fix(compiler): report errors for missing binding names (#34595)

Currently, would-be binding attributes that are missing binding names
are not parsed as bindings, and fall through as regular attributes. In
some cases, this can lead to a runtime error; trying to assign `#` as a
DOM attribute in an element like in `<div #></div>` fails because `#` is
not a valid attribute name.

Attributes composed of binding prefixes but not defining a binding
should be considered invalid, as this almost certainly indicates an
unintentional elision of a binding by the developer. This commit
introduces error reporting for attributes with a binding name prefix but
no actual binding name.

Closes https://github.com/angular/vscode-ng-language-service/issues/293.

PR Close #34595

packages/compiler/src/render3/r3_template_transform.ts

@@ -21,7 +21,7 @@ import * as t from './r3_ast';
 import {I18N_ICU_VAR_PREFIX, isI18nRootNode} from './view/i18n/util';
 
 const BIND_NAME_REGEXP =
-    /^(?:(?:(?:(bind-)|(let-)|(ref-|#)|(on-)|(bindon-)|(@))(.+))|\[\(([^\)]+)\)\]|\[([^\]]+)\]|\(([^\)]+)\))$/;
+    /^(?:(?:(?:(bind-)|(let-)|(ref-|#)|(on-)|(bindon-)|(@))(.*))|\[\(([^\)]+)\)\]|\[([^\]]+)\]|\(([^\)]+)\))$/;
 
 // Group 1 = "bind-"
 const KW_BIND_IDX = 1;
@@ -399,7 +399,10 @@ class HtmlAstToIvyAst implements html.Visitor {
       valueSpan: ParseSourceSpan|undefined, variables: t.Variable[]) {
     if (identifier.indexOf('-') > -1) {
       this.reportError(`"-" is not allowed in variable names`, sourceSpan);
+    } else if (identifier.length === 0) {
+      this.reportError(`Variable does not have a name`, sourceSpan);
     }
+
     variables.push(new t.Variable(identifier, value, sourceSpan, valueSpan));
   }
 
@@ -408,6 +411,8 @@ class HtmlAstToIvyAst implements html.Visitor {
       valueSpan: ParseSourceSpan|undefined, references: t.Reference[]) {
     if (identifier.indexOf('-') > -1) {
       this.reportError(`"-" is not allowed in reference names`, sourceSpan);
+    } else if (identifier.length === 0) {
+      this.reportError(`Reference does not have a name`, sourceSpan);
     }
 
     references.push(new t.Reference(identifier, value, sourceSpan, valueSpan));