From 30e79255c4228d977cfd0e5e9bb329a7d970f996 Mon Sep 17 00:00:00 2001
From: Paul King <paulk@asert.com.au>
Date: Fri, 28 Aug 2026 06:38:11 +1000
Subject: [PATCH] GROOVY-12305: STC: record narrowed type of instanceof-guarded
 property expression for static compilation

---
 .../stc/StaticTypeCheckingVisitor.java        |  8 ++++++-
 .../stc/FieldsAndPropertiesSTCTest.groovy     | 24 +++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java b/src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java
index ac48070d093..f74ee46f309 100644
--- a/src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java
+++ b/src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java
@@ -861,6 +861,12 @@ public void visitPropertyExpression(final PropertyExpression expression) {
         boolean readOnly = !typeCheckingContext.isTargetOfEnclosingAssignment(expression);
         if (existsProperty(expression, readOnly)
                 || extension.handleUnresolvedProperty(expression)) {
+            if (readOnly) { // GROOVY-12305: record narrowed type of instanceof-guarded receiver for later use
+                ClassNode temporaryType = getInferredTypeFromTempInfo(expression, expression.getNodeMetaData(INFERRED_TYPE));
+                if (temporaryType != null && !isObjectType(temporaryType)) {
+                    expression.putNodeMetaData(INFERRED_TYPE, temporaryType);
+                }
+            }
             return; // resolved or excused
         }
         recordMissingProperty(expression);
@@ -7428,7 +7434,7 @@ protected List<ClassNode> getTemporaryTypesForExpression(final Expression expres
     }
 
     private ClassNode getInferredTypeFromTempInfo(final Expression expression, final ClassNode expressionType) {
-        if (expression instanceof VariableExpression && !isPrimitiveType(expressionType)) {
+        if ((expression instanceof VariableExpression || expression instanceof PropertyExpression) && !isPrimitiveType(expressionType)) {
             List<ClassNode> tempTypes = getTemporaryTypesForExpression(expression);
             if (!tempTypes.isEmpty()) {
                 ClassNode   superclass;
diff --git a/src/test/groovy/groovy/transform/stc/FieldsAndPropertiesSTCTest.groovy b/src/test/groovy/groovy/transform/stc/FieldsAndPropertiesSTCTest.groovy
index 26dcbf13e61..c9c97db48e0 100644
--- a/src/test/groovy/groovy/transform/stc/FieldsAndPropertiesSTCTest.groovy
+++ b/src/test/groovy/groovy/transform/stc/FieldsAndPropertiesSTCTest.groovy
@@ -1321,6 +1321,30 @@ class FieldsAndPropertiesSTCTest extends StaticTypeCheckingTestCase {
         '''
     }
 
+    // GROOVY-12305
+    @Test
+    void testMapPropertyAccess19() {
+        assertScript '''
+            def test(Map foo) {
+                foo.a instanceof Map ? foo.a.b : foo.a
+            }
+            assert test(a: [b: 'c']) == 'c'
+            assert test(a: 'x') == 'x'
+        '''
+
+        assertScript '''
+            def test(Map foo) {
+                if (foo.a instanceof Map) {
+                    foo.a.b
+                } else {
+                    foo.a
+                }
+            }
+            assert test(a: [b: 'c']) == 'c'
+            assert test(a: 'x') == 'x'
+        '''
+    }
+
     @Test
     void testTypeCheckerDoesNotThinkPropertyIsReadOnly() {
         assertScript '''