Modification time of an element with an open workspace propagates into consumer element's sandbox

[AlgebraicWolf]

When an element has a dependency with an open workspace, that dependency's artifacts get staged with their real mtimes instead of the magic timestamp. This can cause differences between builds with and without the workspace.

Steps to reproduce

A small project to reproduce the issue:

.
├── a.txt
├── elements
│   ├── a.bst
│   ├── alpine.bst
│   └── b.bst
└── project.conf

The context of a.txt are irrelevant, it can be left empty. elements/a.bst carries a.txt:

kind: import

sources:
  - kind: local
    path: a.txt

config:
  target: /

elements/b.bst has a.bst and alpine.bst as build dependencies:

kind: manual

build-depends:
  - alpine.bst
  - a.bst

project.conf and alpine.bst are set up to pull alpine image

alpine.bst:

kind: import
description: |

    Alpine Linux base runtime

sources:
- kind: tar

  # This is a post doctored, trimmed down system image
  # of the Alpine linux distribution.
  #
  url: alpine:integration-tests-base.v1.x86_64.tar.xz
  ref: 3eb559250ba82b64a68d86d0636a6b127aa5f6d25d3601a79f79214dc9703639

project.conf:

# Unique project name
name: bug-repro

# Required BuildStream version
min-version: 2.7

# Subdirectory where elements are stored
element-path: elements

aliases:
  alpine: https://bst-integration-test-images.ams3.cdn.digitaloceanspaces.com/

When no workspace is open, building b.bst, opening its build sandbox, and checking the mtime of a.txt shows that all is well, and modification time is normalised:

$ bst build b.bst
...
$ bst shell --build b.bst
...
[20440600@b.bst:/buildstream/repro/b.bst]$ stat /a.txt 
  File: /a.txt
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 31h/49d Inode: 2           Links: 1
Access: (0644/-rw-r--r--)  Uid: (1876721912/ UNKNOWN)   Gid: (1174200513/ UNKNOWN)
Access: 2011-11-11 11:11:11.000000000
Modify: 2011-11-11 11:11:11.000000000
Change: 2011-11-11 11:11:11.000000000

If a.bst's workspace is opened first, the modification time is no longer the magic timestamp but the actual a.bst's build time instead:

$ bst workspace open a.bst
...
$ bst build b.bst
...
$ bst shell --build b.bst
...
[e1f40f6c@b.bst:/buildstream/repro/b.bst]$ stat /a.txt
  File: /a.txt
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 31h/49d Inode: 3           Links: 1
Access: (0644/-rw-r--r--)  Uid: (1876721912/ UNKNOWN)   Gid: (1174200513/ UNKNOWN)
Access: 2011-11-11 11:11:11.000000000
Modify: 2026-08-25 11:06:30.000000000
Change: 2011-11-11 11:11:11.000000000

[abderrahim]

When an element has an open workspace, it is expected that the sources from element are staged with their mtime. But that shouldn't transfer to the artifact.

I suspect this would be specifically a bug in the import plugin, and it wouldn't be reproducible with another plugin.

[AlgebraicWolf]

I suspect this would be specifically a bug in the import plugin, and it wouldn't be reproducible with another plugin.

import here is a simplification, it was originally discovered with manual plugin.