refactor(compiler): extract save/restore view logic to separate phase

Saving and restoring the view is significant enough that it makes sense to handle it independently. This makes for easier reasoning about how view save/restore works. Co-authored-by: Alex Rickabaugh <[email protected]>
angular · dylhunn · Apr 18, 2023 · Apr 26, 2023 · Apr 26, 2023 · Apr 26, 2023
commit a0093d2917996a03f02c216bc33f0ec42f598d91
diff --git a/packages/compiler/src/template/pipeline/src/emit.ts b/packages/compiler/src/template/pipeline/src/emit.ts
@@ -27,13 +27,15 @@ import {phaseVariableOptimization} from './phases/variable_optimization';
 import {phaseChaining} from './phases/chaining';
 import {phaseMergeNextContext} from './phases/next_context_merging';
 import {phaseNgContainer} from './phases/ng_container';
+import {phaseSaveRestoreView} from './phases/save_restore_view';
 
 /**
  * Run all transformation phases in the correct order against a `ComponentCompilation`. After this
  * processing, the compilation should be in a state where it can be emitted via `emitTemplateFn`.s
  */
 export function transformTemplate(cpl: ComponentCompilation): void {
   phaseGenerateVariables(cpl);
+  phaseSaveRestoreView(cpl);
   phaseResolveNames(cpl);
   phaseResolveContexts(cpl);
   phaseLocalRefs(cpl);

diff --git a/packages/compiler/src/template/pipeline/src/phases/generate_variables.ts b/packages/compiler/src/template/pipeline/src/phases/generate_variables.ts
@@ -40,12 +40,11 @@ function recursivelyProcessView(view: ViewCompilation, parentScope: Scope|null):
   // Extract a `Scope` from this view.
   const scope = getScopeForView(view, parentScope);
 
-  // Start the view creation block with an operation to save the current view context. This may be
-  // used to restore the view context in any listeners that may be present.
-  view.create.prepend([
-    ir.createVariableOp<ir.CreateOp>(
-        view.tpl.allocateXrefId(), scope.savedViewVariable, new ir.GetCurrentViewExpr()),
-  ]);
+  // Embedded views require an operation to save/restore the view context.
+  if (view.parent !== null) {
+    // Start the view creation block with an operation to save the current view context. This may be
+    // used to restore the view context in any listeners that may be present.
+  }
 
   for (const op of view.create) {
     switch (op.kind) {
@@ -54,26 +53,8 @@ function recursivelyProcessView(view: ViewCompilation, parentScope: Scope|null):
         recursivelyProcessView(view.tpl.views.get(op.xref)!, scope);
         break;
       case ir.OpKind.Listener:
-        // Listeners get a preamble which starts with a call to restore the view.
-        const preambleOps = [
-          ir.createVariableOp<ir.UpdateOp>(
-              view.tpl.allocateXrefId(), scope.viewContextVariable,
-              new ir.RestoreViewExpr(view.xref)),
-          // And includes all variables available to this view.
-          ...generateVariablesInScopeForView(view, scope)
-        ];
-
-        op.handlerOps.prepend(preambleOps);
-
-        // The "restore view" operation in listeners requires a call to `resetView` to reset the
-        // context prior to returning from the listener operation. Find any `return` statements in
-        // the listener body and wrap them in a call to reset the view.
-        for (const handlerOp of op.handlerOps) {
-          if (handlerOp.kind === ir.OpKind.Statement &&
-              handlerOp.statement instanceof o.ReturnStatement) {
-            handlerOp.statement.value = new ir.ResetViewExpr(handlerOp.statement.value);
-          }
-        }
+        // Prepend variables to listener handler functions.
+        op.handlerOps.prepend(generateVariablesInScopeForView(view, scope));
         break;
     }
   }
@@ -94,8 +75,6 @@ interface Scope {
 
   viewContextVariable: ir.SemanticVariable;
 
-  savedViewVariable: ir.SemanticVariable;
-
   contextVariables: Map<string, ir.SemanticVariable>;
 
   /**
@@ -148,11 +127,6 @@ function getScopeForView(view: ViewCompilation, parent: Scope|null): Scope {
       name: null,
       view: view.xref,
     },
-    savedViewVariable: {
-      kind: ir.SemanticVariableKind.SavedView,
-      name: null,
-      view: view.xref,
-    },
     contextVariables: new Map<string, ir.SemanticVariable>(),
     references: [],
     parent,

diff --git a/packages/compiler/src/template/pipeline/src/phases/save_restore_view.ts b/packages/compiler/src/template/pipeline/src/phases/save_restore_view.ts
@@ -0,0 +1,56 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import * as o from '../../../../output/output_ast';
+import * as ir from '../../ir';
+import type {ComponentCompilation} from '../compilation';
+
+export function phaseSaveRestoreView(cpl: ComponentCompilation): void {
+  for (const view of cpl.views.values()) {
+    if (view === cpl.root) {
+      // Save/restore operations are not necessary for the root view.
+      continue;
+    }
+
+    view.create.prepend([
+      ir.createVariableOp<ir.CreateOp>(
+          view.tpl.allocateXrefId(), {
+            kind: ir.SemanticVariableKind.SavedView,
+            name: null,
+            view: view.xref,
+          },
+          new ir.GetCurrentViewExpr()),
+    ]);
+
+    for (const op of view.create) {
+      if (op.kind !== ir.OpKind.Listener) {
+        continue;
+      }
+
+      op.handlerOps.prepend([
+        ir.createVariableOp<ir.UpdateOp>(
+            view.tpl.allocateXrefId(), {
+              kind: ir.SemanticVariableKind.Context,
+              name: null,
+              view: view.xref,
+            },
+            new ir.RestoreViewExpr(view.xref)),
+      ]);
+
+      // The "restore view" operation in listeners requires a call to `resetView` to reset the
+      // context prior to returning from the listener operation. Find any `return` statements in
+      // the listener body and wrap them in a call to reset the view.
+      for (const handlerOp of op.handlerOps) {
+        if (handlerOp.kind === ir.OpKind.Statement &&
+            handlerOp.statement instanceof o.ReturnStatement) {
+          handlerOp.statement.value = new ir.ResetViewExpr(handlerOp.statement.value);
+        }
+      }
+    }
+  }
+}