[Rd] install.packages(): About an option for installing archived versions

[Patrick Schratz]

Dear list,

Various helpers exist in the wild to install older archived versions of 
CRAN packages, for example `remotes::install_version() ` or 
`versions::install.version()`.
The former makes use of an “archive.rds” file stored in the CRAN 
/Meta directory: 
https://github.com/r-lib/remotes/blob/9b5dc29102a486df2f42c88bb19027a7cd54a721/R/install-version.R#L68

Given its existence, I was wondering why there is no official support in 
`install.packages()`?
I was browsing the mailing archives of r-devel but surprisingly could 
not find a previous discussion about it.
`remotes::install_version()` only uses the tarballs and enforces 
installation from source.
If it’s due to dependency issues, i.e. that there is no guarantee that 
older versions work with the current versions of CRAN packages, then the 
availability of downloading and installing the tarballs manually from 
the Archive web page could also be questioned per se.
I think people know that they are on their own in this situation and 
that there is no guarantee for archived versions to function properly, 
especially of one goes back substantially in time.
A simple note in ?install.packages() could further clarify this.

A few questions:

- Does an archive for older binaries exist for CRAN packages?
- How is CRAN creating “archive.rds”?
- Would a PR adding this functionality to `install.packages()` be 
accepted by R-core?

Patrick

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