Fix segfault with Ptr<T> extension using 'This' type reference (#7719)

* Fix segfault with Ptr<T> extension using 'This' type reference

Set LookupOptions::NoDeref when looking up target type members within
extension declarations to prevent automatic pointer dereferencing that
was causing breadcrumb handling issues and segfaults.

Fixes #7656

Co-authored-by: Yong He <csyonghe@users.noreply.github.com>

* Enhance test for ptr-extension-this-type to verify correctness with interpreter

- Changed function to return sizeof(This) - sizeof(Ptr<int>) + 1
- Modified test to use interpreter with filecheck to verify result equals 1
- Added main() function that calls the extension method and prints result
- Verifies that 'This' correctly refers to Ptr<int> in extension context

Co-authored-by: Yong He <csyonghe@users.noreply.github.com>

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Yong He <csyonghe@users.noreply.github.com>

2 files changed, 45 insertions, 1 deletions

diff --git a/source/slang/slang-lookup.cpp b/source/slang/slang-lookup.cpp
index 604cee2b7..a9b472776 100644
--- a/source/slang/slang-lookup.cpp
+++ b/source/slang/slang-lookup.cpp
@@ -959,7 +959,23 @@ static void _lookUpInScopes(
                     }
                 }
 
-                _lookUpMembersInType(astBuilder, name, type, request, result, breadcrumbPtr);
+                // When looking up in an extension declaration, we should not automatically
+                // dereference pointer types, as the 'This' type should refer to the
+                // extension target type itself, not the pointed-to type.
+                LookupRequest modifiedRequest = request;
+                if (aggTypeDeclBaseRef.as<ExtensionDecl>())
+                {
+                    modifiedRequest.options = (LookupOptions)((uint32_t)modifiedRequest.options |
+                                                              (uint32_t)LookupOptions::NoDeref);
+                }
+
+                _lookUpMembersInType(
+                    astBuilder,
+                    name,
+                    type,
+                    modifiedRequest,
+                    result,
+                    breadcrumbPtr);
             }
             else
             {
diff --git a/tests/bugs/ptr-extension-this-type.slang b/tests/bugs/ptr-extension-this-type.slang
new file mode 100644
index 000000000..627db5302
--- /dev/null
+++ b/tests/bugs/ptr-extension-this-type.slang
@@ -0,0 +1,28 @@
+//TEST:INTERPRET(filecheck=CHECK):
+
+// Test for issue #7656: Compiler segfault with Ptr<T> extension referring to This
+// This test ensures that the compiler doesn't segfault when 'This' is used in Ptr<T> extensions
+
+public interface IThing
+{
+    int f(This other);
+}
+
+public extension Ptr<int>: IThing
+{
+    public int f(This other)
+    {
+        // Test that 'This' refers to Ptr<int>, not the pointed-to type int
+        return sizeof(This) - sizeof(Ptr<int>) + 1;
+    }
+}
+
+void main()
+{
+    Ptr<int> p;
+    Ptr<int> other;
+    int result = p.f(other);
+    
+    // CHECK: 1
+    printf("%d\n", result);
+}
\ No newline at end of file