Log what nix flake check does

[9999years]

There's still room for improvement, but this produces much more informative output with -v:

$ nix flake check -v
evaluating flake...
checking flake output 'checks'...
checking derivation 'checks.aarch64-darwin.ghcid-ng-tests'...
derivation evaluated to /nix/store/nh7dlvsrhds4cxl91mvgj4h5cbq6skmq-ghcid-ng-test-0.3.0.drv
checking derivation 'checks.aarch64-darwin.ghcid-ng-clippy'...
derivation evaluated to /nix/store/9cb5a6wmp6kf6hidqw9wphidvb8bshym-ghcid-ng-clippy-0.3.0.drv
checking derivation 'checks.aarch64-darwin.ghcid-ng-doc'...
derivation evaluated to /nix/store/8brdd3jbawfszpbs7vdpsrhy80as1il8-ghcid-ng-doc-0.3.0.drv
checking derivation 'checks.aarch64-darwin.ghcid-ng-fmt'...
derivation evaluated to /nix/store/wjhs0l1njl5pyji53xlmfjrlya0wmz8p-ghcid-ng-fmt-0.3.0.drv
checking derivation 'checks.aarch64-darwin.ghcid-ng-audit'...
derivation evaluated to /nix/store/z0mps8dyj2ds7c0fn0819y5h5611033z-ghcid-ng-audit-0.3.0.drv
checking flake output 'packages'...
checking derivation 'packages.aarch64-darwin.default'...
derivation evaluated to /nix/store/41abbdyglw5x9vcsvd89xan3ydjf8d7r-ghcid-ng-0.3.0.drv
checking flake output 'apps'...
checking flake output 'devShells'...
checking derivation 'devShells.aarch64-darwin.default'...
derivation evaluated to /nix/store/bc935gz7dylzmcpdb5cczr8gngv8pmdb-nix-shell.drv
running 5 flake checks...
warning: The check omitted these incompatible systems: aarch64-linux, x86_64-darwin, x86_64-linux
Use '--all-systems' to check all.

In the future, it would be nice to print out the output paths and whether or not they were actually built (sometimes the checks are cached).

Motivation/Context

See #8882:

As of Nix 2.17.0, when I run nix flake check, the output doesn't tell me what was checked:

$ nix flake check
warning: The check omitted these incompatible systems: aarch64-linux, x86_64-darwin, x86_64-linux
Use '--all-systems' to check all.

Checklist for maintainers

Maintainers: tick if completed or explain if not relevant

• agreed on idea
• agreed on implementation strategy
• tests, as appropriate
  • functional tests - tests/**.sh
  • unit tests - src/*/tests
  • integration tests - tests/nixos/*
• documentation in the manual
• documentation in the internal API docs
• code and comments are self-explanatory
• commit message explains why the change was made
• new feature or incompatible change: updated release notes

[9999years]

By the way, I'm very confused by the logging code in nix. When logged at lvlChatty, the message is displayed on the current line and erased when another log message is emitted. When logged at lvlInfo, the result is the same, except that when --verbose is used subsequent log messages are printed on new lines. I can't find the code that's responsible for this anywhere — as far as I can tell, the --verbose flag just controls which levels of log messages are shown or not:

nix/src/libmain/common-args.cc

Line 15 in 6f62361

.handler = {[]() { verbosity = (Verbosity) (verbosity + 1); }},

nix/src/libutil/logging.cc

Lines 91 to 92 in 6f62361

	if (lvl <= verbosity && !s.empty())
	log(lvl, s + "...");

I though this might have something to do with the progress bar logger, but the various --option log-format values didn't seem to have any effect:

nix/src/libmain/loggers.cc

Lines 23 to 41 in 6f62361

	Logger * makeDefaultLogger() {
	switch (defaultLogFormat) {
	case LogFormat::raw:
	return makeSimpleLogger(false);
	case LogFormat::rawWithLogs:
	return makeSimpleLogger(true);
	case LogFormat::internalJSON:
	return makeJSONLogger(*makeSimpleLogger(true));
	case LogFormat::bar:
	return makeProgressBar();
	case LogFormat::barWithLogs: {
	auto logger = makeProgressBar();
	logger->setPrintBuildLogs(true);
	return logger;
	}
	default:
	abort();
	}
	}

Any pointers here would be appreciated.

[9999years]

I was surprised to notice that nix flake check only builds the checks -- I would have expected it to build the packages, devShells, apps, and so on as well. Perhaps a future PR can address that?

[phip1611]

Any update here? Would love to see this too!

[tomberek]

Looks good. Log level changes are helpful. Needs a conflict rebase.

[9999years]

@tomberek Rebased to fix conflicts, PTAL

[9999years]

Actually, I'll need to give this some more attention. Even though the logs are emitted at lvlInfo, they seem to only be printed temporarily, even at -v, and are erased when the 'activity' ends. Really weird behavior.

EDIT: Nevermind, I just forgot to make install. 🤦