Provide better error message

Provide better error message on failure to construct classes.

Author: mantono

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

@@ -83,7 +83,13 @@ private constructor(
 ): Comparable<Dependency> {
     private val instance: LazyValue<Any> = LazyValue(constructor)
 
-    fun getInstance(): Any = instance()
+    fun getInstance(): Any {
+        return try {
+            instance()
+        } catch (e: Exception) {
+            throw DependencyException(key, e)
+        }
+    }
 
     override fun toString(): String = key
 
@@ -99,12 +105,11 @@ private constructor(
 private fun classKey(clazz: Class<*>): String = clazz.canonicalName ?: clazz.descriptorString()
 
 internal class DependencyException(
-    val clazz: Class<*>,
-    override val cause: DependencyException? = null
+    val key: String,
+    override val cause: Exception? = null
 ) : Exception() {
-    override val message: String = if (cause != null) {
-        "Unable to provide dependency for class $clazz: \n\t${cause.message}"
-    } else {
-        "Unable to provide dependency for class $clazz"
-    }
+    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
 }

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

@@ -3,6 +3,7 @@ package io.nexure.capsule
 import org.junit.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertNull
+import kotlin.test.assertTrue
 
 class CapsuleTest {
     @Test
@@ -162,7 +163,6 @@ class CapsuleTest {
         assertEquals(listOf("3", "2", "1"), third.getMany<Greeter>().map { it.hello() })
     }
 
-
     @Test
     fun `test only needed dependency in created on call to get()`() {
         val parent = Capsule {
@@ -182,6 +182,25 @@ class CapsuleTest {
         val greeter: Greeter = child.get()
         assertEquals("foo", greeter.hello())
     }
+
+    @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"
+        }
+
+        val capsule = Capsule {}
+        try {
+            val g = capsule.get<ComplexGreeter>()
+            assertTrue(false)
+        } catch (e: DependencyException) {
+            assertEquals("double", e.rootKey())
+            assertEquals("Unable to provide dependency for class double", e.message)
+        }
+    }
 }
 
 interface Greeter {