Do not crash in the presence of macro applications.

lib/src/model/method.dart

@@ -113,7 +113,8 @@ class Method extends ModelElement
       return null;
     }
     var parent = element.enclosingElement as InterfaceElement;
-    for (var t in parent.allSupertypes) {
+    var parentDeclaration = parent.augmented?.declaration ?? parent;
+    for (var t in parentDeclaration.allSupertypes) {
       Element? e = t.getMethod(element.name);
       if (e != null) {
         assert(

lib/src/model/package_builder.dart

@@ -4,7 +4,6 @@
 
 import 'dart:async';
 
-import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
 import 'package:analyzer/dart/analysis/context_root.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ -136,8 +135,7 @@ class PubPackageBuilder implements PackageBuilder {
 
   late final Map<String, List<Folder>> _packageMap;
 
-  late final AnalysisContextCollection _contextCollection =
-      AnalysisContextCollectionImpl(
+  late final _contextCollection = AnalysisContextCollectionImpl(
     includedPaths: [_config.inputDir],
     // TODO(jcollins-g): should we pass excluded directories here instead of
     // handling it ourselves?
@@ -464,6 +462,8 @@ class PubPackageBuilder implements PackageBuilder {
       specialFiles.difference(files),
       addingSpecials: true,
     );
+    // Shutdown macro support.
+    await _contextCollection.dispose();
   }
 
   /// Throws an exception if any configured-to-be-included files were not found

lib/src/model/source_code_mixin.dart

@@ -13,7 +13,8 @@ mixin SourceCode implements Documentable {
 
   Element? get element;
 
-  bool get hasSourceCode => config.includeSource && sourceCode.isNotEmpty;
+  bool get hasSourceCode =>
+      config.includeSource && !element.isAugmentation && sourceCode.isNotEmpty;
 
   Library? get library;
 
@@ -22,3 +23,18 @@ mixin SourceCode implements Documentable {
     return modelNode == null ? '' : modelNode.sourceCode;
   }
 }
+
+extension on Element? {
+  /// Whether `this` is an augmentation method or property.
+  ///
+  /// This property should only be referenced for elements whose source code we
+  /// may wish to refer to.
+  bool get isAugmentation {
+    final self = this;
+    return switch (self) {
+      ExecutableElement() => self.augmentationTarget != null,
+      PropertyInducingElement() => self.augmentationTarget != null,
+      _ => false,
+    };
+  }
+}