Adds a global term ordering for ORDER BY

Allows having a global order on the results even if it's unspecified by SPARQL.

This ordering is likely to change in the future (addition of proper support of other datatypes...).

lib/src/sparql/eval.rs

@@ -2567,7 +2567,21 @@ fn cmp_terms(dataset: &DatasetView, a: Option<&EncodedTerm>, b: Option<&EncodedT
             a => match b {
                 _ if b.is_named_node() || b.is_blank_node() => Ordering::Greater,
                 _ if b.is_triple() => Ordering::Less,
-                b => partial_cmp_literals(dataset, a, b).unwrap_or(Ordering::Equal),
+                b => {
+                    if let Some(ord) = partial_cmp_literals(dataset, a, b) {
+                        ord
+                    } else if let (Ok(Term::Literal(a)), Ok(Term::Literal(b))) =
+                        (dataset.decode_term(a), dataset.decode_term(b))
+                    {
+                        (a.value(), a.datatype(), a.language()).cmp(&(
+                            b.value(),
+                            b.datatype(),
+                            b.language(),
+                        ))
+                    } else {
+                        Ordering::Equal // Should never happen
+                    }
+                }
             },
         },
         (Some(_), None) => Ordering::Greater,

testsuite/oxigraph-tests/sparql/manifest.ttl

@@ -25,6 +25,7 @@
     :halloween_problem
     :nested_path
     :nested_expression
+    :order_terms
     ) .
 
 :small_unicode_escape_with_multibytes_char rdf:type mf:NegativeSyntaxTest ;
@@ -108,3 +109,8 @@
 :nested_expression rdf:type mf:PositiveSyntaxTest11 ;
     mf:name "A very nested expression" ;
     mf:action <nested_expression.rq> .
+
+:order_terms rdf:type mf:QueryEvaluationTest ;
+    mf:name "literals have an order for ORDER BY" ;
+    mf:action [ qt:query <order_terms.rq> ] ;
+    mf:result <order_terms.ttl> .

testsuite/oxigraph-tests/sparql/order_terms.rq

@@ -0,0 +1,3 @@
+SELECT ?o WHERE {
+    VALUES ?o { 4.0 "v" "u"@en "a" "d"@de "c"@en "b" "foo"^^<http://example.com/h> 1 "2021-30-30"^^<http://www.w3.org/2001/XMLSchema#date> "2020-30-29T00:00:00"^^<http://www.w3.org/2001/XMLSchema#dateTime> d }
+} ORDER BY ?o

testsuite/oxigraph-tests/sparql/order_terms.ttl

@@ -0,0 +1,66 @@
+@prefix rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
+@prefix rs:      <http://www.w3.org/2001/sw/DataAccess/tests/result-set#> .
+
+[]  rdf:type    rs:ResultSet ;
+    rs:resultVariable
+                "o" ;
+    rs:solution [ rs:binding  [ rs:value    -1e3 ;
+                                rs:variable "o"
+                              ] ;
+                  rs:index  1
+                ] ;
+    rs:solution [ rs:binding  [ rs:value    1 ;
+                                rs:variable "o"
+                              ] ;
+                  rs:index  2
+                ] ;
+    rs:solution [ rs:binding  [ rs:value    "2020-30-29T00:00:00"^^<http://www.w3.org/2001/XMLSchema#dateTime> ;
+                                rs:variable "o"
+                              ] ;
+                  rs:index  3
+                ] ;
+    rs:solution [ rs:binding  [ rs:value    "2021-30-30"^^<http://www.w3.org/2001/XMLSchema#date> ;
+                                rs:variable "o"
+                              ] ;
+                  rs:index  4
+                ] ;
+    rs:solution [ rs:binding  [ rs:value    4.0 ;
+                                rs:variable "o"
+                              ] ;
+                  rs:index  5
+                ] ;
+    rs:solution [ rs:binding  [ rs:value    "a" ;
+                                rs:variable "o"
+                              ] ;
+                  rs:index  6
+                ] ;
+    rs:solution [ rs:binding  [ rs:value    "b" ;
+                                rs:variable "o"
+                              ] ;
+                  rs:index  7
+                ] ;
+    rs:solution [ rs:binding  [ rs:value    "c"@en ;
+                                rs:variable "o"
+                              ] ;
+                  rs:index  8
+                ] ;
+    rs:solution [ rs:binding  [ rs:value    "d"@de ;
+                                rs:variable "o"
+                              ] ;
+                  rs:index  9
+                ] ;
+    rs:solution [ rs:binding  [ rs:value    "foo"^^<http://example.com/h> ;
+                                rs:variable "o"
+                              ] ;
+                  rs:index  10
+                ] ;
+    rs:solution [ rs:binding  [ rs:value    "u"@en ;
+                                rs:variable "o"
+                              ] ;
+                  rs:index  11
+                ] ;
+    rs:solution [ rs:binding  [ rs:value    "v" ;
+                                rs:variable "o"
+                              ] ;
+                  rs:index  12
+                ] .