Fixes #287 and other failures statically checking SDK tests

This adds some defensiveness to override checking and other checks.

It fixes all known crashers running dartanalyzer in strong mode on language, co19, etc.

R=leafp@google.com

Review URL: https://codereview.chromium.org/1303913003 .

pkg/dev_compiler/lib/src/checker/checker.dart

@@ -83,12 +83,14 @@ class _OverrideChecker {
   void _checkSuperOverrides(ClassDeclaration node) {
     var seen = new Set<String>();
     var current = node.element.type;
+    var visited = new Set<InterfaceType>();
     do {
+      visited.add(current);
       current.mixins.reversed
           .forEach((m) => _checkIndividualOverridesFromClass(node, m, seen));
       _checkIndividualOverridesFromClass(node, current.superclass, seen);
       current = current.superclass;
-    } while (!current.isObject);
+    } while (!current.isObject && !visited.contains(current));
   }
 
   /// Checks that implementations correctly override all reachable interfaces.
@@ -152,10 +154,21 @@ class _OverrideChecker {
   /// invalid override, for [InterfaceType]s we use [errorLocation] instead.
   void _checkInterfacesOverrides(
       cls, Iterable<InterfaceType> interfaces, Set<String> seen,
-      {bool includeParents: true, AstNode errorLocation}) {
+      {Set<InterfaceType> visited,
+      bool includeParents: true,
+      AstNode errorLocation}) {
     var node = cls is ClassDeclaration ? cls : null;
     var type = cls is InterfaceType ? cls : node.element.type;
 
+    if (visited == null) {
+      visited = new Set<InterfaceType>();
+    } else if (visited.contains(type)) {
+      // Malformed type.
+      return;
+    } else {
+      visited.add(type);
+    }
+
     // Check direct overrides on [type]
     for (var interfaceType in interfaces) {
       if (node != null) {
@@ -186,7 +199,7 @@ class _OverrideChecker {
       // No need to copy [seen] here because we made copies above when reporting
       // errors on mixins.
       _checkInterfacesOverrides(parent, interfaces, seen,
-          includeParents: true, errorLocation: loc);
+          visited: visited, includeParents: true, errorLocation: loc);
     }
   }
 
@@ -232,6 +245,7 @@ class _OverrideChecker {
           var setter = element.setter;
           bool found = _checkSingleOverride(getter, baseType, variable, member);
           if (!variable.isFinal &&
+              !variable.isConst &&
               _checkSingleOverride(setter, baseType, variable, member)) {
             found = true;
           }
@@ -389,10 +403,12 @@ class CodeChecker extends RecursiveAstVisitor {
         : rules.provider.iterableType;
     var loopVariable = node.identifier != null
         ? node.identifier
-        : node.loopVariable.identifier;
-    var iteratorType = loopVariable.staticType;
-    var checkedType = iterableType.substitute4([iteratorType]);
-    checkAssignment(expr, checkedType);
+        : node.loopVariable?.identifier;
+    if (loopVariable != null) {
+      var iteratorType = loopVariable.staticType;
+      var checkedType = iterableType.substitute4([iteratorType]);
+      checkAssignment(expr, checkedType);
+    }
     node.visitChildren(this);
   }
 

pkg/dev_compiler/lib/src/checker/resolver.dart

@@ -154,11 +154,11 @@ class LibraryResolverWithInference extends LibraryResolver {
       var element = cls.element;
       var type = element.type;
       if (seen.contains(type)) return;
+      seen.add(type);
       for (var supertype in element.allSupertypes) {
         var supertypeClass = typeToDeclaration[supertype];
         if (supertypeClass != null) visit(supertypeClass);
       }
-      seen.add(type);
 
       if (_options.inferFromOverrides) {
         // Infer field types from overrides first, otherwise from initializers.
@@ -466,7 +466,10 @@ class RestrictedResolverVisitor extends ResolverVisitor {
     var element = node.element;
     if (element is FieldFormalParameterElement) {
       if (element.type.isDynamic) {
-        element.type = element.field.type;
+        // In malformed code, there may be no actual field.
+        if (element.field != null) {
+          element.type = element.field.type;
+        }
       }
     }
     super.visitFieldFormalParameter(node);

pkg/dev_compiler/lib/src/checker/rules.dart

@@ -264,7 +264,8 @@ class RestrictedRules extends TypeRules {
       return true;
     }
 
-    throw new StateError("Unexpected type");
+    // We should not see any other type aside from malformed code.
+    return false;
   }
 
   /// Check that f1 is a subtype of f2. [ignoreReturn] is used in the DDC
@@ -407,6 +408,10 @@ class RestrictedRules extends TypeRules {
       return isSubTypeOf(bound, t2);
     }
 
+    if (t2 is TypeParameterType) {
+      return false;
+    }
+
     if (t2.isDartCoreFunction) {
       if (t1 is FunctionType) return true;
       if (t1.element is ClassElement) {
@@ -513,6 +518,10 @@ class RestrictedRules extends TypeRules {
   }
 
   DartType elementType(Element e) {
+    if (e == null) {
+      // Malformed code - just return dynamic.
+      return provider.dynamicType;
+    }
     return (e as dynamic).type;
   }
 
@@ -704,6 +713,7 @@ class DownwardsInference {
     // Check that we were not passed any type arguments
     if (classTypeName.typeArguments != null) return false;
     // Infer type arguments
+    if (t is! InterfaceType) return false;
     var targs = _matchTypes(type, t);
     if (targs == null) return false;
     if (e.staticElement == null) return false;