Migrate code analysis to FIR

[artem-zinnatullin]

After multiple discussions with JetBrains people, I was explained that Kotlin compiler is getting rearchitectured, in particular IR (intermediate representation) is getting split into Frontend IR (FIR) and Backend IR parts.

Currently, Ketolang hooks into IrGenerationExtension.

Ketolang code analysis should be moved to FIR when FIR is stabilized (currently in Alpha):

• IntelliJ will be running FIR analysis via compiler and configured compiler plugins to validate code in IDE, which will automatically integrate Ketolang analysis into IntelliJ! (errors)
• New IR architecture is faster than current IR — JB claims 4x improvement, since it doesn't rely on complete type inference nor complete code DOM tree being prepared in many cases nor global map of PSI symbols to parsed resolutions
• FIR is the right place to analyze code and generate stubs of declarations, Backend IR is the right place to generate actual IR bodies

Ketolang code generation (if added) should be moved to Backend IR:

• This way it won't slow down IntelliJ by generating code during code analysis, only FIR is going to be run in IntelliJ
• Code generated in Backend IR or IrGenerationExtension is not available for IntelliJ within the same module, however FIR can generate declarations of the members while Backend IR can later inflate them with IR bodies.

See:

• https://github.com/JetBrains/kotlin/tree/master/docs/fir
• https://kotlinlang.org/docs/whatsnew17.html

JB contact for this: Dmitry Novozhilov @demiurg906