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 #1707.

R=golang-dev, gri, r
CC=golang-dev
https://golang.org/cl/5421057

1 files changed, 2 insertions, 2 deletions

diff --git a/test/named1.go b/test/named1.go
index fe71df844f..64e492886e 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
 }