Bizarre Error Message (Go 1.9.2)

[Jon Forrest]

I'm learning Go. Whenever I learn a new programming language I like to try to recreate the Unix 'ls' command
in that language. I've found that such an exercise is often a good way to get familiar with what a language offers.

Here's my environment:

$ go version
go version go1.9.2 linux/amd64
$ cat /etc/redhat-release
CentOS Linux release 7.4.1708 (Core)

Consider the following trivial program which I've saved as "ls.go":

package main

import (
    "fmt"
    "os"
)

func main() {
    for _, arg := range os.Args[1:] {
        fi, err := os.Stat(arg)
        if err != nil {
            fmt.Println(err)
            return
        }
        switch mode := fi.Mode(); {
        case mode.IsRegular():
            fmt.Println("regular file")
        case mode.IsDir():
            fmt.Println("directory")
        }
    }
}


When I run 'go build ls.go' and then './ls ls.go' I see the output I expect, which is
'regular file'.

However, when I run 'go run ls.go ls.go' I get the bizarre message

can't load package: package main: case-insensitive file name collision: "ls.go" and "ls.go"

This is on an xfs filesystem.

I don't understand why this error message appeared, nor what it's trying to tell me.
Plus, I don't understand why running the result of 'go build' works, but building
and running the program using 'go run' fails.

Cordially,
Jon Forrest

[Ian Lance Taylor]

`go run` takes multiple files as arguments. When you type `go run
ls.go ls.go` you are asking the go tool to build a Go program that
consists of the contents of ls.go repeated twice. Before it even gets
to that point, it says "wait, you've told me the same file name twice,
that can't be right" and then it starts talking about a
case-insensitive file name which is certainly confusing. This is kind
of hard to avoid using `go run`, as it takes any argument that ends
with ".go" as meaning a Go file to compile.

Ian

[Raffaele Sena]

Or you use the "standard" unix trick:

go run ls.go -- ls.go

Ian

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[Karan Chaudhary]

`go run` takes multiple files as arguments. 

Interesting.  Didn't know this was possible.  Until now i used to fallback to using go build if code was distributed over multiple files. (When i'm testing some case which includes few files)