Closures: deterministic order of captured variables in query plans

basex-core/src/main/java/org/basex/query/func/Closure.java

@@ -95,7 +95,7 @@ public Closure(final InputInfo info, final Expr expr, final Params params, final
     this.params = params;
     this.anns = anns;
     this.vs = vs;
-    this.global = global == null ? new HashMap<>() : new HashMap<>(global);
+    this.global = global == null ? new HashMap<>() : new LinkedHashMap<>(global);
     props = new FlagCache(flag -> {
       for(final Expr ex : this.global.values()) {
         if(ex.has(flag)) return true;
@@ -197,7 +197,7 @@ public Expr optimize(final CompileContext cc) {
             cc.info(OPTINLINE_X, entry);
             for(final Entry<Var, Expr> expr2 : cl.global.entrySet()) {
               final Var var2 = cc.copy(expr2.getKey(), null);
-              if(add == null) add = new HashMap<>();
+              if(add == null) add = new LinkedHashMap<>();
               add.put(var2, expr2.getValue());
               expr2.setValue(new VarRef(cl.info, var2).optimize(cc));
             }
@@ -335,15 +335,15 @@ public Expr inline(final InlineContext ic) throws QueryException {
   public Expr copy(final CompileContext cc, final IntObjectMap<Var> vm) {
     final VarScope scope = new VarScope();
 
-    final HashMap<Var, Expr> outer = new HashMap<>();
+    final HashMap<Var, Expr> outer = new LinkedHashMap<>();
     global.forEach((key, value) -> outer.put(key, value.copy(cc, vm)));
 
     cc.pushScope(scope);
     try {
       final IntObjectMap<Var> innerVars = new IntObjectMap<>();
       vs.copy(cc, innerVars);
 
-      final HashMap<Var, Expr> bindings = new HashMap<>();
+      final HashMap<Var, Expr> bindings = new LinkedHashMap<>();
       outer.forEach((key, value) -> bindings.put(innerVars.get(key.id), value));
 
       final Var[] prms = params.clone();

basex-core/src/main/java/org/basex/query/func/PartFunc.java

@@ -112,7 +112,7 @@ private Expr closure(final Expr func, final FuncType ft, final int nargs,
     cc.pushScope(vs);
     try {
       // the function and the supplied arguments are evaluated once, when the closure is created
-      final HashMap<Var, Expr> global = new HashMap<>();
+      final HashMap<Var, Expr> global = new LinkedHashMap<>();
       final Var fn = vs.addNew(new QNm(FUNCTION), func.seqType(), cc.qc, info);
       global.put(fn, func);
 

basex-core/src/main/java/org/basex/query/util/parse/LocalVars.java

@@ -119,7 +119,7 @@ private QNm[] inScopeNames() {
    * @return global map or {@code null}
    */
   public HashMap<Var, Expr> pushContext(final boolean global) {
-    final HashMap<Var, Expr> map = global ? new HashMap<>() : null;
+    final HashMap<Var, Expr> map = global ? new LinkedHashMap<>() : null;
     vars.add(new VarContext(map));
     return map;
   }

basex-core/src/test/java/org/basex/query/ast/FuncItemTest.java

@@ -2,8 +2,10 @@
 
 import static org.basex.query.QueryError.*;
 import static org.basex.query.func.Function.*;
+import static org.junit.jupiter.api.Assertions.*;
 
 import org.basex.*;
+import org.basex.query.*;
 import org.basex.query.expr.*;
 import org.basex.query.func.*;
 import org.basex.query.value.item.*;
@@ -745,4 +747,37 @@ declare record local:rec(i as xs:integer, inc as fn(local:rec) as local:rec := f
     query(java + "let $f as fn() as xs:string* := $j return count($f())", 0);
     error(java + "let $f as fn() as xs:integer := $j return $f()", INVTYPE_X);
   }
+
+  /**
+   * Plans of closures with several captured variables are identical across compilations.
+   * @throws Exception exception
+   */
+  @Test public void closurePlanOrder() throws Exception {
+    final String vars = "let $a := <a/>, $b := <b/>, $c := <c/>, $d := <d/> ";
+    final String[] queries = {
+      // parsed closure
+      vars + "return fn() { ($a, $b, $c, $d) }",
+      "let $n := <n/>, $m := <m/>, $o := <o/> return "
+          + "deep-equal(fn($x) { fn() { $x, $n, $o } }, fn($y) { fn() { $y, $m, $o } })",
+      // nested closure is inlined into the surrounding closure
+      vars + "let $f := fn() { ($a, $b, $c, $d) } return fn() { $f() }",
+      // closure is copied when the function body is inlined
+      "declare %basex:inline(1000) function local:f($x) { "
+          + "let $a := <a/>, $b := <b/>, $c := <c/> return fn() { ($a, $b, $c, $x) } }; "
+          + "local:f(<x/>), local:f(<y/>)",
+      // partial function application is rewritten to a closure
+      "replace(?, random:uuid(), random:uuid(), random:uuid())"
+    };
+    for(final String query : queries) {
+      String first = null;
+      for(int r = 0; r < 100; r++) {
+        try(QueryProcessor qp = new QueryProcessor(query, context)) {
+          qp.optimize();
+          final String plan = qp.toXml().serialize().toString();
+          if(first == null) first = plan;
+          else assertEquals(first, plan, "Run " + r + ": " + query);
+        }
+      }
+    }
+  }
 }