gob: use pointers in bootstrapType so interfaces behave properly

and don't lead to a nil reflect.Type.
Fixes #1626.

R=rsc
CC=golang-dev
https://golang.org/cl/4289062

src/pkg/gob/type.go

@@ -222,22 +222,45 @@ func (t *CommonType) name() string { return t.Name }
 
 var (
 	// Primordial types, needed during initialization.
-	tBool      = bootstrapType("bool", false, 1)
-	tInt       = bootstrapType("int", int(0), 2)
-	tUint      = bootstrapType("uint", uint(0), 3)
-	tFloat     = bootstrapType("float", float64(0), 4)
-	tBytes     = bootstrapType("bytes", make([]byte, 0), 5)
-	tString    = bootstrapType("string", "", 6)
-	tComplex   = bootstrapType("complex", 0+0i, 7)
-	tInterface = bootstrapType("interface", interface{}(nil), 8)
+	// Always passed as pointers so the interface{} type
+	// goes through without losing its interfaceness.
+	tBool      = bootstrapType("bool", (*bool)(nil), 1)
+	tInt       = bootstrapType("int", (*int)(nil), 2)
+	tUint      = bootstrapType("uint", (*uint)(nil), 3)
+	tFloat     = bootstrapType("float", (*float64)(nil), 4)
+	tBytes     = bootstrapType("bytes", (*[]byte)(nil), 5)
+	tString    = bootstrapType("string", (*string)(nil), 6)
+	tComplex   = bootstrapType("complex", (*complex128)(nil), 7)
+	tInterface = bootstrapType("interface", (*interface{})(nil), 8)
 	// Reserve some Ids for compatible expansion
-	tReserved7 = bootstrapType("_reserved1", struct{ r7 int }{}, 9)
-	tReserved6 = bootstrapType("_reserved1", struct{ r6 int }{}, 10)
-	tReserved5 = bootstrapType("_reserved1", struct{ r5 int }{}, 11)
-	tReserved4 = bootstrapType("_reserved1", struct{ r4 int }{}, 12)
-	tReserved3 = bootstrapType("_reserved1", struct{ r3 int }{}, 13)
-	tReserved2 = bootstrapType("_reserved1", struct{ r2 int }{}, 14)
-	tReserved1 = bootstrapType("_reserved1", struct{ r1 int }{}, 15)
+	tReserved7 = bootstrapType("_reserved1", (*struct {
+		r7 int
+	})(nil),
+		9)
+	tReserved6 = bootstrapType("_reserved1", (*struct {
+		r6 int
+	})(nil),
+		10)
+	tReserved5 = bootstrapType("_reserved1", (*struct {
+		r5 int
+	})(nil),
+		11)
+	tReserved4 = bootstrapType("_reserved1", (*struct {
+		r4 int
+	})(nil),
+		12)
+	tReserved3 = bootstrapType("_reserved1", (*struct {
+		r3 int
+	})(nil),
+		13)
+	tReserved2 = bootstrapType("_reserved1", (*struct {
+		r2 int
+	})(nil),
+		14)
+	tReserved1 = bootstrapType("_reserved1", (*struct {
+		r1 int
+	})(nil),
+		15)
 )
 
 // Predefined because it's needed by the Decoder
@@ -564,9 +587,10 @@ func checkId(want, got typeId) {
 	}
 }
 
-// used for building the basic types; called only from init()
+// used for building the basic types; called only from init().  the incoming
+// interface always refers to a pointer.
 func bootstrapType(name string, e interface{}, expect typeId) typeId {
-	rt := reflect.Typeof(e)
+	rt := reflect.Typeof(e).(*reflect.PtrType).Elem()
 	_, present := types[rt]
 	if present {
 		panic("bootstrap type already present: " + name + ", " + rt.String())