Verify analyzer target directory exists (#2768)

packages/riverpod_graph/README.md

@@ -8,3 +8,29 @@ The graph generated is generated using [Mermaid](https://mermaid-js.github.io/me
 Here is graph example, generated from the Flutter Devtool project (which uses Riverpod).
 
 ![Devtool graph](../../resources/devtool_graph.jpeg)
+
+## Generating a graph
+
+Assuming you are working on `riverpod_graph` in this repo.  You can test against other projects with relative references. Generating a graph against the `examples/todos` project would look like:
+
+```
+cd <the riverpod_graph directory>
+```
+
+mermaid.js markup
+```bash
+dart run riverpod_graph path/to/folder
+```
+
+d2 markup
+```bash
+dart run riverpod_graph path/to/folder -f d2
+```
+
+Assuming you have activated, installed, riverpod_graph in the global dart cache:
+
+mermaid.js markup
+```bash
+cd <the lib directory of the program you wish to analyze>
+$ dart pub global run riverpod_graph .
+```

packages/riverpod_graph/lib/src/analyze.dart

@@ -19,6 +19,8 @@ Future<void> analyze(
     resourceProvider: PhysicalResourceProvider.INSTANCE,
   );
 
+  verifyRootDirectoryExists(rootDirectory);
+
   // Often one context is returned, but depending on the project structure we
   // can see multiple contexts.
   for (final context in collection.contexts) {
@@ -88,6 +90,18 @@ Future<void> analyze(
   }
 }
 
+///
+///Throws an exception if the directory doesn't exist
+///
+bool verifyRootDirectoryExists(String rootDirectory) {
+  if (!Directory(rootDirectory).existsSync()) {
+    throw FileSystemException(
+      'Requested scanning target directory does not exist $rootDirectory',
+    );
+  }
+  return true;
+}
+
 /// Output formats supported by riverpod_graph
 enum SupportFormat {
   /// Mermaid.js format
@@ -101,7 +115,19 @@ String _buildD2(ProviderGraph providerGraph) {
   const _watchLineStyle = '{style.stroke-width: 4}';
   const _readLineStyle = '{style.stroke-dash: 4}';
 
-  final buffer = StringBuffer();
+  final buffer = StringBuffer('''
+Legend: {
+  Type: {
+    Widget.shape: circle
+    Provider
+  }
+  Arrows: {
+    "." -> "..": read: {style.stroke-dash: 4}
+    "." -> "..": listen
+    "." -> "..": watch: {style.stroke-width: 4}
+  }
+}
+''');
 
   for (final node in providerGraph.consumerWidgets) {
     buffer.writeln('${node.definition.name}.shape: Circle');
@@ -156,10 +182,10 @@ flowchart TB
     style stop1 height:0px;
     start2[ ] --->|listen| stop2[ ]
     style start2 height:0px;
-    style stop2 height:0px; 
+    style stop2 height:0px;
     start3[ ] ===>|watch| stop3[ ]
     style start3 height:0px;
-    style stop3 height:0px; 
+    style stop3 height:0px;
   end
 
   subgraph Type

packages/riverpod_graph/test/analyze_test.dart

@@ -0,0 +1,20 @@
+import 'dart:io';
+
+import 'package:riverpod_graph/src/analyze.dart';
+
+import 'package:test/test.dart';
+
+void main() {
+  group('flutter graph analyzer tests', () {
+    test('throw exception if analysis target directory does not exist', () {
+      expect(
+        () => verifyRootDirectoryExists('dogfood'),
+        throwsA(isA<FileSystemException>()),
+      );
+    });
+
+    test('returns true if analysis target directory does exist', () {
+      expect(verifyRootDirectoryExists('.'), true);
+    });
+  });
+}