Warn on malformed URI query parameter

[bryanhonof]

Motivation

#10370 explains how github:nixos/nixpkgs?refnixpkgs-unstable is currently just accepted as is.
It never really checks if the query part of the URI is a tuple of 2 strings, separated by an equal sign.

Context

Fixes #10370

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[bryanhonof]

Outputs looks like this:

$ ./outputs/out/bin/nix --extra-experimental-features 'nix-command flakes' flake metadata 'github:nixos/nixpkgs?refnixpkgs-unstable&bla'
warning: invalid URI query 'refnixpkgs-unstable', did you forget an equals sign `=`?
warning: invalid URI query 'bla', did you forget an equals sign `=`?

[tomberek]

This will restrict all URIs from using non-key/value query parameters. So even http endpoints will not accept them. If we warn or error, it would be specific to the kind of URL it is, flake or store or fetch url, etc.

[bryanhonof]

@tomberek So, you'd rather do the check on the individual store level?
Because, I don't think these kinds of queries ever make it outside of parsing.

Since this checks if the string contains a =, and if it doesn't, just skips it.

nix/src/libutil/url.cc

Lines 82 to 85 in 96a2dda

	if (e != std::string::npos)
	result.emplace(
	s.substr(0, e),
	percentDecode(std::string_view(s).substr(e + 1)));

So, if there's already existing behavior depending on queries that don't have an = in them, I'd like to better understand how it works.

[tomberek]

Fair point. In that case this is strictly improving the warnings. I'm not sure there are too many usages of the non-"=" query string.

[roberth]

LGTM

[nixos-discourse]

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

https://discourse.nixos.org/t/2024-08-26-nix-team-meeting-minutes-172/51300/1

[nixos-discourse]

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

https://discourse.nixos.org/t/2024-08-28-nix-team-meeting-minutes-173/51302/1

[Mic92]

I am getting warnings now for simple cases like this:

nix-shell-env % nix build .#uefi-firmware
warning: dubious URI query 'uefi-firmware' is missing equal sign '='
[1/12/16 built, 31 copied (1333.3 MiB), 286.1 MiB DL] building edk2-src: removing `.git'...

basically any flake attribute.

[Mic92]

Revert in #11439

[tomberek]

Might need an initial check to see if the query string is empty.