fix(compiler-cli): report error when a reference target is missing instead of crashing (#39805)

If a template declares a reference to a missing target then referring to
that reference from elsewhere in the template would crash the template
type checker, due to a regression introduced in #38618. This commit
fixes the crash by ensuring that the invalid reference will resolve to
a variable of type any.

Fixes #39744

PR Close #39805

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

@@ -458,6 +458,26 @@ class TcbReferenceOp extends TcbOp {
   }
 }
 
+/**
+ * A `TcbOp` which is used when the target of a reference is missing. This operation generates a
+ * variable of type any for usages of the invalid reference to resolve to. The invalid reference
+ * itself is recorded out-of-band.
+ */
+class TcbInvalidReferenceOp extends TcbOp {
+  constructor(private readonly tcb: Context, private readonly scope: Scope) {
+    super();
+  }
+
+  // The declaration of a missing reference is only needed when the reference is resolved.
+  readonly optional = true;
+
+  execute(): ts.Identifier {
+    const id = this.tcb.allocateId();
+    this.scope.addStatement(tsCreateVariable(id, NULL_AS_ANY));
+    return id;
+  }
+}
+
 /**
  * A `TcbOp` which constructs an instance of a directive with types inferred from its inputs. The
  * inputs themselves are not checked here; checking of inputs is achieved in `TcbDirectiveInputsOp`.
@@ -1353,13 +1373,15 @@ class Scope {
   private checkAndAppendReferencesOfNode(node: TmplAstElement|TmplAstTemplate): void {
     for (const ref of node.references) {
       const target = this.tcb.boundTarget.getReferenceTarget(ref);
-      if (target === null) {
-        this.tcb.oobRecorder.missingReferenceTarget(this.tcb.id, ref);
-        continue;
-      }
 
       let ctxIndex: number;
-      if (target instanceof TmplAstTemplate || target instanceof TmplAstElement) {
+      if (target === null) {
+        // The reference is invalid if it doesn't have a target, so report it as an error.
+        this.tcb.oobRecorder.missingReferenceTarget(this.tcb.id, ref);
+
+        // Any usages of the invalid reference will be resolved to a variable of type any.
+        ctxIndex = this.opQueue.push(new TcbInvalidReferenceOp(this.tcb, this)) - 1;
+      } else if (target instanceof TmplAstTemplate || target instanceof TmplAstElement) {
         ctxIndex = this.opQueue.push(new TcbReferenceOp(this.tcb, this, ref, node, target)) - 1;
       } else {
         ctxIndex =

packages/compiler-cli/test/ngtsc/template_typecheck_spec.ts

@@ -1080,6 +1080,29 @@ export declare class AnimationEvent {
       expect(getSourceCodeForDiagnostic(diags[0])).toBe('unknownTarget');
     });
 
+    it('should treat an unknown local ref target as type any', () => {
+      env.write('test.ts', `
+        import {Component, NgModule} from '@angular/core';
+
+        @Component({
+          selector: 'test',
+          template: '<div #ref="unknownTarget">{{ use(ref) }}</div>',
+        })
+        class TestCmp {
+          use(ref: string): string { return ref; }
+        }
+
+        @NgModule({
+          declarations: [TestCmp],
+        })
+        class Module {}
+      `);
+      const diags = env.driveDiagnostics();
+      expect(diags.length).toBe(1);
+      expect(diags[0].messageText).toBe(`No directive found with exportAs 'unknownTarget'.`);
+      expect(getSourceCodeForDiagnostic(diags[0])).toBe('unknownTarget');
+    });
+
     it('should report an error with an unknown pipe', () => {
       env.write('test.ts', `
         import {Component, NgModule} from '@angular/core';