From 0e0588572f3b046127839422e1855607676d5884 Mon Sep 17 00:00:00 2001
From: Marco Manino <mrcmnn@gmail.com>
Date: Tue, 13 Feb 2024 17:48:19 +0100
Subject: [PATCH 1/2] Checking for methodset existance

---
 interp/interpreter.go |  4 ++++
 testdata/init.go      | 11 +++++++++++
 2 files changed, 15 insertions(+)

diff --git a/interp/interpreter.go b/interp/interpreter.go
index 605f4d8fc6..e0074ba26a 100644
--- a/interp/interpreter.go
+++ b/interp/interpreter.go
@@ -427,6 +427,10 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 				if err != nil {
 					return nil, mem, r.errorAt(inst, err)
 				}
+				if typecodePtr.offset() == 0 {
+					locals[inst.localIndex] = literalValue{uint8(0)}
+					break
+				}
 				typecodePtrOffset, err := typecodePtr.addOffset(-int64(r.pointerSize))
 				if err != nil {
 					return nil, mem, r.errorAt(inst, err) // unlikely
diff --git a/testdata/init.go b/testdata/init.go
index fa470fd54f..8b34db3f38 100644
--- a/testdata/init.go
+++ b/testdata/init.go
@@ -109,3 +109,14 @@ func sliceString(s string, start, end int) string {
 func sliceSlice(s []int, start, end int) []int {
 	return s[start:end]
 }
+
+type outside struct{}
+
+func init() {
+	_, _ = any(0).(interface{ DoesNotExist() })
+	_, _ = any("").(interface{ DoesNotExist() })
+	_, _ = any(outside{}).(interface{ DoesNotExist() })
+
+	type inside struct{}
+	_, _ = any(inside{}).(interface{ DoesNotExist() })
+}

From a5a92cba4a628f59e2e4d1a9b446199ad86bc574 Mon Sep 17 00:00:00 2001
From: Marco Manino <mrcmnn@gmail.com>
Date: Mon, 18 Mar 2024 08:32:17 +0100
Subject: [PATCH 2/2] Adding a comment

---
 interp/interpreter.go | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/interp/interpreter.go b/interp/interpreter.go
index e0074ba26a..ea5eeaa12e 100644
--- a/interp/interpreter.go
+++ b/interp/interpreter.go
@@ -427,13 +427,20 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 				if err != nil {
 					return nil, mem, r.errorAt(inst, err)
 				}
+				// typecodePtr always point to the numMethod field in the type
+				// description struct. The methodSet, when present, comes right
+				// before the numMethod field (the compiler doesn't generate
+				// method sets for concrete types without methods).
+				// Considering that the compiler doesn't emit interface type
+				// asserts for interfaces with no methods (as the always succeed)
+				// then if the offset is zero, this assert must always fail.
 				if typecodePtr.offset() == 0 {
 					locals[inst.localIndex] = literalValue{uint8(0)}
 					break
 				}
 				typecodePtrOffset, err := typecodePtr.addOffset(-int64(r.pointerSize))
 				if err != nil {
-					return nil, mem, r.errorAt(inst, err) // unlikely
+					return nil, mem, r.errorAt(inst, err)
 				}
 				methodSetPtr, err := mem.load(typecodePtrOffset, r.pointerSize).asPointer(r)
 				if err != nil {