The unused tool, with the -export flag, also reports the following error variables to be unused:

• ErrHeaderTooLong
• ErrShortBody
• ErrNotSupported
• ErrMissingContentLength
• ErrNoCookie
• ErrLineTooLong

However I have not checked if they are obsolete as with ErrWriteAfterFlush.

All of those are part of the public API and cannot be removed under the Go 1 compatibility guarantee. Also, most of these are defined in terms of their net/http/internal counterpart, are returned from internal and used by users of net/http.

As an aside, unused -exported is not at all useful for the standard library, except when checking internal packages. All exported identifiers in the stdlib are by their nature used by users of Go.

On Wed, Apr 6, 2016 at 12:34 PM, Dominik Honnef notifications@github.com
wrote:

All of those are part of the public API and cannot be removed under the Go
1 compatibility guarantee. Also, most of these are defined in terms of
their net/http/internal counterpart are returned from internal and used
by users of net/http.

At least ErrWriteAfterFLush seems to be obsolete. Of course it can not be
removed, but a comment can be added to explain that it is no more used.

IMHO, a variable without a comment and that appears to be never used, only
cause confusion for users (at least for me).

CL https://golang.org/cl/22658 mentions this issue.