Provide more structured error data in exception

Author: mantono

lib/src/main/kotlin/io/nexure/capsule/Capsule.kt

@@ -110,6 +110,14 @@ internal class DependencyException(
 ) : Exception() {
     constructor(clazz: Class<*>, cause: Exception? = null) : this(classKey(clazz), cause)
 
-    override val message: String = "Unable to provide dependency for class ${rootKey()}"
-    fun rootKey(): String = if (this.cause is DependencyException) this.cause.key else this.key
+    fun children(): List<String> {
+        val childClasses: List<String> =
+            if (cause is DependencyException) cause.children() else emptyList()
+
+        return listOf(key) + childClasses
+    }
+
+    override val message: String =
+        "Unable to provide dependency for class, " +
+            "since no explicit implementation was registered in chain: ${children()}"
 }

lib/src/test/kotlin/io/nexure/capsule/CapsuleTest.kt

@@ -185,24 +185,44 @@ class CapsuleTest {
 
     @Test
     fun `DependencyException should provide context on which class creation that failed`() {
-        class ComplexGreeter(
-            val string: String,
-            val double: Double
-        ) : Greeter {
-            override fun hello(): String = "foo"
+        try {
+            val capsule = Capsule {}
+            capsule.get<GrandParent>()
+            assertTrue(false)
+        } catch (e: DependencyException) {
+            val expected = listOf(
+                "io.nexure.capsule.GrandParent",
+                "io.nexure.capsule.Parent",
+                "io.nexure.capsule.Child",
+                "double"
+            )
+            assertEquals(expected, e.children())
         }
+    }
 
-        val capsule = Capsule {}
+    @Test
+    fun `DependencyException should provide context on which class creation that failed from first missing class`() {
         try {
-            val g = capsule.get<ComplexGreeter>()
+            val capsule = Capsule {
+                GrandParent(get())
+            }
+            capsule.get<GrandParent>()
             assertTrue(false)
         } catch (e: DependencyException) {
-            assertEquals("double", e.rootKey())
-            assertEquals("Unable to provide dependency for class double", e.message)
+            val expected = listOf(
+                "io.nexure.capsule.Parent",
+                "io.nexure.capsule.Child",
+                "double"
+            )
+            assertEquals(expected, e.children())
         }
     }
 }
 
+class Child(val double: Double)
+class Parent(val child: Child)
+class GrandParent(val parent: Parent)
+
 interface Greeter {
     fun hello(): String
 }