allow direct conversion between string and named []byte, []rune

The allowed conversions before and after are:
        type Tstring string
        type Tbyte []byte
        type Trune []rune

        string <-> string  // ok
        string <-> []byte  // ok
        string <-> []rune // ok
        string <-> Tstring // ok
        string <-> Tbyte // was illegal, now ok
        string <-> Trune // was illegal, now ok

        Tstring <-> string  // ok
        Tstring <-> []byte  // ok
        Tstring <-> []rune // ok
        Tstring <-> Tstring // ok
        Tstring <-> Tbyte // was illegal, now ok
        Tstring <-> Trune // was illegal, now ok

Update spec, compiler, tests.  Use in a few packages.

We agreed on this a few months ago but never implemented it.

Fixes issue 1707.

R=golang-dev, gri, r
CC=golang-dev
http://codereview.appspot.com/5421057

3 files changed, 101 insertions, 5 deletions

diff --git a/test/convert1.go b/test/convert1.go
new file mode 100644
index 000000000..9de1b7e01
--- /dev/null
+++ b/test/convert1.go
@@ -0,0 +1,96 @@
+// errchk $G -e $D/$F.go
+
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+type Tbyte []byte
+type Trune []rune
+type Tint64 []int64
+type Tstring string
+
+func main() {
+	s := "hello"
+	sb := []byte("hello")
+	sr := []rune("hello")
+	si := []int64{'h', 'e', 'l', 'l', 'o'}
+
+	ts := Tstring(s)
+	tsb := Tbyte(sb)
+	tsr := Trune(sr)
+	tsi := Tint64(si)
+
+	_ = string(s)
+	_ = []byte(s)
+	_ = []rune(s)
+	_ = []int64(s) // ERROR "cannot convert.*\[\]int64"
+	_ = Tstring(s)
+	_ = Tbyte(s)
+	_ = Trune(s)
+	_ = Tint64(s) // ERROR "cannot convert.*Tint64"
+
+	_ = string(sb)
+	_ = []byte(sb)
+	_ = []rune(sb)  // ERROR "cannot convert.*\[\]rune"
+	_ = []int64(sb) // ERROR "cannot convert.*\[\]int64"
+	_ = Tstring(sb)
+	_ = Tbyte(sb)
+	_ = Trune(sb)  // ERROR "cannot convert.*Trune"
+	_ = Tint64(sb) // ERROR "cannot convert.*Tint64"
+
+	_ = string(sr)
+	_ = []byte(sr) // ERROR "cannot convert.*\[\]byte"
+	_ = []rune(sr)
+	_ = []int64(sr) // ERROR "cannot convert.*\[\]int64"
+	_ = Tstring(sr)
+	_ = Tbyte(sr) // ERROR "cannot convert.*Tbyte"
+	_ = Trune(sr)
+	_ = Tint64(sr) // ERROR "cannot convert.*Tint64"
+
+	_ = string(si) // ERROR "cannot convert.* string"
+	_ = []byte(si) // ERROR "cannot convert.*\[\]byte"
+	_ = []rune(si) // ERROR "cannot convert.*\[\]rune"
+	_ = []int64(si)
+	_ = Tstring(si) // ERROR "cannot convert.*Tstring"
+	_ = Tbyte(si)   // ERROR "cannot convert.*Tbyte"
+	_ = Trune(si)   // ERROR "cannot convert.*Trune"
+	_ = Tint64(si)
+
+	_ = string(ts)
+	_ = []byte(ts)
+	_ = []rune(ts)
+	_ = []int64(ts) // ERROR "cannot convert.*\[\]int64"
+	_ = Tstring(ts)
+	_ = Tbyte(ts)
+	_ = Trune(ts)
+	_ = Tint64(ts) // ERROR "cannot convert.*Tint64"
+
+	_ = string(tsb)
+	_ = []byte(tsb)
+	_ = []rune(tsb)  // ERROR "cannot convert.*\[\]rune"
+	_ = []int64(tsb) // ERROR "cannot convert.*\[\]int64"
+	_ = Tstring(tsb)
+	_ = Tbyte(tsb)
+	_ = Trune(tsb)  // ERROR "cannot convert.*Trune"
+	_ = Tint64(tsb) // ERROR "cannot convert.*Tint64"
+
+	_ = string(tsr)
+	_ = []byte(tsr) // ERROR "cannot convert.*\[\]byte"
+	_ = []rune(tsr)
+	_ = []int64(tsr) // ERROR "cannot convert.*\[\]int64"
+	_ = Tstring(tsr)
+	_ = Tbyte(tsr) // ERROR "cannot convert.*Tbyte"
+	_ = Trune(tsr)
+	_ = Tint64(tsr) // ERROR "cannot convert.*Tint64"
+
+	_ = string(tsi) // ERROR "cannot convert.* string"
+	_ = []byte(tsi) // ERROR "cannot convert.*\[\]byte"
+	_ = []rune(tsi) // ERROR "cannot convert.*\[\]rune"
+	_ = []int64(tsi)
+	_ = Tstring(tsi) // ERROR "cannot convert.*Tstring"
+	_ = Tbyte(tsi)   // ERROR "cannot convert.*Tbyte"
+	_ = Trune(tsi)   // ERROR "cannot convert.*Trune"
+	_ = Tint64(tsi)
+}
diff --git a/test/convlit.go b/test/convlit.go
index 2e3b15bda..1e82d1f2f 100644
--- a/test/convlit.go
+++ b/test/convlit.go
@@ -54,12 +54,12 @@ var _ = []byte(ss)
 var _ []rune = ss // ERROR "cannot use|incompatible|invalid"
 var _ []byte = ss // ERROR "cannot use|incompatible|invalid"
 
-// named slice is not
+// named slice is now ok
 type Trune []rune
 type Tbyte []byte
 
-var _ = Trune("abc") // ERROR "convert|incompatible|invalid"
-var _ = Tbyte("abc") // ERROR "convert|incompatible|invalid"
+var _ = Trune("abc") // ok
+var _ = Tbyte("abc") // ok
 
 // implicit is still not
 var _ Trune = "abc" // ERROR "cannot use|incompatible|invalid"
diff --git a/test/named1.go b/test/named1.go
index fe71df844..64e492886 100644
--- a/test/named1.go
+++ b/test/named1.go
@@ -54,8 +54,8 @@ func main() {
 
 	_, bb := <-c
 	asBool(bb) // ERROR "cannot use.*type bool.*as type Bool"
-	_, b = <-c     // ERROR "cannot .* bool.*type Bool"
+	_, b = <-c // ERROR "cannot .* bool.*type Bool"
 	_ = b
 
-	asString(String(slice)) // ERROR "cannot .*type Slice.*type String"
+	asString(String(slice)) // ok
 }