cmd/cue/cmd: support byte in get go

Much like the last change to teach it about uintptr,
do the same about byte, an alias for uint8 in Go.

Note that the get_go code already had special cases to handle byte
slices and arrays, but byte arrays had no test coverage here,
so we add a test case for them as well.

Fixes #1336.

Change-Id: I040b12da56077cee60e699aa31d1ebcd78e6bc28
Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/536752
Unity-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Roger Peppe <rogpeppe@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

Author: mvdan

cmd/cue/cmd/get_go.go

@@ -1132,6 +1132,8 @@ func (e *extractor) makeType(expr types.Type) (result cueast.Expr) {
 		switch t := x.String(); t {
 		case "uintptr":
 			return e.ident("uint64", false)
+		case "byte":
+			return e.ident("uint8", false)
 		default:
 			return e.ident(t, false)
 		}

cmd/cue/cmd/testdata/script/get_go_types.txt

@@ -65,6 +65,8 @@ type Foozer struct {
 
 	Ptr uintptr
 
+	Byte byte
+
 	// Time is mapped to CUE's internal type.
 	Time time.Time
 
@@ -81,6 +83,7 @@ type Foozer struct {
 	Array1 [5]int
 	Array2 [5]interface{}
 	Array3 *[5]json.Marshaler
+	Array4 [5]byte
 
 	Intf  Interface `protobuf:"varint,2,name=intf"`
 	Intf2 interface{}
@@ -397,6 +400,7 @@ import (
 	AnyText:     string             @go(,encoding.TextMarshaler)
 	bar?:        int & >10          @go(Bar)
 	Ptr:         uint64             @go(,uintptr)
+	Byte:        uint8              @go(,byte)
 
 	// Time is mapped to CUE's internal type.
 	Time:    time.Time
@@ -412,6 +416,7 @@ import (
 	Array1:  5 * [int]    @go(,[5]int)
 	Array2:  5 * [_]      @go(,[5]interface{})
 	Array3?: null | 5*[_] @go(,*[5]json.Marshaler)
+	Array4:  bytes        @go(,[5]byte)
 	Intf:    #Interface   @protobuf(2,varint,name=intf)
 	Intf2:   _            @go(,interface{})
 	Intf3: {