Make xpath() do something useful with XPath expressions that return scalars.

Previously, xpath() simply returned an empty array if the expression did
not yield a node set.  This is useless for expressions that return scalars,
such as one with name() at the top level.  Arrange to return the scalar
value as a single-element xml array, instead.  (String values will be
suitably escaped.)

This change will also cause xpath_exists() to return true, not false,
for such expressions.

Florian Pflug, reviewed by Radoslaw Smogura

3 files changed, 104 insertions, 0 deletions

diff --git a/src/test/regress/expected/xml.out b/src/test/regress/expected/xml.out
index 5cd602107b2..5dfa44b5b99 100644
--- a/src/test/regress/expected/xml.out
+++ b/src/test/regress/expected/xml.out
@@ -601,6 +601,42 @@ SELECT xpath('//@value', '<root value="&lt;"/>');
  {&lt;}
 (1 row)
 
+SELECT xpath('''<<invalid>>''', '<root/>');
+           xpath           
+---------------------------
+ {&lt;&lt;invalid&gt;&gt;}
+(1 row)
+
+SELECT xpath('count(//*)', '<root><sub/><sub/></root>');
+ xpath 
+-------
+ {3}
+(1 row)
+
+SELECT xpath('count(//*)=0', '<root><sub/><sub/></root>');
+  xpath  
+---------
+ {false}
+(1 row)
+
+SELECT xpath('count(//*)=3', '<root><sub/><sub/></root>');
+ xpath  
+--------
+ {true}
+(1 row)
+
+SELECT xpath('name(/*)', '<root><sub/><sub/></root>');
+ xpath  
+--------
+ {root}
+(1 row)
+
+SELECT xpath('/nosuchtag', '<root/>');
+ xpath 
+-------
+ {}
+(1 row)
+
 -- Test xmlexists and xpath_exists
 SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>');
  xmlexists 
@@ -614,6 +650,12 @@ SELECT xmlexists('//town[text() = ''Cwmbran'']' PASSING BY REF '<towns><town>Bid
  t
 (1 row)
 
+SELECT xmlexists('count(/nosuchtag)' PASSING BY REF '<root/>');
+ xmlexists 
+-----------
+ t
+(1 row)
+
 SELECT xpath_exists('//town[text() = ''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
  xpath_exists 
 --------------
@@ -626,6 +668,12 @@ SELECT xpath_exists('//town[text() = ''Cwmbran'']','<towns><town>Bidford-on-Avon
  t
 (1 row)
 
+SELECT xpath_exists('count(/nosuchtag)', '<root/>'::xml);
+ xpath_exists 
+--------------
+ t
+(1 row)
+
 INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
 INSERT INTO xmltest VALUES (5, '<menu><beers><name>Molson</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
 INSERT INTO xmltest VALUES (6, '<myns:menu xmlns:myns="http://myns.com"><myns:beers><myns:name>Budvar</myns:name><myns:cost>free</myns:cost><myns:name>Carling</myns:name><myns:cost>lots</myns:cost></myns:beers></myns:menu>'::xml);
diff --git a/src/test/regress/expected/xml_1.out b/src/test/regress/expected/xml_1.out
index 53675f5536f..c6c0e7ac887 100644
--- a/src/test/regress/expected/xml_1.out
+++ b/src/test/regress/expected/xml_1.out
@@ -516,6 +516,42 @@ LINE 1: SELECT xpath('//@value', '<root value="&lt;"/>');
                                  ^
 DETAIL:  This functionality requires the server to be built with libxml support.
 HINT:  You need to rebuild PostgreSQL using --with-libxml.
+SELECT xpath('''<<invalid>>''', '<root/>');
+ERROR:  unsupported XML feature
+LINE 1: SELECT xpath('''<<invalid>>''', '<root/>');
+                                        ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+HINT:  You need to rebuild PostgreSQL using --with-libxml.
+SELECT xpath('count(//*)', '<root><sub/><sub/></root>');
+ERROR:  unsupported XML feature
+LINE 1: SELECT xpath('count(//*)', '<root><sub/><sub/></root>');
+                                   ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+HINT:  You need to rebuild PostgreSQL using --with-libxml.
+SELECT xpath('count(//*)=0', '<root><sub/><sub/></root>');
+ERROR:  unsupported XML feature
+LINE 1: SELECT xpath('count(//*)=0', '<root><sub/><sub/></root>');
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+HINT:  You need to rebuild PostgreSQL using --with-libxml.
+SELECT xpath('count(//*)=3', '<root><sub/><sub/></root>');
+ERROR:  unsupported XML feature
+LINE 1: SELECT xpath('count(//*)=3', '<root><sub/><sub/></root>');
+                                     ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+HINT:  You need to rebuild PostgreSQL using --with-libxml.
+SELECT xpath('name(/*)', '<root><sub/><sub/></root>');
+ERROR:  unsupported XML feature
+LINE 1: SELECT xpath('name(/*)', '<root><sub/><sub/></root>');
+                                 ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+HINT:  You need to rebuild PostgreSQL using --with-libxml.
+SELECT xpath('/nosuchtag', '<root/>');
+ERROR:  unsupported XML feature
+LINE 1: SELECT xpath('/nosuchtag', '<root/>');
+                                   ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+HINT:  You need to rebuild PostgreSQL using --with-libxml.
 -- Test xmlexists and xpath_exists
 SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>');
 ERROR:  unsupported XML feature
@@ -529,6 +565,12 @@ LINE 1: ...sts('//town[text() = ''Cwmbran'']' PASSING BY REF '<towns><t...
                                                              ^
 DETAIL:  This functionality requires the server to be built with libxml support.
 HINT:  You need to rebuild PostgreSQL using --with-libxml.
+SELECT xmlexists('count(/nosuchtag)' PASSING BY REF '<root/>');
+ERROR:  unsupported XML feature
+LINE 1: ...LECT xmlexists('count(/nosuchtag)' PASSING BY REF '<root/>')...
+                                                             ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+HINT:  You need to rebuild PostgreSQL using --with-libxml.
 SELECT xpath_exists('//town[text() = ''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
 ERROR:  unsupported XML feature
 LINE 1: ...ELECT xpath_exists('//town[text() = ''Toronto'']','<towns><t...
@@ -541,6 +583,12 @@ LINE 1: ...ELECT xpath_exists('//town[text() = ''Cwmbran'']','<towns><t...
                                                              ^
 DETAIL:  This functionality requires the server to be built with libxml support.
 HINT:  You need to rebuild PostgreSQL using --with-libxml.
+SELECT xpath_exists('count(/nosuchtag)', '<root/>'::xml);
+ERROR:  unsupported XML feature
+LINE 1: SELECT xpath_exists('count(/nosuchtag)', '<root/>'::xml);
+                                                 ^
+DETAIL:  This functionality requires the server to be built with libxml support.
+HINT:  You need to rebuild PostgreSQL using --with-libxml.
 INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
 ERROR:  unsupported XML feature
 LINE 1: INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</n...
diff --git a/src/test/regress/sql/xml.sql b/src/test/regress/sql/xml.sql
index 3270e157214..3623dbc254e 100644
--- a/src/test/regress/sql/xml.sql
+++ b/src/test/regress/sql/xml.sql
@@ -177,12 +177,20 @@ SELECT xpath('//loc:piece/@id', '<local:data xmlns:local="http://127.0.0.1"><loc
 SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
 SELECT xpath('//text()', '<root>&lt;</root>');
 SELECT xpath('//@value', '<root value="&lt;"/>');
+SELECT xpath('''<<invalid>>''', '<root/>');
+SELECT xpath('count(//*)', '<root><sub/><sub/></root>');
+SELECT xpath('count(//*)=0', '<root><sub/><sub/></root>');
+SELECT xpath('count(//*)=3', '<root><sub/><sub/></root>');
+SELECT xpath('name(/*)', '<root><sub/><sub/></root>');
+SELECT xpath('/nosuchtag', '<root/>');
 
 -- Test xmlexists and xpath_exists
 SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>');
 SELECT xmlexists('//town[text() = ''Cwmbran'']' PASSING BY REF '<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>');
+SELECT xmlexists('count(/nosuchtag)' PASSING BY REF '<root/>');
 SELECT xpath_exists('//town[text() = ''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
 SELECT xpath_exists('//town[text() = ''Cwmbran'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
+SELECT xpath_exists('count(/nosuchtag)', '<root/>'::xml);
 
 INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
 INSERT INTO xmltest VALUES (5, '<menu><beers><name>Molson</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);