refactor(next): decouple execution engine from SPARQL AST

docs/next-engine-ast-boundary.md

@@ -1,58 +1,31 @@
 # Engine / AST dependency boundary
 
-The target is an execution engine independent of parser and SPARQL AST types.
-The current engine still exposes three dependencies. `NextModuleBoundaryTest`
-inventories them as exact source-path / referenced-type pairs, rather than
-exempting whole files or packages.
+The query execution engine is independent of parser and SPARQL AST types.
+`NextModuleBoundaryTest` enforces this invariant with zero exceptions across all
+engine sources.
 
-## Existing exceptions
+## Decoupling history
 
-Paths below are relative to `next/query/impl/engine`.
+Previously, three source files in `next/query/impl/engine` retained AST dependencies:
 
-| Source | AST type | Current use and callers |
-| --- | --- | --- |
-| `model/Filter.java` | `TermAst` | Return types of `getFilterExpression()` and `coreseNextSource()`. `NextFilterFromAst` implements both in the bridge. `Exp` delegates the first; `AstBackedExprTest` checks its result. No production caller of `coreseNextSource()` was found in `next`. |
-| `pattern/Exp.java` | `TermAst` | Return type of `getFilterExpression()`, delegating to `Filter`. No production caller of this accessor was found in `next`. |
-| `pattern/Query.java` | `QueryAst` | Field `ast` and accessors `getAST()`, `getGlobalAST()`, `setAST()`. `CoreseAstQueryBuilder` sets the source AST for each query form; `QueryTest` tests the accessors. No external production reader of these accessors was found in `next`. |
-
-This is a source-reference inventory, not a statement that these APIs can be
-removed without checking downstream clients. Bridge implementations may still
-own AST objects internally after the engine contracts stop exposing their types.
+- `model/Filter.java`: returned `TermAst` via `getFilterExpression()` and `coreseNextSource()`.
+  These AST accessors were removed from the engine interface; the bridge implementation
+  `NextFilterFromAst` retains AST-level access internally where needed.
+- `pattern/Exp.java`: exposed `getFilterExpression()` delegating to `Filter`. Removed as it
+  had no engine callers.
+- `pattern/Query.java`: retained `QueryAst ast` with `getAST()`, `getGlobalAST()`, and `setAST()`.
+  Removed from `Query`; query builder compilation produces pure engine operator trees.
 
 ## Guard behavior
 
+- Zero exceptions: `EXISTING_ENGINE_AST_DEPENDENCIES` is empty.
 - Parser dependencies have no exceptions.
 - Both the actual `query.impl.sparql.ast` package and the historical
   `query.impl.ast` package are checked.
 - Imports, wildcard imports, static references and fully qualified references
-  are detected by the existing source-reference matching approach.
-- Adding a type to an already listed file is rejected.
-- Adding an existing AST type to another file is rejected.
-- Removing a dependency requires removing its exception in the same change.
-
-The source scanner also sees fully qualified names in comments and strings. It
-does not perform bytecode or transitive dependency analysis. Its regression test
-uses synthetic sources to check new files, new types, wildcard imports and fully
-qualified references outside imports.
-
-## Follow-up: remove the exceptions
-
-1. Check repository-wide and downstream uses of the source-AST accessors before
-   removing them; assess compatibility of these implementation classes.
-2. Remove the unused `Exp` forwarding accessor and the AST accessors from the
-   engine `Filter` contract. Keep source-AST access inside the bridge where needed;
-   adapt `AstBackedExprTest` to test bridge behavior rather than an engine AST API.
-3. Remove AST retention from `Query` if no required consumer exists. If diagnostics
-   need source information, keep it in a bridge-owned structure with an explicit
-   lifecycle, rather than replacing typed accessors with `Object` or unsafe casts.
-4. Remove the corresponding builder writes and accessor-only tests. Preserve
-   behavioral tests for query forms, expressions and subqueries.
-5. Delete each exception as its dependency disappears, then restore the strict
-   no-AST-dependencies invariant in the engine package documentation.
-
-Do not introduce new runtime behavior as part of this follow-up. Validate with
-the architecture tests, the full core test suite and a comparison against the
-existing W3C baseline.
+  are detected by the source-reference scanner.
+- Any new dependency on parser or AST packages within `query/impl/engine` causes
+  `NextModuleBoundaryTest.queryEngineMustNotAddParserOrAstDependencies` to fail immediately.
 
 ## Validation
 

src/main/java/fr/inria/corese/core/next/query/impl/engine/model/Filter.java

@@ -1,27 +1,14 @@
 package fr.inria.corese.core.next.query.impl.engine.model;
 
-
-import fr.inria.corese.core.next.query.impl.sparql.ast.TermAst;
-
 import java.util.List;
-import java.util.Optional;
-
 
 /**
- * Native filter contract backed by the Corese-next SPARQL AST.
+ * Native filter contract for the Corese-next execution engine.
  *
  * @author Olivier Corby, Edelweiss, INRIA 2010
  */
 public interface Filter {
 
-    /**
-     * When non-empty, the Corese-next AST node this filter was produced from
-     * (filter expression: {@link TermAst} / constraint subtypes).
-     */
-    default Optional<TermAst> coreseNextSource() {
-        return Optional.empty();
-    }
-
     /**
      * List of variable names contained in the filter
      *
@@ -33,8 +20,6 @@ default Optional<TermAst> coreseNextSource() {
     /** Evaluable expression processed by the native KGRAM evaluator. */
     Expr getExp();
 
-    TermAst getFilterExpression();
-
     /**
      * Does filter contain a bound() function
      *

src/main/java/fr/inria/corese/core/next/query/impl/engine/package-info.java

@@ -7,11 +7,10 @@
  *
  * <h2>Architectural Invariants &amp; Development Guardrails</h2>
  * <ul>
- *   <li><b>AST Boundary</b>: New dependencies on parser or AST classes are forbidden.
- *   Three existing source/type dependencies in {@code Filter}, {@code Exp}, and
- *   {@code Query} remain explicitly inventoried by {@code NextModuleBoundaryTest}.
- *   Removing these exceptions is tracked in {@code docs/next-engine-ast-boundary.md};
- *   the target architecture executes compiled logical operators only.</li>
+ *   <li><b>AST Boundary</b>: Dependencies on parser or AST classes are strictly forbidden.
+ *   The execution engine operates exclusively on compiled logical operators and patterns;
+ *   zero AST dependencies exist or are permitted, as enforced by {@code NextModuleBoundaryTest}
+ *   and documented in {@code docs/next-engine-ast-boundary.md}.</li>
  *   <li><b>Storage Isolation</b>: Query evaluation and triple access must strictly
  *   transit through the {@link fr.inria.corese.core.next.query.impl.engine.spi.Producer}
  *   and Storage SPI abstractions.</li>

src/main/java/fr/inria/corese/core/next/query/impl/engine/pattern/Exp.java

@@ -14,7 +14,6 @@
 import fr.inria.corese.core.next.query.impl.engine.model.PointerType;
 import fr.inria.corese.core.next.query.impl.engine.model.Regex;
 import fr.inria.corese.core.next.query.impl.engine.spi.Producer;
-import fr.inria.corese.core.next.query.impl.sparql.ast.TermAst;
 
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -548,10 +547,6 @@ public void setFilter(Filter f) {
         }
     }
 
-    public TermAst getFilterExpression() {
-        return getFilter().getFilterExpression();
-    }
-
     public void addFilter(Filter f) {
         lFilter.add(f);
     }

src/main/java/fr/inria/corese/core/next/query/impl/engine/pattern/Query.java

@@ -11,7 +11,6 @@
 import fr.inria.corese.core.next.query.impl.engine.spi.Producer;
 import fr.inria.corese.core.next.query.impl.engine.filter.Compile;
 import fr.inria.corese.core.next.query.impl.engine.eval.Message;
-import fr.inria.corese.core.next.query.impl.sparql.ast.QueryAst;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -88,7 +87,6 @@ public final class Query extends Exp {
     // SPIN graph
     Query query;
     Query outerQuery;
-    QueryAst ast;
     Object object;
 
     // current transformer if any
@@ -287,18 +285,6 @@ public void setObject(Object o) {
         object = o;
     }
 
-    public QueryAst getGlobalAST() {
-        return getGlobalQuery().getAST();
-    }
-
-    public QueryAst getAST() {
-        return ast;
-    }
-
-    public void setAST(QueryAst o) {
-        ast = o;
-    }
-
     public int getPlanProfile() {
         return planner;
     }

src/main/java/fr/inria/corese/core/next/query/impl/sparql/bridge/CoreseAstQueryBuilder.java

@@ -72,7 +72,6 @@ public Query toNextQuery(AskQueryAst askQueryAst) {
                 compiler);
         SolutionModifierCompiler.applyOrderBy(query, askQueryAst.solutionModifier(), compiler);
         query.setAsk(true);
-        query.setAST(askQueryAst);
         return query;
     }
 
@@ -104,7 +103,6 @@ public Query toNextQuery(SelectQueryAst selectQueryAst) {
         if (query.getHaving() != null && !query.hasGroupBy()) {
             query.setAggregate(true);
         }
-        query.setAST(selectQueryAst);
         return query;
     }
 
@@ -131,7 +129,6 @@ public Query toNextQuery(DescribeQueryAst describeQueryAst) {
                 compiler);
         SolutionModifierCompiler.applyOrderBy(query, describeQueryAst.solutionModifier(), compiler);
         DescribeQueryCompiler.compile(query, describeQueryAst, compiler);
-        query.setAST(describeQueryAst);
         return query;
     }
 
@@ -157,7 +154,6 @@ public Query toNextQuery(ConstructQueryAst constructQueryAst) {
                 compiler);
         SolutionModifierCompiler.applyOrderBy(query, constructQueryAst.solutionModifier(), compiler);
         ConstructQueryCompiler.compile(query, constructQueryAst, compiler);
-        query.setAST(constructQueryAst);
         return query;
     }
 

src/main/java/fr/inria/corese/core/next/query/impl/sparql/bridge/NextFilterFromAst.java

@@ -53,7 +53,6 @@ public Expr getExp() {
         return owner;
     }
 
-    @Override
     public TermAst getFilterExpression() {
         return owner.sourceAst().orElseThrow();
     }
@@ -83,7 +82,6 @@ public boolean isRecExist() {
         return owner.isRecExist();
     }
 
-    @Override
     public Optional<TermAst> coreseNextSource() {
         return owner.sourceAst();
     }

src/test/java/fr/inria/corese/core/next/architecture/NextModuleBoundaryTest.java

@@ -27,12 +27,9 @@ class NextModuleBoundaryTest {
             "\\bfr\\.inria\\.corese\\.core(?:\\.[A-Za-z_$][A-Za-z0-9_$]*)+");
     private static final Pattern STATIC_IMPORT_PREFIX = Pattern.compile("^static\\s+");
 
+    // Engine must not depend on parser or AST types: zero exceptions.
     // Exact source/type pairs only: see docs/next-engine-ast-boundary.md.
-    // Equality below also requires removing exceptions when their dependencies disappear.
-    private static final Set<String> EXISTING_ENGINE_AST_DEPENDENCIES = Set.of(
-            "model/Filter.java -> fr.inria.corese.core.next.query.impl.sparql.ast.TermAst",
-            "pattern/Exp.java -> fr.inria.corese.core.next.query.impl.sparql.ast.TermAst",
-            "pattern/Query.java -> fr.inria.corese.core.next.query.impl.sparql.ast.QueryAst");
+    private static final Set<String> EXISTING_ENGINE_AST_DEPENDENCIES = Set.of();
 
     @Test
     void sharedCodeMustNotDependOnDomainModules() throws IOException {
@@ -105,7 +102,7 @@ void queryEngineMustNotAddParserOrAstDependencies() throws IOException {
     }
 
     @Test
-    void engineBoundaryFindsSyntaxReferencesBeyondExistingExceptions(@TempDir Path sources)
+    void engineBoundaryDetectsForbiddenSyntaxReferences(@TempDir Path sources)
             throws IOException {
         Path filter = sources.resolve("model/Filter.java");
         Files.createDirectories(filter.getParent());
@@ -121,8 +118,8 @@ class Filter {
         Files.writeString(sources.resolve("NewOperator.java"),
                 "import fr.inria.corese.core.next.query.impl.sparql.ast.TermAst;");
         Set<String> unexpected = engineSyntaxDependencies(sources);
-        unexpected.removeAll(EXISTING_ENGINE_AST_DEPENDENCIES);
         assertEquals(Set.of(
+                "model/Filter.java -> fr.inria.corese.core.next.query.impl.sparql.ast.TermAst",
                 "model/Filter.java -> fr.inria.corese.core.next.query.impl.sparql.ast.QueryAst",
                 "model/Filter.java -> fr.inria.corese.core.next.query.impl.sparql.parser.SparqlParser",
                 "model/Filter.java -> fr.inria.corese.core.next.query.impl.sparql.ast.VarAst",

src/test/java/fr/inria/corese/core/next/query/impl/engine/pattern/QueryTest.java

@@ -4,8 +4,6 @@
 import fr.inria.corese.core.next.query.impl.engine.model.ExpType;
 import fr.inria.corese.core.next.query.impl.engine.model.Filter;
 import fr.inria.corese.core.next.query.impl.engine.model.Node;
-import fr.inria.corese.core.next.query.impl.sparql.ast.QueryAst;
-import fr.inria.corese.core.next.query.impl.sparql.parser.SparqlParser;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Nested;
@@ -649,26 +647,6 @@ void testIsTransformationTemplate() {
         }
     }
 
-    @Nested
-    @DisplayName("AST Tests")
-    class ASTTests {
-
-        @Test
-        @DisplayName("Should set and get AST")
-        void testSetAndGetAST() {
-            QueryAst ast = new SparqlParser().parse("SELECT * WHERE { ?s ?p ?o }");
-            query.setAST(ast);
-            assertSame(ast, query.getAST(), "AST should match");
-        }
-
-        @Test
-        @DisplayName("Should get global AST")
-        void testGetGlobalAST() {
-            assertDoesNotThrow(() -> query.getGlobalAST(),
-                    "Getting global AST should not throw");
-        }
-    }
-
     @Nested
     @DisplayName("Global Query Tests")
     class GlobalQueryTests {

src/test/java/fr/inria/corese/core/next/query/impl/sparql/bridge/AstBackedExprTest.java

@@ -66,7 +66,7 @@ void boundExpressionAndFilterView() {
         assertNotNull(boundExpr.getFilter());
         assertTrue(boundExpr.getFilter().isBound());
         assertEquals(List.of("y"), boundExpr.getFilter().getVariables());
-        assertEquals(boundAst, boundExpr.getFilter().getFilterExpression());
+        assertEquals(boundAst, ((NextFilterFromAst) boundExpr.getFilter()).getFilterExpression());
     }
 
     @Test