[breaking] Add env variable to let tools know the cli version and the gRPC client version

[cmaglie]

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• Tests for the changes have been added (for bug fixes / features)
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• UPGRADING.md has been updated with a migration guide (for breaking changes)

What kind of change does this PR introduce?

Adds a new environment variable ARDUINO_MODE that is passed on all tools launched by the CLI.
The value of the variable may be:
* cli if the arduino-cli is used from terminal or scripts as a pure command-line tool.
* daemon if the arduino-cli is launched as a daemon.

Adds an ARDUINO_USER_AGENT environment variable to all the tools launched for compile and upload.
The variable is in HTTP user-agent format and contains the version of the CLI and possibly the version of the gRPC client of the user if this information is available.
Some examples:

ARDUINO_USER_AGENT=arduino-cli/0.21.0
ARDUINO_USER_AGENT=arduino-cli/0.21.0 ArduinoIDE/2.0.0-rc3

Does this PR introduce a breaking change, and is titled accordingly?
Yes, there are some breaking changes in the golang API.

[cmaglie]

It looks like we have a regression on MacOS, I'm setting this PR as draft until I found the reason.

[per1234]

I know this is still WIP, but I want to add a "to do" that the final proposal should include documentation. Otherwise it will end up as one of those esoteric features nobody remembers a year from now.

It isn't clear to me which is the ideal place to document this. The available options are probably:

• arduino-cli daemon command docs
• Platform Specification

Any opinions on the location?

[cmaglie]

IMHO https://arduino.github.io/arduino-cli/dev/platform-specification/#tools is the best place, I'll write down some notes there.

[cmaglie]

@PaulStoffregen
After a brief internal discussion, I've changed the env variable to ARDUINO_USER_AGENT (more detailed description in the opening post of this PR: #1640 (comment)).

The rationale is that the previous ARDUINO_MODE=cli/daemon does not contain enough information to determine if the process is running on a GUI, there are some corner cases like:

• running the gRPC daemon as a backend for an HTTP service endpoint: in this case we don't want to display a GUI in a headless server
• other software that uses the CLI daemon that does not necessarily have a GUI
• in general, running the daemon does not imply running a GUI

I guess you would like to check if the user agent contains the string ArduinoIDE to actually display a GUI.

[per1234]

Please also document the breaking changes to the public Go package API according to the standard policy:
https://arduino.github.io/arduino-cli/dev/CONTRIBUTING/#breaking

[per1234]

Thanks Cristian!

[PaulStoffregen]

Thanks!!

Today I'm still working on porting my pluggable serial monitor code to Windows. Hoping I can wrap that up tonight, and then tomorrow start using the next nightly build with this environment variable.

[cmaglie]

Do not rush on this one, we need to fix also the Arduino IDE to fully support it arduino/arduino-ide#790