Fix NPE in default value typechecks

PiperOrigin-RevId: 747495719
Change-Id: Ia0049e7ed25ee173abc20b3716243a902b210d70

Author: comius

src/main/java/net/starlark/java/eval/Eval.java

@@ -50,6 +50,7 @@
 import net.starlark.java.syntax.TokenKind;
 import net.starlark.java.syntax.UnaryOperatorExpression;
 import net.starlark.java.types.StarlarkType;
+import net.starlark.java.types.Types.CallableType;
 
 final class Eval {
 
@@ -167,6 +168,7 @@ private static StarlarkFunction newFunction(StarlarkThread.Frame fr, Resolver.Fu
     Object[] defaults = null;
     int nparams =
         rfn.getParameters().size() - (rfn.hasKwargs() ? 1 : 0) - (rfn.hasVarargs() ? 1 : 0);
+    CallableType functionType = rfn.getFunctionType();
     for (int i = 0; i < nparams; i++) {
       Expression expr = rfn.getParameters().get(i).getDefaultValue();
       if (expr == null && defaults == null) {
@@ -179,14 +181,16 @@ private static StarlarkFunction newFunction(StarlarkThread.Frame fr, Resolver.Fu
       defaults[i - (nparams - defaults.length)] = defaultValue;
 
       // Typecheck the default value
-      StarlarkType parameterType = rfn.getFunctionType().getParameterTypeByPos(i);
-      if (!TypeChecker.isValueSubtypeOf(defaultValue, parameterType)) {
-        throw Starlark.errorf(
-            "%s(): parameter '%s' has default value of type '%s', declares '%s'",
-            rfn.getName(),
-            rfn.getParameterNames().get(i),
-            TypeChecker.type(defaultValue),
-            parameterType);
+      if (functionType != null) {
+        StarlarkType parameterType = functionType.getParameterTypeByPos(i);
+        if (!TypeChecker.isValueSubtypeOf(defaultValue, parameterType)) {
+          throw Starlark.errorf(
+              "%s(): parameter '%s' has default value of type '%s', declares '%s'",
+              rfn.getName(),
+              rfn.getParameterNames().get(i),
+              TypeChecker.type(defaultValue),
+              parameterType);
+        }
       }
     }
     if (defaults == null) {

src/test/java/net/starlark/java/eval/TypeCheckTest.java

@@ -67,6 +67,8 @@ public void lambdaDoesntFail() throws Exception {
         "def f(a: None):", //
         "  x = lambda y: 1",
         "  x(1)",
+        "  y = lambda y = 1: 1",
+        "  y(1)",
         "f(None)");
   }