Implement advanceEvaluation API for planner

runtime/src/main/java/dev/cel/runtime/CelRuntimeImpl.java

@@ -255,8 +255,8 @@ public Object trace(PartialVars partialVars, CelEvaluationListener listener)
       }
 
       @Override
-      public Object advanceEvaluation(UnknownContext context) {
-        throw new UnsupportedOperationException("Unsupported operation.");
+      public Object advanceEvaluation(UnknownContext context) throws CelEvaluationException {
+        return program.eval(context.toPartialVars());
       }
     };
   }

runtime/src/main/java/dev/cel/runtime/UnknownContext.java

@@ -107,6 +107,11 @@ public GlobalResolver variableResolver() {
     return variableResolver;
   }
 
+  PartialVars toPartialVars() {
+    return PartialVars.of(
+        name -> Optional.ofNullable(variableResolver.resolve(name)), unresolvedAttributes);
+  }
+
   /**
    * Creates a new unknown context that is a copy of the current context with the provided
    * additional attribute values.

runtime/src/test/java/dev/cel/runtime/CelRuntimeTest.java

@@ -142,13 +142,18 @@ public void evaluate_v1alpha1CheckedExpr() throws Exception {
   public void advanceEvaluation_withUnknownTracking_noSelfReferenceInMerge(String expression)
       throws Exception {
     Cel cel =
-        CelFactory.standardCelBuilder()
+        runtimeFlavor
+            .builder()
             .setStandardMacros(CelStandardMacro.STANDARD_MACROS)
             .addCompilerLibraries(CelExtensions.bindings())
             .setContainer(CelContainer.ofName("cel.expr.conformance.test"))
             .addVar("unknown_attr", SimpleType.INT)
             .addVar("my_list", ListType.create(SimpleType.INT))
-            .setOptions(CelOptions.current().enableUnknownTracking(true).build())
+            .setOptions(
+                CelOptions.current()
+                    .enableHeterogeneousNumericComparisons(true)
+                    .enableUnknownTracking(true)
+                    .build())
             .build();
 
     CelUnknownSet result =
@@ -170,6 +175,59 @@ public void advanceEvaluation_withUnknownTracking_noSelfReferenceInMerge(String
     assertThat(result.attributes()).containsExactly(CelAttribute.create("unknown_attr"));
   }
 
+  @Test
+  public void advanceEvaluation_withUnknownContext_tracksUnknowns() throws Exception {
+    Cel cel =
+        runtimeFlavor
+            .builder()
+            .setOptions(
+                CelOptions.current()
+                    .enableHeterogeneousNumericComparisons(true)
+                    .enableUnknownTracking(true)
+                    .build())
+            .setContainer(CelContainer.ofName("com.google"))
+            .addVar("com.google.a", SimpleType.BOOL)
+            .addVar("com.google.b", SimpleType.BOOL)
+            .setResultType(SimpleType.BOOL)
+            .build();
+    CelRuntime.Program program = cel.createProgram(cel.compile("b ? a : false").getAst());
+    UnknownContext context =
+        UnknownContext.create(
+            name -> name.equals("com.google.b") ? Optional.of(true) : Optional.empty(),
+            ImmutableList.of(CelAttributePattern.fromQualifiedIdentifier("com.google.a")));
+
+    CelUnknownSet unknownResult = (CelUnknownSet) program.advanceEvaluation(context);
+
+    assertThat(unknownResult.attributes())
+        .containsExactly(CelAttribute.fromQualifiedIdentifier("com.google.a"));
+  }
+
+  @Test
+  public void advanceEvaluation_withResolvedUnknownContext_evaluatesResult() throws Exception {
+    Cel cel =
+        runtimeFlavor
+            .builder()
+            .setOptions(
+                CelOptions.current()
+                    .enableHeterogeneousNumericComparisons(true)
+                    .enableUnknownTracking(true)
+                    .build())
+            .setContainer(CelContainer.ofName("com.google"))
+            .addVar("com.google.a", SimpleType.BOOL)
+            .addVar("com.google.b", SimpleType.BOOL)
+            .setResultType(SimpleType.BOOL)
+            .build();
+    CelRuntime.Program program = cel.createProgram(cel.compile("a || b").getAst());
+    ImmutableMap<String, Boolean> vars =
+        ImmutableMap.of("com.google.a", true, "com.google.b", false);
+    UnknownContext context =
+        UnknownContext.create(name -> Optional.ofNullable(vars.get(name)), ImmutableList.of());
+
+    Object resolvedResult = program.advanceEvaluation(context);
+
+    assertThat(resolvedResult).isEqualTo(true);
+  }
+
   @Test
   public void newWellKnownTypeMessage_withDifferentDescriptorInstance() throws Exception {
     CelCompiler celCompiler =

runtime/src/test/java/dev/cel/runtime/UnknownContextTest.java

@@ -167,4 +167,20 @@ public void withResolvedAttributes_attributeResolverPartialsShadowed() {
                 CelAttribute.fromQualifiedIdentifier("qualified.Identifier.field2")))
         .isEmpty();
   }
+
+  @Test
+  public void toPartialVars_preservesResolverAndUnknowns() {
+    CelAttributePattern pattern =
+        CelAttributePattern.fromQualifiedIdentifier("qualified.Identifier");
+    UnknownContext context =
+        UnknownContext.create(
+            name -> name.equals("x") ? Optional.of("val") : Optional.empty(),
+            ImmutableList.of(pattern));
+
+    PartialVars partialVars = context.toPartialVars();
+
+    assertThat(partialVars.resolver().find("x")).hasValue("val");
+    assertThat(partialVars.resolver().find("missing")).isEmpty();
+    assertThat(partialVars.unknowns()).containsExactly(pattern);
+  }
 }