Use variables (including Version) with multiple packages

[BatmanAoD]

There should be a way to use Knope's variables, including Version, with multiple packages.

[old description]

Since determining the version of a package is nontrivial, and it's often useful in scripts (e.g. in CI), I think it would be a great feature if Knope could detect the current version(s) of packages and print that, without doing anything else.

Users could probably parse this information out of knope release --dry-run, but that's a bit awkward.

The primary use case I'm thinking of is to replace stuff like git describe --abbrev=0 --tags | sed 's/v//', so the output must be easy to parse. For a standard, single package, it could just print the version it finds; for multiple packages, it could print <name>=<version>, one on each line. Just like release, when a package has multiple versioned files and their versions don't match, it should just print an error of some kind.

[dbanty]

For single packages, this would work today:

[[workflows]]
name = "print-version"

[[workflows.steps]]
type = "Command"
command = "echo $version"
variables = { "$version" = "Version" }

For multi-package setups, we'd have to decide on something new. We really need a way to use variables with multiple packages anyway 😅.

Would you want all versions in a single workflow (output with JSON maybe?) or run a specific workflow to get a specific package version?

[dbanty]

(I guess my suggestion is exactly what you had in #885)

[BatmanAoD]

I completely forgot I had asked for that, and didn't see it in the issues list when I searched 😅

[dbanty]

Converting this issue to specifically figure out outputting versions for multiple packages (since #885 / #994 will cover the single-package case)

[BatmanAoD]

I've updated the issue title & description accordingly.

[BatmanAoD]

I can think of three possible approaches here:

• "namespace" the ChangelogEntry and Version variables:

  [[workflows.steps]]
  type = "Command"
  command = "echo \"$version\""
  
  [workflows.steps.variables]
  "$version" = "packagename.Version"

• Let workflows specify steps that only apply to specific packages; each step is performed separately for each package in the list:

  [[workflows.steps]]
  type = "Command"
  packages: ["packagename"]
  command = "echo \"$version\""
  
  [workflows.steps.variables]
  "$version" = "Version"

• Enable defining workflows that are specific to a package:

  [packages.packagename]
  versioned_files = ["crates/packagename/Cargo.toml", "Cargo.lock"]
  scopes = ["packagename"]
  
  [[packages.packagename.workflows]]

I think the second option, workflow steps that run separately in each package from an explicit list, looks like it has the right balance of flexibility without requiring too much code-duplication in common cases, and I would expect it to be not terribly difficult to implement.

...I also have a few half-baked alternatives that might be worth mentioning in case they spark an idea:

• Introduce a new top-level value, something like [[single_package_workflows]], that defines workflows that run on a specific package, ignoring other packages.
• Introduce "workspaces". Having a knope.toml within a specific crate, instead of at the workspace root, appears to work already, so maybe Knope could also have a way to "mix" single-package and multi-package modes by having a multi-package config at the root level and single-package configs in each package. [Edit: having Knope.toml in a subdirectory apparently doesn't currently work, because it fails to detect the git repository in the parent directory.)