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

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;

src/backend/utils/adt/xml.c

@@ -52,6 +52,7 @@
 #include <libxml/tree.h>
 #include <libxml/uri.h>
 #include <libxml/xmlerror.h>
+#include <libxml/xmlsave.h>
 #include <libxml/xmlversion.h>
 #include <libxml/xmlwriter.h>
 #include <libxml/xpath.h>
@@ -146,6 +147,8 @@ static bool print_xml_decl(StringInfo buf, const xmlChar *version,
 static bool xml_doctype_in_content(const xmlChar *str);
 static xmlDocPtr xml_parse(text *data, XmlOptionType xmloption_arg,
 						   bool preserve_whitespace, int encoding,
+						   XmlOptionType *parsed_xmloptiontype,
+						   xmlNodePtr *parsed_nodes,
 						   Node *escontext);
 static text *xml_xmlnodetoxmltype(xmlNodePtr cur, PgXmlErrorContext *xmlerrcxt);
 static int	xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
@@ -273,7 +276,7 @@ xml_in(PG_FUNCTION_ARGS)
 	 * Note: we don't need to worry about whether a soft error is detected.
 	 */
 	doc = xml_parse(vardata, xmloption, true, GetDatabaseEncoding(),
-					fcinfo->context);
+					NULL, NULL, fcinfo->context);
 	if (doc != NULL)
 		xmlFreeDoc(doc);
 
@@ -400,7 +403,7 @@ xml_recv(PG_FUNCTION_ARGS)
 	 * Parse the data to check if it is well-formed XML data.  Assume that
 	 * xml_parse will throw ERROR if not.
 	 */
-	doc = xml_parse(result, xmloption, true, encoding, NULL);
+	doc = xml_parse(result, xmloption, true, encoding, NULL, NULL, NULL);
 	xmlFreeDoc(doc);
 
 	/* Now that we know what we're dealing with, convert to server encoding */
@@ -619,15 +622,182 @@ xmltotext(PG_FUNCTION_ARGS)
 
 
 text *
-xmltotext_with_xmloption(xmltype *data, XmlOptionType xmloption_arg)
+xmltotext_with_options(xmltype *data, XmlOptionType xmloption_arg, bool indent)
 {
-	if (xmloption_arg == XMLOPTION_DOCUMENT && !xml_is_document(data))
+#ifdef USE_LIBXML
+	text	   *volatile result;
+	xmlDocPtr	doc;
+	XmlOptionType parsed_xmloptiontype;
+	xmlNodePtr	content_nodes;
+	volatile xmlBufferPtr buf = NULL;
+	volatile	xmlSaveCtxtPtr ctxt = NULL;
+	ErrorSaveContext escontext = {T_ErrorSaveContext};
+	PgXmlErrorContext *xmlerrcxt;
+#endif
+
+	if (xmloption_arg != XMLOPTION_DOCUMENT && !indent)
+	{
+		/*
+		 * We don't actually need to do anything, so just return the
+		 * binary-compatible input.  For backwards-compatibility reasons,
+		 * allow such cases to succeed even without USE_LIBXML.
+		 */
+		return (text *) data;
+	}
+
+#ifdef USE_LIBXML
+	/* Parse the input according to the xmloption */
+	doc = xml_parse(data, xmloption_arg, true, GetDatabaseEncoding(),
+					&parsed_xmloptiontype, &content_nodes,
+					(Node *) &escontext);
+	if (doc == NULL || escontext.error_occurred)
+	{
+		if (doc)
+			xmlFreeDoc(doc);
+		/* A soft error must be failure to conform to XMLOPTION_DOCUMENT */
 		ereport(ERROR,
 				(errcode(ERRCODE_NOT_AN_XML_DOCUMENT),
 				 errmsg("not an XML document")));
+	}
+
+	/* If we weren't asked to indent, we're done. */
+	if (!indent)
+	{
+		xmlFreeDoc(doc);
+		return (text *) data;
+	}
+
+	/* Otherwise, we gotta spin up some error handling. */
+	xmlerrcxt = pg_xml_init(PG_XML_STRICTNESS_ALL);
+
+	PG_TRY();
+	{
+		size_t		decl_len = 0;
+
+		/* The serialized data will go into this buffer. */
+		buf = xmlBufferCreate();
+
+		if (buf == NULL || xmlerrcxt->err_occurred)
+			xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
+						"could not allocate xmlBuffer");
+
+		/* Detect whether there's an XML declaration */
+		parse_xml_decl(xml_text2xmlChar(data), &decl_len, NULL, NULL, NULL);
+
+		/*
+		 * Emit declaration only if the input had one.  Note: some versions of
+		 * xmlSaveToBuffer leak memory if a non-null encoding argument is
+		 * passed, so don't do that.  We don't want any encoding conversion
+		 * anyway.
+		 */
+		if (decl_len == 0)
+			ctxt = xmlSaveToBuffer(buf, NULL,
+								   XML_SAVE_NO_DECL | XML_SAVE_FORMAT);
+		else
+			ctxt = xmlSaveToBuffer(buf, NULL,
+								   XML_SAVE_FORMAT);
+
+		if (ctxt == NULL || xmlerrcxt->err_occurred)
+			xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
+						"could not allocate xmlSaveCtxt");
+
+		if (parsed_xmloptiontype == XMLOPTION_DOCUMENT)
+		{
+			/* If it's a document, saving is easy. */
+			if (xmlSaveDoc(ctxt, doc) == -1 || xmlerrcxt->err_occurred)
+				xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
+							"could not save document to xmlBuffer");
+		}
+		else if (content_nodes != NULL)
+		{
+			/*
+			 * Deal with the case where we have non-singly-rooted XML.
+			 * libxml's dump functions don't work well for that without help.
+			 * We build a fake root node that serves as a container for the
+			 * content nodes, and then iterate over the nodes.
+			 */
+			xmlNodePtr	root;
+			xmlNodePtr	newline;
+
+			root = xmlNewNode(NULL, (const xmlChar *) "content-root");
+			if (root == NULL || xmlerrcxt->err_occurred)
+				xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
+							"could not allocate xml node");
+
+			/* This attaches root to doc, so we need not free it separately. */
+			xmlDocSetRootElement(doc, root);
+			xmlAddChild(root, content_nodes);
 
-	/* It's actually binary compatible, save for the above check. */
-	return (text *) data;
+			/*
+			 * We use this node to insert newlines in the dump.  Note: in at
+			 * least some libxml versions, xmlNewDocText would not attach the
+			 * node to the document even if we passed it.  Therefore, manage
+			 * freeing of this node manually, and pass NULL here to make sure
+			 * there's not a dangling link.
+			 */
+			newline = xmlNewDocText(NULL, (const xmlChar *) "\n");
+			if (newline == NULL || xmlerrcxt->err_occurred)
+				xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
+							"could not allocate xml node");
+
+			for (xmlNodePtr node = root->children; node; node = node->next)
+			{
+				/* insert newlines between nodes */
+				if (node->type != XML_TEXT_NODE && node->prev != NULL)
+				{
+					if (xmlSaveTree(ctxt, newline) == -1 || xmlerrcxt->err_occurred)
+					{
+						xmlFreeNode(newline);
+						xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
+									"could not save newline to xmlBuffer");
+					}
+				}
+
+				if (xmlSaveTree(ctxt, node) == -1 || xmlerrcxt->err_occurred)
+				{
+					xmlFreeNode(newline);
+					xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
+								"could not save content to xmlBuffer");
+				}
+			}
+
+			xmlFreeNode(newline);
+		}
+
+		if (xmlSaveClose(ctxt) == -1 || xmlerrcxt->err_occurred)
+		{
+			ctxt = NULL;		/* don't try to close it again */
+			xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
+						"could not close xmlSaveCtxtPtr");
+		}
+
+		result = (text *) xmlBuffer_to_xmltype(buf);
+	}
+	PG_CATCH();
+	{
+		if (ctxt)
+			xmlSaveClose(ctxt);
+		if (buf)
+			xmlBufferFree(buf);
+		if (doc)
+			xmlFreeDoc(doc);
+
+		pg_xml_done(xmlerrcxt, true);
+
+		PG_RE_THROW();
+	}
+	PG_END_TRY();
+
+	xmlBufferFree(buf);
+	xmlFreeDoc(doc);
+
+	pg_xml_done(xmlerrcxt, false);
+
+	return result;
+#else
+	NO_XML_SUPPORT();
+	return NULL;
+#endif
 }
 
 
@@ -762,7 +932,7 @@ xmlparse(text *data, XmlOptionType xmloption_arg, bool preserve_whitespace)
 	xmlDocPtr	doc;
 
 	doc = xml_parse(data, xmloption_arg, preserve_whitespace,
-					GetDatabaseEncoding(), NULL);
+					GetDatabaseEncoding(), NULL, NULL, NULL);
 	xmlFreeDoc(doc);
 
 	return (xmltype *) data;
@@ -902,7 +1072,7 @@ xml_is_document(xmltype *arg)
 	 * We'll report "true" if no soft error is reported by xml_parse().
 	 */
 	doc = xml_parse((text *) arg, XMLOPTION_DOCUMENT, true,
-					GetDatabaseEncoding(), (Node *) &escontext);
+					GetDatabaseEncoding(), NULL, NULL, (Node *) &escontext);
 	if (doc)
 		xmlFreeDoc(doc);
 
@@ -1491,6 +1661,14 @@ xml_doctype_in_content(const xmlChar *str)
  * and xmloption_arg and preserve_whitespace are options for the
  * transformation.
  *
+ * If parsed_xmloptiontype isn't NULL, *parsed_xmloptiontype is set to the
+ * XmlOptionType actually used to parse the input (typically the same as
+ * xmloption_arg, but a DOCTYPE node in the input can force DOCUMENT mode).
+ *
+ * If parsed_nodes isn't NULL and the input is not an XML document, the list
+ * of parsed nodes from the xmlParseBalancedChunkMemory call will be returned
+ * to *parsed_nodes.
+ *
  * Errors normally result in ereport(ERROR), but if escontext is an
  * ErrorSaveContext, then "safe" errors are reported there instead, and the
  * caller must check SOFT_ERROR_OCCURRED() to see whether that happened.
@@ -1503,8 +1681,10 @@ xml_doctype_in_content(const xmlChar *str)
  * yet do not use SAX - see xmlreader.c)
  */
 static xmlDocPtr
-xml_parse(text *data, XmlOptionType xmloption_arg, bool preserve_whitespace,
-		  int encoding, Node *escontext)
+xml_parse(text *data, XmlOptionType xmloption_arg,
+		  bool preserve_whitespace, int encoding,
+		  XmlOptionType *parsed_xmloptiontype, xmlNodePtr *parsed_nodes,
+		  Node *escontext)
 {
 	int32		len;
 	xmlChar    *string;
@@ -1574,6 +1754,13 @@ xml_parse(text *data, XmlOptionType xmloption_arg, bool preserve_whitespace,
 				parse_as_document = true;
 		}
 
+		/* initialize output parameters */
+		if (parsed_xmloptiontype != NULL)
+			*parsed_xmloptiontype = parse_as_document ? XMLOPTION_DOCUMENT :
+				XMLOPTION_CONTENT;
+		if (parsed_nodes != NULL)
+			*parsed_nodes = NULL;
+
 		if (parse_as_document)
 		{
 			/*
@@ -1620,7 +1807,8 @@ xml_parse(text *data, XmlOptionType xmloption_arg, bool preserve_whitespace,
 			if (*(utf8string + count))
 			{
 				res_code = xmlParseBalancedChunkMemory(doc, NULL, NULL, 0,
-													   utf8string + count, NULL);
+													   utf8string + count,
+													   parsed_nodes);
 				if (res_code != 0 || xmlerrcxt->err_occurred)
 				{
 					xml_errsave(escontext, xmlerrcxt,
@@ -4305,7 +4493,7 @@ wellformed_xml(text *data, XmlOptionType xmloption_arg)
 	 * We'll report "true" if no soft error is reported by xml_parse().
 	 */
 	doc = xml_parse(data, xmloption_arg, true,
-					GetDatabaseEncoding(), (Node *) &escontext);
+					GetDatabaseEncoding(), NULL, NULL, (Node *) &escontext);
 	if (doc)
 		xmlFreeDoc(doc);
 

src/include/catalog/catversion.h

@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202303141
+#define CATALOG_VERSION_NO	202303151
 
 #endif

src/include/nodes/parsenodes.h

@@ -840,6 +840,7 @@ typedef struct XmlSerialize
 	XmlOptionType xmloption;	/* DOCUMENT or CONTENT */
 	Node	   *expr;
 	TypeName   *typeName;
+	bool		indent;			/* [NO] INDENT */
 	int			location;		/* token location, or -1 if unknown */
 } XmlSerialize;
 

src/include/nodes/primnodes.h

@@ -1464,7 +1464,7 @@ typedef enum XmlExprOp
 	IS_XMLPARSE,				/* XMLPARSE(text, is_doc, preserve_ws) */
 	IS_XMLPI,					/* XMLPI(name [, args]) */
 	IS_XMLROOT,					/* XMLROOT(xml, version, standalone) */
-	IS_XMLSERIALIZE,			/* XMLSERIALIZE(is_document, xmlval) */
+	IS_XMLSERIALIZE,			/* XMLSERIALIZE(is_document, xmlval, indent) */
 	IS_DOCUMENT					/* xmlval IS DOCUMENT */
 } XmlExprOp;
 
@@ -1489,6 +1489,8 @@ typedef struct XmlExpr
 	List	   *args;
 	/* DOCUMENT or CONTENT */
 	XmlOptionType xmloption pg_node_attr(query_jumble_ignore);
+	/* INDENT option for XMLSERIALIZE */
+	bool		indent;
 	/* target type/typmod for XMLSERIALIZE */
 	Oid			type pg_node_attr(query_jumble_ignore);
 	int32		typmod pg_node_attr(query_jumble_ignore);

src/include/parser/kwlist.h

@@ -205,6 +205,7 @@ PG_KEYWORD("in", IN_P, RESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("include", INCLUDE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("including", INCLUDING, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("increment", INCREMENT, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("indent", INDENT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("index", INDEX, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("indexes", INDEXES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("inherit", INHERIT, UNRESERVED_KEYWORD, BARE_LABEL)

src/include/utils/xml.h

@@ -77,7 +77,8 @@ extern xmltype *xmlparse(text *data, XmlOptionType xmloption_arg, bool preserve_
 extern xmltype *xmlpi(const char *target, text *arg, bool arg_is_null, bool *result_is_null);
 extern xmltype *xmlroot(xmltype *data, text *version, int standalone);
 extern bool xml_is_document(xmltype *arg);
-extern text *xmltotext_with_xmloption(xmltype *data, XmlOptionType xmloption_arg);
+extern text *xmltotext_with_options(xmltype *data, XmlOptionType xmloption_arg,
+									bool indent);
 extern char *escape_xml(const char *str);
 
 extern char *map_sql_identifier_to_xml_name(const char *ident, bool fully_escaped, bool escape_period);

src/test/regress/expected/xml.out

@@ -486,6 +486,192 @@ SELECT xmlserialize(content 'good' as char(10));
 
 SELECT xmlserialize(document 'bad' as text);
 ERROR:  not an XML document
+-- indent
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text INDENT);
+      xmlserialize       
+-------------------------
+ <foo>                  +
+   <bar>                +
+     <val x="y">42</val>+
+   </bar>               +
+ </foo>                 +
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val></bar></foo>' AS text INDENT);
+      xmlserialize       
+-------------------------
+ <foo>                  +
+   <bar>                +
+     <val x="y">42</val>+
+   </bar>               +
+ </foo>
+(1 row)
+
+-- no indent
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+               xmlserialize                
+-------------------------------------------
+ <foo><bar><val x="y">42</val></bar></foo>
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+               xmlserialize                
+-------------------------------------------
+ <foo><bar><val x="y">42</val></bar></foo>
+(1 row)
+
+-- indent non singly-rooted xml
+SELECT xmlserialize(DOCUMENT '<foo>73</foo><bar><val x="y">42</val></bar>' AS text INDENT);
+ERROR:  not an XML document
+SELECT xmlserialize(CONTENT  '<foo>73</foo><bar><val x="y">42</val></bar>' AS text INDENT);
+     xmlserialize      
+-----------------------
+ <foo>73</foo>        +
+ <bar>                +
+   <val x="y">42</val>+
+ </bar>
+(1 row)
+
+-- indent non singly-rooted xml with mixed contents
+SELECT xmlserialize(DOCUMENT 'text node<foo>73</foo>text node<bar><val x="y">42</val></bar>' AS text INDENT);
+ERROR:  not an XML document
+SELECT xmlserialize(CONTENT  'text node<foo>73</foo>text node<bar><val x="y">42</val></bar>' AS text INDENT);
+      xmlserialize      
+------------------------
+ text node             +
+ <foo>73</foo>text node+
+ <bar>                 +
+   <val x="y">42</val> +
+ </bar>
+(1 row)
+
+-- indent singly-rooted xml with mixed contents
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val><val x="y">text node<val>73</val></val></bar></foo>' AS text INDENT);
+                xmlserialize                 
+---------------------------------------------
+ <foo>                                      +
+   <bar>                                    +
+     <val x="y">42</val>                    +
+     <val x="y">text node<val>73</val></val>+
+   </bar>                                   +
+ </foo>                                     +
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val><val x="y">text node<val>73</val></val></bar></foo>' AS text INDENT);
+                xmlserialize                 
+---------------------------------------------
+ <foo>                                      +
+   <bar>                                    +
+     <val x="y">42</val>                    +
+     <val x="y">text node<val>73</val></val>+
+   </bar>                                   +
+ </foo>
+(1 row)
+
+-- indent empty string
+SELECT xmlserialize(DOCUMENT '' AS text INDENT);
+ERROR:  not an XML document
+SELECT xmlserialize(CONTENT  '' AS text INDENT);
+ xmlserialize 
+--------------
+ 
+(1 row)
+
+-- whitespaces
+SELECT xmlserialize(DOCUMENT '  ' AS text INDENT);
+ERROR:  not an XML document
+SELECT xmlserialize(CONTENT  '  ' AS text INDENT);
+ xmlserialize 
+--------------
+   
+(1 row)
+
+-- indent null
+SELECT xmlserialize(DOCUMENT NULL AS text INDENT);
+ xmlserialize 
+--------------
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  NULL AS text INDENT);
+ xmlserialize 
+--------------
+ 
+(1 row)
+
+-- indent with XML declaration
+SELECT xmlserialize(DOCUMENT '<?xml version="1.0" encoding="UTF-8"?><foo><bar><val>73</val></bar></foo>' AS text INDENT);
+              xmlserialize              
+----------------------------------------
+ <?xml version="1.0" encoding="UTF-8"?>+
+ <foo>                                 +
+   <bar>                               +
+     <val>73</val>                     +
+   </bar>                              +
+ </foo>                                +
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<?xml version="1.0" encoding="UTF-8"?><foo><bar><val>73</val></bar></foo>' AS text INDENT);
+   xmlserialize    
+-------------------
+ <foo>            +
+   <bar>          +
+     <val>73</val>+
+   </bar>         +
+ </foo>
+(1 row)
+
+-- indent containing DOCTYPE declaration
+SELECT xmlserialize(DOCUMENT '<!DOCTYPE a><a/>' AS text INDENT);
+ xmlserialize 
+--------------
+ <!DOCTYPE a>+
+ <a/>        +
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<!DOCTYPE a><a/>' AS text INDENT);
+ xmlserialize 
+--------------
+ <!DOCTYPE a>+
+ <a/>        +
+ 
+(1 row)
+
+-- indent xml with empty element
+SELECT xmlserialize(DOCUMENT '<foo><bar></bar></foo>' AS text INDENT);
+ xmlserialize 
+--------------
+ <foo>       +
+   <bar/>    +
+ </foo>      +
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<foo><bar></bar></foo>' AS text INDENT);
+ xmlserialize 
+--------------
+ <foo>       +
+   <bar/>    +
+ </foo>
+(1 row)
+
+-- 'no indent' = not using 'no indent'
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text) = xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+ ?column? 
+----------
+ t
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val></bar></foo>' AS text) = xmlserialize(CONTENT '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+ ?column? 
+----------
+ t
+(1 row)
+
 SELECT xml '<foo>bar</foo>' IS DOCUMENT;
  ?column? 
 ----------

src/test/regress/expected/xml_1.out

@@ -309,6 +309,140 @@ ERROR:  unsupported XML feature
 LINE 1: SELECT xmlserialize(document 'bad' as text);
                                      ^
 DETAIL:  This functionality requires the server to be built with libxml support.
+-- indent
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val><...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val></bar></foo>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val><...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+-- no indent
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val><...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val><...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+-- indent non singly-rooted xml
+SELECT xmlserialize(DOCUMENT '<foo>73</foo><bar><val x="y">42</val></bar>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(DOCUMENT '<foo>73</foo><bar><val x="y">4...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+SELECT xmlserialize(CONTENT  '<foo>73</foo><bar><val x="y">42</val></bar>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(CONTENT  '<foo>73</foo><bar><val x="y">4...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+-- indent non singly-rooted xml with mixed contents
+SELECT xmlserialize(DOCUMENT 'text node<foo>73</foo>text node<bar><val x="y">42</val></bar>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(DOCUMENT 'text node<foo>73</foo>text nod...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+SELECT xmlserialize(CONTENT  'text node<foo>73</foo>text node<bar><val x="y">42</val></bar>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(CONTENT  'text node<foo>73</foo>text nod...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+-- indent singly-rooted xml with mixed contents
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val><val x="y">text node<val>73</val></val></bar></foo>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val><...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val><val x="y">text node<val>73</val></val></bar></foo>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val><...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+-- indent empty string
+SELECT xmlserialize(DOCUMENT '' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(DOCUMENT '' AS text INDENT);
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+SELECT xmlserialize(CONTENT  '' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(CONTENT  '' AS text INDENT);
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+-- whitespaces
+SELECT xmlserialize(DOCUMENT '  ' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(DOCUMENT '  ' AS text INDENT);
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+SELECT xmlserialize(CONTENT  '  ' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(CONTENT  '  ' AS text INDENT);
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+-- indent null
+SELECT xmlserialize(DOCUMENT NULL AS text INDENT);
+ xmlserialize 
+--------------
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  NULL AS text INDENT);
+ xmlserialize 
+--------------
+ 
+(1 row)
+
+-- indent with XML declaration
+SELECT xmlserialize(DOCUMENT '<?xml version="1.0" encoding="UTF-8"?><foo><bar><val>73</val></bar></foo>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(DOCUMENT '<?xml version="1.0" encoding="...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+SELECT xmlserialize(CONTENT  '<?xml version="1.0" encoding="UTF-8"?><foo><bar><val>73</val></bar></foo>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(CONTENT  '<?xml version="1.0" encoding="...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+-- indent containing DOCTYPE declaration
+SELECT xmlserialize(DOCUMENT '<!DOCTYPE a><a/>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(DOCUMENT '<!DOCTYPE a><a/>' AS text INDE...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+SELECT xmlserialize(CONTENT  '<!DOCTYPE a><a/>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(CONTENT  '<!DOCTYPE a><a/>' AS text INDE...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+-- indent xml with empty element
+SELECT xmlserialize(DOCUMENT '<foo><bar></bar></foo>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(DOCUMENT '<foo><bar></bar></foo>' AS tex...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+SELECT xmlserialize(CONTENT  '<foo><bar></bar></foo>' AS text INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(CONTENT  '<foo><bar></bar></foo>' AS tex...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+-- 'no indent' = not using 'no indent'
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text) = xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val><...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val></bar></foo>' AS text) = xmlserialize(CONTENT '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val><...
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
 SELECT xml '<foo>bar</foo>' IS DOCUMENT;
 ERROR:  unsupported XML feature
 LINE 1: SELECT xml '<foo>bar</foo>' IS DOCUMENT;

src/test/regress/expected/xml_2.out

@@ -466,6 +466,192 @@ SELECT xmlserialize(content 'good' as char(10));
 
 SELECT xmlserialize(document 'bad' as text);
 ERROR:  not an XML document
+-- indent
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text INDENT);
+      xmlserialize       
+-------------------------
+ <foo>                  +
+   <bar>                +
+     <val x="y">42</val>+
+   </bar>               +
+ </foo>                 +
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val></bar></foo>' AS text INDENT);
+      xmlserialize       
+-------------------------
+ <foo>                  +
+   <bar>                +
+     <val x="y">42</val>+
+   </bar>               +
+ </foo>
+(1 row)
+
+-- no indent
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+               xmlserialize                
+-------------------------------------------
+ <foo><bar><val x="y">42</val></bar></foo>
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+               xmlserialize                
+-------------------------------------------
+ <foo><bar><val x="y">42</val></bar></foo>
+(1 row)
+
+-- indent non singly-rooted xml
+SELECT xmlserialize(DOCUMENT '<foo>73</foo><bar><val x="y">42</val></bar>' AS text INDENT);
+ERROR:  not an XML document
+SELECT xmlserialize(CONTENT  '<foo>73</foo><bar><val x="y">42</val></bar>' AS text INDENT);
+     xmlserialize      
+-----------------------
+ <foo>73</foo>        +
+ <bar>                +
+   <val x="y">42</val>+
+ </bar>
+(1 row)
+
+-- indent non singly-rooted xml with mixed contents
+SELECT xmlserialize(DOCUMENT 'text node<foo>73</foo>text node<bar><val x="y">42</val></bar>' AS text INDENT);
+ERROR:  not an XML document
+SELECT xmlserialize(CONTENT  'text node<foo>73</foo>text node<bar><val x="y">42</val></bar>' AS text INDENT);
+      xmlserialize      
+------------------------
+ text node             +
+ <foo>73</foo>text node+
+ <bar>                 +
+   <val x="y">42</val> +
+ </bar>
+(1 row)
+
+-- indent singly-rooted xml with mixed contents
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val><val x="y">text node<val>73</val></val></bar></foo>' AS text INDENT);
+                xmlserialize                 
+---------------------------------------------
+ <foo>                                      +
+   <bar>                                    +
+     <val x="y">42</val>                    +
+     <val x="y">text node<val>73</val></val>+
+   </bar>                                   +
+ </foo>                                     +
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val><val x="y">text node<val>73</val></val></bar></foo>' AS text INDENT);
+                xmlserialize                 
+---------------------------------------------
+ <foo>                                      +
+   <bar>                                    +
+     <val x="y">42</val>                    +
+     <val x="y">text node<val>73</val></val>+
+   </bar>                                   +
+ </foo>
+(1 row)
+
+-- indent empty string
+SELECT xmlserialize(DOCUMENT '' AS text INDENT);
+ERROR:  not an XML document
+SELECT xmlserialize(CONTENT  '' AS text INDENT);
+ xmlserialize 
+--------------
+ 
+(1 row)
+
+-- whitespaces
+SELECT xmlserialize(DOCUMENT '  ' AS text INDENT);
+ERROR:  not an XML document
+SELECT xmlserialize(CONTENT  '  ' AS text INDENT);
+ xmlserialize 
+--------------
+   
+(1 row)
+
+-- indent null
+SELECT xmlserialize(DOCUMENT NULL AS text INDENT);
+ xmlserialize 
+--------------
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  NULL AS text INDENT);
+ xmlserialize 
+--------------
+ 
+(1 row)
+
+-- indent with XML declaration
+SELECT xmlserialize(DOCUMENT '<?xml version="1.0" encoding="UTF-8"?><foo><bar><val>73</val></bar></foo>' AS text INDENT);
+              xmlserialize              
+----------------------------------------
+ <?xml version="1.0" encoding="UTF-8"?>+
+ <foo>                                 +
+   <bar>                               +
+     <val>73</val>                     +
+   </bar>                              +
+ </foo>                                +
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<?xml version="1.0" encoding="UTF-8"?><foo><bar><val>73</val></bar></foo>' AS text INDENT);
+   xmlserialize    
+-------------------
+ <foo>            +
+   <bar>          +
+     <val>73</val>+
+   </bar>         +
+ </foo>
+(1 row)
+
+-- indent containing DOCTYPE declaration
+SELECT xmlserialize(DOCUMENT '<!DOCTYPE a><a/>' AS text INDENT);
+ xmlserialize 
+--------------
+ <!DOCTYPE a>+
+ <a/>        +
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<!DOCTYPE a><a/>' AS text INDENT);
+ xmlserialize 
+--------------
+ <!DOCTYPE a>+
+ <a/>        +
+ 
+(1 row)
+
+-- indent xml with empty element
+SELECT xmlserialize(DOCUMENT '<foo><bar></bar></foo>' AS text INDENT);
+ xmlserialize 
+--------------
+ <foo>       +
+   <bar/>    +
+ </foo>      +
+ 
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<foo><bar></bar></foo>' AS text INDENT);
+ xmlserialize 
+--------------
+ <foo>       +
+   <bar/>    +
+ </foo>
+(1 row)
+
+-- 'no indent' = not using 'no indent'
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text) = xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+ ?column? 
+----------
+ t
+(1 row)
+
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val></bar></foo>' AS text) = xmlserialize(CONTENT '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+ ?column? 
+----------
+ t
+(1 row)
+
 SELECT xml '<foo>bar</foo>' IS DOCUMENT;
  ?column? 
 ----------

src/test/regress/sql/xml.sql

@@ -132,6 +132,42 @@ SELECT xmlserialize(content data as character varying(20)) FROM xmltest;
 SELECT xmlserialize(content 'good' as char(10));
 SELECT xmlserialize(document 'bad' as text);
 
+-- indent
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text INDENT);
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val></bar></foo>' AS text INDENT);
+-- no indent
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+-- indent non singly-rooted xml
+SELECT xmlserialize(DOCUMENT '<foo>73</foo><bar><val x="y">42</val></bar>' AS text INDENT);
+SELECT xmlserialize(CONTENT  '<foo>73</foo><bar><val x="y">42</val></bar>' AS text INDENT);
+-- indent non singly-rooted xml with mixed contents
+SELECT xmlserialize(DOCUMENT 'text node<foo>73</foo>text node<bar><val x="y">42</val></bar>' AS text INDENT);
+SELECT xmlserialize(CONTENT  'text node<foo>73</foo>text node<bar><val x="y">42</val></bar>' AS text INDENT);
+-- indent singly-rooted xml with mixed contents
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val><val x="y">text node<val>73</val></val></bar></foo>' AS text INDENT);
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val><val x="y">text node<val>73</val></val></bar></foo>' AS text INDENT);
+-- indent empty string
+SELECT xmlserialize(DOCUMENT '' AS text INDENT);
+SELECT xmlserialize(CONTENT  '' AS text INDENT);
+-- whitespaces
+SELECT xmlserialize(DOCUMENT '  ' AS text INDENT);
+SELECT xmlserialize(CONTENT  '  ' AS text INDENT);
+-- indent null
+SELECT xmlserialize(DOCUMENT NULL AS text INDENT);
+SELECT xmlserialize(CONTENT  NULL AS text INDENT);
+-- indent with XML declaration
+SELECT xmlserialize(DOCUMENT '<?xml version="1.0" encoding="UTF-8"?><foo><bar><val>73</val></bar></foo>' AS text INDENT);
+SELECT xmlserialize(CONTENT  '<?xml version="1.0" encoding="UTF-8"?><foo><bar><val>73</val></bar></foo>' AS text INDENT);
+-- indent containing DOCTYPE declaration
+SELECT xmlserialize(DOCUMENT '<!DOCTYPE a><a/>' AS text INDENT);
+SELECT xmlserialize(CONTENT  '<!DOCTYPE a><a/>' AS text INDENT);
+-- indent xml with empty element
+SELECT xmlserialize(DOCUMENT '<foo><bar></bar></foo>' AS text INDENT);
+SELECT xmlserialize(CONTENT  '<foo><bar></bar></foo>' AS text INDENT);
+-- 'no indent' = not using 'no indent'
+SELECT xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text) = xmlserialize(DOCUMENT '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
+SELECT xmlserialize(CONTENT  '<foo><bar><val x="y">42</val></bar></foo>' AS text) = xmlserialize(CONTENT '<foo><bar><val x="y">42</val></bar></foo>' AS text NO INDENT);
 
 SELECT xml '<foo>bar</foo>' IS DOCUMENT;
 SELECT xml '<foo>bar</foo><bar>foo</bar>' IS DOCUMENT;