fix(ivy): type checking - handle $implicit ng-template variables (#30675)

When an `ng-template` element has a variable declaration without a value,
it is assigned the value of the `$implicit` property in the embedded view's
context. The template compiler inserts a property access to `$implicit` for
template variables without a value, however the type-check code generation
logic did not. This resulted in incorrect type-checking code being generated.

Fixes FW-1326

PR Close #30675

packages/compiler-cli/src/ngtsc/typecheck/src/type_check_block.ts

@@ -122,7 +122,7 @@ class TcbVariableOp extends TcbOp {
     const id = this.tcb.allocateId();
     const initializer = ts.createPropertyAccess(
         /* expression */ ctx,
-        /* name */ this.variable.value);
+        /* name */ this.variable.value || '$implicit');
 
     // Declare the variable, and return its identifier.
     this.scope.addStatement(tsCreateVariable(id, initializer));

packages/compiler-cli/src/ngtsc/typecheck/test/type_check_block_spec.ts

@@ -45,6 +45,16 @@ describe('type check blocks', () => {
     expect(tcb(TEMPLATE)).toContain('_t1.htmlFor = "test";');
   });
 
+  it('should handle implicit vars on ng-template', () => {
+    const TEMPLATE = `<ng-template let-a></ng-template>`;
+    expect(tcb(TEMPLATE)).toContain('var _t2 = _t1.$implicit;');
+  });
+
+  it('should handle implicit vars when using microsyntax', () => {
+    const TEMPLATE = `<div *ngFor="let user of users"></div>`;
+    expect(tcb(TEMPLATE)).toContain('var _t2 = _t1.$implicit;');
+  });
+
   it('should generate a forward element reference correctly', () => {
     const TEMPLATE = `
       {{ i.value }}