[CFE] Fix crash in expression compilation caused by having dill builders in source builders scope

This should fix https://github.com/flutter/flutter/issues/97500
and the reproducable part of https://github.com/flutter/devtools/issues/3599

Change-Id: I16b45e4cc8074e0b0a62ae3220d91ae1424bacf3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/231004
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>

pkg/front_end/lib/src/fasta/incremental_compiler.dart

@@ -1731,6 +1731,16 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
         }
       }
 
+      // Setup scope first in two-step process:
+      // 1) Create a new SourceLibraryBuilder, add imports and setup (import)
+      //    scope.
+      // 2) Create a new SourceLibraryBuilder, using a nested scope of the scope
+      //    we just created as the scope. The import scopes have been setup via
+      //    the parent chain.
+      // This is done to create the correct "layering" (i.e. definitions from
+      // the "self" library first, then imports while not having dill builders
+      // directly in the scope of a source builder (which can crash things in
+      // some circumstances).
       SourceLibraryBuilder debugLibrary = new SourceLibraryBuilder(
         importUri: libraryUri,
         fileUri: debugExprUri,
@@ -1784,6 +1794,16 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
         debugLibrary.addImportsToScope();
         _ticker.logMs("Added imports");
       }
+      debugLibrary = new SourceLibraryBuilder(
+        importUri: libraryUri,
+        fileUri: debugExprUri,
+        packageLanguageVersion:
+            new ImplicitLanguageVersion(libraryBuilder.library.languageVersion),
+        loader: lastGoodKernelTarget.loader,
+        scope: debugLibrary.scope.createNestedScope("expression"),
+        nameOrigin: libraryBuilder,
+        isUnsupported: libraryBuilder.isUnsupported,
+      );
 
       HybridFileSystem hfs =
           lastGoodKernelTarget.fileSystem as HybridFileSystem;

pkg/front_end/test/spell_checking_list_code.txt

@@ -671,6 +671,7 @@ launched
 launcher
 layer
 layered
+layering
 layers
 layout
 lc

pkg/front_end/testcases/expression.status

@@ -1,5 +1,3 @@
 # Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
-
-platform_isandroid.expression: Crash

pkg/front_end/testcases/expression/platform_isandroid.expression.yaml.expect

@@ -0,0 +1,4 @@
+Errors: {
+}
+static method /*isLegacy, from org-dartlang-debug:synthetic_debug_expression */ debugExpr() → dynamic
+  return dart.io::Platform::isAndroid;