go source for verification 2026-05-22

test/devirtualization_nil_panics.go

@@ -0,0 +1,100 @@
+// run
+
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"fmt"
+	"runtime"
+	"strings"
+)
+
+type A interface{ A() }
+
+type Impl struct{}
+
+func (*Impl) A() {}
+
+type Impl2 struct{}
+
+func (*Impl2) A() {}
+
+func main() {
+	shouldNilPanic(28, func() {
+		var v A
+		v.A()
+		v = &Impl{}
+	})
+	shouldNilPanic(36, func() {
+		var v A
+		defer func() {
+			v = &Impl{}
+		}()
+		v.A()
+	})
+	shouldNilPanic(43, func() {
+		var v A
+		f := func() {
+			v = &Impl{}
+		}
+		v.A()
+		f()
+	})
+
+	// Make sure that both devirtualized and non devirtualized
+	// variants have the panic at the same line.
+	shouldNilPanic(55, func() {
+		var v A
+		defer func() {
+			v = &Impl{}
+		}()
+		v. // A() is on a sepearate line
+			A()
+	})
+	shouldNilPanic(64, func() {
+		var v A
+		defer func() {
+			v = &Impl{}
+			v = &Impl2{} // assign different type, such that the call below does not get devirtualized
+		}()
+		v. // A() is on a sepearate line
+			A()
+	})
+}
+
+var cnt = 0
+
+func shouldNilPanic(wantLine int, f func()) {
+	cnt++
+	defer func() {
+		p := recover()
+		if p == nil {
+			panic("no nil deref panic")
+		}
+		if strings.Contains(fmt.Sprintf("%s", p), "invalid memory address or nil pointer dereference") {
+			callers := make([]uintptr, 128)
+			n := runtime.Callers(0, callers)
+			callers = callers[:n]
+
+			frames := runtime.CallersFrames(callers)
+			line := -1
+			for f, next := frames.Next(); next; f, next = frames.Next() {
+				if f.Func.Name() == fmt.Sprintf("main.main.func%v", cnt) {
+					line = f.Line
+					break
+				}
+			}
+
+			if line != wantLine {
+				panic(fmt.Sprintf("invalid line number in panic = %v; want = %v", line, wantLine))
+			}
+
+			return
+		}
+		panic(p)
+	}()
+	f()
+}