func path/filepath.Ext

3 uses

	path/filepath (current package)
		path.go#L220: func Ext(path string) string {

	golang.org/x/tools/go/packages
		golist.go#L612: 				if ext := filepath.Ext(f); ext != ".go" && ext != "" { // ext == "" means the file is from the cache, so probably cgo-processed file

	net/http
		fs.go#L235: 		ctype = mime.TypeByExtension(filepath.Ext(name))

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