Re: [PATCH 5/6] odb/transaction: add transaction env interface

[Patrick Steinhardt <ps@pks.im>]

On Tue, Jun 23, 2026 at 11:19:19PM -0500, Justin Tobler wrote:
> The ODB transaction backend is responsible for creating/managing its own
> staging area for writing objects. Other child processes spawned by Git
> may need to access to uncommitted objects or write new objects in the

s/may need to access to/may need access to/

> staging area though.
> 
> Introduce `odb_transaction_env()` which is expected to provide the set
> of environment variables needed by a child process to access the
> transaction staging area.

Possessive s is missing, I think.

> diff --git a/object-file.c b/object-file.c
> index 696f05dc2d..14064d188a 100644
> --- a/object-file.c
> +++ b/object-file.c
> @@ -1691,6 +1691,16 @@ static int odb_transaction_files_commit(struct odb_transaction *base)
>  	return 0;
>  }
>  
> +static const char **odb_transaction_files_env(struct odb_transaction *base)
> +{
> +	struct odb_transaction_files *transaction =
> +		container_of(base, struct odb_transaction_files, base);
> +
> +	odb_transaction_files_prepare(&transaction->base);
> +
> +	return tmp_objdir_env(transaction->objdir);
> +}
> +
>  int odb_transaction_files_begin(struct odb_source *source,
>  				struct odb_transaction **out)
>  {

Makes sense. Transactions may have a different way to quarantine the
write than using a quarantine directory. So making this functionality
pluggable so that backends may expose a separate set of environment
variables feels sensible.

> diff --git a/odb/transaction.h b/odb/transaction.h
> index 7898770071..536458297b 100644
> --- a/odb/transaction.h
> +++ b/odb/transaction.h
> @@ -32,6 +32,16 @@ struct odb_transaction {
>  	int (*write_object_stream)(struct odb_transaction *transaction,
>  				   struct odb_write_stream *stream, size_t len,
>  				   struct object_id *oid);
> +
> +	/*
> +	 * This callback is expected to return a NULL-terminated array of
> +	 * environment variables that a child process should inherit so
> +	 * that its object writes participate in the transaction. The
> +	 * returned array is owned by the backend and remains valid until
> +	 * the transaction ends. May return NULL when the backend does not
> +	 * need to expose any state to child processes.
> +	 */
> +	const char **(*env)(struct odb_transaction *transaction);

Would it make more sense to adapt this function so that:

  - It receives a `struct strvec` as input that the environment
    variables are to be amended to.

  - It returns a normal error code to indicate errors?

Patrick