Add a reusable '0' literal for the module transform

Author: rbuckton

src/compiler/factory/emitNode.ts

@@ -2,6 +2,8 @@ namespace ts {
     /**
      * Associates a node with the current transformation, initializing
      * various transient transformation properties.
+     * 
+     * This function should only be called when writing to an emit node.
      * @internal
      */
     export function getOrCreateEmitNode(node: Node): EmitNode {
@@ -20,6 +22,9 @@ namespace ts {
 
             node.emitNode = {} as EmitNode;
         }
+        else {
+            Debug.assert(!(node.emitNode?.flags! & EmitFlags.Reusable), "Invalid attempt to modify a reusable node.");
+        }
 
         return node.emitNode;
     }

src/compiler/factory/utilities.ts

@@ -18,7 +18,7 @@ namespace ts {
                     : factory.createElementAccessExpression(target, memberName),
                 memberName
             );
-            getOrCreateEmitNode(expression).flags |= EmitFlags.NoNestedSourceMaps;
+            addEmitFlags(expression, EmitFlags.NoNestedSourceMaps);
             return expression;
         }
     }
@@ -479,8 +479,7 @@ namespace ts {
 
             if (create) {
                 const parseNode = getOriginalNode(node, isSourceFile);
-                const emitNode = getOrCreateEmitNode(parseNode);
-                return emitNode.externalHelpersModuleName || (emitNode.externalHelpersModuleName = factory.createUniqueName(externalHelpersModuleNameText));
+                return parseNode?.emitNode?.externalHelpersModuleName || (getOrCreateEmitNode(parseNode).externalHelpersModuleName = factory.createUniqueName(externalHelpersModuleNameText));
             }
         }
     }

src/compiler/transformers/module/module.ts

@@ -42,6 +42,7 @@ namespace ts {
         context.enableSubstitution(SyntaxKind.ShorthandPropertyAssignment); // Substitutes shorthand property assignments for imported/exported symbols.
         context.enableEmitNotification(SyntaxKind.SourceFile); // Restore state when substituting nodes in a file.
 
+        let zeroLiteral: NumericLiteral | undefined;
         const moduleInfoMap: ExternalModuleInfo[] = []; // The ExternalModuleInfo for each file.
         const deferredExports: (Statement[] | undefined)[] = []; // Exports to defer until an EndOfDeclarationMarker is found.
 
@@ -1811,16 +1812,22 @@ namespace ts {
             return result;
         }
 
+        function getZeroLiteral() {
+            zeroLiteral ||= factory.createNumericLiteral(0);
+            setEmitFlags(zeroLiteral, EmitFlags.Reusable);
+            return zeroLiteral;
+        }
+
         function substituteCallExpression(node: CallExpression) {
             if (isIdentifier(node.expression) && getImportOrExportBindingReference(node.expression, /*removeEntry*/ false)) {
                 return isCallChain(node) ?
                     factory.updateCallChain(node,
-                        setTextRange(factory.createComma(factory.createNumericLiteral(0), node.expression), node.expression),
+                        setTextRange(factory.createComma(getZeroLiteral(), node.expression), node.expression),
                         node.questionDotToken,
                         /*typeArguments*/ undefined,
                         node.arguments) :
                     factory.updateCallExpression(node,
-                        setTextRange(factory.createComma(factory.createNumericLiteral(0), node.expression), node.expression),
+                        setTextRange(factory.createComma(getZeroLiteral(), node.expression), node.expression),
                         /*typeArguments*/ undefined,
                         node.arguments);
             }
@@ -1831,7 +1838,7 @@ namespace ts {
             if (isIdentifier(node.tag) && getImportOrExportBindingReference(node.tag, /*removeEntry*/ false)) {
                 return factory.updateTaggedTemplateExpression(
                     node,
-                    setTextRange(factory.createComma(factory.createNumericLiteral(0), node.tag), node.tag),
+                    setTextRange(factory.createComma(getZeroLiteral(), node.tag), node.tag),
                     /*typeArguments*/ undefined,
                     node.template);
             }

src/compiler/types.ts

@@ -6624,6 +6624,7 @@ namespace ts {
         /*@internal*/ TypeScriptClassWrapper = 1 << 25, // The node is an IIFE class wrapper created by the ts transform.
         /*@internal*/ NeverApplyImportHelper = 1 << 26, // Indicates the node should never be wrapped with an import star helper (because, for example, it imports tslib itself)
         /*@internal*/ IgnoreSourceNewlines = 1 << 27,   // Overrides `printerOptions.preserveSourceNewlines` to print this node (and all descendants) with default whitespace.
+        /*@internal*/ Reusable = 1 << 28,       // Marks this node as reusable across multiple transforms. Once marked reusable, no other emit flags or emit node values may be modified.
     }
 
     export interface EmitHelperBase {