go.tools/importer: change type of print{,ln} built-ins.

Before: func(any, ...interface{}).
After:  func(any, ...any)

They are no longer variadic, so you can't write print(x, y...).

(Recall that print(1) and print(interface{}(1)) behave
differently and that this is useful.)

Fixes bug 6560

R=gri
CC=golang-dev
https://golang.org/cl/14455054

importer/pkginfo.go

@@ -135,12 +135,12 @@ func (info *PackageInfo) BuiltinCallSignature(e *ast.CallExpr) *types.Signature
 			types.NewVar(token.NoPos, nil, "", t0),
 			types.NewVar(token.NoPos, nil, "", t1))
 
-	case "print", "println": // print{,ln}(any, ...interface{})
-		isVariadic = true
-		// Note, arg0 may have any type, not necessarily tEface.
-		params = append(params,
-			types.NewVar(token.NoPos, nil, "", info.TypeOf(e.Args[0])),
-			types.NewVar(token.NoPos, nil, "", types.NewSlice(tEface)))
+	case "print", "println": // print{,ln}(any, ...)
+		// Note, args may have any type, not necessarily tEface.
+		var params []*types.Var
+		for _, arg := range e.Args {
+			params = append(params, types.NewVar(token.NoPos, nil, "", info.TypeOf(arg)))
+		}
 
 	case "close":
 		params = append(params, types.NewVar(token.NoPos, nil, "", info.TypeOf(e.Args[0])))

ssa/interp/ops.go

@@ -972,17 +972,14 @@ func callBuiltin(caller *frame, callpos token.Pos, fn *ssa.Builtin, args []value
 		}
 		return nil
 
-	case "print", "println": // print(anytype, ...interface{})
+	case "print", "println": // print(any, ...)
 		ln := fn.Name() == "println"
 		var buf bytes.Buffer
-		buf.WriteString(toString(args[0]))
-		if len(args) == 2 {
-			for _, arg := range args[1].([]value) {
-				if ln {
-					buf.WriteRune(' ')
-				}
-				buf.WriteString(toString(arg))
+		for i, arg := range args {
+			if i > 0 && ln {
+				buf.WriteRune(' ')
 			}
+			buf.WriteString(toString(arg))
 		}
 		if ln {
 			buf.WriteRune('\n')

ssa/interp/testdata/coverage.go

@@ -151,6 +151,8 @@ func init() {
 }
 
 func main() {
+	print() // legal
+
 	if counter != 2*3*5 {
 		panic(counter)
 	}