Add --config flag to diagnose command

Users can specify where they hold the AppSignal client config in their
apps using the `--config` flag. This value if given will be taken into
account to preload the file and to validate the config.

.changesets/add---config-flag-to-diagnose-command.md

@@ -0,0 +1,7 @@
+---
+bump: "patch"
+type: "add"
+---
+
+Add the --config flag to diagnose command to specify a custom path for your AppSignal configuration file to
+be taken into account when running the diagnose of your AppSignal installation.

src/diagnose.ts

@@ -158,7 +158,8 @@ export class DiagnoseTool {
         path: logFilePath ? path.dirname(logFilePath) : ""
       },
       "appsignal.cjs": {
-        path: Configuration.clientFilePath || ""
+        path:
+          this.getCustomClientFilePath() || Configuration.clientFilePath || ""
       },
       "appsignal.log": {
         path: logFilePath || "",
@@ -217,13 +218,15 @@ export class DiagnoseTool {
    * object from the initialized client. Otherwise, return a default config object.
    */
   private getConfigObject(): Configuration {
+    const clientFilePath =
+      this.getCustomClientFilePath() || Configuration.clientFilePath
     // The file is required to execute the client initialization
     // that stores the config object on the global object, making
     // it available calling `Client.config` later.
-    if (Configuration.clientFilePath) {
+    if (clientFilePath) {
       process.env._APPSIGNAL_DIAGNOSE = "true"
       try {
-        require(Configuration.clientFilePath)
+        require(clientFilePath)
       } catch (e: any) {
         Client.integrationLogger.error(
           `Error loading AppSignal client file ${e.message}`
@@ -273,6 +276,20 @@ export class DiagnoseTool {
     )
   }
 
+  private getCustomClientFilePath() {
+    const flagIndex = process.argv.indexOf("--config")
+
+    if (flagIndex !== -1 && flagIndex + 1 < process.argv.length) {
+      const filePath = process.argv[flagIndex + 1]
+
+      if (path.isAbsolute(filePath)) {
+        return filePath
+      } else {
+        return path.resolve(filePath)
+      }
+    }
+  }
+
   public async sendReport(data: Record<string, any>) {
     data.config.options = this.getConfigData()
     data.config.sources = this.getSources()