From d5fcb386864232c4b315ea7f9838e455a2ce3cda Mon Sep 17 00:00:00 2001
From: Joe Tsai <joetsai@digital-static.net>
Date: Sun, 18 Jul 2021 17:32:48 -0700
Subject: [PATCH] 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   | 20 ++++++++++++++++++++
 cmp/report_reflect.go |  3 ++-
 cmp/testdata/diffs    | 24 ++++++++++++++++++++++++
 3 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/cmp/compare_test.go b/cmp/compare_test.go
index dc0bfe0..a435209 100644
--- a/cmp/compare_test.go
+++ b/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",
 	}}
 }
 
diff --git a/cmp/report_reflect.go b/cmp/report_reflect.go
index 33f0357..76c04fd 100644
--- a/cmp/report_reflect.go
+++ b/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)
 			}
 		}
diff --git a/cmp/testdata/diffs b/cmp/testdata/diffs
index a3d5909..96ea191 100644
--- a/cmp/testdata/diffs
+++ b/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{