[config feature] revert source.<name>.replace-with in a project directory

[Etavioxy]

Problem

config "source.<name>.replace-with" can't be revert.

I use this in global scope (~/.cargo/config.toml)

[source.crates-io]
replace-with = 'ustc'

[source.ustc]
registry = "sparse+https://mirrors.ustc.edu.cn/crates.io-index/"

I tried to revert this source change in a specific project for using the official 'crates-io' source. So I use this

# ~/project/.cargo/config.toml
[source.crates-io]
replace-with = ""

It goes wrong

Caused by:
could not find a configured source with the name `` when attempting to lookup `crates-io` 

Proposed Solution

No response

Notes

No response

[epage]

As a workaround, you could organize your filesystem around your different source replacements.

• ~/
  • crates-io/
    • .cargo/config.toml: no source replacement
    • foo/
  • ustc/
    • .cargo/config.toml: source replacement
    • bar/

In general, I believe we'd like ways to revert config. Unsure if we should do that in one off ways or find a more general way of doing this.

[Etavioxy]

The problem is that the replace-with parameter has no default value. It could be set one.