Avoid realizing data in preprocessor function concatenate when cubes overlap

[bouweandela]

Description

Avoid realizing data in preprocessor function concatenate when cubes overlap.

---

Before you get started

• ☝ Create an issue to discuss what you are going to do

Checklist

It is the responsibility of the author to make sure the pull request is ready to review. The icons indicate whether the item will be subject to the 🛠 Technical or 🧪 Scientific review.

• 🧪 The new functionality is relevant and scientifically sound
• 🛠 This pull request has a descriptive title and labels
• 🛠 Code is written according to the code quality guidelines
• 🧪 and 🛠 Documentation is available
• 🛠 Unit tests have been added
• 🛠 Changes are backward compatible
• 🛠 The list of authors is up to date
• 🛠 All checks below this pull request were successful

---

To help with the number pull requests:

• 🙏 We kindly ask you to review two other open pull requests in this repository

[codecov]

Codecov Report

Merging #2109 (6ff7304) into main (cf3824e) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2109   +/-   ##
=======================================
  Coverage   93.08%   93.08%           
=======================================
  Files         237      237           
  Lines       12793    12793           
=======================================
  Hits        11909    11909           
  Misses        884      884           

Impacted Files	Coverage Δ
esmvalcore/preprocessor/_io.py	86.74% <100.00%> (ø)

[valeriupredoi]

Thanks, bud! I am a bit rusty when it comes to scalar cubes - are we 100% sure a scalar cube is always of shape () or if it got an AuxCoord could be (1, )? A test would prob be needed, but let's just get this in

[bouweandela]

are we 100% sure a scalar cube is always of shape () or if it got an AuxCoord could be (1, )?

I would be really surprised if Cube.shape was not the same as Cube.data.shape.

A test would prob be needed

I assume you wrote some very thorough tests when you implemented this, no? Codecov reports 100% coverage, so I would expect the functional tests to work. I could add a test that lazy input results in lazy output?

[valeriupredoi]

am gonna merge since am 99.9% sure my use case above is a non-issue. Do you want to include this in the 2.9 release @bouweandela ? It's a small fix that may bear a hefty weight