rust-lang/cargo · error · anyhow::Error

`{key}.workspace = false` is unsupported

Error message

`{key}.workspace = false` is unsupported

What it means

Thrown by `Dependency::from_toml` (the editor used by `cargo add`/`cargo rm`) at src/workspace/editor/dependency.rs:318. When a dependency table contains a `workspace` key whose value is `false`, cargo rejects it because `workspace = false` is semantically a no-op — the absence of the key already means "do not inherit from workspace.dependencies". Only the positive `workspace = true` form is meaningful.

Source

Thrown at src/workspace/editor/dependency.rs:318

                    let mut src = PathSource::new(path);
                    src.base = base;
                    if let Some(value) = table.get("version") {
                        src = src.set_version(value.as_str().ok_or_else(|| {
                            invalid_type(key, "version", value.type_name(), "string")
                        })?);
                    }
                    src.into()
                } else if let Some(version) = table.get("version") {
                    let src = RegistrySource::new(version.as_str().ok_or_else(|| {
                        invalid_type(key, "version", version.type_name(), "string")
                    })?);
                    src.into()
                } else if let Some(workspace) = table.get("workspace") {
                    let workspace_bool = workspace.as_bool().ok_or_else(|| {
                        invalid_type(key, "workspace", workspace.type_name(), "bool")
                    })?;
                    if !workspace_bool {
                        anyhow::bail!("`{key}.workspace = false` is unsupported")
                    }
                    let src = WorkspaceSource::new();
                    src.into()
                } else {
                    anyhow::bail!(
                        "dependency ({key}) specified without \
                        providing a local path, Git repository, version, or \
                        workspace dependency to use"
                    );
                };
            let registry = if let Some(value) = table.get("registry") {
                Some(
                    value
                        .as_str()
                        .ok_or_else(|| invalid_type(key, "registry", value.type_name(), "string"))?
                        .to_owned(),
                )
            } else {

View on GitHub (pinned to 0e07a15537)

Solutions

1. Delete the `workspace = false` pair so the line becomes `foo = "1.0"` (or whatever the real source is).
2. If you intended inheritance, change it to `foo = { workspace = true }` and define `foo` under `[workspace.dependencies]` in the workspace root.

Example fix

# before
foo = { workspace = false }
# after
foo = "1.0"
# (or, to inherit)
foo = { workspace = true }

// before invoking the manifest editor, scrub `workspace = false`
for (_k, item) in doc.as_table().iter() {
    if let Some(t) = item.as_table_like() {
        if matches!(t.get("workspace").and_then(|v| v.as_bool()), Some(false)) {
            // remove or convert before calling Dependency::from_toml
        }
    }
}

When it happens

Trigger: A `[dependencies]` entry written as `foo = { workspace = false }`, or `cargo add` leaving behind `{ workspace = false }` in a member Cargo.toml. The branch is reached only when the table has no `git`/`path`/`version` and `table.get("workspace")` yields a bool `false`.

Common situations: Hand-editing a manifest after removing workspace inheritance; tools/generators that emit `workspace = false` defensively; misunderstanding that `false` must be expressed by omitting the key.

Related errors

• `default-features = false` cannot override workspace's `defa
• package `{}` cannot be tested because it requires dev-depend
• {}package(s) `{}` not found in workspace `{}`
• no library targets found in packages: {}
• invalid feature `{}` in required-features of target `{}`: `d

AI-assisted analysis of rust-lang/cargo@0e07a15537 (2026-08-06). Data as JSON: /data/errors/f0694d5f41c1071a.json. Report an issue: GitHub.