runtime: make execution error panic values implement the Error interface

Make execution panics implement Error as
mandated by https://golang.org/ref/spec#Run_time_panics,
instead of panics with strings.

Fixes #14965

Change-Id: I7827f898b9b9c08af541db922cc24fa0800ff18a
Reviewed-on: https://go-review.googlesource.com/21214
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 12 insertions, 1 deletions

diff --git a/src/runtime/error.go b/src/runtime/error.go
index 3e1ec4bc5a..15f6bdf014 100644
--- a/src/runtime/error.go
+++ b/src/runtime/error.go
@@ -50,6 +50,17 @@ func (e errorString) Error() string {
 	return "runtime error: " + string(e)
 }
 
+// plainError represents a runtime error described a string without
+// the prefix "runtime error: " after invoking errorString.Error().
+// See Issue #14965.
+type plainError string
+
+func (e plainError) RuntimeError() {}
+
+func (e plainError) Error() string {
+	return string(e)
+}
+
 type stringer interface {
 	String() string
 }
@@ -82,5 +93,5 @@ func printany(i interface{}) {
 
 // called from generated code
 func panicwrap(pkg, typ, meth string) {
-	panic("value method " + pkg + "." + typ + "." + meth + " called using nil *" + typ + " pointer")
+	panic(plainError("value method " + pkg + "." + typ + "." + meth + " called using nil *" + typ + " pointer"))
 }