Handle unknown namespaces

2 files changed, 23 insertions, 0 deletions

diff --git a/src/main/java/org/shedlang/compiler/typechecker/NamespaceDependencyLineariser.java b/src/main/java/org/shedlang/compiler/typechecker/NamespaceDependencyLineariser.java
index 1afeb258..8fa1876d 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/NamespaceDependencyLineariser.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/NamespaceDependencyLineariser.java
@@ -3,6 +3,7 @@ package org.shedlang.compiler.typechecker;
 import org.shedlang.compiler.ast.untyped.UntypedNamespaceNode;
 import org.shedlang.compiler.sources.Sources;
 import org.shedlang.compiler.typechecker.errors.CircularNamespaceDependencyError;
+import org.shedlang.compiler.typechecker.errors.UnknownNamespaceError;
 import org.shedlang.compiler.types.NamespaceName;
 
 import java.util.ArrayList;
@@ -41,6 +42,10 @@ public class NamespaceDependencyLineariser {
                     }
 
                     var untypedNamespaceNode = nodesByName.get(name);
+                    if (untypedNamespaceNode == null) {
+                        throw new UnknownNamespaceError(name, Sources.NULL);
+                    }
+
                     for (var import_ : untypedNamespaceNode.imports()) {
                         add(import_.namespaceName());
                     }
diff --git a/src/main/java/org/shedlang/compiler/typechecker/errors/UnknownNamespaceError.java b/src/main/java/org/shedlang/compiler/typechecker/errors/UnknownNamespaceError.java
new file mode 100644
index 00000000..ad598e2a
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/typechecker/errors/UnknownNamespaceError.java
@@ -0,0 +1,18 @@
+package org.shedlang.compiler.typechecker.errors;
+
+import org.shedlang.compiler.errors.SourceError;
+import org.shedlang.compiler.sources.Source;
+import org.shedlang.compiler.types.NamespaceName;
+
+public class UnknownNamespaceError extends SourceError {
+    private final NamespaceName unknownNamespaceName;
+
+    public UnknownNamespaceError(NamespaceName unknownNamespaceName, Source source) {
+        super("Unknown namespace: " + unknownNamespaceName, source);
+        this.unknownNamespaceName = unknownNamespaceName;
+    }
+
+    public NamespaceName unknownNamespaceName() {
+        return unknownNamespaceName;
+    }
+}