fix(analysis): report an unreadable SDK cleanly instead of crashing

ae412a7 routed filesystem failures to exit 2, but the analyzer throws its own
FileSystemException (package:analyzer/file_system), which the dart:io catch
in bin/pipe.dart never matched. A project whose package_config still named a
moved Flutter SDK therefore crashed with exit 255 and a stack trace. Found
by dogfooding on word_alive after its SDK moved.

Analyzer.create now turns that into a PipeException naming the SDK path, with
the remedy to re-run flutter pub get or pass --sdk.

lib/src/analysis.dart

@@ -5,8 +5,10 @@ import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/diagnostic/diagnostic.dart';
+import 'package:analyzer/file_system/file_system.dart' as fs;
 import 'package:analyzer/file_system/physical_file_system.dart';
 
+import 'errors.dart';
 import 'project.dart';
 import 'sdk.dart';
 
@@ -127,11 +129,25 @@ class Analyzer {
       explicit: sdkOverride,
       flutterRootHint: project.flutterRoot,
     );
-    final collection = AnalysisContextCollection(
+    final AnalysisContextCollection collection;
-      includedPaths: [project.root],
+    try {
-      resourceProvider: PhysicalResourceProvider.INSTANCE,
+      collection = AnalysisContextCollection(
-      sdkPath: resolution.sdkPath,
+        includedPaths: [project.root],
-    );
+        resourceProvider: PhysicalResourceProvider.INSTANCE,
+        sdkPath: resolution.sdkPath,
+      );
+    } on fs.FileSystemException catch (error) {
+      // The analyzer throws its own FileSystemException, not dart:io's, so the
+      // catch in bin/pipe.dart does not see it. The usual cause is a project
+      // whose package_config still names a Flutter SDK that has moved.
+      throw PipeException(
+        'cannot read the Dart SDK at ${resolution.sdkPath}: ${error.message} '
+        '(${error.path})',
+        remedy:
+            'run `flutter pub get` in the project so its package_config '
+            'names the current SDK, or pass --sdk <dart-sdk-path>',
+      );
+    }
     return Analyzer._(collection, resolution);
   }
 

test/sdk_unreadable_test.dart

@@ -0,0 +1,37 @@
+import 'dart:io';
+
+import 'package:pipe/src/cli.dart';
+import 'package:pipe/src/errors.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test(
+    'an SDK the analyzer cannot read is a clean error, not a crash',
+    () async {
+      // A project whose package_config names a Flutter SDK that has since moved
+      // left the analyzer unable to read the SDK's allowed_experiments.json. The
+      // analyzer throws its own FileSystemException, which bin/pipe.dart's
+      // dart:io catch never saw: exit 255 and a stack trace.
+      final sdk = Directory.systemTemp.createTempSync('pipe-hollow-sdk');
+      addTearDown(() => sdk.deleteSync(recursive: true));
+      File('${sdk.path}/version').writeAsStringSync('3.13.0\n');
+      Directory('${sdk.path}/lib').createSync();
+
+      await expectLater(
+        PipeRunner().run([
+          'check',
+          'test/fixtures/stuck_loading',
+          '--sdk',
+          sdk.path,
+        ]),
+        throwsA(
+          isA<PipeException>().having(
+            (error) => error.remedy,
+            'remedy',
+            contains('flutter pub get'),
+          ),
+        ),
+      );
+    },
+  );
+}