Fix textual printing of byte slices

There are two bugs being fixed:

1.  The hueristic for whether a slice of byte looks like text
    should check whether a rune IsPrint OR IsSpace, and not both.
    Only a single rune (i.e., U+0020) ever satisfies both conditions.

    Previously, it would print as:
        MyBytes{0x68, 0x65, 0x6c, 0x6c, 0x6f}
    and now it would now print as:
        MyBytes(MyBytes("hello"))

2.  If we're printing as string, then we should set skipType=true
    since we already explicitly format the value with the type.

    Previously, it would print as:
        MyBytes(MyBytes("hello"))
    and now it would now print as:
        MyBytes("hello")

cmp/compare_test.go

@@ -1317,6 +1317,26 @@ using the AllowUnexported option.`, "\n"),
 		x:      "d5c14bdf6bac81c27afc5429500ed750\n25483503b557c606dad4f144d27ae10b\n90bdbcdbb6ea7156068e3dcfb7459244\n978f480a6e3cced51e297fbff9a506b7\n",
 		y:      "Xd5c14bdf6bac81c27afc5429500ed750\nX25483503b557c606dad4f144d27ae10b\nX90bdbcdbb6ea7156068e3dcfb7459244\nX978f480a6e3cced51e297fbff9a506b7\n",
 		reason: "all lines are different, so diffing based on lines is pointless",
+	}, {
+		label:  label + "/StringifiedBytes",
+		x:      struct{ X []byte }{[]byte("hello, world!")},
+		y:      struct{ X []byte }{},
+		reason: "[]byte should be printed as text since it is printable text",
+	}, {
+		label:  label + "/NonStringifiedBytes",
+		x:      struct{ X []byte }{[]byte("\xde\xad\xbe\xef")},
+		y:      struct{ X []byte }{},
+		reason: "[]byte should not be printed as text since it is binary data",
+	}, {
+		label:  label + "/StringifiedNamedBytes",
+		x:      struct{ X MyBytes }{MyBytes("hello, world!")},
+		y:      struct{ X MyBytes }{},
+		reason: "MyBytes should be printed as text since it is printable text",
+	}, {
+		label:  label + "/NonStringifiedNamedBytes",
+		x:      struct{ X MyBytes }{MyBytes("\xde\xad\xbe\xef")},
+		y:      struct{ X MyBytes }{},
+		reason: "MyBytes should not be printed as text since it is binary data",
 	}}
 }
 

cmp/report_reflect.go

@@ -207,9 +207,10 @@ func (opts formatOptions) FormatValue(v reflect.Value, parentKind reflect.Kind,
 		// Check whether this is a []byte of text data.
 		if t.Elem() == reflect.TypeOf(byte(0)) {
 			b := v.Bytes()
-			isPrintSpace := func(r rune) bool { return unicode.IsPrint(r) && unicode.IsSpace(r) }
+			isPrintSpace := func(r rune) bool { return unicode.IsPrint(r) || unicode.IsSpace(r) }
 			if len(b) > 0 && utf8.Valid(b) && len(bytes.TrimFunc(b, isPrintSpace)) == 0 {
 				out = opts.formatString("", string(b))
+				skipType = true
 				return opts.WithTypeMode(emitType).FormatType(t, out)
 			}
 		}

cmp/testdata/diffs

@@ -1096,6 +1096,30 @@
   	"978f480a6e3cced51e297fbff9a506b7\n",
   }, "")
 >>> TestDiff/Reporter/AllLinesDiffer
+<<< TestDiff/Reporter/StringifiedBytes
+  struct{ X []uint8 }{
+- 	X: []uint8("hello, world!"),
++ 	X: nil,
+  }
+>>> TestDiff/Reporter/StringifiedBytes
+<<< TestDiff/Reporter/NonStringifiedBytes
+  struct{ X []uint8 }{
+- 	X: []uint8{0xde, 0xad, 0xbe, 0xef},
++ 	X: nil,
+  }
+>>> TestDiff/Reporter/NonStringifiedBytes
+<<< TestDiff/Reporter/StringifiedNamedBytes
+  struct{ X cmp_test.MyBytes }{
+- 	X: cmp_test.MyBytes("hello, world!"),
++ 	X: nil,
+  }
+>>> TestDiff/Reporter/StringifiedNamedBytes
+<<< TestDiff/Reporter/NonStringifiedNamedBytes
+  struct{ X cmp_test.MyBytes }{
+- 	X: cmp_test.MyBytes{0xde, 0xad, 0xbe, 0xef},
++ 	X: nil,
+  }
+>>> TestDiff/Reporter/NonStringifiedNamedBytes
 <<< TestDiff/EmbeddedStruct/ParentStructA/Inequal
   teststructs.ParentStructA{
   	privateStruct: teststructs.privateStruct{