go/printer: forbid empty line before first comment in block

To improve readability when exported fields are removed,
forbid the printer from emitting an empty line before the first comment
in a const, var, or type block.
Also, when printing the "Has filtered or unexported fields." message,
add an empty line before it to separate the message from the struct
or interfact contents.

Before the change:
<<<
type NamedArg struct {

        // Name is the name of the parameter placeholder.
        //
        // If empty, the ordinal position in the argument list will be
        // used.
        //
        // Name must omit any symbol prefix.
        Name string

        // Value is the value of the parameter.
        // It may be assigned the same value types as the query
        // arguments.
        Value interface{}
        // contains filtered or unexported fields
}
>>>

After the change:
<<<
type NamedArg struct {
        // Name is the name of the parameter placeholder.
        //
        // If empty, the ordinal position in the argument list will be
        // used.
        //
        // Name must omit any symbol prefix.
        Name string

        // Value is the value of the parameter.
        // It may be assigned the same value types as the query
        // arguments.
        Value interface{}

        // contains filtered or unexported fields
}
>>>

Fixes #18264

Change-Id: I9fe17ca39cf92fcdfea55064bd2eaa784ce48c88
Reviewed-on: https://go-review.googlesource.com/71990
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

6 files changed, 0 insertions, 6 deletions

diff --git a/src/net/http/httputil/dump_test.go b/src/net/http/httputil/dump_test.go
index f881020fef..a403c88eaa 100644
--- a/src/net/http/httputil/dump_test.go
+++ b/src/net/http/httputil/dump_test.go
@@ -27,7 +27,6 @@ type dumpTest struct {
 }
 
 var dumpTests = []dumpTest{
-
 	// HTTP/1.1 => chunked coding; body; empty trailer
 	{
 		Req: http.Request{
diff --git a/src/net/http/httputil/persist.go b/src/net/http/httputil/persist.go
index cbedf25ad1..24c9c73474 100644
--- a/src/net/http/httputil/persist.go
+++ b/src/net/http/httputil/persist.go
@@ -173,7 +173,6 @@ func (sc *ServerConn) Pending() int {
 // Response.Close field to true. Write should be considered operational until
 // it returns an error, regardless of any errors returned on the Read side.
 func (sc *ServerConn) Write(req *http.Request, resp *http.Response) error {
-
 	// Retrieve the pipeline ID of this request/response pair
 	sc.mu.Lock()
 	id, ok := sc.pipereq[req]
diff --git a/src/net/http/internal/chunked.go b/src/net/http/internal/chunked.go
index 63f321d03b..7f83a56f1c 100644
--- a/src/net/http/internal/chunked.go
+++ b/src/net/http/internal/chunked.go
@@ -192,7 +192,6 @@ type chunkedWriter struct {
 // NOTE: Note that the corresponding chunk-writing procedure in Conn.Write has
 // a bug since it does not check for success of io.WriteString
 func (cw *chunkedWriter) Write(data []byte) (n int, err error) {
-
 	// Don't send 0-length data. It looks like EOF for chunked encoding.
 	if len(data) == 0 {
 		return 0, nil
diff --git a/src/net/http/requestwrite_test.go b/src/net/http/requestwrite_test.go
index eb65b9f736..74b01db6da 100644
--- a/src/net/http/requestwrite_test.go
+++ b/src/net/http/requestwrite_test.go
@@ -813,7 +813,6 @@ func TestRequestWriteError(t *testing.T) {
 // try to restore it. It always dumps the whole body.
 // And it doesn't support https.
 func dumpRequestOut(req *Request, onReadHeaders func()) ([]byte, error) {
-
 	// Use the actual Transport code to record what we would send
 	// on the wire, but not using TCP.  Use a Transport with a
 	// custom dialer that returns a fake net.Conn that waits
diff --git a/src/net/http/server.go b/src/net/http/server.go
index 91f481ed50..4329e61e60 100644
--- a/src/net/http/server.go
+++ b/src/net/http/server.go
@@ -2231,7 +2231,6 @@ func (mux *ServeMux) shouldRedirect(path string) bool {
 // If there is no registered handler that applies to the request,
 // Handler returns a ``page not found'' handler and an empty pattern.
 func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {
-
 	// CONNECT requests are not canonicalized.
 	if r.Method == "CONNECT" {
 		// If r.URL.Path is /tree and its handler is not registered,
diff --git a/src/net/mail/message_test.go b/src/net/mail/message_test.go
index 5d5d6e4e9c..b1bb31e982 100644
--- a/src/net/mail/message_test.go
+++ b/src/net/mail/message_test.go
@@ -727,7 +727,6 @@ func TestAddressString(t *testing.T) {
 
 // Check if all valid addresses can be parsed, formatted and parsed again
 func TestAddressParsingAndFormatting(t *testing.T) {
-
 	// Should pass
 	tests := []string{
 		`<Bob@example.com>`,