encoding/json: stop escaping U+2028 and U+2029 in Compact

Compact has been inconsistently escaping only some problematic characters
(U+2028 and U+2029), but not others (<, > and &). This change addresses
this inconsistency by removing the escaping of U+2028 and U+2029.

Callers who need to escape the output of Compact should use HTMLEscape
which escapes <, >, &, U+2028 and U+2029.

Fixes #34070
Fixes #30357
Updates #5836

Change-Id: Icfce7691d2b8b1d9b05ba7b64d2d1e4f3b67871b
GitHub-Last-Rev: 38859fe3e2fd586bbd45175c2742f7b123836bf3
GitHub-Pull-Request: golang/go#34804
Reviewed-on: https://go-review.googlesource.com/c/go/+/200217Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/encoding/json/indent.go

@@ -28,7 +28,7 @@ func compact(dst *bytes.Buffer, src []byte, escape bool) error {
 			start = i + 1
 		}
 		// Convert U+2028 and U+2029 (E2 80 A8 and E2 80 A9).
-		if c == 0xE2 && i+2 < len(src) && src[i+1] == 0x80 && src[i+2]&^1 == 0xA8 {
+		if escape && c == 0xE2 && i+2 < len(src) && src[i+1] == 0x80 && src[i+2]&^1 == 0xA8 {
 			if start < i {
 				dst.Write(src[start:i])
 			}

src/encoding/json/scanner_test.go

@@ -48,6 +48,7 @@ var examples = []example{
 	{`[1,2,3]`, "[\n\t1,\n\t2,\n\t3\n]"},
 	{`{"x":1}`, "{\n\t\"x\": 1\n}"},
 	{ex1, ex1i},
+	{"{\"\":\"<>&\u2028\u2029\"}", "{\n\t\"\": \"<>&\u2028\u2029\"\n}"}, // See golang.org/issue/34070
 }
 
 var ex1 = `[true,false,null,"x",1,1.5,0,-5e+2]`
@@ -89,8 +90,8 @@ func TestCompactSeparators(t *testing.T) {
 	tests := []struct {
 		in, compact string
 	}{
-		{"{\"\u2028\": 1}", `{"\u2028":1}`},
-		{"{\"\u2029\" :2}", `{"\u2029":2}`},
+		{"{\"\u2028\": 1}", "{\"\u2028\":1}"},
+		{"{\"\u2029\" :2}", "{\"\u2029\":2}"},
 	}
 	for _, tt := range tests {
 		var buf bytes.Buffer