Report errors when trying to build decompiled text for light class

compiler/light-classes/src/org/jetbrains/kotlin/asJava/builder/LightClassBuilder.kt

@@ -23,16 +23,19 @@ import com.intellij.openapi.project.Project
 import com.intellij.openapi.util.SystemInfo
 import com.intellij.openapi.vfs.VirtualFile
 import com.intellij.psi.ClassFileViewProvider
+import com.intellij.psi.PsiElement
 import com.intellij.psi.PsiManager
 import com.intellij.psi.impl.compiled.ClsFileImpl
 import com.intellij.psi.impl.java.stubs.PsiJavaFileStub
 import com.intellij.psi.impl.java.stubs.impl.PsiJavaFileStubImpl
+import com.intellij.psi.impl.source.tree.TreeElement
 import org.jetbrains.kotlin.codegen.state.GenerationState
 import org.jetbrains.kotlin.config.CompilerConfiguration
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.psi.KtFile
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.diagnostics.Diagnostics
+import java.lang.StringBuilder
 
 data class LightClassBuilderResult(val stub: PsiJavaFileStub, val bindingContext: BindingContext, val diagnostics: Diagnostics)
 
@@ -86,6 +89,32 @@ private fun createJavaFileStub(project: Project, packageFqName: FqName, files: C
         override fun getPackageName() = packageFqName.asString()
 
         override fun isPhysical() = false
+
+        override fun appendMirrorText(indentLevel: Int, buffer: StringBuilder) {
+            if (files.size == 1) {
+                LOG.error("Mirror text should never be calculated for light classes generated from a single file")
+            }
+            super.appendMirrorText(indentLevel, buffer)
+        }
+
+
+        override fun setMirror(element: TreeElement) {
+            if (files.size == 1) {
+                LOG.error("Mirror element should never be set for light classes generated from a single file")
+            }
+            super.setMirror(element)
+        }
+
+        override fun getMirror(): PsiElement {
+            if (files.size == 1) {
+                LOG.error("Mirror element should never be calculated for light classes generated from a single file")
+            }
+            return super.getMirror()
+        }
+
+        override fun getText(): String {
+            return files.singleOrNull()?.text ?: super.getText()
+        }
     }
 
     javaFileStub.psi = fakeFile

compiler/light-classes/src/org/jetbrains/kotlin/asJava/elements/KtLightElementBase.kt

@@ -31,10 +31,13 @@ abstract class KtLightElementBase(private val parent: PsiElement): LightElement(
 
     override fun getText() = kotlinOrigin?.text ?: ""
     override fun getTextRange() = kotlinOrigin?.textRange ?: TextRange.EMPTY_RANGE
+    override fun getTextOffset() = kotlinOrigin?.textOffset ?: 0
+    override fun getStartOffsetInParent() = kotlinOrigin?.startOffsetInParent ?: 0
     override fun isWritable() = kotlinOrigin?.isWritable ?: false
     override fun getNavigationElement() = kotlinOrigin?.navigationElement ?: this
     override fun getUseScope() = kotlinOrigin?.useScope ?: super.getUseScope()
     override fun getContainingFile() = parent.containingFile
     override fun getPresentation() = (kotlinOrigin ?: this).let { ItemPresentationProviders.getItemPresentation(it) }
     override fun isValid() = parent.isValid
-}
+    override fun findElementAt(offset: Int) = kotlinOrigin?.findElementAt(offset)
+}

compiler/light-classes/src/org/jetbrains/kotlin/asJava/elements/lightAnnotations.kt

@@ -97,6 +97,7 @@ class KtLightAnnotationForSourceEntry(
         override fun getNavigationElement() = originalExpression
         override fun isPhysical(): Boolean = originalExpression?.containingFile == kotlinOrigin.containingFile
         override fun getTextRange() = originalExpression?.textRange ?: TextRange.EMPTY_RANGE
+        override fun getStartOffsetInParent() = originalExpression?.startOffsetInParent ?: 0
         override fun getParent() = parent
         override fun getText() = originalExpression?.text.orEmpty()
         override fun getContainingFile(): PsiFile? = if (isPhysical) kotlinOrigin.containingFile else delegate.containingFile