Move pyquote into main codebase

We added pyquote in b429839d (tests: Show pickles in a way that can be
copy-pasted into Python). However in the next patch this functionality
will be needed for the encoder to fix encoding of strings at protocol 0.
Thus we need this function to be not test-only.

Plain code movement here, no semantic change.

ogorek_test.go

@@ -10,7 +10,6 @@ import (
 	"reflect"
 	"strconv"
 	"testing"
-	"unicode/utf8"
 )
 
 func bigInt(s string) *big.Int {
@@ -875,58 +874,6 @@ func TestUnquoteCharEOF(t *testing.T) {
 	}
 }
 
-
-// pyquote, similarly to strconv.Quote, quotes s with " but does not use "\u" and "\U" inside.
-//
-// We need to avoid \u and friends, since for regular strings Python translates
-// \u to \\u, not an UTF-8 character.
-//
-// Dumping strings in a way that is possible to copy/paste into Python and use
-// pickletools.dis and pickle.loads there to verify a pickle is handy.
-func pyquote(s string) string {
-	const hexdigits = "0123456789abcdef"
-	out := make([]byte, 0, len(s))
-
-	for {
-		r, width := utf8.DecodeRuneInString(s)
-		if width == 0 {
-			break
-		}
-
-		emitRaw := false
-
-		switch {
-		// invalid & everything else goes in numeric byte escapes
-		case r == utf8.RuneError:
-			fallthrough
-		default:
-			emitRaw = true
-
-		case r == '\\' || r == '"':
-			out = append(out, '\\', byte(r))
-
-		case strconv.IsPrint(r):
-			out = append(out, s[:width]...)
-
-		case r < ' ':
-			rq := strconv.QuoteRune(r) // e.g. "'\n'"
-			rq = rq[1:len(rq)-1]       // ->   `\n`
-			out = append(out, rq...)
-		}
-
-		if emitRaw {
-			for i := 0; i < width; i++ {
-				out = append(out, '\\', 'x', hexdigits[s[i]>>4], hexdigits[s[i]&0xf])
-			}
-		}
-
-		s = s[width:]
-	}
-
-
-	return "\"" + string(out) + "\""
-}
-
 // like io.LimitedReader but for writes
 // XXX it would be good to have it in stdlib
 type LimitedWriter struct {

pyquote.go

+package ogórek
+
+import (
+	"strconv"
+	"unicode/utf8"
+)
+
+// pyquote, similarly to strconv.Quote, quotes s with " but does not use "\u" and "\U" inside.
+//
+// We need to avoid \u and friends, since for regular strings Python translates
+// \u to \\u, not an UTF-8 character.
+//
+// Dumping strings in a way that is possible to copy/paste into Python and use
+// pickletools.dis and pickle.loads there to verify a pickle is handy.
+func pyquote(s string) string {
+	const hexdigits = "0123456789abcdef"
+	out := make([]byte, 0, len(s))
+
+	for {
+		r, width := utf8.DecodeRuneInString(s)
+		if width == 0 {
+			break
+		}
+
+		emitRaw := false
+
+		switch {
+		// invalid & everything else goes in numeric byte escapes
+		case r == utf8.RuneError:
+			fallthrough
+		default:
+			emitRaw = true
+
+		case r == '\\' || r == '"':
+			out = append(out, '\\', byte(r))
+
+		case strconv.IsPrint(r):
+			out = append(out, s[:width]...)
+
+		case r < ' ':
+			rq := strconv.QuoteRune(r) // e.g. "'\n'"
+			rq = rq[1:len(rq)-1]       // ->   `\n`
+			out = append(out, rq...)
+		}
+
+		if emitRaw {
+			for i := 0; i < width; i++ {
+				out = append(out, '\\', 'x', hexdigits[s[i]>>4], hexdigits[s[i]&0xf])
+			}
+		}
+
+		s = s[width:]
+	}
+
+
+	return "\"" + string(out) + "\""
+}