Keep declared and refined function return types separate in FuncType

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

@@ -206,9 +206,8 @@ public Expr optimize(final CompileContext cc) {
       cc.removeScope(this);
     }
 
-    final SeqType st = expr.seqType();
-    final SeqType dt = declType == null || st.instanceOf(declType) ? st : declType;
-    exprType.assign(FuncType.get(anns, dt, params));
+    // declared type for instance-of/coercion (item()* if none), body type as refined return type
+    exprType.assign(FuncType.get(anns, declType, params).withRefinedType(expr.seqType()));
 
     // only evaluate if:
     // - the closure is empty, so we don't lose variables

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

@@ -107,7 +107,7 @@ public Expr optimize(final CompileContext cc) throws QueryException {
       if(!updating && ft.anns.contains(Annotation.UPDATING)) {
         throw FUNCUP_X.get(info, func);
       }
-      exprType.assign(ft.declType);
+      exprType.assign(ft.refinedType);
     }
 
     if(func instanceof XQStruct) {

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

@@ -67,7 +67,7 @@ public Expr optimize(final CompileContext cc) throws QueryException {
           args[placeholderPerm == null ? a : placeholderPerm[a]] = ft.argTypes[e];
           ++a;
         }
-        exprType.assign(FuncType.get(ft.declType, args).seqType());
+        exprType.assign(FuncType.get(ft.declType, args).withRefinedType(ft.refinedType).seqType());
       }
     }
     return this;
@@ -114,7 +114,7 @@ private FuncItem funcItem(final FItem func, final QueryContext qc) throws QueryE
     final boolean updating = anns.contains(Annotation.UPDATING);
     final DynFuncCall expr = new DynFuncCall(info, updating, false, func, args);
 
-    final FuncType type = FuncType.get(anns, ft.declType, params);
+    final FuncType type = FuncType.get(anns, ft.declType, params).withRefinedType(ft.refinedType);
     return new FuncItem(info, expr, params, anns, type, vs.stackSize(), null, qc.focus.copy());
   }
 

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

@@ -150,7 +150,8 @@ public QNm paramName(final int pos) {
 
   @Override
   public FuncType funcType() {
-    return FuncType.get(anns, declType, params);
+    // refined return type: the body type (via seqType), consistent with call-result typing
+    return FuncType.get(anns, declType, params).withRefinedType(seqType());
   }
 
   @Override

basex-core/src/main/java/org/basex/query/func/array/ArrayBuild.java

@@ -43,7 +43,7 @@ protected Expr opt(final CompileContext cc) throws QueryException {
 
     arg(1, arg -> refineFunc(arg, cc, st.with(Occ.EXACTLY_ONE), Types.INTEGER_O));
     final FuncType ft = arg(1).funcType();
-    if(ft != null) exprType.assign(ArrayType.get(ft.declType));
+    if(ft != null) exprType.assign(ArrayType.get(ft.refinedType));
     return this;
   }
 

basex-core/src/main/java/org/basex/query/func/array/ArrayForEach.java

@@ -41,7 +41,7 @@ protected Expr opt(final CompileContext cc) throws QueryException {
 
     // assign type after coercion (expression might have changed)
     final FuncType ft = arg(1).funcType();
-    if(ft != null) exprType.assign(ArrayType.get(ft.declType));
+    if(ft != null) exprType.assign(ArrayType.get(ft.refinedType));
 
     return this;
   }

basex-core/src/main/java/org/basex/query/func/array/ArrayForEachPair.java

@@ -47,7 +47,7 @@ protected Expr opt(final CompileContext cc) throws QueryException {
 
     // assign type after coercion (expression might have changed)
     final FuncType ft = arg(2).funcType();
-    if(ft != null) exprType.assign(ArrayType.get(ft.declType));
+    if(ft != null) exprType.assign(ArrayType.get(ft.refinedType));
 
     return this;
   }

basex-core/src/main/java/org/basex/query/func/fn/FnApply.java

@@ -57,7 +57,7 @@ protected Expr opt(final CompileContext cc) throws QueryException {
     }
 
     ft = arg(0).funcType();
-    if(ft != null) exprType.assign(ft.declType);
+    if(ft != null) exprType.assign(ft.refinedType);
     return this;
   }
 

basex-core/src/main/java/org/basex/query/func/fn/FnFoldLeft.java

@@ -124,12 +124,12 @@ protected final Expr optType(final CompileContext cc, final boolean array, final
         final SeqType[] types = { left ? st : i1t, left ? i1t : st, Types.INTEGER_O };
         arg(2, arg -> refineFunc(action, cc, types));
         ost = st;
-        st = st.union(arg(2).funcType().declType);
+        st = st.union(arg(2).funcType().refinedType);
       } while(!st.eq(ost));
       exprType.assign(st);
     } else {
       final FuncType ft = action.funcType();
-      if(ft != null) exprType.assign(ist.oneOrMore() ? ft.declType : zst.union(ft.declType));
+      if(ft != null) exprType.assign(ist.oneOrMore() ? ft.refinedType : zst.union(ft.refinedType));
     }
     return this;
   }

basex-core/src/main/java/org/basex/query/func/fn/FnForEachPair.java

@@ -22,7 +22,7 @@ public final Iter iter(final QueryContext qc) throws QueryException {
     final FItem action = toFunction(arg(2), 3, this instanceof UpdateForEachPair, qc);
 
     return new Iter() {
-      final long size = action.funcType().declType.one() ?
+      final long size = action.funcType().refinedType.one() ?
         Math.min(input1.size(), input2.size()) : -1;
       final HofArgs args = new HofArgs(3, action);
       Iter iter = Empty.ITER;
@@ -64,7 +64,7 @@ protected final Expr opt(final CompileContext cc) throws QueryException {
     // assign type after refinement
     final FuncType ft = arg(2).funcType();
     if(ft != null) {
-      final SeqType declType = ft.declType;
+      final SeqType declType = ft.refinedType;
       final boolean oneOrMore = st1.oneOrMore() && st2.oneOrMore() && declType.oneOrMore();
       final long size = declType.zero() ? 0 : declType.one() ?
         Math.min(input1.size(), input2.size()) : -1;

basex-core/src/main/java/org/basex/query/func/fn/FnGenerate.java

@@ -45,7 +45,7 @@ protected Expr opt(final CompileContext cc) throws QueryException {
         final SeqType[] types = { st, Types.INTEGER_O };
         arg(1, arg -> refineFunc(step, cc, types));
         ost = st;
-        st = st.union(arg(1).funcType().declType);
+        st = st.union(arg(1).funcType().refinedType);
       } while(!st.eq(ost));
       exprType.assign(st.with(Occ.ONE_OR_MORE));
     }

basex-core/src/main/java/org/basex/query/func/fn/FnPartialApply.java

@@ -68,7 +68,7 @@ public Value value(final QueryContext qc) throws QueryException {
       funcCall = new DynFuncCall(info,
           new PartFunc(info, ExprList.concat(funcArgs, function), placeholders, null), args);
     }
-    return new FuncItem(info, funcCall, params, AnnList.EMPTY, FuncType.get(ft.declType, argTypes),
-        params.length, null);
+    return new FuncItem(info, funcCall, params, AnnList.EMPTY,
+        FuncType.get(ft.declType, argTypes).withRefinedType(ft.refinedType), params.length, null);
   }
-}
+}

basex-core/src/main/java/org/basex/query/func/fn/FnWhileDo.java

@@ -38,7 +38,7 @@ protected final Expr opt(final CompileContext cc) throws QueryException {
         final SeqType[] types = { st, Types.INTEGER_O };
         arg(a, arg -> refineFunc(action, cc, types));
         ost = st;
-        st = st.union(arg(a).funcType().declType);
+        st = st.union(arg(a).funcType().refinedType);
       } while(!st.eq(ost));
 
       final SeqType[] types = { st, Types.INTEGER_O };
@@ -48,7 +48,7 @@ protected final Expr opt(final CompileContext cc) throws QueryException {
       exprType.assign(st);
     } else {
       final FuncType ft = action.funcType();
-      if(ft != null) exprType.assign(st.union(ft.declType));
+      if(ft != null) exprType.assign(st.union(ft.refinedType));
     }
     return this;
   }

basex-core/src/main/java/org/basex/query/func/hof/HofFoldLeft1.java

@@ -37,7 +37,7 @@ protected Expr opt(final CompileContext cc) {
     if(input.seqType().zero()) return input;
 
     final FuncType ft = action.funcType();
-    if(ft != null) exprType.assign(ft.declType);
+    if(ft != null) exprType.assign(ft.refinedType);
     return this;
   }
 }

basex-core/src/main/java/org/basex/query/func/hof/HofScanLeft.java

@@ -45,7 +45,7 @@ protected Expr opt(final CompileContext cc) throws QueryException {
 
     SeqType st = zero.seqType();
     final FuncType ft = action.funcType();
-    if(ft != null) st = st.union(ft.declType);
+    if(ft != null) st = st.union(ft.refinedType);
     exprType.assign(st.with(Occ.ZERO_OR_MORE));
     return this;
   }

basex-core/src/main/java/org/basex/query/func/map/MapBuild.java

@@ -52,15 +52,15 @@ protected Expr opt(final CompileContext cc) throws QueryException {
     Type kt = fiKey || keys.size() == 0 ? s1t.type : BasicType.ITEM;
     if(fiKey) {
       arg(1, arg -> refineFunc(arg, cc, s1t));
-      kt = arg(1).funcType().declType.type;
+      kt = arg(1).funcType().refinedType.type;
     }
     kt = kt.atomic();
 
     final boolean fiValue = value instanceof FuncItem || value instanceof Closure;
     SeqType vt = fiValue || value.size() == 0 ? s1t : Types.ITEM_ZM;
     if(fiValue) {
       arg(2, arg -> refineFunc(arg, cc, s1t));
-      vt = arg(2).funcType().declType;
+      vt = arg(2).funcType().refinedType;
     }
     assignType(kt, vt);
     return this;

basex-core/src/main/java/org/basex/query/func/map/MapForEach.java

@@ -23,7 +23,7 @@ public Iter iter(final QueryContext qc) throws QueryException {
     final FItem action = toFunction(arg(1), 3, this instanceof UpdateMapForEach, qc);
 
     return new Iter() {
-      final long size = action.funcType().declType.one() ? map.structSize() : -1;
+      final long size = action.funcType().refinedType.one() ? map.structSize() : -1;
       final BasicIter<Item> keys = map.keys().iter();
       final HofArgs args = new HofArgs(3, action);
       Iter iter = Empty.ITER;
@@ -65,7 +65,7 @@ protected final Expr opt(final CompileContext cc) throws QueryException {
 
     final FuncType ft = arg(1).funcType();
     if(ft != null) {
-      final SeqType st = ft.declType;
+      final SeqType st = ft.refinedType;
       exprType.assign(st.type.seqType(Occ.ZERO_OR_MORE), st.one() ? map.structSize() : -1);
     }
     return this;

basex-core/src/main/java/org/basex/query/func/map/MapMerge.java

@@ -245,7 +245,7 @@ Value get(final Item key, final Value old, final Value value, final QueryContext
 
     @Override
     SeqType type(final SeqType st) {
-      return st.union(function.funcType().declType);
+      return st.union(function.funcType().refinedType);
     }
   }
 }

basex-core/src/main/java/org/basex/query/func/xquery/XQueryForEach.java

@@ -46,7 +46,7 @@ protected Expr opt(final CompileContext cc) throws QueryException {
     if(arg(2) == Empty.UNDEFINED) {
       final FuncType ft = action.funcType();
       if(ft != null) {
-        final SeqType dt = ft.declType;
+        final SeqType dt = ft.refinedType;
         exprType.assign(dt.with(dt.occ.multiply(input.seqType().occ)));
       }
     }

basex-core/src/main/java/org/basex/query/func/xquery/XQueryForkAny.java

@@ -53,7 +53,7 @@ protected Expr opt(final CompileContext cc) throws QueryException {
       return new DynFuncCall(info, coerceFunc(0, cc)).optimize(cc);
     }
     final FuncType ft = functions.funcType();
-    if(ft != null) exprType.assign(ft.declType);
+    if(ft != null) exprType.assign(ft.refinedType);
     return this;
   }
 }

basex-core/src/main/java/org/basex/query/func/xquery/XQueryForkJoin.java

@@ -54,7 +54,7 @@ protected Expr opt(final CompileContext cc) throws QueryException {
     if(results == Boolean.TRUE) {
       final FuncType ft = functions.funcType();
       if(ft != null) {
-        final SeqType dt = ft.declType;
+        final SeqType dt = ft.refinedType;
         exprType.assign(dt.with(dt.occ.multiply(st.occ)));
       }
     } else if(results == Boolean.FALSE) {

basex-core/src/main/java/org/basex/query/func/xquery/XQueryReduce.java

@@ -35,8 +35,8 @@ protected Expr opt(final CompileContext cc) {
     // result type: union of the seed type and the declared action/combine types
     SeqType st = init.seqType();
     final FuncType at = arg(2).funcType(), ct = arg(3).funcType();
-    if(at != null) st = st.union(at.declType);
-    if(ct != null) st = st.union(ct.declType);
+    if(at != null) st = st.union(at.refinedType);
+    if(ct != null) st = st.union(ct.refinedType);
     exprType.assign(st);
     return this;
   }

basex-core/src/main/java/org/basex/query/value/item/FItem.java

@@ -107,15 +107,13 @@ public FItem coerceTo(final FuncType ft, final QueryContext qc, final CompileCon
 
       // add type check if return types differ
       final SeqType dt = ft.declType;
-      FuncType tp = funcType();
       if(!body.seqType().instanceOf(dt)) {
         body = new TypeCheck(info, body, dt);
         if(cc != null) body = body.optimize(cc);
       }
 
-      // adopt type of optimized body if it is more specific than passed on type
-      final SeqType bt = body.seqType();
-      tp = cc != null && !bt.eq(dt) && bt.instanceOf(dt) ? FuncType.get(bt, argTypes) : ft;
+      // advertise the target type; keep the body type as refined return type for result typing
+      final FuncType tp = cc != null ? ft.withRefinedType(body.seqType()) : ft;
       body.markTailCalls(null);
       return new FuncItem(info, body, vars, annotations(), tp, vs.stackSize(), funcName());
     } finally {