Better error messages

pmd-test/src/main/kotlin/net/sourceforge/pmd/lang/ast/test/AstMatcherDsl.kt

@@ -138,10 +138,20 @@ class NWrapper<N : Node> private constructor(val it: N,
                 childType.isInstance(toWrap)
             }
 
-            @Suppress("UNCHECKED_CAST")
-            val wrapper = NWrapper(toWrap as M, matcherPath + childType, ignoreChildrenMatchers)
+            val childPath = matcherPath + childType
 
-            wrapper.spec()
+            @Suppress("UNCHECKED_CAST")
+            val wrapper = NWrapper(toWrap as M, childPath, ignoreChildrenMatchers)
+
+            try {
+                wrapper.spec()
+            } catch (e: AssertionError) {
+                if (e.message?.matches("At (/.*?|<root>):.*".toRegex()) == false) {
+                    // the exception has no path, let's add one
+                    throw AssertionError(formatErrorMessage(childPath, e.message ?: "No explanation provided"), e)
+                }
+                throw e
+            }
 
             assertFalse(formatErrorMessage(matcherPath + childType, "Wrong number of children, expected ${wrapper.nextChildMatcherIdx}, actual ${wrapper.it.numChildren}")) {
                 !ignoreChildrenMatchers && wrapper.nextChildMatcherIdx != wrapper.it.numChildren

pmd-test/src/test/kotlin/net/sourceforge/pmd/lang/ast/test/DslTest.kt

@@ -90,6 +90,37 @@ class DslTest : FunSpec({
         }
     }
 
+    failureTest("All assertions should have a node path",
+            messageContains = setOf("At /LocalVariableDeclaration/Type:", "expected: \"bratwurst\"")) {
+
+        parseStatement("int[] i = 0;") should matchNode<ASTLocalVariableDeclaration> {
+
+            child<ASTType> {
+
+                // this fails
+                it.typeImage shouldBe "bratwurst"
+
+            }
+
+            unspecifiedChild()
+        }
+    }
+
+    failureTest("Child assertions should have a node path",
+            messageContains = setOf("At /LocalVariableDeclaration/Type:", "expected", "type", "LambdaExpression")) {
+
+        parseStatement("int[] i = 0;") should matchNode<ASTLocalVariableDeclaration> {
+
+            child<ASTType> {
+
+                // this fails
+                child<ASTLambdaExpression> { }
+            }
+
+            unspecifiedChild()
+        }
+    }
+
     failureTest("Leaf nodes should assert that they have no children",
             messageContains = setOf("number", "children", "expected 0")) {