Compiler check for 'when' exhaustiveness requires that module
descriptors of a sealed class and its inheritors are the same (reference
identity matters). Prior to this commit and under some conditions they
were not. Details follow below.
Resolution related data structures (resolution facades) are organized
into trees (sdks, libs, and modules have their own nodes/facades,
module/class descriptors are stored inside). And the trees themselves
are put into a map associating so called PlatformAnalysisSettings and
GlobalFacades (plays a role of a root). PlatformAnalysisSettings is an
abstraction describing target platform and sdk of a module. The more
combinations exist for a project the more facades are used. Please, see
KotlinCacheService for more details.
So why a module can have multiple ModuleDescriptor-s?
Every tree mentioned above is an isolated resolution environment
containing its own instances of the outer world descriptors. Say, if a
project has modules X, Y, Z and we consider X then all three might have
their own vision of X, i.e. 3 descriptors exist at a time.
What descriptor instance does compiler get?
The path starts when the user opens a file in the editor and
highlighting pass starts (see usages of
ResolutionUtils#analyzeWithAllCompilerChecks). Module descriptor stored
in the resolution tree of the file's module gets injected into the
compiler's context. Starting from this moment compiler sees other
modules through the prism of a single resolution facade (tree).
Descriptors residing outside are alien.
This commit allows IdeSealedClassInheritorsProvider to figure out what
PlatformAnalysisSettings are associated with the resolution facade (read
ModuleDescriptor) seen by the compiler. Later on the same facade is used
to provide correct instances of sealed inheritors back to the compiler.
The main purpose is to show that old frontend and FIR work differently
in the case of the conflicts of local and top level classes/objects
See the tests that marked with // IGNORE_FIR
Corresponding ticket is ^KT-45192
This removes another dependency of 'ir.tree' on 'frontend', and among
other things, makes it possible to implement TranslationPluginContext
for FIR in the future.
Mikhael Bogdanov