bug277: tests for conversion syntax

- accepted by gccgo, gofmt
- some not accepted by 6g
- spec revision forthcoming

R=rsc
CC=golang-dev
https://golang.org/cl/1279041

test/bugs/bug277.go

+// $G $D/$F.go || echo BUG should compile
+
+// Copyright 2010 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.
+
+// Test cases for conversion syntax.
+
+package main
+
+type (
+	A [3]int
+	S struct {
+		x int
+	}
+	P *S
+	F func(x int) int
+	I interface {
+		m(x int) int
+	}
+	L []int
+	M map[string]int
+	C chan int
+)
+
+func (s S) m(x int) int { return x }
+
+var (
+	a A = [...]int{1, 2, 3}
+	s S = struct{ x int }{0}
+	p P = &s
+	f F = func(x int) int { return x }
+	i I = s
+	l L = []int{}
+	m M = map[string]int{"foo": 0}
+	c C = make(chan int)
+)
+
+func main() {
+	a = A(a)
+	a = [3]int(a)
+	s = struct {
+		x int
+	}(s)
+	p = (*S)(p)
+	f = func(x int) int(f)
+	i = (interface {
+		m(x int) int
+	})(s) // this is accepted by 6g
+	i = interface {
+		m(x int) int
+	}(s) // this is not accepted by 6g (but should be)
+	l = []int(l)
+	m = map[string]int(m)
+	c = chan int(c)
+	_ = chan<- int(c)
+	_ = <-(chan int)(c)
+	_ = <-(<-chan int)(c)
+}
+
+/*
+6g bug277.go
+bug277.go:46: syntax error: unexpected (, expecting {
+bug277.go:50: syntax error: unexpected interface
+bug277.go:53: non-declaration statement outside function body
+bug277.go:54: non-declaration statement outside function body
+bug277.go:55: syntax error: unexpected LCHAN
+bug277.go:56: syntax error: unexpected LCHAN
+bug277.go:57: non-declaration statement outside function body
+bug277.go:58: non-declaration statement outside function body
+bug277.go:59: syntax error: unexpected }
+*/

test/golden.out

@@ -180,3 +180,15 @@ BUG: bug260 failed
 
 =========== bugs/bug274.go
 BUG: errchk: command succeeded unexpectedly
+
+=========== bugs/bug277.go
+bugs/bug277.go:46: syntax error: unexpected (, expecting {
+bugs/bug277.go:50: syntax error: unexpected interface
+bugs/bug277.go:53: non-declaration statement outside function body
+bugs/bug277.go:54: non-declaration statement outside function body
+bugs/bug277.go:55: syntax error: unexpected LCHAN
+bugs/bug277.go:56: syntax error: unexpected LCHAN
+bugs/bug277.go:57: non-declaration statement outside function body
+bugs/bug277.go:58: non-declaration statement outside function body
+bugs/bug277.go:59: syntax error: unexpected }
+BUG should compile