Add partial eval support to the REPL.

.bazeliskrc

@@ -0,0 +1 @@
+USE_BAZEL_VERSION=6.4.0

cel/cel_test.go

@@ -1688,6 +1688,71 @@ func TestPartialVars(t *testing.T) {
 	}
 }
 
+func TestPartialVarsExtendedEnv(t *testing.T) {
+	env := testEnv(t,
+		Variable("x", IntType),
+		Variable("y", IntType),
+	)
+
+	// Use env to make sure internals are all initialized.
+	ast, iss := env.Compile("x == y")
+
+	if iss.Err() != nil {
+		t.Fatalf("env.Compile() failed: %v", iss.Err())
+	}
+	prg, err := env.Program(ast, EvalOptions(OptPartialEval))
+	if err != nil {
+		t.Fatalf("env.Program() failed: %v", err)
+	}
+
+	act, err := env.PartialVars(map[string]any{"x": 1, "y": 1})
+
+	if err != nil {
+		t.Fatalf("env.PartialVars failed: %v", err)
+	}
+	val, _, err := prg.Eval(act)
+	if err != nil {
+		t.Fatalf("Eval failed: %v", err)
+	}
+
+	if val != types.True {
+		t.Fatalf("want: %v, got: %v", types.True, val)
+	}
+
+	// Now test that a sub environment is correctly copied.
+	env2, err := env.Extend(Variable("z", IntType))
+	if err != nil {
+		t.Fatalf("env.Extend failed: %v", err)
+	}
+
+	ast, iss = env2.Compile("x == y && y == z")
+
+	if iss.Err() != nil {
+		t.Fatalf("env.Compile() failed: %v", iss.Err())
+	}
+	prg, err = env2.Program(ast, EvalOptions(OptPartialEval))
+	if err != nil {
+		t.Fatalf("env.Program() failed: %v", err)
+	}
+
+	act, err = env2.PartialVars(map[string]any{"z": 1, "y": 1})
+
+	if err != nil {
+		t.Fatalf("env.PartialVars failed: %v", err)
+	}
+	val, _, err = prg.Eval(act)
+	if err != nil {
+		t.Fatalf("Eval failed: %v", err)
+	}
+	if !types.IsUnknown(val) {
+		t.Fatalf("Wanted unknown, got %v", val)
+	}
+
+	if !reflect.DeepEqual(val, types.NewUnknown(1, types.NewAttributeTrail("x"))) {
+		t.Fatalf("Wanted Unknown(x (1)), got: %v", val)
+	}
+}
+
 func TestResidualAstAttributeQualifiers(t *testing.T) {
 	env := testEnv(t,
 		Variable("x", MapType(StringType, DynType)),

cel/env.go

@@ -308,18 +308,14 @@ func (e *Env) Extend(opts ...EnvOption) (*Env, error) {
 	chkOptsCopy := make([]checker.Option, len(e.chkOpts))
 	copy(chkOptsCopy, e.chkOpts)
 
-	// Copy the declarations if needed.
-	varsCopy := []*decls.VariableDecl{}
 	if chk != nil {
 		// If the type-checker has already been instantiated, then the e.declarations have been
 		// validated within the chk instance.
 		chkOptsCopy = append(chkOptsCopy, checker.ValidatedDeclarations(chk))
-	} else {
-		// If the type-checker has not been instantiated, ensure the unvalidated declarations are
-		// provided to the extended Env instance.
-		varsCopy = make([]*decls.VariableDecl, len(e.variables))
-		copy(varsCopy, e.variables)
 	}
+	// vars are used by PartialVars to infer unknown attribute paths.
+	varsCopy := make([]*decls.VariableDecl, len(e.variables))
+	copy(varsCopy, e.variables)
 
 	// Copy macros and program options
 	macsCopy := make([]parser.Macro, len(e.macros))

common/types/unknown.go

@@ -222,7 +222,9 @@ func (u *Unknown) Equal(other ref.Val) ref.Val {
 // String implements the Stringer interface
 func (u *Unknown) String() string {
 	var str strings.Builder
-	for id, attrs := range u.attributeTrails {
+	ids := u.IDs()
+	for _, id := range ids {
+		attrs := u.attributeTrails[id]
 		if str.Len() != 0 {
 			str.WriteString(", ")
 		}