
+				*op->resvalue =
+					PointerGetDatum(xmltotext_with_options(DatumGetXmlP(value),
+														   xexpr->xmloption,
+														   xexpr->indent));
 				*op->resnull = false;
 			}
 			break;

src/backend/parser/gram.y

@@ -613,7 +613,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <node>	xml_root_version opt_xml_root_standalone
 %type <node>	xmlexists_argument
 %type <ival>	document_or_content
-%type <boolean> xml_whitespace_option
+%type <boolean>	xml_indent_option xml_whitespace_option
 %type <list>	xmltable_column_list xmltable_column_option_list
 %type <node>	xmltable_column_el
 %type <defelt>	xmltable_column_option_el
@@ -702,7 +702,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	HANDLER HAVING HEADER_P HOLD HOUR_P
 
 	IDENTITY_P IF_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
-	INCLUDING INCREMENT INDEX INDEXES INHERIT INHERITS INITIALLY INLINE_P
+	INCLUDING INCREMENT INDENT INDEX INDEXES INHERIT INHERITS INITIALLY INLINE_P
 	INNER_P INOUT INPUT_P INSENSITIVE INSERT INSTEAD INT_P INTEGER
 	INTERSECT INTERVAL INTO INVOKER IS ISNULL ISOLATION
 
@@ -15532,13 +15532,14 @@ func_expr_common_subexpr:
 					$$ = makeXmlExpr(IS_XMLROOT, NULL, NIL,
 									 list_make3($3, $5, $6), @1);
 				}
-			| XMLSERIALIZE '(' document_or_content a_expr AS SimpleTypename ')'
+			| XMLSERIALIZE '(' document_or_content a_expr AS SimpleTypename xml_indent_option ')'
 				{
 					XmlSerialize *n = makeNode(XmlSerialize);
 
 					n->xmloption = $3;
 					n->expr = $4;
 					n->typeName = $6;
+					n->indent = $7;
 					n->location = @1;
 					$$ = (Node *) n;
 				}
@@ -15592,6 +15593,11 @@ document_or_content: DOCUMENT_P						{ $$ = XMLOPTION_DOCUMENT; }
 			| CONTENT_P								{ $$ = XMLOPTION_CONTENT; }
 		;
 
+xml_indent_option: INDENT							{ $$ = true; }
+			| NO INDENT								{ $$ = false; }
+			| /*EMPTY*/								{ $$ = false; }
+		;
+
 xml_whitespace_option: PRESERVE WHITESPACE_P		{ $$ = true; }
 			| STRIP_P WHITESPACE_P					{ $$ = false; }
 			| /*EMPTY*/								{ $$ = false; }
@@ -16828,6 +16834,7 @@ unreserved_keyword:
 			| INCLUDE
 			| INCLUDING
 			| INCREMENT
+			| INDENT
 			| INDEX
 			| INDEXES
 			| INHERIT
@@ -17384,6 +17391,7 @@ bare_label_keyword:
 			| INCLUDE
 			| INCLUDING
 			| INCREMENT
+			| INDENT
 			| INDEX
 			| INDEXES
 			| INHERIT

src/backend/parser/parse_expr.c

@@ -2331,6 +2331,7 @@ transformXmlSerialize(ParseState *pstate, XmlSerialize *xs)
 	typenameTypeIdAndMod(pstate, xs->typeName, &targetType, &targetTypmod);
 
 	xexpr->xmloption = xs->xmloption;
+	xexpr->indent = xs->indent;
 	xexpr->location = xs->location;
 	/* We actually only need these to be able to parse back the expression. */
 	xexpr->type = targetType;