From 7ffcb504df2e14610cfb4fd219dbb5cfb3c30f15 Mon Sep 17 00:00:00 2001
From: Kristiyan Kostadinov <crisbeto@abv.bg>
Date: Tue, 4 Mar 2025 14:49:51 +0100
Subject: [PATCH] refactor(compiler): account for host element in binder
 (#60267)

Updates the `R3TargetBinder` to ingest host element nodes.

PR Close #60267
---
 packages/compiler/src/render3/view/t2_api.ts  |  5 ++-
 .../compiler/src/render3/view/t2_binder.ts    | 35 ++++++++++++++-----
 2 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/packages/compiler/src/render3/view/t2_api.ts b/packages/compiler/src/render3/view/t2_api.ts
index 59ceaa5b627..62254d8ad32 100644
--- a/packages/compiler/src/render3/view/t2_api.ts
+++ b/packages/compiler/src/render3/view/t2_api.ts
@@ -19,6 +19,7 @@ import {
   Element,
   ForLoopBlock,
   ForLoopBlockEmpty,
+  HostElement,
   IfBlockBranch,
   LetDeclaration,
   Node,
@@ -40,7 +41,8 @@ export type ScopedNode =
   | DeferredBlockError
   | DeferredBlockLoading
   | DeferredBlockPlaceholder
-  | Content;
+  | Content
+  | HostElement;
 
 /** Possible values that a reference can be resolved to. */
 export type ReferenceTarget<DirectiveT> =
@@ -68,6 +70,7 @@ export type TemplateEntity = Reference | Variable | LetDeclaration;
  */
 export interface Target {
   template?: Node[];
+  host?: HostElement;
 }
 
 /**
diff --git a/packages/compiler/src/render3/view/t2_binder.ts b/packages/compiler/src/render3/view/t2_binder.ts
index 88a0b3b4f47..47c90aaf4ca 100644
--- a/packages/compiler/src/render3/view/t2_binder.ts
+++ b/packages/compiler/src/render3/view/t2_binder.ts
@@ -31,6 +31,7 @@ import {
   Element,
   ForLoopBlock,
   ForLoopBlockEmpty,
+  HostElement,
   HoverDeferredTrigger,
   Icu,
   IfBlock,
@@ -169,7 +170,7 @@ export class R3TargetBinder<DirectiveT extends DirectiveMeta> implements TargetB
    * metadata about the types referenced in the template.
    */
   bind(target: Target): BoundTarget<DirectiveT> {
-    if (!target.template) {
+    if (!target.template && !target.host) {
       throw new Error('Empty bound targets are not supported');
     }
 
@@ -221,6 +222,21 @@ export class R3TargetBinder<DirectiveT extends DirectiveMeta> implements TargetB
       );
     }
 
+    // Bind the host element in a separate scope. Note that it only uses the
+    // `TemplateBinder` since directives don't apply inside a host context.
+    if (target.host) {
+      TemplateBinder.applyWithScope(
+        target.host,
+        Scope.apply(target.host),
+        expressions,
+        symbols,
+        nestingLevel,
+        usedPipes,
+        eagerPipes,
+        deferBlocks,
+      );
+    }
+
     return new R3BoundTarget(
       target,
       directives,
@@ -280,7 +296,7 @@ class Scope implements Visitor {
    * Process a template (either as a `Template` sub-template with variables, or a plain array of
    * template `Node`s) and construct its `Scope`.
    */
-  static apply(template: Node[]): Scope {
+  static apply(template: ScopedNode | Node[]): Scope {
     const scope = Scope.newRootScope();
     scope.ingest(template);
     return scope;
@@ -315,7 +331,7 @@ class Scope implements Visitor {
       nodeOrNodes instanceof Content
     ) {
       nodeOrNodes.children.forEach((node) => node.visit(this));
-    } else {
+    } else if (!(nodeOrNodes instanceof HostElement)) {
       // No overarching `Template` instance, so process the nodes directly.
       nodeOrNodes.forEach((node) => node.visit(this));
     }
@@ -702,7 +718,7 @@ class TemplateBinder extends RecursiveAstVisitor implements Visitor {
   /**
    * Process a template and extract metadata about expressions and symbols within.
    *
-   * @param nodes the nodes of the template to process
+   * @param nodeOrNodes the nodes of the template to process
    * @param scope the `Scope` of the template being processed.
    * @returns three maps which contain metadata about the template: `expressions` which interprets
    * special `AST` nodes in expressions as pointing to references or variables declared within the
@@ -712,7 +728,7 @@ class TemplateBinder extends RecursiveAstVisitor implements Visitor {
    * at 1.
    */
   static applyWithScope(
-    nodes: Node[],
+    nodeOrNodes: ScopedNode | Node[],
     scope: Scope,
     expressions: Map<AST, TemplateEntity>,
     symbols: Map<TemplateEntity, Template>,
@@ -721,7 +737,7 @@ class TemplateBinder extends RecursiveAstVisitor implements Visitor {
     eagerPipes: Set<string>,
     deferBlocks: DeferBlockScopes,
   ): void {
-    const template = nodes instanceof Template ? nodes : null;
+    const template = nodeOrNodes instanceof Template ? nodeOrNodes : null;
     // The top-level template has nesting level 0.
     const binder = new TemplateBinder(
       expressions,
@@ -734,7 +750,7 @@ class TemplateBinder extends RecursiveAstVisitor implements Visitor {
       template,
       0,
     );
-    binder.ingest(nodes);
+    binder.ingest(nodeOrNodes);
   }
 
   private ingest(nodeOrNodes: ScopedNode | Node[]): void {
@@ -777,6 +793,9 @@ class TemplateBinder extends RecursiveAstVisitor implements Visitor {
     ) {
       nodeOrNodes.children.forEach((node) => node.visit(this));
       this.nestingLevel.set(nodeOrNodes, this.level);
+    } else if (nodeOrNodes instanceof HostElement) {
+      // Host elements are always at the top level.
+      this.nestingLevel.set(nodeOrNodes, 0);
     } else {
       // Visit each node from the top-level template.
       nodeOrNodes.forEach(this.visitNode);
@@ -967,7 +986,7 @@ class TemplateBinder extends RecursiveAstVisitor implements Visitor {
  *
  * See `BoundTarget` for documentation on the individual methods.
  */
-export class R3BoundTarget<DirectiveT extends DirectiveMeta> implements BoundTarget<DirectiveT> {
+class R3BoundTarget<DirectiveT extends DirectiveMeta> implements BoundTarget<DirectiveT> {
   /** Deferred blocks, ordered as they appear in the template. */
   private deferredBlocks: DeferredBlock[];