generate an app per Rust workspace binary

[haraldh]

$ nix run 'github:rvolosatovs/nixify?dir=examples/rust-hello-multibin'
[...]

error: unable to execute '/nix/store/gm2sj4fii5pfyj0ghlfs5h2d5adg4bkx-rust-hello-multibin-0.1.0/bin/rust-hello-multibin': No such file or directory

[rvolosatovs]

Thanks for the report and sorry for a late response!
The fact that nix run does not work for this one is expected. cargo run also does not work with that crate:

error: `cargo run` could not determine which binary to run. Use the `--bin` option to specify a binary, or the `default-run` manifest key.
available binaries: bye, hello-other-path

The error message should certainly be improved though

[haraldh]

$ nix flake show --no-write-lock-file  'github:rvolosatovs/nixify?dir=examples/rust-hello-multibin'
[...]
github:rvolosatovs/nixify/e7295eaafb29bdb709fd449118c7cec30d4bbce3?dir=examples/rust-hello-multibin
├───apps
│   ├───aarch64-darwin
│   │   ├───default: app
│   │   ├───rust-hello-multibin: app
│   │   └───rust-hello-multibin-debug: app
│   ├───aarch64-linux
│   │   ├───default: app
│   │   ├───rust-hello-multibin: app
│   │   └───rust-hello-multibin-debug: app
│   ├───x86_64-darwin
│   │   ├───default: app
│   │   ├───rust-hello-multibin: app
│   │   └───rust-hello-multibin-debug: app
│   └───x86_64-linux
│       ├───default: app
│       ├───rust-hello-multibin: app
│       └───rust-hello-multibin-debug: app
[...]

Seems like there should be some app ... right?

[rvolosatovs]

$ nix flake show --no-write-lock-file  'github:rvolosatovs/nixify?dir=examples/rust-hello-multibin'
[...]
github:rvolosatovs/nixify/e7295eaafb29bdb709fd449118c7cec30d4bbce3?dir=examples/rust-hello-multibin
├───apps
│   ├───aarch64-darwin
│   │   ├───default: app
│   │   ├───rust-hello-multibin: app
│   │   └───rust-hello-multibin-debug: app
│   ├───aarch64-linux
│   │   ├───default: app
│   │   ├───rust-hello-multibin: app
│   │   └───rust-hello-multibin-debug: app
│   ├───x86_64-darwin
│   │   ├───default: app
│   │   ├───rust-hello-multibin: app
│   │   └───rust-hello-multibin-debug: app
│   └───x86_64-linux
│       ├───default: app
│       ├───rust-hello-multibin: app
│       └───rust-hello-multibin-debug: app
[...]

Seems like there should be some app ... right?

Right, so cases where there are multiple binaries in a workspace are a bit tricky, right now, for example, we have this funky logic for OCI where, if there is a binary with the same name as the crate we're building or there's only one binary being built, then we assume that's the command we want to execute.

nixify/lib/rust/mkAttrs.nix

Lines 735 to 740 in c2134e5

	// optionalAttrs (bins' ? ${pname'}) {
	config.Cmd = [pname'];
	}
	// optionalAttrs (length bins == 1) {
	config.Cmd = bins;
	}

I think what really should happen here is that there should be a Nix app generated per binary in the workspace (with appropriate executable being run on nix run) and a Nix package per workspace to build all of it

We already know exactly which binaries cargo will build

nixify/lib/rust/crateBins.nix

Lines 106 to 150 in c2134e5

	trace' "crateBins" {
	inherit
	autobins
	bin
	cargoToml
	includeCrate
	isPackage
	src
	workspace
	;
	}
	optionals
	includeCrate (
	# NOTE: `listToAttrs` seems to discard keys already present in the set
	attrValues (
	optionalAttrs (autobins && pathExists "${src}/src/main.rs") {
	"src/main.rs" = cargoToml.package.name;
	}
	// listToAttrs (optionals (autobins && pathExists "${src}/src/bin") (map (name:
	nameValuePair "src/bin/${name}" (removeSuffix ".rs" name))
	(attrNames (filterAttrs (name: type: type == "regular" && hasSuffix ".rs" name || type == "directory") (readDir "${src}/src/bin")))))
	// listToAttrs (map (
	{
	name,
	path ? null,
	...
	}:
	if path != null
	then nameValuePair path name
	else if autobins && pathExists "${src}/src/main.rs" && name == cargoToml.package.name
	then nameValuePair "src/main.rs" name
	else if autobins && pathExists "${src}/src/bin/${name}.rs"
	then nameValuePair "src/bin/${name}.rs" name
	else if autobins && pathExists "${src}/src/bin/${name}/main.rs"
	then nameValuePair "src/bin/${name}/main.rs" name
	else throw "failed to determine `${name}` binary path, please file a bug report and explicitly set `path` in `Cargo.toml` to temporarily work around this issue"
	)
	bin)
	)
	)
	++ optionals (build'.workspace || !isPackage || packagesSelected) (flatten (map f workspace));
	in
	if build ? bins && length build.bins > 0
	then build.bins
	else unique (f src)

, it's just the matter of setting up the plumbing to extract those binaries from the workspace package. Those packages should be Nix "apps", the workspace package should be just that - a Nix package, not an "app" as it's marked now.

So, in result, rust-hello-multibin and rust-hello-multibin-debug would not show up in apps, those would keep only being available in packages.
We would, however have bye and hello-other-path apps available.
For rust-hello-multibin specifically, there would be no default app (but there would be a default package - the workspace build), but otherwise I think default app should be set if either:

• there is only one binary in the workspace
• there is a binary with the same name as the top-level crate being built

basically, the same logic that already exists for OCI

Does that make sense?

[haraldh]

totally makes sense and would be exactly what I need :-)