Re: [BuildStream] Proposal: bst commands don't fetch elements implicitly

[Sander Striker <s striker striker nl>]

Hi,

On Sun, Oct 28, 2018 at 2:19 PM Phil Dawson via BuildStream-list <buildstream-list gnome org> wrote:

Hi all,

This is a write up of a discussion which happened at the Manchester

gathering after originally being raised at [1].

If we wish bst to follow the principle of least surprise, we should

minimize the number of operations performed implicitly when invoking

bst commands. To this end, it is proposed here that we change the

default behaviour of bst commands such that sources are not fetched

unless this is explicitly requested.

Consistency typically helps in preventing surprising behavior, as raised in [1].

That said, let's aim for the best user experience here.  It might be that the other

commands mentioned, for example bst [artifact] checkout, should actually pull

(but not build), implicitly.

 

Note that as this proposal would alter BuildStream's cli, any

implementation should be completed prior to the 1.4 release.

Current Behaviour

------------------------------

Currently BuildStream will automatically fetch sources which are not

cached when running the following bst commands:

- workspace open

- workspace reset

- source-bundle

- shell (with --build option)

- build

The exception to the above is junction elements, which are fetched at

load time by build, fetch, track, pull, push and checkout.

Proposed Behaviour

---------------------------------

Only `bst build` should fetch sources by default. There is an option

like --fetch for the remaining commands. These should only fetch

elements if this option is present.

It seems a bit silly to not have workspace open implicitly fetch.  The purpose of this command is to interact with the sources.  The same goes for source-checkout.  I am

unclear on workspace reset.  Maybe you can explain that case a bit more?

And when SourceCache makes its debut, I would want the option for bst build to

not fetch sources either, and only rely on what is available in SourceCache.

 

If unfetched sources are required and the --fetch flag is not given,

the command should should fail and recommend the user run a bst fetch

command or the repeat the command with the --fetch option.

This seems a bit silly if it is going to be the common case.  If you tell me what to

run, why don't you take care of it for me?

 

Alternatively,

if running in interactive mode, the user should be presented with the

option to fetch, continue, quit etc.

[1] https://gitlab.com/BuildStream/buildstream/merge_requests/820#note_104008640

Cheers,

Sander

 

Best regards,

Phil

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Cheers,

Sander