Merge pull request #9180 from HerringtonDarkholme/interface

[Fix #9004] Improve error message for extending interface

src/compiler/checker.ts

@@ -853,7 +853,8 @@ namespace ts {
 
             if (!result) {
                 if (nameNotFoundMessage) {
-                    if (!checkAndReportErrorForMissingPrefix(errorLocation, name, nameArg)) {
+                    if (!checkAndReportErrorForMissingPrefix(errorLocation, name, nameArg) &&
+                       !checkAndReportErrorForExtendingInterface(errorLocation)) {
                         error(errorLocation, nameNotFoundMessage, typeof nameArg === "string" ? nameArg : declarationNameToString(nameArg));
                     }
                 }
@@ -937,6 +938,31 @@ namespace ts {
             return false;
         }
 
+
+        function checkAndReportErrorForExtendingInterface(errorLocation: Node): boolean {
+            let parentClassExpression = errorLocation;
+            while (parentClassExpression) {
+                const kind = parentClassExpression.kind;
+                if (kind === SyntaxKind.Identifier || kind === SyntaxKind.PropertyAccessExpression) {
+                    parentClassExpression = parentClassExpression.parent;
+                    continue;
+                }
+                if (kind === SyntaxKind.ExpressionWithTypeArguments) {
+                    break;
+                }
+                return false;
+            }
+            if (!parentClassExpression) {
+                return false;
+            }
+            const expression = (<ExpressionWithTypeArguments>parentClassExpression).expression;
+            if (resolveEntityName(expression, SymbolFlags.Interface, /*ignoreErrors*/ true)) {
+                error(errorLocation, Diagnostics.Cannot_extend_an_interface_0_Did_you_mean_implements, getTextOfNode(expression));
+                return true;
+            }
+            return false;
+         }
+
         function checkResolvedBlockScopedVariable(result: Symbol, errorLocation: Node): void {
             Debug.assert((result.flags & SymbolFlags.BlockScopedVariable) !== 0);
             // Block-scoped variables cannot be used before their definition
@@ -10137,7 +10163,7 @@ namespace ts {
             }
             const prop = getPropertyOfType(apparentType, right.text);
             if (!prop) {
-                if (right.text) {
+                if (right.text && !checkAndReportErrorForExtendingInterface(node)) {
                     error(right, Diagnostics.Property_0_does_not_exist_on_type_1, declarationNameToString(right), typeToString(type.flags & TypeFlags.ThisType ? apparentType : type));
                 }
                 return unknownType;

src/compiler/diagnosticMessages.json

@@ -1935,6 +1935,10 @@
         "category": "Error",
         "code": 2688
     },
+    "Cannot extend an interface '{0}'. Did you mean 'implements'?": {
+        "category": "Error",
+        "code": 2689
+    },
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
         "code": 4000