Do not use the real document overlays for now

The text mutation utilities cannot handle the mutations
touching the underlay document content.

For now, use an empty "underlay" document, so that the
overlay result of that stub and the real file is equivalent
to the real file, which the mutation utilities can handle
just fine.

lsp/src/main/kotlin/org/gradle/declarative/lsp/DeclarativeTextDocumentService.kt

@@ -59,10 +59,13 @@ import org.gradle.internal.declarativedsl.analysis.SchemaTypeRefContext
 import org.gradle.internal.declarativedsl.dom.DeclarativeDocument
 import org.gradle.internal.declarativedsl.dom.DocumentResolution
 import org.gradle.internal.declarativedsl.dom.mutation.MutationParameterKind
+import org.gradle.internal.declarativedsl.dom.operations.overlay.DocumentOverlay
 import org.gradle.internal.declarativedsl.dom.operations.overlay.DocumentOverlayResult
 import org.gradle.internal.declarativedsl.dom.resolution.DocumentResolutionContainer
-import org.gradle.internal.declarativedsl.evaluator.main.AnalysisDocumentUtils
+import org.gradle.internal.declarativedsl.evaluator.main.AnalysisDocumentUtils.resolvedDocument
+import org.gradle.internal.declarativedsl.evaluator.main.AnalysisSequenceResult
 import org.gradle.internal.declarativedsl.evaluator.main.SimpleAnalysisEvaluator
+import org.gradle.internal.declarativedsl.evaluator.runner.stepResultOrPartialResult
 import org.slf4j.LoggerFactory
 import java.net.URI
 import java.util.concurrent.CompletableFuture
@@ -104,11 +107,9 @@ class DeclarativeTextDocumentService : TextDocumentService {
             val uri = URI(it.textDocument.uri)
             val text = it.textDocument.text
             val dom = parse(uri, text)
-            if (dom != null) {
+            run {
                 documentStore.storeInitial(uri, text, dom)
                 processDocument(uri)
-            } else {
-                documentStore.remove(uri)
             }
         }
     }
@@ -121,12 +122,8 @@ class DeclarativeTextDocumentService : TextDocumentService {
                 val version = it.textDocument.version
                 val text = change.text
                 val dom = parse(uri, change.text)
-                if (dom != null) {
-                    documentStore.storeVersioned(uri, version, text, dom)
-                    processDocument(uri)
-                } else {
-                    documentStore.remove(uri)
-                }
+                documentStore.storeVersioned(uri, version, text, dom)
+                processDocument(uri)
             }
         }
     }
@@ -304,21 +301,24 @@ class DeclarativeTextDocumentService : TextDocumentService {
         )
     }
 
-    private fun parse(uri: URI, text: String): DocumentOverlayResult? {
+    private fun parse(uri: URI, text: String): DocumentOverlayResult {
+        fun AnalysisSequenceResult.lastStepDocument() =
+            stepResults.values.last().stepResultOrPartialResult.resolvedDocument()
+
         val fileName = uri.path.substringAfterLast('/')
-        val fileSchema = schemaAnalysisEvaluator.evaluate(fileName, text)
-        val settingsSchema = schemaAnalysisEvaluator.evaluate(
-            declarativeResources.settingsFile.name, 
-            declarativeResources.settingsFile.takeIf { it.canRead() }?.readText().orEmpty()
-        )
-
-        val document = AnalysisDocumentUtils.documentWithModelDefaults(settingsSchema, fileSchema)
-        when (document != null) {
-            true -> LOGGER.trace("Parsed declarative model for document: {}", uri)
-            false -> LOGGER.error("Failed to parse declarative model for document: {}", uri)
-        }
-
-        return document!!
+        val document = schemaAnalysisEvaluator.evaluate(fileName, text).lastStepDocument()
+
+        // Workaround: for now, the mutation utilities cannot handle mutations that touch the underlay document content.
+        // To avoid that, use an empty document as an underlay instead of the real document produced from the
+        // settings file.
+        // TODO: carry both the real overlay and the document produced from just the current file, run the mutations
+        //       against the latter for now.
+        // TODO: once the mutation utilities start handling mutations across the overlay, pass them the right overlay.
+        val emptyUnderlay = schemaAnalysisEvaluator.evaluate("empty-underlay/build.gradle.dcl", "").lastStepDocument()
+
+        LOGGER.trace("Parsed declarative model for document: {}", uri)
+
+        return DocumentOverlay.overlayResolvedDocuments(emptyUnderlay, document)
     }
 
     private fun <T> withDom(uri: URI, work: (DocumentOverlayResult, String) -> T): T? {