Workspaces

Cabin treats a workspace as a package graph rooted at one cabin.toml that declares a [workspace] table. The root manifest may itself be a package ([package] is allowed alongside [workspace]) or a pure workspace root ([workspace] only).

Cabin workspaces support:

• recursive member discovery through path globs;
• [workspace.exclude] to drop unwanted directories;
• [workspace.default-members] to pick a subset for the no-flag default;
• [workspace.dependencies] / [workspace.dev-dependencies] plus dep = { workspace = true } for shared, kind-specific dependency requirements;
• root discovery from member directories so commands "just work" when invoked anywhere under the workspace;
• consistent package selection flags across the commands that operate on a workspace.

All workspace operations are local-only and deterministic.

Manifest syntax

[workspace]
members = [
  "libs/*",
  "tools/driver",
]
exclude = [
  "libs/experimental",
  "third_party/*",
]
default-members = [
  "libs/core",
  "tools/driver",
]

[workspace.dependencies]
fmt    = ">=10 <11"
spdlog = "^1.12"

A member cabin.toml opts into a shared dependency with:

[dependencies]
fmt = { workspace = true }

Rules

• members and exclude entries are paths or single-* trailing globs (e.g. libs/*). Multi-level globs (a/*/b) are intentionally rejected with a clear error.
• Excluded paths are removed from the candidate set before any member is loaded. An exclude pattern that does not drop at least one member is reported as unused exclude pattern.
• default-members entries must resolve to declared members. Unknown entries produce workspace default member 'libs/missing' is not listed in workspace.members.
• Duplicate member paths are deduplicated deterministically; the resulting member order is sorted.
• Two workspace members may not share a [package].name.
• Nested workspaces are rejected. The loader rejects the case where a member directory's cabin.toml declares its own [workspace] table; the upward discovery walk additionally errors when a cabin.toml with [workspace] sits above another cabin.toml with [workspace] regardless of whether the outer claims the inner as a member (see "Workspace root discovery" below).
• dep = { workspace = true } looks up the [workspace.<kind>-dependencies] table that matches the section it was declared in ([dependencies] → [workspace.dependencies], [dev-dependencies] → [workspace.dev-dependencies]). The lookup is strictly kind-specific — a { workspace = true } under [dev-dependencies] does not fall back to [workspace.dependencies]. If the matching workspace table does not declare the dependency, Cabin reports a clear error naming the dependency, the declaring section, and the expected workspace section.
• workspace = true cannot be combined with path = "..." or version = "..."; pick exactly one source.

Backwards compatibility

• Manifests without [workspace] keep behaving as single-package projects.
• Manifests with [workspace] members = [...] keep working unchanged. The new fields (exclude, default-members, dependencies) are all optional.
• Older lockfiles, package archives, and registry index entries are unaffected.

Workspace root discovery

When the user runs cabin <subcommand> without an explicit --manifest-path, Cabin walks upward from the current directory and looks for a cabin.toml whose root declares a [workspace] table.

• Zero workspace roots above the cwd → fall back to ./cabin.toml exactly as before.
• Exactly one workspace root → use it as the entry point.
• Two or more stacked workspace roots → discovery errors out with nested workspace detected: nearest workspace is <inner> but outer workspace is <outer>. This rule strict: previous releases either silently picked the outer or let the loader's member-list rejection produce a similar-looking error only when the outer happened to claim the inner as a member. The strict rule means stacking workspaces is always surfaced to the user, regardless of how the outer's [workspace] table is configured.

When discovery returns an error, the user is expected to disambiguate by passing --manifest-path explicitly. A user-supplied --manifest-path /some/path/cabin.toml always wins — root discovery only triggers when the user did not pass --manifest-path at all.

Discovery never touches the network and never crosses unusual filesystem boundaries (it stops at the filesystem root).

Package-selection flags

The same flag bundle applies to cabin build, cabin metadata, cabin resolve, cabin fetch, cabin package, and cabin publish:

--workspace                      operate on every workspace member
-p, --package <PACKAGE>          operate on the named member; repeatable
--default-members                operate on [workspace.default-members]
--exclude <PACKAGE>              drop a member from --workspace / default

Default behavior with no flags

Context	Selected packages
Single-package project	Just that package.
Workspace root with [workspace.default-members]	The declared default-members.
Workspace root without [workspace.default-members]	All workspace members.
Inside a member directory	Same as the workspace root above (root discovery picks it up).

Constraints

• --workspace, -p / --package, and --default-members are mutually exclusive.
• Selection flags: --exclude is only valid in combination with --workspace or --default-members. Older behavior also accepted --exclude with the no-flag "current package" default; Cabin made the rule stricter (closer to Cargo) so a typo on a single-package project surfaces a clear error rather than silently doing the wrong thing.
• Unknown package names (whether selected or excluded) produce package 'foo' is not a member of this workspace; available members: alpha, beta, gamma.

Per-command notes

• cabin metadata reports workspace.members, workspace.default_members, workspace.excluded_members, and workspace.selected_packages. All four lists are sorted by package name (or path, for excluded_members) so the JSON shape is deterministic.
• cabin build plans only the C/C++ targets in the selected packages. Cabin does not currently offer a single-target selector flag, so the build always enumerates every default-buildable target in the selected packages. Unselected packages are not built, so the resulting build.ninja is the smallest graph that covers the request.
• cabin resolve walks the selected package closure — the resolved selection plus every local path-dependency reachable from it — and unions every reachable member's versioned dependencies into a single resolution. The workspace loader added the closure walk so a registry dep declared by a path-dep lib reaches the resolver when the user picks app. The selection-aware closure extends all the way down into registry materialization: when the loader expands versioned dependencies into the package graph, it only requires registry entries for packages reachable from the selected closure. Versioned deps of unrelated workspace members (or unrelated path-deps) are silently skipped, so cabin resolve -p app no longer requires the index to know about an unrelated member's dependency on spdlog. The lockfile, by contrast, is still workspace-wide once produced — selection only affects what the loader has to materialize for this command.

Pure workspace roots (no [package]) work too: cabin resolve --workspace over a workspace root that only has members with [dependencies] produces a lockfile rooted at a synthetic __workspace_<dirname> 0.0.0 identity. Member-level requirement conflicts (fmt = "^10" and fmt = "^11" in two members) surface as a clear incompatible workspace requirements for 'fmt' error. - cabin update keeps its historical --package <name> meaning: refresh only the named registry dependency. To avoid colliding with that flag, cabin update exposes a reduced workspace-selection bundle — --workspace, --default-members, and --exclude — but not -p / --package. Existing scripts that pass cabin update --package <dep> keep working unchanged.

Cabin makes the scope explicit: cabin update --package <name> only targets direct versioned dependencies of the root package — those declared under [dependencies] (or the workspace-inherited equivalent) of the manifest you are updating. Transitive locked packages cannot be refreshed individually; to update a transitive lockfile entry, drop the --package flag (cabin update) so resolution rolls forward every relaxable constraint, or scope the refresh to a wider selection (cabin update --workspace, etc.). An unknown or transitive name produces "package 'foo' is not a direct versioned dependency of <root>; cabin update --package only refreshes direct dependencies declared in [dependencies]". - cabin fetch validates the workspace selection up-front (so cabin fetch -p missing errors even when the workspace has no versioned deps) and then unions selected members' versioned deps for the resolution. The artifact cache itself remains workspace-flat — every required artifact is downloaded exactly once. - cabin package in a workspace requires exactly one --package <name> selection. The workspace root itself is not packageable. - cabin publish in a workspace requires exactly one --package <name> selection for both --dry-run and --registry-dir flows.

-p / --package <name> always matches by package name (the [package].name declared by the member). Workspace member paths (libs/core) are never accepted by --package; they live only inside the manifest's [workspace] members = [...] list.

Worked examples

LLVM-style monorepo

# cabin.toml at the repository root
[workspace]
members = [
  "llvm",
  "lld",
  "lldb",
  "clang",
  "clang-tools-extra",
  "compiler-rt/*",
]
exclude = [
  "third-party/*",
]
default-members = [
  "llvm",
  "clang",
]

[workspace.dependencies]
fmt = "^11"

# Build the default (llvm + clang).
cabin build

# Build the entire monorepo, minus the LLDB tests.
cabin build --workspace --exclude lldb

# Build only one component.
cabin build -p llvm -p clang

# Inspect what Cabin sees.
cabin metadata

Per-team monorepo with shared dependencies

[workspace]
members = ["services/*", "libs/*"]

[workspace.dependencies]
fmt    = ">=10 <11"
spdlog = "^1.12"

# services/api/cabin.toml
[package]
name = "api"
version = "0.1.0"

[dependencies]
fmt    = { workspace = true }
spdlog = { workspace = true }

[target.api]
type = "executable"
sources = ["src/main.cc"]

Bumping fmt from >=10 <11 to ^12 then becomes a one-line change at the workspace root rather than a dozen individual member edits.

Boundaries

Workspace support covers the local package graph and the workspace-aware command surfaces documented above: dependency kinds, feature unification, target-conditioned dependencies, profiles, toolchain settings, compiler-cache settings, config discovery, patches, source replacement, vendoring / offline mode, and dev / test / example target kinds all participate in workspace selection where their owning feature requires it.

The remaining non-goals are network-side registry operation and remote publication. Cabin can read sparse HTTP indexes and publish to a local file registry, but it does not implement a registry server, HTTP publish, registry authentication, or a remote build cache.