From 7b44fcd865370d5ecf7471b04ad1b4e013e63708 Mon Sep 17 00:00:00 2001
From: Damian Gryski <damian@gryski.com>
Date: Fri, 24 Feb 2023 23:48:31 -0800
Subject: [PATCH] runtime: properly turn pointer into empty interface when
 hashing

---
 src/runtime/hashmap.go |  2 +-
 testdata/map.go        | 34 ++++++++++++++++++++++++++++++++++
 testdata/map.txt       |  1 +
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/src/runtime/hashmap.go b/src/runtime/hashmap.go
index 2db09f59..e00b223d 100644
--- a/src/runtime/hashmap.go
+++ b/src/runtime/hashmap.go
@@ -563,7 +563,7 @@ func hashmapInterfaceHash(itf interface{}, seed uintptr) uint32 {
 }
 
 func hashmapInterfacePtrHash(iptr unsafe.Pointer, size uintptr, seed uintptr) uint32 {
-	_i := *(*_interface)(iptr)
+	_i := *(*interface{})(iptr)
 	return hashmapInterfaceHash(_i, seed)
 }
 
diff --git a/testdata/map.go b/testdata/map.go
index d3088991..d746cf9f 100644
--- a/testdata/map.go
+++ b/testdata/map.go
@@ -129,6 +129,8 @@ func main() {
 	floatcmplx()
 
 	mapgrow()
+
+	interfacerehash()
 }
 
 func floatcmplx() {
@@ -274,3 +276,35 @@ func mapgrow() {
 	}
 	println("done")
 }
+
+type Counter interface {
+	count() int
+}
+
+type counter struct {
+	i int
+}
+
+func (c *counter) count() int {
+	return c.i
+}
+
+func interfacerehash() {
+	m := make(map[Counter]int)
+
+	for i := 0; i < 20; i++ {
+		c := &counter{i}
+		m[c] = i
+	}
+
+	var failures int
+	for k, v := range m {
+		if got := m[k]; got != v {
+			println("lookup failure got", got, "want", v)
+			failures++
+		}
+	}
+	if failures == 0 {
+		println("no interface lookup failures")
+	}
+}
diff --git a/testdata/map.txt b/testdata/map.txt
index 6bf04c80..d5e553b1 100644
--- a/testdata/map.txt
+++ b/testdata/map.txt
@@ -80,3 +80,4 @@ tested growing of a map
 2
 2
 done
+no interface lookup failures