The "free" in "createFreeFakeLambdaDescriptor" and such refers to the
fact that there are no references to type parameters from outside the
current declaration. This is necessary because at the point where the
metadata is written, the type parameters may not even be in scope (e.g.
local delegated properties are serialized at class level, but may refer
to function-scope type parameters).
Since LocalDeclarationsLowering is a BodyLoweringPass, local
functions inside one declaration are handled independently of local
functions in the other declaration. This can lead to name clashes, in
case a local function with the same name and signature is declared in
overloads in the same container, which results in a signature clash
error in JVM IR.
The issue became more common with the introduction of adapted function
references, where psi2ir generates a local adapter-function with a
predefined name, which can easily clash with another reference to the
same target in an overload. This led to a compilation error when
bootstrapping Kotlin with JVM IR, for example in GradleIRBuilder.kt
where there are a lot of references to the same function.
Now FE IR -> BE IR transformation is performed in multiple stages
controller by Fir2IrConverter. Stages are
* files & classes registration
* supertypes & type parameters handling
* functions & properties signature generation
* body generation
After each step we have guarantee (with exception of local classes &
type inference combination, and external symbols) that required symbols
(class/function/property/variable/type parameter)
are already bound to real declarations and have correct parents.
This commit also fixes incorrect parents for local classes
* fixed NoSuchMethod caused by mismatched signatures of the "invoke" method generated for lambda arguments
* added test cases in invoke.kt for KFunction and anonymous functions
* added a transformer to wrap the last expression in the bodies of lambdas with return
Otherwise, it's complicated to work with nested lambdas:
outer/inner ones may be replaced independently and still refer
to the old one instances.
So in the changed test, if we don't apply the commit, will remain
implicit return and receiver types for the nested lambda
Anyway, once we decided to leave immutable semantics,
replacements are not necessary anymore
Alexander Udalov