Allow publishing packages without a module

Removes the check that requires a module to be specified when publishing
a package.

Removed because modules should not be mandatory - packages with just a
file system, or with a command that uses the module of a dependency are
perfectly valid.

lib/cli/src/commands/publish.rs

@@ -50,8 +50,6 @@ pub struct Publish {
 
 #[derive(Debug, Error)]
 enum PublishError {
-    #[error("Cannot publish without a module.")]
-    NoModule,
     #[error("Unable to publish the \"{module}\" module because \"{}\" is not a file", path.display())]
     SourceMustBeFile { module: String, path: PathBuf },
     #[error("Unable to load the bindings for \"{module}\" because \"{}\" doesn't exist", path.display())]
@@ -115,7 +113,10 @@ impl Publish {
         builder
             .finish()
             .map_err(|e| anyhow::anyhow!("failed to finish .tar.gz builder: {e}"))?;
-        let tar_archive_data = builder.into_inner().map_err(|_| PublishError::NoModule)?;
+        let tar_archive_data = builder
+            .into_inner()
+            // NOTE: only fails if `Builder::finish()` was not called.
+            .expect("tar archive .finish() was not called");
         let archive_name = "package.tar.gz".to_string();
         let archive_dir = tempfile::TempDir::new()?;
         let archive_dir_path: &std::path::Path = archive_dir.as_ref();
@@ -172,7 +173,7 @@ fn construct_tar_gz(
     cwd: &Path,
 ) -> Result<(Option<String>, Option<String>), anyhow::Error> {
     let package = &manifest.package;
-    let modules = manifest.module.as_ref().ok_or(PublishError::NoModule)?;
+    let modules = manifest.module.as_deref().unwrap_or_default();
 
     let readme = match package.readme.as_ref() {
         None => None,