fix(cli): allow creating new migration files with only the "extension" option

.changeset/unlucky-files-swim.md

@@ -0,0 +1,5 @@
+---
+'@emigrate/cli': patch
+---
+
+Fix a logical error that didn't allow creating new migration files with only the "extension" option

packages/cli/src/new-command.ts

@@ -37,24 +37,30 @@ export default async function newCommand({ directory, template, plugins = [], ex
     filename = `${getTimestampPrefix()}_${sanitizeMigrationName(name)}.${stripLeadingPeriod(
       extension ?? fileExtension,
     )}`;
-  } else if (plugins.length > 0) {
-    const generatorPlugin = await getOrLoadPlugin('generator', plugins);
-
-    if (!generatorPlugin) {
-      throw new Error('No generator plugin found, please specify a generator plugin using the plugin option');
   }
 
+  let hasGeneratedFile = Boolean(filename && content !== undefined);
+
+  if (plugins.length > 0 && !hasGeneratedFile) {
+    const generatorPlugin = await getOrLoadPlugin('generator', plugins);
+
+    if (generatorPlugin) {
       const generated = await generatorPlugin.generateMigration(name);
 
       filename = generated.filename;
       content = generated.content;
-  } else if (extension) {
+    }
+  }
+
+  hasGeneratedFile = Boolean(filename && content !== undefined);
+
+  if (extension && !hasGeneratedFile) {
     content = '';
     filename = `${getTimestampPrefix()}_${sanitizeMigrationName(name)}.${stripLeadingPeriod(extension)}`;
   }
 
   if (!filename || content === undefined) {
-    throw new Error('Unexpected error, missing filename or content for migration file');
+    throw new ShowUsageError('No generator plugin found, please specify a generator plugin using the plugin option');
   }
 
   const directoryPath = path.resolve(process.cwd(), directory);