From daaa38ff412a7ba1bb4a09fc783148275a8b23cf Mon Sep 17 00:00:00 2001
From: Andy Seaborne <andy@apache.org>
Date: Sat, 19 Nov 2022 21:48:12 +0000
Subject: [PATCH] GH-1615: Variable scope checking for LATERAL

---
 .../jena/sparql/lang/SyntaxVarScope.java      | 58 +++++++++++++++++--
 1 file changed, 53 insertions(+), 5 deletions(-)

diff --git a/jena-arq/src/main/java/org/apache/jena/sparql/lang/SyntaxVarScope.java b/jena-arq/src/main/java/org/apache/jena/sparql/lang/SyntaxVarScope.java
index 38d7f960afd..cb79fd01ce8 100644
--- a/jena-arq/src/main/java/org/apache/jena/sparql/lang/SyntaxVarScope.java
+++ b/jena-arq/src/main/java/org/apache/jena/sparql/lang/SyntaxVarScope.java
@@ -222,12 +222,15 @@ public void visit(ElementGroup el) {
                 // Tests.
                 if ( e instanceof ElementBind ) {
                     Collection<Var> accScope = calcScopeAll(el.getElements(), i);
-                    check(accScope, (ElementBind)e);
+                    checkBIND(accScope, (ElementBind)e);
                 }
-
                 if ( e instanceof ElementService ) {
                     Collection<Var> accScope = calcScopeAll(el.getElements(), i);
-                    check(accScope, (ElementService)e);
+                    checkSERVICE(accScope, (ElementService)e);
+                }
+                if ( e instanceof ElementLateral ) {
+                    Collection<Var> accScope = calcScopeAll(el.getElements(), i);
+                    checkLATERAL(accScope, e);
                 }
             }
         }
@@ -246,19 +249,64 @@ private static Collection<Var> calcScope(List<Element> elements, int start, int
             return accScope;
         }
 
-        private static void check(Collection<Var> scope, ElementBind el) {
+        private static void checkBIND(Collection<Var> scope, ElementBind el) {
             Var var = el.getVar();
             if ( scope.contains(var) )
                 throw new QueryParseException("BIND: Variable used when already in-scope: " + var + " in " + el, -1, -1);
             checkExpr(scope, el.getExpr(), var);
         }
 
-        private static void check(Collection<Var> scope, ElementService el) {
+        private static void checkSERVICE(Collection<Var> scope, ElementService el) {
             if ( ARQ.isStrictMode() && el.getServiceNode().isVariable() ) {
                 Var var = Var.alloc(el.getServiceNode());
                 if ( !scope.contains(var) )
                     throw new QueryParseException("SERVICE: Variable not already in-scope: " + var + " in " + el, -1, -1);
             }
         }
+
+        private void checkLATERAL(Collection<Var> accScope, Element el) {
+            // Look for BIND/VALUES/SELECT-AS inside LATERAL
+            ElementVisitor checker = new ElementVisitorBase() {
+                @Override
+                public void visit(ElementBind eltBind) {
+                    if ( accScope.contains(eltBind.getVar()) )
+                        throw new QueryParseException("BIND: Variable " + eltBind.getVar() + " defined", -1, -1);
+                }
+                // @Override public void visit(ElementAssign eltAssign) {} -- LET -
+                // always OK
+
+                @Override
+                public void visit(ElementData eltData) {
+                    eltData.getVars().forEach(v -> {
+                        if ( accScope.contains(v) )
+                            throw new QueryParseException("VALUES: Variable " + v + " defined", -1, -1);
+                    });
+                }
+
+                @Override
+                public void visit(ElementSubQuery eltSubQuery) {
+                    // Only called when there is an expression.
+                    eltSubQuery.getQuery().getProject().forEachExpr((var, expr) -> {
+                        if ( accScope.contains(var) )
+                            throw new QueryParseException("SELECT: Variable " + var + " defined", -1 ,-1);
+                    });
+                    // Check inside query pattern
+                    Query subQuery = eltSubQuery.getQuery();
+                    Collection<Var> accScope2 = accScope;
+                    //eltSubQuery.getQuery().setResultVars();
+                    if ( ! subQuery.isQueryResultStar() ) {
+                        List<Var> projectVars = eltSubQuery.getQuery().getProject().getVars();
+                        // Calculate variables passed down : scope which are in the project vars.
+                        accScope2 = new ArrayList<>(accScope);
+                        accScope2.removeIf(v->!projectVars.contains(v));
+                    }
+                    Element el2 = eltSubQuery.getQuery().getQueryPattern();
+                    checkLATERAL(accScope2, el2);
+                }
+            };
+
+            // Does not walk into subqueries but we need to change the scoep for sub-queries.
+            ElementWalker.walk(el, checker);
+        }
     }
 }