feat(#136): adds '_extensionName' option on ParsingExtension to avoid duplicate runs

Author: joelgallant

app-config-core/src/parsed-value.test.ts

@@ -60,6 +60,22 @@ describe('parseValue', () => {
     return false;
   };
 
+  const appendExtension = (suffix: string): ParsingExtension => (value) => {
+    if (typeof value === 'string') {
+      return (parse) => parse(value + suffix);
+    }
+
+    return false;
+  };
+
+  const namedAppendExtension = (suffix: string): ParsingExtension => {
+    const extension = appendExtension(suffix);
+
+    return Object.assign(extension, {
+      extensionName: 'namedAppendExtension',
+    });
+  };
+
   const secretExtension: ParsingExtension = (_, [keyType, key]) => {
     if (keyType === InObject && key === '$secret') {
       return (parse) => parse('revealed!', { shouldFlatten: true });
@@ -175,11 +191,21 @@ describe('parseValue', () => {
   it('allows the same extension to be applied twice', async () => {
     const source = new LiteralSource('string');
     const parsed = await parseValue(await source.readValue(), source, [
-      uppercaseExtension,
-      uppercaseExtension,
+      appendExtension('-appended'),
+      appendExtension('-appended2'),
+    ]);
+
+    expect(parsed.toJSON()).toEqual('string-appended-appended2');
+  });
+
+  it('respects extensionName', async () => {
+    const source = new LiteralSource('string');
+    const parsed = await parseValue(await source.readValue(), source, [
+      namedAppendExtension('-appended'),
+      namedAppendExtension('-appended2'),
     ]);
 
-    expect(parsed.toJSON()).toEqual('STRING');
+    expect(parsed.toJSON()).toEqual('string-appended');
   });
 
   it('allows the same extension apply at different levels of a tree', async () => {

app-config-core/src/parsed-value.ts

@@ -17,11 +17,18 @@ export type ParsingExtensionKey =
   | [typeof InArray, number]
   | [typeof Root];
 
-export type ParsingExtension = (
-  value: Json,
-  key: ParsingExtensionKey,
-  context: ParsingExtensionKey[],
-) => false | ParsingExtensionTransform;
+export interface ParsingExtension {
+  (value: Json, key: ParsingExtensionKey, context: ParsingExtensionKey[]):
+    | ParsingExtensionTransform
+    | false;
+
+  /**
+   * A globally unique string that identifies what parsing extension this is.
+   *
+   * Used to avoid running the same extension twice when included twice.
+   */
+  extensionName?: string;
+}
 
 export type ParsingExtensionTransform = (
   parse: (
@@ -351,7 +358,7 @@ async function parseValueInner(
   context: ParsingExtensionKey[],
   root: Json,
   parent?: JsonObject | Json[],
-  visitedExtensions: ParsingExtension[] = [],
+  visitedExtensions: Set<ParsingExtension | string> = new Set(),
 ): Promise<ParsedValue> {
   const [currentKey] = context.slice(-1);
   const contextualKeys = context.slice(0, context.length - 1);
@@ -367,13 +374,20 @@ async function parseValueInner(
   // for this reason, we pass "parse" as a function to extensions, so they can recurse as needed
   for (const extension of extensions) {
     // we track visitedExtensions so that calling `parse` in an extension doesn't hit that same extension with the same value
-    if (visitedExtensions.includes(extension)) continue;
+    if (visitedExtensions.has(extension)) continue;
+    if (extension.extensionName && visitedExtensions.has(extension.extensionName)) continue;
 
     const applicable = extension(value, currentKey, contextualKeys);
 
-    if (applicable && !applicableExtension) {
+    if (applicable) {
       applicableExtension = applicable;
-      visitedExtensions.push(extension);
+      visitedExtensions.add(extension);
+
+      if (extension.extensionName) {
+        visitedExtensions.add(extension.extensionName);
+      }
+
+      break;
     }
   }
 

app-config-extension-utils/src/index.ts

@@ -14,6 +14,12 @@ export function composeExtensions(extensions: ParsingExtension[]): ParsingExtens
   };
 }
 
+export function named(name: string, parsingExtension: ParsingExtension): ParsingExtension {
+  Object.defineProperty(parsingExtension, '_extensionName', { value: name });
+
+  return parsingExtension;
+}
+
 export function forKey(
   key: string | string[],
   parsingExtension: ParsingExtension,