Reduce minimum length for specialize string diffing (#275)

The original threshold of 64 was chosen without much thought.
Lower it to 32 now that we have some concrete examples
that it is aesthetically better.

Co-authored-by: Damien Neil <neild@users.noreply.github.com>

cmp/compare_test.go

@@ -1338,6 +1338,19 @@ using the AllowUnexported option.`, "\n"),
 		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",
+	}, {
+		label: label + "/ShortJSON",
+		x: `{
+	"id": 1,
+	"foo": true,
+	"bar": true,
+}`,
+		y: `{
+	"id": 1434180,
+	"foo": true,
+	"bar": true,
+}`,
+		reason: "short multiline JSON should prefer triple-quoted string diff as it is more readable",
 	}}
 }
 

cmp/report_slices.go

@@ -80,7 +80,7 @@ func (opts formatOptions) CanFormatDiffSlice(v *valueNode) bool {
 	}
 
 	// Use specialized string diffing for longer slices or strings.
-	const minLength = 64
+	const minLength = 32
 	return vx.Len() >= minLength && vy.Len() >= minLength
 }
 

cmp/testdata/diffs

@@ -1122,6 +1122,18 @@
 + 	X: nil,
   }
 >>> TestDiff/Reporter/NonStringifiedNamedBytes
+<<< TestDiff/Reporter/ShortJSON
+  (
+  	"""
+  	{
+- 		"id": 1,
++ 		"id": 1434180,
+  		"foo": true,
+  		"bar": true,
+  	}
+  	"""
+  )
+>>> TestDiff/Reporter/ShortJSON
 <<< TestDiff/EmbeddedStruct/ParentStructA/Inequal
   teststructs.ParentStructA{
   	privateStruct: teststructs.privateStruct{