Implement basic evaluate for qualified expressions

Fixes #33

Author: fwcd

adapter/src/main/kotlin/org/javacs/ktda/adapter/KotlinDebugAdapter.kt

@@ -354,7 +354,18 @@ class KotlinDebugAdapter(
 
 	override fun loadedSources(args: LoadedSourcesArguments): CompletableFuture<LoadedSourcesResponse> = notImplementedDAPMethod()
 
-	override fun evaluate(args: EvaluateArguments): CompletableFuture<EvaluateResponse> = notImplementedDAPMethod()
+	override fun evaluate(args: EvaluateArguments): CompletableFuture<EvaluateResponse> = async.compute {
+		val variable = (args.frameId
+			.let(converter::toInternalStackFrame)
+				?: throw KotlinDAException("Could not find stack frame with ID ${args.frameId}"))
+			.evaluate(args.expression)
+			?.let(converter::toDAPVariable)
+
+		EvaluateResponse().apply {
+			result = variable?.value ?: "unknown"
+			variablesReference = variable?.variablesReference ?: 0
+		}
+	}
 
 	override fun stepInTargets(args: StepInTargetsArguments): CompletableFuture<StepInTargetsResponse> = notImplementedDAPMethod()
 

adapter/src/main/kotlin/org/javacs/ktda/core/scope/BasicVariableTreeNode.kt

@@ -0,0 +1,8 @@
+package org.javacs.ktda.core.scope
+
+data class BasicVariableTreeNode(
+    override val name: String,
+    override val value: String? = null,
+    override val type: String? = null,
+    override val childs: List<VariableTreeNode>? = null
+) : VariableTreeNode

adapter/src/main/kotlin/org/javacs/ktda/core/stack/StackFrame.kt

@@ -7,4 +7,6 @@ interface StackFrame {
 	val name: String
 	val position: Position?
 	val scopes: List<VariableTreeNode>
+
+	fun evaluate(expression: String): VariableTreeNode?
 }

adapter/src/main/kotlin/org/javacs/ktda/jdi/stack/JDIStackFrame.kt

@@ -16,6 +16,35 @@ class JDIStackFrame(
 	override val scopes: List<VariableTreeNode> by lazy { listOf(
 		JDILocalScope(frame)
 	) }
+
 	// TODO: Scope "Fields"
 	// TODO: Argument values?
+
+	private fun evaluateQualified(qualName: List<String>, variables: List<VariableTreeNode> = scopes.flatMap { it.childs ?: emptyList() }): VariableTreeNode? =
+		qualName.firstOrNull().let { qual ->
+			val rest = qualName.drop(1)
+			variables
+				.filter { it.name == qual }
+				.mapNotNull { if (rest.isEmpty()) it else evaluateQualified(rest, it.childs ?: emptyList()) }
+				.firstOrNull()
+		}
+
+	override fun evaluate(expression: String): VariableTreeNode? {
+		// TODO: Implement proper expression parsing
+		//
+		// Note that expression parsing is not part of the JDI
+		// (see https://www.oracle.com/technetwork/java/javase/tech/faqs-jsp-142584.html#QV1)
+		// There is a JDI-compatible expression parser in the JDPA examples.
+		// Unfortunately, however, it is not exported by the jdk/jdi module
+		// and as such cannot be imported:
+		// 
+		// com.sun.tools.example.debug.expr.ExpressionParser
+		//
+		// Creating JDI values from primitives and strings is possible though,
+		// using VirtualMachine.mirrorOf.
+
+		val qualified = expression.split(".")
+		return evaluateQualified(qualified)
+			?: evaluateQualified(listOf("this") + qualified)
+	}
 }