xmerl: Fix XPath relational operators <, <= and >=

Author: tomciopp

lib/xmerl/src/xmerl_xpath_pred.erl

@@ -166,15 +166,15 @@ comp_expr('>', E1, E2, C) ->
 comp_expr('<', E1, E2, C) ->
     N1 = expr(E1,C),
     N2 = expr(E2,C),
-    ?boolean(compare_ineq_format(N1,N2,C) > compare_ineq_format(N2,N1,C));
+    ?boolean(compare_ineq_format(N1,N2,C) < compare_ineq_format(N2,N1,C));
 comp_expr('>=', E1, E2, C) ->
     N1 = expr(E1,C),
     N2 = expr(E2,C),
-    ?boolean(compare_ineq_format(N1,N2,C) > compare_ineq_format(N2,N1,C));
+    ?boolean(compare_ineq_format(N1,N2,C) >= compare_ineq_format(N2,N1,C));
 comp_expr('<=', E1, E2, C) ->
     N1 = expr(E1,C),
     N2 = expr(E2,C),
-    ?boolean(compare_ineq_format(N1,N2,C) > compare_ineq_format(N2,N1,C));
+    ?boolean(compare_ineq_format(N1,N2,C) =< compare_ineq_format(N2,N1,C));
 comp_expr('=', E1, E2, C) ->
     N1 = expr(E1,C),
     N2 = expr(E2,C),

lib/xmerl/test/xmerl_SUITE.erl

@@ -45,7 +45,8 @@
 all() ->
     [doctests,
      {group, cpd_tests}, xpath_text1, xpath_main,
-     xpath_abbreviated_syntax, xpath_functions, xpath_namespaces,
+     xpath_abbreviated_syntax, xpath_functions, xpath_relational,
+     xpath_namespaces,
      {group, misc}, {group, eventp_tests},
      {group, ticket_tests}, {group, app_test},
      {group, appup_test}, {group, format_test}].
@@ -192,6 +193,10 @@ xpath_functions(Config) ->
     file:set_cwd(filename:join(datadir(Config),xpath)),
     ok = xpath_abbrev:functions().
 
+xpath_relational(Config) ->
+    file:set_cwd(filename:join(datadir(Config),xpath)),
+    ok = xpath_abbrev:relational_operators().
+
 xpath_namespaces(Config) ->
     file:set_cwd(filename:join(datadir(Config),xpath)),
     ok = xpath_abbrev:namespaces().

lib/xmerl/test/xmerl_SUITE_data/xpath/xpath_abbrev.erl

@@ -8,6 +8,7 @@
 -module(xpath_abbrev).
 
 -export([test/0, check_node_set/2, ticket_6873/0, ticket_7496/0, functions/0]).
+-export([relational_operators/0]).
 -export([namespaces/0]).
 
 -include_lib("common_test/include/ct.hrl").
@@ -218,6 +219,34 @@ ticket_7496() ->
     ok = Test(Doc3,"//*[starts-with(local-name(),'p')]",
               [parent,pet,pet]).
 
+%% Regression test for the relational operators '<', '<=' and '>='.
+%% These three clauses of xmerl_xpath_pred:comp_expr/4 each carried the
+%% body of '>' (a copy-paste error), so every one evaluated as 'a > b'.
+%% The cases below fail on the buggy code (each selects [e,f] / [] instead
+%% of the expected node sets) and pass once the operators are correct.
+relational_operators() ->
+    Test = fun(Doc, XPath, Exp) ->
+                   Result = xmerl_xpath:string(XPath, Doc),
+                   Exp = [Name || #xmlElement{name = Name} <- Result],
+                   ok
+           end,
+    {Doc,_} = xmerl_scan:string("<a><b/><c/><d/><e/><f/></a>"),
+
+    %% Relational predicates over position() (number vs number).
+    ok = Test(Doc, "/a/*[position() < 3]",  [b, c]),
+    ok = Test(Doc, "/a/*[position() <= 3]", [b, c, d]),
+    ok = Test(Doc, "/a/*[position() >= 3]", [d, e, f]),
+    ok = Test(Doc, "/a/*[position() > 3]",  [e, f]),
+
+    %% Constant relational predicates, independent of position(): each is a
+    %% boolean that is true, so it selects every child.
+    All = [b, c, d, e, f],
+    ok = Test(Doc, "/a/*[2 < 3]",  All),
+    ok = Test(Doc, "/a/*[3 <= 3]", All),
+    ok = Test(Doc, "/a/*[3 >= 3]", All),
+    ok = Test(Doc, "/a/*[3 > 2]",  All),
+    ok.
+
 
 functions() ->
     Test = fun(Doc, XPath, Exp) ->