Tests validating implicit const handling (#910). (#911)

See: #910.

Author: pq

analysis_options.yaml

@@ -1,5 +1,7 @@
 analyzer:
   strong-mode: true
+  language:
+    enablePreviewDart2: true
   exclude:
     # ignore vscode .history files
     - .history/**

pubspec.yaml

@@ -6,7 +6,7 @@ homepage: https://github.com/dart-lang/linter
 environment:
   sdk: '>=1.12.0 <2.0.0'
 dependencies:
-  analyzer: ^0.31.0-alpha.2
+  analyzer: ^0.31.2-alpha.0
   args: '>=0.12.1 <2.0.0'
   glob: ^1.0.3
   meta: ^1.0.2

test/rules/prefer_const_constructors.dart

@@ -5,7 +5,15 @@
 // test w/ `pub run test -N prefer_const_constructors`
 
 class A {
-  const A();
+  const A({A parent});
+  const A.a();
+}
+
+void accessA_0() {
+  A a = A(); //OK
+  A a1 = A(
+    parent: A.a(), //OK
+  );
 }
 
 void accessA_1() {