Allow incremental compiler to just create outline

Change-Id: I996787821f01f21bb41be837e6d4c25a2114e017
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/95384
Commit-Queue: Jens Johansen <jensj@google.com>
Reviewed-by: Peter von der Ahé <ahe@google.com>

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

@@ -293,12 +293,14 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
           userCode.loader.builders[entryPoints.first] != null) {
         userCode.loader.first = userCode.loader.builders[entryPoints.first];
       }
-      await userCode.buildOutlines();
+      Component componentWithDill = await userCode.buildOutlines();
 
       // This is not the full component. It is the component including all
       // libraries loaded from .dill files.
-      Component componentWithDill =
-          await userCode.buildComponent(verify: c.options.verify);
+      if (!outlineOnly) {
+        componentWithDill =
+            await userCode.buildComponent(verify: c.options.verify);
+      }
       if (componentWithDill != null) {
         this.invalidatedUris.clear();
         hasToCheckPackageUris = false;

pkg/front_end/test/incremental_load_from_dill_test.dart

@@ -33,7 +33,7 @@ import 'package:front_end/src/fasta/severity.dart' show Severity;
 import 'package:kernel/binary/ast_from_binary.dart' show BinaryBuilder;
 
 import 'package:kernel/kernel.dart'
-    show Class, Component, Field, Library, Procedure;
+    show Class, Component, EmptyStatement, Field, Library, Procedure;
 
 import 'package:kernel/target/targets.dart' show TargetFlags;
 
@@ -405,13 +405,14 @@ Future<Null> newWorldTest(
         entries.add(base.resolve(entry));
       }
     }
+    bool outlineOnly = world["outlineOnly"] == true;
     if (brandNewWorld) {
       if (world["fromComponent"] == true) {
         compiler = new TestIncrementalCompiler.fromComponent(
-            options, entries.first, newestWholeComponent);
+            options, entries.first, newestWholeComponent, outlineOnly);
       } else {
-        compiler =
-            new TestIncrementalCompiler(options, entries.first, initializeFrom);
+        compiler = new TestIncrementalCompiler(
+            options, entries.first, initializeFrom, outlineOnly);
       }
     }
 
@@ -434,6 +435,18 @@ Future<Null> newWorldTest(
         entryPoints: entries,
         fullComponent:
             brandNewWorld ? false : (noFullComponent ? false : true));
+    if (outlineOnly) {
+      for (Library lib in component.libraries) {
+        for (Class c in lib.classes) {
+          for (Procedure p in c.procedures) {
+            if (p.function.body is! EmptyStatement) throw "Got body";
+          }
+        }
+        for (Procedure p in lib.procedures) {
+          if (p.function.body is! EmptyStatement) throw "Got body";
+        }
+      }
+    }
     performErrorAndWarningCheck(
         world, gotError, formattedErrors, gotWarning, formattedWarnings);
     util.throwOnEmptyMixinBodies(component);
@@ -808,18 +821,20 @@ class TestIncrementalCompiler extends IncrementalCompiler {
   }
 
   TestIncrementalCompiler(CompilerOptions options, this.entryPoint,
-      [Uri initializeFrom])
+      [Uri initializeFrom, bool outlineOnly])
       : super(
             new CompilerContext(
                 new ProcessedOptions(options: options, inputs: [entryPoint])),
-            initializeFrom);
+            initializeFrom,
+            outlineOnly);
 
   TestIncrementalCompiler.fromComponent(CompilerOptions options,
-      this.entryPoint, Component componentToInitializeFrom)
+      this.entryPoint, Component componentToInitializeFrom, [bool outlineOnly])
       : super.fromComponent(
             new CompilerContext(
                 new ProcessedOptions(options: options, inputs: [entryPoint])),
-            componentToInitializeFrom);
+            componentToInitializeFrom,
+            outlineOnly);
 
   @override
   void recordInvalidatedImportUrisForTesting(List<Uri> uris) {

pkg/front_end/testcases/incremental_initialize_from_dill/outline_only.yaml

@@ -0,0 +1,17 @@
+# Copyright (c) 2019, 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.md file.
+
+# Compile an application with the option of only getting an outline.
+
+type: newworld
+strong: true
+worlds:
+  - entry: main.dart
+    sources:
+      main.dart: |
+        main() {
+          print("hello");
+          b();
+        }
+    outlineOnly: true