cz bump crashes with version_provider=cargo on workspace virtual manifest (missing [package] / TypeError on version.workspace) #1732

Description

Commitizen crashes when using version_provider = "cargo" on a Cargo workspace virtual manifest (root Cargo.toml contains [workspace] and [workspace.package] but no [package]). Our workspace members inherit version via version.workspace = true. Running cz bump fails inside commitizen/providers/cargo_provider.py while trying to update Cargo.lock.

This prevents using Commitizen’s cargo provider for monorepo-style Rust workspaces where the version is centralized in [workspace.package].version.

Steps to reproduce

1. Create a Cargo workspace that uses a virtual manifest at the root (no [package]), with a centralized version:

   # ./Cargo.toml (workspace root)
   [workspace]
   members = ["crates/a"]
   
   [workspace.package]
   version = "0.1.0"
   edition = "2024"

2. Create a member crate that inherits the version via version.workspace = true:

   # ./crates/a/Cargo.toml
   [package]
   name = "a"
   version.workspace = true
   edition.workspace = true

3. Configure Commitizen to use the cargo provider:

   # ./cz.toml
   [tool.commitizen]
   name = "cz_conventional_commits"
   version_scheme = "semver"
   version_provider = "cargo"
   tag_format = "v$version"
   update_changelog_on_bump = true

4. Run:

   cz bump --yes

5. Observe the crash inside commitizen/providers/cargo_provider.py (during manifest parsing / Cargo.lock update).

Current behavior

cz bump crashes with exceptions from cargo_provider.py:

• tomlkit.exceptions.NonExistentKey: 'Key "package" does not exist.' (root manifest has no [package])
• then TypeError: string indices must be integers, not 'str' (when accessing package_content["version"]["workspace"] for members)

The command terminates without completing the bump/tag operation.

Desired behavior

cz bump should support Cargo workspaces with a virtual manifest (root Cargo.toml has [workspace] / [workspace.package] but no [package]) and members using version.workspace = true.

Concretely:

• Read and bump the canonical version from [workspace.package].version.
• Do not assume [package] exists in the workspace root manifest.
• When scanning/updating member manifests, correctly handle version.workspace = true (a nested table / boolean) without type errors.

Screenshots

No response

Environment

(computation) juncheng@localhost:~/projects/computation$ cz version --report
Commitizen Version: 4.10.1
Python Version: 3.11.12 (main, Apr 9 2025, 04:04:00) [Clang 20.1.0 ]
Operating System: Linux