fix(core): improve error when multiple components match the same element

Closes #7067

modules/@angular/compiler/src/template_parser/template_parser.ts

@@ -644,7 +644,11 @@ class TemplateParseVisitor implements html.Visitor {
   private _assertOnlyOneComponent(directives: DirectiveAst[], sourceSpan: ParseSourceSpan) {
     const componentTypeNames = this._findComponentDirectiveNames(directives);
     if (componentTypeNames.length > 1) {
-      this._reportError(`More than one component: ${componentTypeNames.join(',')}`, sourceSpan);
+      this._reportError(
+          `More than one component matched on this element.\n` +
+              `Make sure that only one component's selector can match a given element.\n` +
+              `Conflicting components: ${componentTypeNames.join(',')}`,
+          sourceSpan);
     }
   }
 
@@ -831,4 +835,4 @@ const NON_BINDABLE_VISITOR = new NonBindableVisitor();
 
 function _isEmptyTextNode(node: html.Node): boolean {
   return node instanceof html.Text && node.value.trim().length == 0;
-}
+}