Add fix for missing @required params.

pkg/analysis_server/lib/src/services/correction/fix_internal.dart

Index: pkg/analysis_server/lib/src/services/correction/fix_internal.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
index c823e4ebee013b703d53a1ab20670908d52e2da6..c42cf926be45776d0f1592967cefa9b7439314e1 100644
--- a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
@@ -267,6 +267,9 @@ class FixProcessor {
       _addFix_createConstructor_insteadOfSyntheticDefault();
       await _addFix_addMissingParameter();
     }
+    if (errorCode == HintCode.MISSING_REQUIRED_PARAM) {

[Brian Wilkerson, 2017/02/14 22:23:12]

We might want to fix the hint code too.

[pquitslund, 2017/02/14 23:41:37]

Probably.  Unfortunately, this will break options files that refer to this code.
 :/ Let's discuss a follow-up.

+      _addFix_addMissingRequiredParameter();
+    }
     if (errorCode == StaticWarningCode.FUNCTION_WITHOUT_CALL) {
       _addFix_addMissingMethodCall();
     }
@@ -549,6 +552,44 @@ class FixProcessor {
     }
   }
 
+  void _addFix_addMissingRequiredParameter() {
+    if (node is SimpleIdentifier && node.parent is MethodInvocation) {

[scheglov, 2017/02/14 22:06:07]

Do we need this functionality for constructors?

[pquitslund, 2017/02/14 23:41:37]

Yes!  Case added and a test.

+      MethodInvocation invocation = node.parent;

[scheglov, 2017/02/14 22:06:07]

I prefer speculatively name "AstNode invocation = node?.parent;" before "if" so
that after "is MethodInvocation" we know that it  actually is. But this might be
a recent change, so it's up to you. We might have many instances of doing just
like you did here, e.g. because this code was translated from Java :-)

[pquitslund, 2017/02/14 23:41:37]

Done.

+      Element targetElement = invocation.methodName.bestElement;
+      if (targetElement is ExecutableElement) {
+        List<ParameterElement> parameters = targetElement.parameters;
+        List<Expression> arguments = invocation.argumentList.arguments;
+        Iterable<String> namedArgs = arguments
+            .where((e) => e is NamedExpression)
+            .map((e) => (e as NamedExpression).name.label.name);
+
+        Iterable<ParameterElement> missingParams = parameters
+            .where((p) => p.isRequired && !namedArgs.contains(p.name));

[scheglov, 2017/02/14 22:06:07]

Maybe materialize using toList().

[pquitslund, 2017/02/14 23:41:37]

Done.

+        if (missingParams.isEmpty) {
+          return;
+        }
+
+        // add proposal
+
+        SourceBuilder sb;
+        NodeList<Expression> args = invocation.argumentList.arguments;

[scheglov, 2017/02/14 22:06:07]

You already have "arguments" above.

[pquitslund, 2017/02/14 23:41:37]

Ah. Good catch!

+
+        if (args.isEmpty) {
+          sb = new SourceBuilder(
+              file, invocation.argumentList.leftParenthesis.offset + 1);
+        } else {
+          sb = new SourceBuilder(file, args.last.endToken.offset + 1);

[scheglov, 2017/02/14 22:06:07]

I think this would work only for single character expressions.
Maybe args.last.end is better?

[pquitslund, 2017/02/14 23:41:37]

Good catch.  Fixed!

+          sb.append(', ');
+        }
+
+        sb.append(missingParams.map((p) => '${p.name}: null').join(', '));
+
+        _insertBuilder(sb, targetElement);
+        _addFix(DartFixKind.ADD_MISSING_REQUIRED_PARAMETER, []);

[scheglov, 2017/02/14 22:06:07]

Should we use different kinds for adding one, and adding multiple required
parameters?

[Brian Wilkerson, 2017/02/14 22:23:12]

Is there any reason not to always add all arguments? We don't have different
fixes for missing methods...

[pquitslund, 2017/02/14 23:41:37]

My thinking was to always just add them all.  If that's annoying in practice, we
can refine...

+      }
+    }
+  }
+
   void _addFix_boolInsteadOfBoolean() {
     SourceRange range = rf.rangeError(error);
     _addReplaceEdit(range, 'bool');