From 9716e0f30b5db95b0fa7ca54908ec5fbf9f1e088 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Tue, 16 Jun 2026 21:36:49 +0100
Subject: Implement full namespace name resolution

---
 .../typechecker/NamespaceNameResolution.java       | 25 ++++++++++++
 .../compiler/typechecker/TypeChecker.java          | 12 ++++--
 .../typechecker/NamespaceNameResolutionTests.java  | 45 ++++++++++++++++++++++
 3 files changed, 78 insertions(+), 4 deletions(-)
 create mode 100644 src/main/java/org/zwobble/hobgoblin/compiler/typechecker/NamespaceNameResolution.java
 create mode 100644 src/test/java/org/zwobble/hobgoblin/compiler/typechecker/NamespaceNameResolutionTests.java

(limited to 'src')

diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/NamespaceNameResolution.java b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/NamespaceNameResolution.java
new file mode 100644
index 0000000..f3f8d89
--- /dev/null
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/NamespaceNameResolution.java
@@ -0,0 +1,25 @@
+package org.zwobble.hobgoblin.compiler.typechecker;
+
+import org.zwobble.hobgoblin.compiler.types.NamespaceName;
+
+import java.util.ArrayList;
+import java.util.Optional;
+
+class NamespaceNameResolution {
+    private NamespaceNameResolution() {}
+
+    static NamespaceName resolveNamespaceName(
+        NamespaceName current,
+        Optional<Integer> importedAncestorDepth,
+        NamespaceName importedNamespaceName
+    ) {
+        if (importedAncestorDepth.isEmpty()) {
+            return importedNamespaceName;
+        }
+
+        // TODO: handle invalid depth (too large).
+        var parts = new ArrayList<>(current.parts().subList(0, current.parts().size() - importedAncestorDepth.get()));
+        parts.addAll(importedNamespaceName.parts());
+        return new NamespaceName(parts);
+    }
+}
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 77b46bc..98b29a9 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/typechecker/TypeChecker.java
@@ -8,6 +8,8 @@ import org.zwobble.hobgoblin.compiler.types.*;
 import java.util.ArrayList;
 import java.util.List;
 
+import static org.zwobble.hobgoblin.compiler.typechecker.NamespaceNameResolution.resolveNamespaceName;
+
 public class TypeChecker {
 
     private TypeChecker() {
@@ -20,11 +22,13 @@ public class TypeChecker {
         var namespaceContext = context.enterNamespace(untyped.namespaceName());
 
         for (var untypedImport : untyped.imports()) {
-            if (untypedImport.ancestorDepth().isPresent()) {
-                throw new UnsupportedOperationException("TODO: relative imports");
-            }
+            var importedNamespace = resolveNamespaceName(
+                untyped.namespaceName(),
+                untypedImport.ancestorDepth(),
+                untypedImport.namespaceName()
+            );
 
-            var importedNamespaceFields = context.namespaceFields(untypedImport.namespaceName());
+            var importedNamespaceFields = context.namespaceFields(importedNamespace);
             for (var importedName : untypedImport.importedNames()) {
                 namespaceContext.define(importedName, importedNamespaceFields.get(importedName));
             }
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/NamespaceNameResolutionTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/NamespaceNameResolutionTests.java
new file mode 100644
index 0000000..7929e7d
--- /dev/null
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/typechecker/NamespaceNameResolutionTests.java
@@ -0,0 +1,45 @@
+package org.zwobble.hobgoblin.compiler.typechecker;
+
+import org.junit.jupiter.api.Test;
+import org.zwobble.hobgoblin.compiler.types.NamespaceName;
+
+import java.util.Optional;
+
+import static org.zwobble.hobgoblin.compiler.typechecker.NamespaceNameResolution.resolveNamespaceName;
+import static org.zwobble.precisely.AssertThat.assertThat;
+import static org.zwobble.precisely.Matchers.equalTo;
+
+public class NamespaceNameResolutionTests {
+    @Test
+    public void whenAncestorDepthIsEmptyThenImportedNamespaceIsUsedAsAbsoluteName() {
+        var current = NamespaceName.of("a", "b");
+        var importedAncestorDepth = Optional.<Integer>empty();
+        var importedNamespaceName = NamespaceName.of("x", "y");
+
+        var result = resolveNamespaceName(current, importedAncestorDepth, importedNamespaceName);
+
+        assertThat(result, equalTo(NamespaceName.of("x", "y")));
+    }
+
+    @Test
+    public void whenAncestorDepthIsZeroThenImportedNamespaceIsJoinedToCurrentNamespace() {
+        var current = NamespaceName.of("a", "b");
+        var importedAncestorDepth = Optional.of(0);
+        var importedNamespaceName = NamespaceName.of("x", "y");
+
+        var result = resolveNamespaceName(current, importedAncestorDepth, importedNamespaceName);
+
+        assertThat(result, equalTo(NamespaceName.of("a", "b", "x", "y")));
+    }
+
+    @Test
+    public void whenAncestorDepthIsGreaterThanZeroThenThatManyPartsAreStrippedOffCurrentNamespaceBeforeJoining() {
+        var current = NamespaceName.of("a", "b", "c");
+        var importedAncestorDepth = Optional.of(2);
+        var importedNamespaceName = NamespaceName.of("x", "y");
+
+        var result = resolveNamespaceName(current, importedAncestorDepth, importedNamespaceName);
+
+        assertThat(result, equalTo(NamespaceName.of("a", "x", "y")));
+    }
+}
-- 
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