From f818776dba8bda2bf6e423da991190f3f4b4ff3f Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Fri, 19 Jun 2026 17:34:46 +0100
Subject: Handle relative import with invalid ancestor depth

---
 .../java/org/zwobble/hobgoblin/compiler/HobgoblinCompiler.java |  3 ++-
 .../compiler/typechecker/NamespaceNameResolution.java          |  9 +++++++--
 .../compiler/typechecker/RootNamespaceHasNoParentError.java    | 10 ++++++++++
 .../zwobble/hobgoblin/compiler/typechecker/TypeChecker.java    |  3 ++-
 4 files changed, 21 insertions(+), 4 deletions(-)
 create mode 100644 src/main/java/org/zwobble/hobgoblin/compiler/typechecker/RootNamespaceHasNoParentError.java

(limited to 'src/main')

diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/HobgoblinCompiler.java b/src/main/java/org/zwobble/hobgoblin/compiler/HobgoblinCompiler.java
index 9dba876..f4c3add 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/HobgoblinCompiler.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/HobgoblinCompiler.java
@@ -84,7 +84,8 @@ public class HobgoblinCompiler {
                     var importedNamespaceName = resolveNamespaceName(
                         namespaceNode.namespaceName(),
                         importNode.ancestorDepth(),
-                        importNode.namespaceName()
+                        importNode.namespaceName(),
+                        importNode.source()
                     );
                     if (!handledNamespaceNames.contains(importedNamespaceName)) {
                         unhandledDependencies.add(
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/NamespaceNameResolution.java b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/NamespaceNameResolution.java
index 28b709f..ec6187d 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/NamespaceNameResolution.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/NamespaceNameResolution.java
@@ -1,5 +1,6 @@
 package org.zwobble.hobgoblin.compiler.typechecker;
 
+import org.zwobble.hobgoblin.compiler.sources.Source;
 import org.zwobble.hobgoblin.compiler.types.NamespaceName;
 
 import java.util.ArrayList;
@@ -11,13 +12,17 @@ public class NamespaceNameResolution {
     public static NamespaceName resolveNamespaceName(
         NamespaceName current,
         Optional<Integer> importedAncestorDepth,
-        NamespaceName importedNamespaceName
+        NamespaceName importedNamespaceName,
+        Source source
     ) {
         if (importedAncestorDepth.isEmpty()) {
             return importedNamespaceName;
         }
 
-        // TODO: handle invalid depth (too large).
+        if (importedAncestorDepth.get() > current.parts().size()) {
+            throw new RootNamespaceHasNoParentError(source);
+        }
+
         // TODO: should always skip right-most part? For instance, within src/line.hob, does ./point reference src/point.hob or src/line/point.hob?
         var parts = new ArrayList<>(current.parts().subList(0, current.parts().size() - importedAncestorDepth.get()));
         parts.addAll(importedNamespaceName.parts());
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/RootNamespaceHasNoParentError.java b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/RootNamespaceHasNoParentError.java
new file mode 100644
index 0000000..f688274
--- /dev/null
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/RootNamespaceHasNoParentError.java
@@ -0,0 +1,10 @@
+package org.zwobble.hobgoblin.compiler.typechecker;
+
+import org.zwobble.hobgoblin.compiler.errors.SourceError;
+import org.zwobble.hobgoblin.compiler.sources.Source;
+
+public class RootNamespaceHasNoParentError extends SourceError {
+    public RootNamespaceHasNoParentError(Source source) {
+        super("Root namespace has no parent", source);
+    }
+}
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
index abc4bec..e9e7e74 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
@@ -25,7 +25,8 @@ public class TypeChecker {
             var importedNamespace = resolveNamespaceName(
                 untyped.namespaceName(),
                 untypedImport.ancestorDepth(),
-                untypedImport.namespaceName()
+                untypedImport.namespaceName(),
+                untypedImport.source()
             );
 
             var importedNamespaceFields = context.namespaceFields(importedNamespace);
-- 
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