/cc @bcmills @jayconrod It looks like it is related to a leading BOM character in router/Router.go.

Reproduced using https://github.com/andyTsing/BEService/commit/07f4a7fdc545629d7e25a2fc88cffad67ad8ee0e

$ xxd router/Router.go 
00000000: efbb bf70 6163 6b61 6765 2072 6f75 7465  ...package route

This is corrected by gofmt:

$ xxd router/Router.go 
00000000: 7061 636b 6167 6520 726f 7574 6572 0a0a  package router..

@andyTsing Thanks for the report! Does go fmt ./router/Router.go resolve this issue on Windows?

@toothrot Thank u,following your advice,when i do: go fmt ./router/Router.go,the problem was solved

Glad to hear that @andyTsing!

If you don't mind, let's re-open this issue to track improving cmd/go to report a better error message when this kind of a situation happens.

@dmitshur OK,It's opened again,I have submitted the correct version. As it is the first time to use github, I am not sure whether @07f4a7f is still intact.
To reproduce the error scenario, manually add the BOM prefix to the router/ router. Go file as described by @toothrot

This is probably a bug in the parser or loader somewhere. Note that the Go spec explicitly allows a leading BOM:

For compatibility with other tools, a compiler may ignore a UTF-8-encoded byte order mark (U+FEFF) if it is the first Unicode code point in the source text. A byte order mark may be disallowed anywhere else in the source.

Curiously, this only manifests as an error in module mode:

_gopath/src/github.com/andyTsing/BEService$ git checkout 07f4a7f
[…]

_gopath/src/github.com/andyTsing/BEService$ GO111MODULE=off go build .

_gopath/src/github.com/andyTsing/BEService$ GO111MODULE=on go build .
router/Router.go:13:2: cannot find package

Under normal circumstances, it is unlikely to encounter such errors...
Later, I recalled that the error was probably caused by opening the.go file using Windows's note.exe,Windows's note.exe processes utf8 format, attaching BOM,The process of the second round made me pay attention to this point. Otherwise, this mistake would be hard to find. Fortunately, @toothrot has rich experience and found the reason.

@andyTsing Why close this issue? We'd like to improve the go command to report a better error message in this rare situation. Having this issue open is how we can track that work. Do you mind if I re-open it?

Ok, I don't mind. I thought there had been no response recently, so I shut it down. Sorry

How's progress? This issue means on Windows go fail in most of the cases when people use any common text editor.

How's progress? This issue means on Windows go fail in most of the cases when people use any common text editor.

I found a solution good for me. that's #46290

you can try to cedit the golang source file go/src/cmd/go/internal/imports/scan.go and then compile the golang.
the code you need to edit is below

func scanFiles(files []string, tags map[string]bool, explicitFiles bool) ([]string, []string, error) {
	imports := make(map[string]bool)
	testImports := make(map[string]bool)
	numFiles := 0
Files:
	for _, name := range files {
		r, err := os.Open(name)
		if err != nil {
			return nil, nil, err
		}
               
               // I add these code to check if the source code is with BOM, if yes, drop the BOM
		var fheader = make([]byte, 3)
		_, err = r.Read(fheader)
		if err != nil {
			fmt.Println("error: ", err)
		}
		if fheader[0] == 0xef && fheader[1] == 0xbb && fheader[2] == 0xbf {
			r.Seek(3, 0)
		} else {
			r.Seek(0, 0)
		}
                ////////// edit end

		var list []string
                // if a file is with BOM, the return list is empty
		data, err := ReadImports(r, false, &list)
		r.Close()
		if err != nil {
			return nil, nil, fmt.Errorf("reading %s: %v", name, err)
		}
// ... ...
}

Hope this method is useful for you.

Change https://golang.org/cl/325990 mentions this issue: cmd/go: ignore UTF8 BOM when reading source code