C++: Fix wobble in PrintAST test

PrintAST.ql orders the functions by location, then in lexicographical order of the function signature. This is supposed to ensure a stable ordering, but functions without a location were not getting assigned an order at all.

cpp/ql/src/semmle/code/cpp/PrintAST.qll

@@ -39,6 +39,26 @@ private Location getRepresentativeLocation(Locatable ast) {
   result = rank[1](Location loc | loc = ast.getLocation() | loc order by loc.toString())
 }
 
+/**
+ * Computes the sort keys to sort the given AST node by location. An AST without
+ * a location gets an empty file name and a zero line and column number.
+ */
+private predicate locationSortKeys(Locatable ast, string file, int line,
+    int column) {
+  if exists(getRepresentativeLocation(ast)) then (
+    exists(Location loc |
+      loc = getRepresentativeLocation(ast) and
+      file = loc.getFile().toString() and
+      line = loc.getStartLine() and
+      column = loc.getStartColumn()
+    )
+  ) else (
+    file = "" and
+    line = 0 and
+    column = 0
+  )
+}
+
 /**
  * Most nodes are just a wrapper around `Locatable`, but we do synthesize new
  * nodes for things like parameter lists and constructor init lists.
@@ -482,12 +502,14 @@ class FunctionNode extends ASTNode {
   }
 
   private int getOrder() {
-    this = rank[result](FunctionNode node, Function function, Location loc |
-      node.getAST() = function and loc = getRepresentativeLocation(function) |
+    this = rank[result](FunctionNode node, Function function, string file, 
+        int line, int column |
+      node.getAST() = function and
+      locationSortKeys(function, file, line, column) |
       node order by 
-        loc.getFile().toString(),
-        loc.getStartLine(),
-        loc.getStartColumn(),
+        file,
+        line,
+        column,
         function.getFullSignature()
     )
   }

cpp/ql/test/library-tests/ir/ir/PrintAST.expected

@@ -2,16 +2,22 @@
 #-----|   params: 
 #-----| __va_list_tag::operator=() -> __va_list_tag &
 #-----|   params: 
-#-----| operator new(unsigned long) -> void *
-#-----|   params: 
-#-----|     0: p#0
-#-----|         Type = unsigned long
 #-----| operator delete(void *, unsigned long) -> void
 #-----|   params: 
 #-----|     0: p#0
 #-----|         Type = void *
 #-----|     1: p#1
 #-----|         Type = unsigned long
+#-----| operator delete[](void *, unsigned long) -> void
+#-----|   params: 
+#-----|     0: p#0
+#-----|         Type = void *
+#-----|     1: p#1
+#-----|         Type = unsigned long
+#-----| operator new(unsigned long) -> void *
+#-----|   params: 
+#-----|     0: p#0
+#-----|         Type = unsigned long
 #-----| operator new(unsigned long, align_val_t) -> void *
 #-----|   params: 
 #-----|     0: p#0
@@ -22,12 +28,6 @@
 #-----|   params: 
 #-----|     0: p#0
 #-----|         Type = unsigned long
-#-----| operator delete[](void *, unsigned long) -> void
-#-----|   params: 
-#-----|     0: p#0
-#-----|         Type = void *
-#-----|     1: p#1
-#-----|         Type = unsigned long
 #-----| operator new[](unsigned long, align_val_t) -> void *
 #-----|   params: 
 #-----|     0: p#0