Kotlin extractor: restore external file-class locations under K2

Why this is needed:
- Under K2, top-level declarations from external binaries are attached directly
  to IrExternalPackageFragment rather than to an IrClass file-class parent.
- That bypassed the normal class-source location path, so some external file-class
  entities ended up without stable binary file locations.
- Missing/unstable locations caused drift in tests that depend on external file
  class member resolution and location facts.

What this changes:
- Resolve binary paths from IrMemberWithContainerSource (JvmPackagePartSource)
  via a dedicated getContainerSourceBinaryPath helper.
- In KotlinUsesExtractor, when extracting top-level external declarations,
  attach file-class location from container-source binary path when available.
- Track external file classes whose locations were emitted to avoid duplicate
  hasLocation facts.

This targets the K2 external file-class location gap (for example file_classes and
external-property-overloads parity).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

java/kotlin-extractor/src/main/kotlin/KotlinUsesExtractor.kt

@@ -996,7 +996,19 @@ open class KotlinUsesExtractor(
                 )
                 return null
             }
-            return extractFileClass(fqName)
+            val fileClassId = extractFileClass(fqName)
+            // Under K2, external file class members sit directly under IrExternalPackageFragment
+            // rather than under their IrClass parent. In that case the file class entity won't
+            // get a location set through the normal extractClassSource path.
+            if (d is IrMemberWithContainerSource && tw.lm.externalFileClassLocationsExtracted.add(fqName)) {
+                val binaryPath =
+                    getContainerSourceBinaryPath(d.containerSource)
+                        ?.let { normalizeExternalFileClassBinaryPath(it, fqName) }
+                        ?: "/!unknown-binary-location/${fqName.asString().replace(".", "/")}.class"
+                val fileId = tw.mkFileId(binaryPath, true)
+                tw.writeHasLocation(fileClassId, tw.getWholeFileLocation(fileId))
+            }
+            return fileClassId
         }
         return useDeclarationParent(parent, canBeTopLevel, classTypeArguments, inReceiverContext)
     }

java/kotlin-extractor/src/main/kotlin/TrapWriter.kt

@@ -51,6 +51,13 @@ class TrapLabelManager {
      * to avoid duplication.
      */
     val fileClassLocationsExtracted = HashSet<IrFile>()
+
+    /**
+     * Tracks external file classes (by FqName) whose location has been set from a binary path.
+     * Used to avoid writing duplicate hasLocation facts for external file class entities extracted
+     * through the K2 code path where declarations sit directly under IrExternalPackageFragment.
+     */
+    val externalFileClassLocationsExtracted = HashSet<org.jetbrains.kotlin.name.FqName>()
 }
 
 /**

java/kotlin-extractor/src/main/kotlin/utils/ClassNames.kt

@@ -176,15 +176,56 @@ fun getIrDeclarationBinaryPath(d: IrDeclaration): String? {
         // This is in a file class.
         val fqName = getFileClassFqName(d)
         if (fqName != null) {
+            if (d is IrMemberWithContainerSource) {
+                val containerBinaryPath = getContainerSourceBinaryPath(d.containerSource)
+                if (containerBinaryPath != null) {
+                    return normalizeExternalFileClassBinaryPath(containerBinaryPath, fqName)
+                }
+            }
             return getUnknownBinaryLocation(fqName.asString())
         }
     }
     return null
 }
 
+/**
+ * Attempts to get the binary file path from a container source (typically a
+ * [JvmPackagePartSource]). Returns null if the path is unavailable.
+ */
+fun getContainerSourceBinaryPath(containerSource: org.jetbrains.kotlin.serialization.deserialization.descriptors.DeserializedContainerSource?): String? {
+    if (containerSource !is JvmPackagePartSource) return null
+    val binaryClass = containerSource.knownJvmBinaryClass ?: return null
+    return when (binaryClass) {
+        is VirtualFileKotlinClass -> {
+            val vf = binaryClass.file
+            val path = vf.path
+            if (vf.fileSystem.protocol == StandardFileSystems.JRT_PROTOCOL)
+                "/${path.split("!/", limit = 2)[1]}"
+            else path
+        }
+        else -> binaryClass.location.takeIf { it.isNotEmpty() }
+    }
+}
+
 private fun getUnknownBinaryLocation(s: String): String {
     return "/!unknown-binary-location/${s.replace(".", "/")}.class"
 }
 
+fun normalizeExternalFileClassBinaryPath(path: String, fqName: FqName): String {
+    if (path.contains(".kotlinc_installed")) {
+        return getUnknownBinaryLocation(fqName.asString())
+    }
+    val normalizedPath = path.replace('\\', '/')
+    val classInternalPath = "${fqName.asString().replace(".", "/")}.class"
+    val classSuffix = "/$classInternalPath"
+    if (normalizedPath.endsWith(classSuffix)) {
+        val classpathRoot = normalizedPath.removeSuffix(classSuffix).substringAfterLast('/')
+        if (classpathRoot.isNotEmpty()) {
+            return "$classpathRoot/$classInternalPath"
+        }
+    }
+    return path
+}
+
 fun getJavaEquivalentClassId(c: IrClass) =
     c.fqNameWhenAvailable?.toUnsafe()?.let { JavaToKotlinClassMap.mapKotlinToJava(it) }