Support new function subtyping rules in dart2js.

sdk/lib/_internal/compiler/implementation/dart_types.dart

Index: sdk/lib/_internal/compiler/implementation/dart_types.dart
diff --git a/sdk/lib/_internal/compiler/implementation/dart_types.dart b/sdk/lib/_internal/compiler/implementation/dart_types.dart
index 9639b3d3c5130421451f63e249b5ab7965e71588..fd08d0c93ef5969a6fdb59340171091af6002818 100644
--- a/sdk/lib/_internal/compiler/implementation/dart_types.dart
+++ b/sdk/lib/_internal/compiler/implementation/dart_types.dart
@@ -999,6 +999,10 @@ class SubtypeVisitor extends DartTypeVisitor<bool, DartType> {
     if (s is !FunctionType) return false;
     FunctionType tf = t;
     FunctionType sf = s;
+    if (!identical(sf.returnType, voidType) &&
+        !isAssignable(tf.returnType, sf.returnType)) {
+      return false;
+    }
     Link<DartType> tps = tf.parameterTypes;
     Link<DartType> sps = sf.parameterTypes;
     while (!tps.isEmpty && !sps.isEmpty) {
@@ -1006,12 +1010,17 @@ class SubtypeVisitor extends DartTypeVisitor<bool, DartType> {
       tps = tps.tail;
       sps = sps.tail;
     }
-    if (!tps.isEmpty || !sps.isEmpty) return false;
-    if (!identical(sf.returnType, voidType) &&
-        !isAssignable(tf.returnType, sf.returnType)) {
+    if (!tps.isEmpty) {
+      // We must have
+      //     t.parameterTypes.length <= s.parameterTypes.length
       return false;
     }
     if (!sf.namedParameters.isEmpty) {
+      if (!sps.isEmpty) {
+        // We must have
+        //     t.parameterTypes.length == s.parameterTypes.length

[karlklose, 2013/04/24 11:59:20]

Perhaps you could define abbreviations for t/s.parameterTypes.length and
t/s.optionalParameterTypes.length to make the invariants easier to read.

[Johnni Winther, 2013/04/25 07:54:12]

Done.

+        return false;
+      }
       // Since named parameters are globally ordered we can determine the
       // subset relation with a linear search for [:sf.NamedParameters:]
       // within [:tf.NamedParameters:].
@@ -1033,23 +1042,44 @@ class SubtypeVisitor extends DartTypeVisitor<bool, DartType> {
         // We didn't find all names.
         return false;
       }
-    }
-    if (!sf.optionalParameterTypes.isEmpty) {
-      Link<DartType> tOptionalParameterType = tf.optionalParameterTypes;
-      Link<DartType> sOptionalParameterType = sf.optionalParameterTypes;
-      while (!tOptionalParameterType.isEmpty &&
-             !sOptionalParameterType.isEmpty) {
-        if (!isAssignable(tOptionalParameterType.head,
-                          sOptionalParameterType.head)) {
-          return false;
-        }
-        sOptionalParameterType = sOptionalParameterType.tail;
-        tOptionalParameterType = tOptionalParameterType.tail;
+    } else {
+      // Check the remaining required parameters of [s] against the optional
+      // parameters of [t].
+      tps = tf.optionalParameterTypes;
+      while (!tps.isEmpty && !sps.isEmpty) {
+        if (!isAssignable(tps.head, sps.head)) return false;
+        tps = tps.tail;
+        sps = sps.tail;
       }
-      if (!sOptionalParameterType.isEmpty) {
-        // We didn't find enough optional parameters.
+      if (!sps.isEmpty) {

[karlklose, 2013/04/24 11:59:20]

It would be nicer to check the number of arguments invariants in one place, but
I guess we do not want to calculate the length of the links and then run through
them again.

[Johnni Winther, 2013/04/25 07:54:12]

Added a TODO for a more readable implementation.

+        // We must have
+        //     t.parameterTypes.length + t.optionalParameterTypes.length
+        //         >= s.parameterTypes.length
         return false;
       }
+      if (!sf.optionalParameterTypes.isEmpty) {
+        // Check the remaining optional parameters of [s] against the remaining
+        // optional parameters of [t].
+        sps = sf.optionalParameterTypes;
+        while (!tps.isEmpty && !sps.isEmpty) {
+          if (!isAssignable(tps.head, sps.head)) return false;
+          tps = tps.tail;
+          sps = sps.tail;
+        }
+        if (!sps.isEmpty) {
+          // We didn't find enough parameters:
+          // We must have
+          //     t.parameterTypes.length + t.optionalParameterTypes.length
+          //       <= s.parameterTypes.length + s.optionalParameterTypes.length
+          return false;
+        }
+      } else {
+        if (!sps.isEmpty) {
+          // We must have
+          //     t.parameterTypes.length == s.parameterTypes.length
+          return false;
+        }
+      }
     }
     return true;
   }