[cfe] Add members to construct nullability in Library and LibraryBuilder

Change-Id: Iaaa9cf0c5a5789e6b303d646c5ed7fb6eed15b9b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/117155
Reviewed-by: Johnni Winther <[email protected]>

Author: Dmitry Stefantsov

pkg/front_end/lib/src/fasta/builder/library_builder.dart

@@ -4,7 +4,7 @@
 
 library fasta.library_builder;
 
-import 'package:kernel/ast.dart' show Library;
+import 'package:kernel/ast.dart' show Library, Nullability;
 
 import '../combinator.dart' show Combinator;
 
@@ -275,6 +275,23 @@ abstract class LibraryBuilder extends ModifierBuilder {
   // TODO(38287): Compute the predicate using the library version instead.
   bool get isNonNullableByDefault => loader.target.enableNonNullable;
 
+  Nullability get nullable {
+    return isNonNullableByDefault ? Nullability.nullable : Nullability.legacy;
+  }
+
+  Nullability get nonNullable {
+    return isNonNullableByDefault
+        ? Nullability.nonNullable
+        : Nullability.legacy;
+  }
+
+  Nullability nullableIfTrue(bool isNullable) {
+    if (isNonNullableByDefault) {
+      return isNullable ? Nullability.nullable : Nullability.nonNullable;
+    }
+    return Nullability.legacy;
+  }
+
   NullabilityBuilder computeNullabilityFromToken(bool markedAsNullable) {
     if (!isNonNullableByDefault) {
       return const NullabilityBuilder.legacy();

pkg/kernel/binary.md

@@ -228,7 +228,7 @@ type Name {
 }
 
 type Library {
-  Byte flags (isExternal, isSynthetic, isNonNullableOptedIn);
+  Byte flags (isExternal, isSynthetic, isNonNullableByDefault);
   UInt languageVersionMajor;
   UInt languageVersionMinor;
   CanonicalNameReference canonicalName;

pkg/kernel/lib/ast.dart

@@ -330,7 +330,7 @@ class Library extends NamedNode
 
   static const int ExternalFlag = 1 << 0;
   static const int SyntheticFlag = 1 << 1;
-  static const int NonNullableOptedInFlag = 1 << 2;
+  static const int NonNullableByDefaultFlag = 1 << 2;
 
   int flags = 0;
 
@@ -355,11 +355,11 @@ class Library extends NamedNode
     flags = value ? (flags | SyntheticFlag) : (flags & ~SyntheticFlag);
   }
 
-  bool get isNonNullableOptedIn => (flags & NonNullableOptedInFlag) != 0;
-  void set isNonNullableOptedIn(bool value) {
+  bool get isNonNullableByDefault => (flags & NonNullableByDefaultFlag) != 0;
+  void set isNonNullableByDefault(bool value) {
     flags = value
-        ? (flags | NonNullableOptedInFlag)
-        : (flags & ~NonNullableOptedInFlag);
+        ? (flags | NonNullableByDefaultFlag)
+        : (flags & ~NonNullableByDefaultFlag);
   }
 
   String name;
@@ -420,6 +420,23 @@ class Library extends NamedNode
     setParents(this.fields, this);
   }
 
+  Nullability get nullable {
+    return isNonNullableByDefault ? Nullability.nullable : Nullability.legacy;
+  }
+
+  Nullability get nonNullable {
+    return isNonNullableByDefault
+        ? Nullability.nonNullable
+        : Nullability.legacy;
+  }
+
+  Nullability nullableIfTrue(bool isNullable) {
+    if (isNonNullableByDefault) {
+      return isNullable ? Nullability.nullable : Nullability.nonNullable;
+    }
+    return Nullability.legacy;
+  }
+
   /// Returns the top-level fields and procedures defined in this library.
   ///
   /// This getter is for convenience, not efficiency.  Consider manually