go/types, types2: fix tracing output for type and expr lists

- support printing of expression and type lists in sprintf
- simplified some code in go/types/exprstring.go
- fixed a typo in syntax package

Change-Id: Ic4bc154200aad95958d5bc2904a9ea17cf518388
Reviewed-on: https://go-review.googlesource.com/c/go/+/377974
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

2 files changed, 19 insertions, 6 deletions

diff --git a/src/go/types/errors.go b/src/go/types/errors.go
index 81c62a82f0..ce62a8cbdd 100644
--- a/src/go/types/errors.go
+++ b/src/go/types/errors.go
@@ -7,6 +7,7 @@
 package types
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"go/ast"
@@ -81,10 +82,27 @@ func sprintf(fset *token.FileSet, qf Qualifier, debug bool, format string, args
 			}
 		case ast.Expr:
 			arg = ExprString(a)
+		case []ast.Expr:
+			var buf bytes.Buffer
+			buf.WriteByte('[')
+			writeExprList(&buf, a)
+			buf.WriteByte(']')
+			arg = buf.String()
 		case Object:
 			arg = ObjectString(a, qf)
 		case Type:
 			arg = typeString(a, qf, debug)
+		case []Type:
+			var buf bytes.Buffer
+			buf.WriteByte('[')
+			for i, x := range a {
+				if i > 0 {
+					buf.WriteString(", ")
+				}
+				buf.WriteString(typeString(x, qf, debug))
+			}
+			buf.WriteByte(']')
+			arg = buf.String()
 		}
 		args[i] = arg
 	}
diff --git a/src/go/types/exprstring.go b/src/go/types/exprstring.go
index aa4f403c1f..544cd84d61 100644
--- a/src/go/types/exprstring.go
+++ b/src/go/types/exprstring.go
@@ -71,12 +71,7 @@ func WriteExpr(buf *bytes.Buffer, x ast.Expr) {
 		ix := typeparams.UnpackIndexExpr(x)
 		WriteExpr(buf, ix.X)
 		buf.WriteByte('[')
-		for i, e := range ix.Indices {
-			if i > 0 {
-				buf.WriteString(", ")
-			}
-			WriteExpr(buf, e)
-		}
+		writeExprList(buf, ix.Indices)
 		buf.WriteByte(']')
 
 	case *ast.SliceExpr: