Isn't this possible through overrideAttrs against src?

It is possible, but the user will then need to hard-code the url from fetchUrl and otherwise to peek inside the derivation to understand what needs to be done.

Sorry, I don't understand the motivation here. The normal way to override a version in nixpkgs is exactly

drv.overrideAttrs(oa : {
  src = ...
};

If this is also possible in this package, why do we need to make it possible using override instead of overrideAttrs?

Sure, let me expand on this a bit! It's true that it is possible to override everything, including the source code, using overrideAttrs. However, this is not a convenient for particular use case of "I want to install a specific version of this package using nix-shell". It's not convenient, b/c you'll need to figure out not only the version and hash of the package (which are usually published by vendors in some easily human-readable form), but the download url as well, and that might be tricky: usually its a template string, constructed from version, platform and other bits, and reconstructing it by hand is not really fun and requires peeking into the derivation source. Moreover, version in particular also often ends up in various attrs, most notably name, and hunting that down also requires some work.

What I am getting at is that it would be really convenient, for one off overrides, to be able to say pkgs.myApp.override { version = "0.92.1"; sha256 ="..."; }, without really picking into derivation's internals. However I see now that, presumably, none of the packages make version/hash overridable, so looks like this is a more general question than just changing this single pattern. I'll rise the more general discussion in the forum.

@matklad I understand your reasoning and motivation now. Here's my concern, which you already summarized (and maybe you can reuse that or link the discussion and I'll add it myself:)

If we were to add a section on overriding package versions in the nixpkgs manual (which we really ought to,) your changes would imply that it would sound like the following:

"Check if the package accepts version and sha256 attributes. If so, use pkg.override. Otherwise, use pkg.overrideAttrs and override the src attribute"

I'm not a fan of this conditional. I think it should be a uniform process.

Started a thread: https://discourse.nixos.org/t/should-version-and-sha256-attributes-of-packages-be-easily-overridable/658

Closing this as it's clear that it's more of a global policy question rather than a particular single package issue.

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixosstag.fcio.net/t/should-version-and-sha256-attributes-of-packages-be-easily-overridable/658/1