fix some linting errors noted by clang-tidy

[2bndy5]

I ran this lib through clang-tidy (with a basic/non-restrictive config -- see added .clang-tidy file) and found some linting errors...

Changes

• enable generation of compilation database for all CMake builds
• add .clang-tidy config file
• resolve implicit casting cases
• resolve else after return cases
• ignore false-positive about "memory allocated with zero size"

No CI checks

Clang-tidy heavily depends on having a compilation database to understand how the sources are compiled. The compilation database is basically a JSON file that stores all compiler commands for each file.

Why not?

A compilation database is specific to the compilation target. To check the Pico SDK examples we'd need to run clang-tidy with different parameters (the -p=build option).

Currently, we're using my side-project called cpp-linter to run clang-format and get PR suggestions. While it could also run clang-tidy and provide similar code suggestions in a PR, cpp-linter would have to be run multiple times for each compilation target. Unfortunately, if cpp-linter is run multiple times in a single CI event, then the PR review from cpp-linter (displayed as ) is overwritten by the last instance of cpp-linter that completed.

How to use clang-tidy going forward

First make sure clang-tidy is installed. Currently, we're using v14 of clang-format, so stick with that version.

sudo apt install clang-tidy-14

Do not attempt this on Windows because this lib cannot be compiled (or even cross-compiled). And we need a compilation database. WSL Ubuntu could be used instead, but the C/C++ std libs may not be exactly what native Linux env uses.

1. generate a compilation database for the desired platform and/or Linux driver

   export RF24_DRIVER=SPIDEV
   mkdir build
   cmake -S . -B build

2. run clang-tidy with the following args:

   clang-tidy-14 -p build RF24*.* utility/$RF24_DRIVER/*.*

Note

Reading the clang-tidy output might be tricky. Later versions of clang tools have improved the clang-tidy output, but you'll often find yourself referring to the clang-tidy docs for some errors.

[github-actions]

Memory usage change @ 48bab9b

Board	flash	%	RAM for global variables	%
arduino:avr:nano	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrzero	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0

Click for full report table

Board	examples/GettingStarted flash	%	examples/GettingStarted RAM for global variables	%	examples/AcknowledgementPayloads flash	%	examples/AcknowledgementPayloads RAM for global variables	%	examples/ManualAcknowledgements flash	%	examples/ManualAcknowledgements RAM for global variables	%	examples/StreamingData flash	%	examples/StreamingData RAM for global variables	%	examples/MulticeiverDemo flash	%	examples/MulticeiverDemo RAM for global variables	%	examples/InterruptConfigure flash	%	examples/InterruptConfigure RAM for global variables	%	examples/scanner flash	%	examples/scanner RAM for global variables	%	examples/encodeRadioDetails flash	%	examples/encodeRadioDetails RAM for global variables	%
arduino:avr:nano	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0
arduino:samd:mkrzero	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0

Click for full report CSV

Board,examples/GettingStarted<br>flash,%,examples/GettingStarted<br>RAM for global variables,%,examples/AcknowledgementPayloads<br>flash,%,examples/AcknowledgementPayloads<br>RAM for global variables,%,examples/ManualAcknowledgements<br>flash,%,examples/ManualAcknowledgements<br>RAM for global variables,%,examples/StreamingData<br>flash,%,examples/StreamingData<br>RAM for global variables,%,examples/MulticeiverDemo<br>flash,%,examples/MulticeiverDemo<br>RAM for global variables,%,examples/InterruptConfigure<br>flash,%,examples/InterruptConfigure<br>RAM for global variables,%,examples/scanner<br>flash,%,examples/scanner<br>RAM for global variables,%,examples/encodeRadioDetails<br>flash,%,examples/encodeRadioDetails<br>RAM for global variables,%
arduino:avr:nano,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0
arduino:samd:mkrzero,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0