feldera · mihaibudiu · Aug 11, 2026 · Aug 7, 2026 · Aug 7, 2026 · Aug 7, 2026
diff --git a/crates/pipeline-manager/src/compiler/sql_compiler.rs b/crates/pipeline-manager/src/compiler/sql_compiler.rs
@@ -1165,7 +1165,7 @@ mod test {
                 .create_pipeline(tenant_id, "p1", "v0", program_code)
                 .await;
             test.sql_compiler_tick().await;
-            test.check_outcome_sql_compiled(tenant_id, pipeline_id, program_code)
+            test.check_outcome_sql_compiled(tenant_id, pipeline_id, program_code, true)
                 .await;
             test.delete_pipeline(tenant_id, pipeline_id, "p1").await;
             test.sql_compiler_tick().await;
@@ -1218,7 +1218,7 @@ mod test {
             .await;
         test.sql_compiler_tick().await;
         let pipeline_descr = test
-            .check_outcome_sql_compiled(tenant_id, pipeline_id, program_code)
+            .check_outcome_sql_compiled(tenant_id, pipeline_id, program_code, false)
             .await;
 
         // Check the types of the table and view
@@ -1406,7 +1406,7 @@ mod test {
             .await;
         test.sql_compiler_tick().await;
         let pipeline_descr = test
-            .check_outcome_sql_compiled(tenant_id, pipeline_id, program_code)
+            .check_outcome_sql_compiled(tenant_id, pipeline_id, program_code, false)
             .await;
 
         // Check materialized outcome
@@ -1471,7 +1471,7 @@ mod test {
 
         // Check result
         let pipeline_descr = test
-            .check_outcome_sql_compiled(tenant_id, pipeline_id, program_code)
+            .check_outcome_sql_compiled(tenant_id, pipeline_id, program_code, false)
             .await;
         let input_connectors = validate_program_info(&pipeline_descr.program_info.clone().unwrap())
             .unwrap()

diff --git a/crates/pipeline-manager/src/compiler/test.rs b/crates/pipeline-manager/src/compiler/test.rs
@@ -218,6 +218,7 @@ impl CompilerTest {
         tenant_id: TenantId,
         pipeline_id: PipelineId,
         program_code: &str,
+        warnings: bool,
     ) -> ExtendedPipelineDescr {
         // Retrieve pipeline descriptor
         let pipeline_descr = self.get_pipeline(tenant_id, pipeline_id).await;
@@ -271,7 +272,9 @@ impl CompilerTest {
         );
         assert_eq!(content_program_sql, program_code);
         assert_ne!(content_schema_json, "");
-        assert_eq!(content_stderr_log, "");
+        if (!warnings) {
+            assert_eq!(content_stderr_log, "");
+        }
         assert_eq!(content_stdout_log, "");
 
         // Return the pipeline descriptor

diff --git a/...er/SQL-compiler/src/main/java/org/dbsp/sqlCompiler/compiler/visitors/inner/Expensive.java b/...er/SQL-compiler/src/main/java/org/dbsp/sqlCompiler/compiler/visitors/inner/Expensive.java
@@ -72,7 +72,6 @@ public VisitDecision preorder(DBSPApplyMethodExpression unused) {
 
     @Override
     public VisitDecision preorder(DBSPBinaryExpression expression) {
-        // Lowered to a runtime function call
         if (expression.opcode == DBSPOpcode.VARIANT_INDEX) {
             this.expensive = true;
             return VisitDecision.STOP;
@@ -82,7 +81,6 @@ public VisitDecision preorder(DBSPBinaryExpression expression) {
 
     @Override
     public VisitDecision preorder(DBSPCastExpression expression) {
-        // VARIANT casts are lowered to runtime function calls
         if (expression.getType().is(DBSPTypeVariant.class) ||
                 expression.source.getType().is(DBSPTypeVariant.class)) {
             this.expensive = true;

diff --git a/...ompiler/src/main/java/org/dbsp/sqlCompiler/compiler/visitors/inner/ResolveReferences.java b/...ompiler/src/main/java/org/dbsp/sqlCompiler/compiler/visitors/inner/ResolveReferences.java
@@ -73,6 +73,7 @@ public VisitDecision preorder(DBSPLetExpression expression) {
         expression.initializer.accept(this);
         this.substitutionContext.newContext();
         this.substitutionContext.substitute(expression.variable.variable, expression);
+        this.reference.declare(expression.variable, expression);
         expression.consumer.accept(this);
         this.substitutionContext.popContext();
         return VisitDecision.STOP;

diff --git a/...compiler/src/main/java/org/dbsp/sqlCompiler/compiler/visitors/outer/CircuitOptimizer.java b/...compiler/src/main/java/org/dbsp/sqlCompiler/compiler/visitors/outer/CircuitOptimizer.java
@@ -96,6 +96,7 @@ void createOptimizer() {
         AnalyzedSet<DBSPOperator> operatorsAnalyzed = new AnalyzedSet<>();
         this.add(new OptimizeWithGraph(compiler,
                 g -> new OptimizeProjections(compiler, true, g, operatorsAnalyzed), 1));
+        this.add(new FuseExpensiveMaps(compiler));
         this.add(new RemoveViewOperators(compiler, false));
         this.add(new UnusedFields(compiler));
         this.add(new Intern(compiler));
@@ -173,6 +174,7 @@ void createOptimizer() {
         this.add(new OptimizeWithGraph(compiler, g -> new StrayGC(compiler, g)));
         // The canonical form is needed if we want the Merkle hashes to be "stable".
         this.add(new CanonicalForm(compiler).getCircuitRewriter(false));
+        this.add(new ConstantViews(compiler));
         this.add(new StaticDeclarations(compiler, new ImplementStatics(compiler, !compiler.options.ioOptions.multiCrates())));
         // From now on we cannot really change the graph anymore.
 

diff --git a/...QL-compiler/src/main/java/org/dbsp/sqlCompiler/compiler/visitors/outer/ConstantViews.java b/...QL-compiler/src/main/java/org/dbsp/sqlCompiler/compiler/visitors/outer/ConstantViews.java
@@ -0,0 +1,44 @@
+package org.dbsp.sqlCompiler.compiler.visitors.outer;
+
+import org.dbsp.sqlCompiler.circuit.OutputPort;
+import org.dbsp.sqlCompiler.circuit.operator.DBSPConstantOperator;
+import org.dbsp.sqlCompiler.circuit.operator.DBSPDifferentiateOperator;
+import org.dbsp.sqlCompiler.circuit.operator.DBSPSinkOperator;
+import org.dbsp.sqlCompiler.compiler.DBSPCompiler;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/** Give a warning when a view is fed from a constant operator
+ * (via potentially a differentiator) */
+public class ConstantViews extends CircuitVisitor {
+    final Set<OutputPort> constant = new HashSet<>();
+
+    public ConstantViews(DBSPCompiler compiler) {
+        super(compiler);
+    }
+
+    @Override
+    public void postorder(DBSPConstantOperator operator) {
+        this.constant.add(operator.outputPort());
+    }
+
+    @Override
+    public void postorder(DBSPDifferentiateOperator operator) {
+        if (this.constant.contains(operator.input())) {
+            this.constant.add(operator.outputPort());
+        }
+    }
+
+    @Override
+    public void postorder(DBSPSinkOperator operator) {
+        if (operator.viewName.equals(DBSPCompiler.ERROR_VIEW_NAME))
+            return;
+        if (this.constant.contains(operator.input())) {
+            this.compiler.reportWarning(
+                    operator.getSourcePosition(),
+                    "View is constant",
+                    "View " + operator.viewName.singleQuote() + " does not depend on any input data");
+        }
+    }
+}