commit 129a5cdc3664668c7ca0f5135f3c9b7b6b2dad4d
author Jaebaek Seo <jaebaek@google.com> Tue Jan 24 17:17:38 2023 -0800
committer Jaebaek Seo <jaebaek@google.com> Mon Feb 06 11:36:08 2023 -0800
tree a445bede202bb25d824738daa18539146448db10
parent bef1765ec051d3b12f8dacc1560c0af61aa8b3c2

Handle SHORTEN_IF_ALEADY_IMPORTED case of KtFirReferenceShortener

For the following example, when we run the reference shortener, it
drops `a.b.c` qualifier, because it matches "FOURTH".
```
package a.b.c

fun <T, E, D> foo(a: T, b: E, c: D) = a.hashCode() + b.hashCode() + c.hashCode() // FIRST
fun <E> E.foo() = hashCode() // SECOND

object Receiver {
    fun <T, E, D> foo(a: T, b: E, c: D) = a.hashCode() + b.hashCode() + c.hashCode() // THIRD
    fun foo(a: Int, b: Boolean, c: String) = a.hashCode() + b.hashCode() + c.hashCode() // FOURTH
    fun test(): Int {
        fun foo(a: Int, b: Boolean, c: Int) = a + b.hashCode() + c // FIFTH
        return <expr>a.b.c.foo(1, false, "bar")</expr>
    }
}
```

As shown in the above example, when SHORTEN_IF_ALEADY_IMPORTED option is
given from a user, the reference shortener has to check whether it can
drop the qualifier without changing the referenced symbol and if it is
possible to do that without adding a new import directive, it deletes
the qualifier.

It needs two steps:
 1. Collect all candidate symbols matching the signature e.g., function
    arguments / type arguments
 2. Determine whether the referenced symbol has the highest reference
    priority when we drops the qualifier depending on scopes

This commit uses `AllCandidatesResolver(shorteningContext.analysisSession.useSiteSession).
getAllCandidates( .. fake FIR call/property-access ..)` for step1.
For step2, we use a heuristic based on scopes of candidates. If a
candidate symbol is under the same scope with the target expression, it
has a `FirLocalScope` which has the high priority. So when we have a
candidate under a `FirLocalScope` and the actual referenced symbol is
different from the candidate, we must avoid dropping its qualifier
because the shortening will change its semantics i.e., reference.

The order of scopes depending on their scope types is:
 1. FirLocalScope
 2. FirClassUseSiteMemberScope / FirNestedClassifierScope
 3. FirExplicitSimpleImportingScope
 4. FirPackageMemberScope
 5. others

Note that for "others" the above rule can be wrong. Please update it if
you find other scopes that have a priority higher than the specified
scopes.

One of non-trivial parts is the priority among multiple
FirClassUseSiteMemberScope and FirNestedClassifierScope. They are
basically scopes for class declarations. We decide their priorities
based on the distance of class declaration from the target expression.

Note that we take a strict approach to reject all false positive. For
example, when we are not sure, we don't shorten it to avoid changing its
semantics.

TODO: One corner case is handling receivers. We have to update
```
private fun shortenIfAlreadyImported(
    firQualifiedAccess: FirQualifiedAccess,
    calledSymbol: FirCallableSymbol<*>,
    expressionInScope: KtExpression,
): Boolean
```

The current implementation cannot handle the following example:
```
package foo
class Foo {
    fun test() {
        // It references FIRST. Removing `foo` lets it reference SECOND.
        <caret>foo.myRun {
            42
        }
    }
}
inline fun <R> myRun(block: () -> R): R = block()         // FIRST
inline fun <T, R> T.myRun(block: T.() -> R): R = block()  // SECOND
```

Tests related to TODO:
 - analysis/analysis-api/testData/components/referenceShortener/referenceShortener/receiver2.kt
 - analysis/analysis-api/testData/components/referenceShortener/referenceShortener/receiver3.kt