Add support for defining a default build profile

[per1234]

Describe the request

Implement the "Using a default profile" component of the "Sketch build profiles and reproducible builds" RFC.

Describe the current behavior

The majority of the "Sketch build profiles and reproducible builds" RFC has now been implemented (#1713).

One missing part is the support for the default_profile key of the sketch project file.

🙁 There is currently no way to define a default profile, to be used when the arduino-cli command operating on a sketch with build profiles does not contain a --profile flag.

Arduino CLI version

0.23.0

Operating system

All

Operating system version

N/A

Additional context

Issue checklist

• I searched for previous requests in the issue tracker
• I verified the feature was still missing when using the latest nightly build
• My request contains all necessary details

[cmaglie]

Here are some use cases and the expected outcome:

Sketch with the following project file:

profiles:
  uno:
    fqbn: arduino:avr:uno
    platforms:
      - platform: arduino:avr (1.8.6)

Case 1:

$ arduino-cli compile

Output: error Missing FQBN (Fully Qualified Board Name)

Case 2:

$ arduino-cli compile --profile uno

Output: compile using profile uno

Case 3:

$ arduino-cli compile --profile uno -b arduino:avr:leonardo

Output: compile using profile uno but overrides FQBN with arduino:avr:leonardo

Case 4:

$ arduino-cli compile -b arduino:avr:uno

Output: compile for arduino:avr:uno without using the profiles

Sketch with the following project file:

profiles:
  uno:
    fqbn: arduino:avr:uno
    platforms:
      - platform: arduino:avr (1.8.6)

  leonardo:
    fqbn: arduino:avr:leonardo
    platforms:
      - platform: arduino:avr (1.8.6)

default_profile: leonardo

Case 5:

$ arduino-cli compile

Output: compiles using the default profile leonardo

Case 6:

$ arduino-cli compile --profile uno

Output: compiles using profile uno

Case 7:

$ arduino-cli compile --profile uno -b arduino:avr:leonardo

Output: compile using profile uno but overrides FQBN with arduino:avr:leonardo

Case 8:

$ arduino-cli compile -b arduino:avr:uno

Output: compile using the default profile leonardo but overrides FQBN with arduino:avr:uno

[alexxus]

Please implement it. It would be so helpful!

I'm forced to use the --profile flag, even if my sketch.yaml file has only one profile. It doesn't make sense!
arduino-cli could simply default to the single profile.

Something like default_profile: leonardo, like suggested by @cmaglie, could be also a good alternative. In fact, it would be almost better than the "magical" defaulting to the single profile. In this case the user would tell, which profile has to be used as the default.