Added skip-libraries-discovery flag in Compile

[cmaglie]

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What kind of change does this PR introduce?
Adds a hidden flag --skip-libraries-discovery, when enabled it does skip the libraries discovery phase and reuses the same libraries used in the latest "full" build. The arduino-language-server uses this feature to dramatically speed up updating and reindexing the sketch. Anyway, this feature is not suitable for direct use because it will produce a wrong build if not used correctly, that's why it's hidden.

Does this PR introduce a breaking change, and is titled accordingly?
No

[kittaakos]

Anyway, this feature is not suitable for direct use because it will produce a wrong build if not used correctly, that's why it's hidden.

When will the LS use the new --skip-libraries-discovery flag?

The arduino-language-server uses this feature to dramatically speed up updating and reindexing the sketch

I assume, the reindexing happens on textDocument/didOpen and textDocument/didChange events. This PR enables the LS to run compile without the discovery. Therefore, it's the IDE2's responsibility to send the build_path to the LS after a verify. But the build_path hash generation is platform and FQBN independent. Isn't it a problem?

a.kitta@Akoss-MacBook-Pro arduino-cli_0.24.0_macOS_64bit % ./arduino-cli version                                   
arduino-cli  Version: 0.24.0 Commit: c1b10f56 Date: 2022-06-22T10:09:11Z
a.kitta@Akoss-MacBook-Pro arduino-cli_0.24.0_macOS_64bit % ./arduino-cli core list                                 
ID           Installed Latest Name                                        
arduino:avr  1.8.5     1.8.5  Arduino AVR Boards                          
arduino:samd 1.8.13    1.8.13 Arduino SAMD Boards (32-bits ARM Cortex-M0+)

a.kitta@Akoss-MacBook-Pro arduino-cli_0.24.0_macOS_64bit % cat ~/Documents/Arduino/sketch_jun22b/sketch_jun22b.ino 
void setup() {}
void loop() {}
a.kitta@Akoss-MacBook-Pro arduino-cli_0.24.0_macOS_64bit % ./arduino-cli compile -b arduino:avr:uno ~/Documents/Arduino/sketch_jun22b --format json | jq '.builder_result.build_path'
"/private/var/folders/z1/xkw1yh5n7rz4n8djprp1mdn80000gn/T/arduino-sketch-2A25CBEDDFEB3508AE8DDDA45D126AAA"
a.kitta@Akoss-MacBook-Pro arduino-cli_0.24.0_macOS_64bit % ./arduino-cli compile -b arduino:samd:mkr1000 ~/Documents/Arduino/sketch_jun22b --format json | jq '.builder_result.build_path'
"/private/var/folders/z1/xkw1yh5n7rz4n8djprp1mdn80000gn/T/arduino-sketch-2A25CBEDDFEB3508AE8DDDA45D126AAA"
a.kitta@Akoss-MacBook-Pro arduino-cli_0.24.0_macOS_64bit % 

The arduino:avr:uno build output will be the same as for the arduino:samd:mkr1000 board. They will override each other.

Snippet from $build_path/sketch/sketch_jun22b.ino.cpp.d with arduino:avr:uno:

/private/var/folders/z1/xkw1yh5n7rz4n8djprp1mdn80000gn/T/arduino-sketch-2A25CBEDDFEB3508AE8DDDA45D126AAA/sketch/sketch_jun22b.ino.cpp.o: \
 /private/var/folders/z1/xkw1yh5n7rz4n8djprp1mdn80000gn/T/arduino-sketch-2A25CBEDDFEB3508AE8DDDA45D126AAA/sketch/sketch_jun22b.ino.cpp \
 /Users/a.kitta/Library/Arduino15/packages/arduino/hardware/avr/1.8.5/cores/arduino/Arduino.h \

...(rest)

Snippet from $build_path/sketch/sketch_jun22b.ino.cpp.d with arduinio:same:mkr1000:

/private/var/folders/z1/xkw1yh5n7rz4n8djprp1mdn80000gn/T/arduino-sketch-2A25CBEDDFEB3508AE8DDDA45D126AAA/sketch/sketch_jun22b.ino.cpp.o: \
 /private/var/folders/z1/xkw1yh5n7rz4n8djprp1mdn80000gn/T/arduino-sketch-2A25CBEDDFEB3508AE8DDDA45D126AAA/sketch/sketch_jun22b.ino.cpp \
 /Users/a.kitta/Library/Arduino15/packages/arduino/hardware/samd/1.8.13/cores/arduino/Arduino.h \

...(rest)

References to the Arduino.h file are different, so all language features will be incorrect in IDE2. For example, Go to Definition. Installing libraries can make the situation more complex. An outdated state could lead to false-positive compiler errors. The invalid state can be "fixed" only by running a verify/upload from the IDE2.

How will the --skip-libraries-discovery flag work in action?

---

Perhaps the LS can do the compile with the lib discovery on textDocument/didOpen and without on textDocument/didChange event. Or maybe the CLI could include the fqbn in the build_path hash generation. Otherwise, the IDE2 could provide incorrect language features to the users without noticing it.

[cmaglie]

Perhaps the LS can do the compile with the lib discovery on textDocument/didOpen and without on textDocument/didChange event. Or maybe the CLI could include the fqbn in the build_path hash generation. Otherwise, the IDE2 could provide incorrect language features to the users without noticing it.

Actually, the LS will only take the libraries.cache file from the verify made by the IDE. This allows the LS to safely skip the libraries discovery (since it was already made by the IDE compilation), it should find the rest of the libraries via the include path.

The build path is forced by the LS to a randomly generated temp dir, so the build made by the LS will not affect the build made by the IDE in any way.

BTW this is very theoretical and very tricky to get right, we should make extensive tests to validate it.