Fix issue intellij-rust#9432 random false-positives caused by GC acti…

…vity

Actually, the bug is a wrong (missing) implementation of CargoBasedCrate.equals/hashCode

src/main/kotlin/org/rust/lang/core/crate/impl/CargoBasedCrate.kt

@@ -21,6 +21,10 @@ import org.rust.lang.core.psi.rustFile
 import org.rust.openapiext.fileId
 import org.rust.openapiext.toPsiFile
 
+/**
+ * [equals]/[hashCode] are based on [cargoTarget] and [id] fields
+ * because these fields equality guarantee other fields equality
+ */
 class CargoBasedCrate(
     override var cargoProject: CargoProject,
     override var cargoTarget: CargoWorkspace.Target,
@@ -72,6 +76,24 @@ class CargoBasedCrate(
     override val normName: String get() = cargoTarget.normName
 
     override fun toString(): String = "${cargoTarget.name}(${kind.name})"
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (javaClass != other?.javaClass) return false
+
+        other as CargoBasedCrate
+
+        if (cargoTarget != other.cargoTarget) return false
+        if (id != other.id) return false
+
+        return true
+    }
+
+    override fun hashCode(): Int {
+        var result = cargoTarget.hashCode()
+        result = 31 * result + (id ?: 0)
+        return result
+    }
 }
 
 // See https://github.com/rust-lang/cargo/blob/5a0c31d81/src/cargo/core/manifest.rs#L775

src/main/kotlin/org/rust/lang/core/crate/impl/CrateGraphServiceImpl.kt

@@ -12,9 +12,12 @@ import com.intellij.openapi.util.SimpleModificationTracker
 import com.intellij.openapi.vfs.VirtualFile
 import com.intellij.openapi.vfs.VirtualFileManager
 import com.intellij.openapi.vfs.VirtualFileWithId
+import com.intellij.psi.util.CachedValue
 import com.intellij.psi.util.CachedValueProvider
+import com.intellij.util.CachedValueImpl
 import com.intellij.util.containers.addIfNotNull
 import gnu.trove.TIntObjectHashMap
+import org.jetbrains.annotations.TestOnly
 import org.rust.cargo.project.model.CargoProject
 import org.rust.cargo.project.model.CargoProjectsService.CargoProjectsListener
 import org.rust.cargo.project.model.CargoProjectsService.Companion.CARGO_PROJECTS_TOPIC
@@ -25,7 +28,6 @@ import org.rust.cargo.project.workspace.PackageOrigin
 import org.rust.lang.core.crate.Crate
 import org.rust.lang.core.crate.CrateGraphService
 import org.rust.lang.core.crate.CratePersistentId
-import org.rust.openapiext.CachedValueDelegate
 import org.rust.openapiext.checkReadAccessAllowed
 import org.rust.openapiext.isUnitTestMode
 import org.rust.stdext.applyWithSymlink
@@ -43,11 +45,14 @@ class CrateGraphServiceImpl(val project: Project) : CrateGraphService {
         })
     }
 
-    private val crateGraph: CrateGraph by CachedValueDelegate {
+    private val crateGraphCachedValue: CachedValue<CrateGraph> = CachedValueImpl {
         val result = buildCrateGraph(project.cargoProjects.allProjects)
         CachedValueProvider.Result(result, cargoProjectsModTracker, VirtualFileManager.VFS_STRUCTURE_MODIFICATIONS)
     }
 
+    private val crateGraph: CrateGraph
+        get() = crateGraphCachedValue.value
+
     override val topSortedCrates: List<Crate>
         get() {
             checkReadAccessAllowed()
@@ -64,6 +69,8 @@ class CrateGraphServiceImpl(val project: Project) : CrateGraphService {
         return rootModFile.applyWithSymlink { if (it is VirtualFileWithId) findCrateById(it.id) else null }
     }
 
+    @TestOnly
+    fun hasUpToDateGraph(): Boolean = crateGraphCachedValue.hasUpToDateValue()
 }
 
 private data class CrateGraph(

src/test/kotlin/org/rustSlowTests/RsGcSoftlyReachableObjectsCacheTest.kt

@@ -0,0 +1,54 @@
+/*
+ * Use of this source code is governed by the MIT license that can be
+ * found in the LICENSE file.
+ */
+
+package org.rustSlowTests
+
+import com.intellij.util.ref.GCUtil
+import org.rust.RsTestBase
+import org.rust.lang.core.crate.crateGraph
+import org.rust.lang.core.crate.impl.CrateGraphServiceImpl
+import org.rust.lang.core.psi.RsStructItem
+import org.rust.lang.core.psi.RsTraitItem
+import org.rust.lang.core.psi.ext.descendantsOfType
+import org.rust.lang.core.psi.ext.withSubst
+import org.rust.lang.core.resolve.RsImplIndexAndTypeAliasCache
+import org.rust.lang.core.types.TraitRef
+import org.rust.lang.core.types.TyFingerprint
+import org.rust.lang.core.types.implLookup
+
+/**
+ * Some tests that involve [GCUtil.tryGcSoftlyReachableObjects] invocation
+ */
+class RsGcSoftlyReachableObjectsCacheTest : RsTestBase() {
+    /**
+     * Issue https://github.com/intellij-rust/intellij-rust/issues/9432
+     *
+     * A kind of test for [org.rust.lang.core.crate.impl.CargoBasedCrate.equals] and
+     * [org.rust.lang.core.crate.hasTransitiveDependencyOrSelf].
+     */
+    fun `test trait selection works after GC collects the crate graph object`() {
+        InlineFile("""
+            struct S;
+            trait Trait {}
+            impl Trait for S {}
+        """.trimIndent())
+
+        val structTy = myFixture.file.descendantsOfType<RsStructItem>().single().declaredType
+        val trait = myFixture.file.descendantsOfType<RsTraitItem>().single()
+
+        // Retrieve impl in order to retain it in the memory and in the cache
+        val impls = RsImplIndexAndTypeAliasCache.getInstance(project)
+            .findPotentialImpls(TyFingerprint.create(structTy)!!)
+
+        fun canSelectImpl(): Boolean =
+            trait.implLookup.canSelect(TraitRef(structTy, trait.withSubst()))
+
+        check(canSelectImpl())
+        GCUtil.tryGcSoftlyReachableObjects { !(project.crateGraph as CrateGraphServiceImpl).hasUpToDateGraph() }
+        check(canSelectImpl())
+
+        check(impls.isNotEmpty()) // use `impls` in order to retain it in the memory until this moment
+    }
+}