Feature mod aliases

[ferryvg]

What is the problem I am trying to address?
We need set source repo url for module

How is the fix applied?
Added new block to download.hcl and method like Mode.Match

Mention the issue number it fixes or add the details of the changes if it doesn't have a specific issue.

Fixes #1315, #1132, #1334

[ferryvg]

Will be updated, because not working for 2+ versions of module

[ferryvg]

go.mod support replace directive
https://github.com/golang/go/wiki/Modules#when-should-i-use-the-replace-directive

[blueworrybear]

@ferryvg
Hi, I'm looking forward to this Alias feature. Although, Go supports replace, it does not mean Alias is not useful.

For example, I cannot access some VCS repositories due to the firewall policy in my department. Although I can use either:

1. go mod replace
2. git insteadof configure
3. Other goproxy server (Unfortunately, sometimes it's not working)

It's more convenience to me if I could set some redirection via Athens. Especially I could help my colleagues to avoid the same painful environment setup when they want to use the same modules.

Therefore, please don't give up working on the feature 👍

BTW, I would like to know what happened for 2+ version of module? As I know, go mod requests using url/to/module/v2 to denote breaking update. However, it seems to me that alias those URL is not impossible. Could we just replace v2 in Alias function?

[letian0805]

This feature is very useful! Why not merge it?

[arschles]

@letian0805 if you'd like this feature, feel free to branch from it and open a new PR. the question I would pose, though, is what happens if you:

• alias github.com/package/1 to github.com/package/2 on your athens server
• run go get github.com/package/2

when the download happens, the go.mod that comes from the server will have module github.com/package/1 in it, so would you not need a replace directive in your own go.mod file anyway?