fix(compiler): do not use constants for colocated shallow references

Currently the TS generated output (not JIT), breaks at runtime because
we emit all variables using the `Final` modifier. i.e. constants.

This breaks shallow references when we run our acceptance signal
tests using AOT.

packages/compiler/src/template/pipeline/ir/src/ops/shared.ts

@@ -68,18 +68,25 @@ export interface VariableOp<OpT extends Op<OpT>> extends Op<OpT> {
    * Expression representing the value of the variable.
    */
   initializer: o.Expression;
+
+  /**
+   * Whether the variable created is a constant.
+   */
+  isConstant: boolean;
 }
 
 /**
  * Create a `VariableOp`.
  */
 export function createVariableOp<OpT extends Op<OpT>>(
-    xref: XrefId, variable: SemanticVariable, initializer: o.Expression): VariableOp<OpT> {
+    xref: XrefId, variable: SemanticVariable, initializer: o.Expression,
+    isConstant: boolean): VariableOp<OpT> {
   return {
     kind: OpKind.Variable,
     xref,
     variable,
     initializer,
+    isConstant,
     ...NEW_OP,
   };
 }

packages/compiler/src/template/pipeline/src/phases/creation_var_colocation.ts

@@ -79,6 +79,8 @@ function processUnit(unit: CompilationUnit): void {
           // initializer to `undefined`, and set the variable to its value after its declaration.
           const initializer = declOp.initializer;
           declOp.initializer = o.literal(undefined);
+          declOp.isConstant = false;
+
           const readVar = new ir.ReadVariableExpr(declOp.xref);
           // TODO: variable naming should run after this and take care of this for us.
           readVar.name = declOp.variable.name;

packages/compiler/src/template/pipeline/src/phases/generate_variables.ts

@@ -179,7 +179,8 @@ function generateVariablesInScopeForView<OpT extends ir.Op<OpT>>(
     // view with a `nextContext` expression. This context switching operation itself declares a
     // variable, because the context of the view may be referenced directly.
     newOps.push(ir.createVariableOp(
-        view.job.allocateXrefId(), scope.viewContextVariable, new ir.NextContextExpr()));
+        view.job.allocateXrefId(), scope.viewContextVariable, new ir.NextContextExpr(),
+        /* isConstant */ true));
   }
 
   // Add variables for all context variables available in this scope's view.
@@ -189,13 +190,15 @@ function generateVariablesInScopeForView<OpT extends ir.Op<OpT>>(
     const variable = value === ir.CTX_REF ? context : new o.ReadPropExpr(context, value);
     // Add the variable declaration.
     newOps.push(ir.createVariableOp(
-        view.job.allocateXrefId(), scope.contextVariables.get(name)!, variable));
+        view.job.allocateXrefId(), scope.contextVariables.get(name)!, variable,
+        /* isConstant */ true));
   }
 
   // Add variables for all local references declared for elements in this scope.
   for (const ref of scope.references) {
     newOps.push(ir.createVariableOp(
-        view.job.allocateXrefId(), ref.variable, new ir.ReferenceExpr(ref.targetId, ref.offset)));
+        view.job.allocateXrefId(), ref.variable, new ir.ReferenceExpr(ref.targetId, ref.offset),
+        /* isConstant */ true));
   }
 
   if (scope.parent !== null) {

packages/compiler/src/template/pipeline/src/phases/reify.ts

@@ -122,6 +122,8 @@ function reifyCreateOperations(unit: CompilationUnit, ops: ir.OpList<ir.CreateOp
         if (op.variable.name === null) {
           throw new Error(`AssertionError: unnamed variable ${op.xref}`);
         }
+        // Optimization for variable co-location. If we know the initializer is undefined,
+        // we don't need to set an explicit one to avoid e.g. a `let b = undefined`.
         let initializer: o.Expression|undefined = op.initializer;
         if (initializer instanceof o.LiteralExpr && initializer.value === undefined) {
           initializer = undefined;
@@ -129,7 +131,8 @@ function reifyCreateOperations(unit: CompilationUnit, ops: ir.OpList<ir.CreateOp
         ir.OpList.replace<ir.CreateOp>(
             op,
             ir.createStatementOp(new o.DeclareVarStmt(
-                op.variable.name, initializer, undefined, o.StmtModifier.Final)));
+                op.variable.name, initializer, undefined,
+                op.isConstant ? o.StmtModifier.Final : undefined)));
         break;
       case ir.OpKind.Namespace:
         switch (op.active) {
@@ -280,7 +283,8 @@ function reifyUpdateOperations(_unit: CompilationUnit, ops: ir.OpList<ir.UpdateO
         ir.OpList.replace<ir.UpdateOp>(
             op,
             ir.createStatementOp(new o.DeclareVarStmt(
-                op.variable.name, op.initializer, undefined, o.StmtModifier.Final)));
+                op.variable.name, op.initializer, undefined,
+                op.isConstant ? o.StmtModifier.Final : undefined)));
         break;
       case ir.OpKind.Conditional:
         if (op.processed === null) {

packages/compiler/src/template/pipeline/src/phases/save_restore_view.ts

@@ -19,7 +19,8 @@ export function phaseSaveRestoreView(job: ComponentCompilationJob): void {
             name: null,
             view: view.xref,
           },
-          new ir.GetCurrentViewExpr()),
+          new ir.GetCurrentViewExpr(), /* isConstant */ true),
+
     ]);
 
     for (const op of view.create) {
@@ -56,7 +57,7 @@ function addSaveRestoreViewOperationToListener(unit: ViewCompilationUnit, op: ir
           name: null,
           view: unit.xref,
         },
-        new ir.RestoreViewExpr(unit.xref)),
+        new ir.RestoreViewExpr(unit.xref), /* isConstant */ true),
   ]);
 
   // The "restore view" operation in listeners requires a call to `resetView` to reset the