go/types: Use left-hand side's type as hint for right-hand

side expression evaluation in assignment operations.

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/7349046

src/pkg/exp/gotype/gotype_test.go

@@ -61,7 +61,7 @@ var tests = []string{
 	"bufio",
 	"bytes",
 
-	// "compress/bzip2",
+	"compress/bzip2",
 	"compress/flate",
 	"compress/gzip",
 	// "compress/lzw",
@@ -80,7 +80,7 @@ var tests = []string{
 	"crypto/elliptic",
 	"crypto/hmac",
 	"crypto/md5",
-	// "crypto/rand",
+	"crypto/rand",
 	"crypto/rc4",
 	"crypto/rsa",
 	"crypto/sha1",
@@ -126,7 +126,7 @@ var tests = []string{
 	"go/parser",
 	"go/printer",
 	"go/scanner",
-	// "go/token",
+	"go/token",
 	"go/types",
 
 	"hash/adler32",
@@ -138,7 +138,7 @@ var tests = []string{
 	"image/color",
 	"image/draw",
 	"image/gif",
-	// "image/jpeg",
+	"image/jpeg",
 	"image/png",
 
 	"index/suffixarray",
@@ -149,7 +149,7 @@ var tests = []string{
 	"log",
 	"log/syslog",
 
-	// "math",
+	"math",
 	//"math/big",
 	"math/cmplx",
 	"math/rand",
@@ -168,7 +168,7 @@ var tests = []string{
 	"net/rpc",
 	"net/rpc/jsonrpc",
 	"net/smtp",
-	// "net/textproto",
+	"net/textproto",
 	"net/url",
 
 	"path",

src/pkg/go/types/stmt.go

@@ -403,11 +403,13 @@ func (check *checker) stmt(s ast.Stmt) {
 				return
 			}
 			var x, y operand
+			// The lhs operand's type doesn't need a hint (from the rhs operand),
+			// because it must be a fully typed variable in this case.
 			check.expr(&x, s.Lhs[0], nil, -1)
 			if x.mode == invalid {
 				return
 			}
-			check.expr(&y, s.Rhs[0], nil, -1)
+			check.expr(&y, s.Rhs[0], x.typ, -1)
 			if y.mode == invalid {
 				return
 			}

src/pkg/go/types/testdata/stmt0.src

@@ -29,6 +29,9 @@ func _() {
 
 	s += "bar"
 	s += 1 /* ERROR "cannot convert.*string" */
+
+	var u64 uint64
+	u64 += 1<<u64
 }
 
 func _incdecs() {
@@ -271,4 +274,4 @@ func _rangeloops() {
 		var xx rune
 		xx = x
 	}
-}
+}