[analyzer] Report error on the first unresolved identifier

When reporting the "The name 'X' isn't a class." error in instance creation expressions, the mentioned name was the last name even when the previous name was unresolved. This lead to the misleading message the "The name 'named' isn't a class." for `new Class.named()` when `Class` was *not* resolved.

This changes the messaging to handle the case where a prefix of the instance creation is not resolved and report "Undefined name 'X'." in such cases, since we don't know whether 'X' was meant to be a class or just a prefix.

Change-Id: I57ef1dfa229647424855b1f9f8d43e1890094563
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/448301
Reviewed-by: Brian Wilkerson <[email protected]>
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Johnni Winther <[email protected]>
Reviewed-by: Erik Ernst <[email protected]>

Author: johnniwinther

pkg/analyzer/lib/src/dart/resolver/named_type_resolver.dart

@@ -538,14 +538,32 @@ class _ErrorHelper {
       var instanceCreation = constructorName.parent;
       if (instanceCreation is InstanceCreationExpression) {
         var errorRange = _getErrorRange(node, skipImportPrefix: true);
-        diagnosticReporter.atOffset(
-          offset: errorRange.offset,
-          length: errorRange.length,
-          diagnosticCode: instanceCreation.isConst
-              ? CompileTimeErrorCode.constWithNonType
-              : CompileTimeErrorCode.newWithNonType,
-          arguments: [node.name.lexeme],
-        );
+        var importPrefix = node.importPrefix;
+        if (importPrefix != null && importPrefix.element == null) {
+          // The constructor name is in two or three parts and the first part,
+          // which is either a prefix or a class name, is unresolved. In this
+          // case, report that the first name is undefined, instead of reporting
+          // that the last name is not a class.
+          // TODO(johnniwinther): We could report "Undefined prefix 'x'." when
+          // we know it can only be a prefix, for instance in `x.y.z()`.
+          String prefixOrClassName = importPrefix.name.lexeme;
+          diagnosticReporter.atOffset(
+            offset: errorRange.offset,
+            length: errorRange.length,
+            diagnosticCode: CompileTimeErrorCode.undefinedIdentifier,
+            arguments: [prefixOrClassName],
+          );
+        } else {
+          String className = node.name.lexeme;
+          diagnosticReporter.atOffset(
+            offset: errorRange.offset,
+            length: errorRange.length,
+            diagnosticCode: instanceCreation.isConst
+                ? CompileTimeErrorCode.constWithNonType
+                : CompileTimeErrorCode.newWithNonType,
+            arguments: [className],
+          );
+        }
         return true;
       }
     }

pkg/analyzer/test/src/dart/resolution/instance_creation_test.dart

@@ -2540,7 +2540,7 @@ void f() {
 }
 
 ''',
-      [error(CompileTimeErrorCode.newWithNonType, 17, 16)],
+      [error(CompileTimeErrorCode.undefinedIdentifier, 17, 16)],
     );
 
     var node = findNode.singleInstanceCreationExpression;
@@ -2577,7 +2577,7 @@ void f() {
 }
 
 ''',
-      [error(CompileTimeErrorCode.newWithNonType, 17, 14)],
+      [error(CompileTimeErrorCode.undefinedIdentifier, 17, 14)],
     );
 
     var node = findNode.singleInstanceCreationExpression;