Issue is on Nightly 58.0a1 (2017-10-02) and OSX 10.11.4. Once open the dev tool, would see the following error. --- WebConsolePanel open failed. undefined: Module `resource://devtools/client/shared/components/Frame.js` is not found at resource://devtools/client/shared/components/Frame.js console.error: WebConsolePanel open failed. undefined: Module `resource://devtools/client/shared/components/Frame.js` is not found at resource://devtools/client/shared/components/Frame.js Message: Module `resource://devtools/client/shared/components/Frame.js` is not found at resource://devtools/client/shared/components/Frame.js Stack: requireHook@resource://devtools/client/shared/browser-loader.js:132:14 @resource://devtools/client/webconsole/new-console-output/components/message.js:23:33 requireHook@resource://devtools/client/shared/browser-loader.js:132:14 @resource://devtools/client/webconsole/new-console-output/components/message-types/console-api-call.js:19:31 requireHook@resource://devtools/client/shared/browser-loader.js:132:14 @resource://devtools/client/webconsole/new-console-output/components/message-container.js:21:22 requireHook@resource://devtools/client/shared/browser-loader.js:132:14 @resource://devtools/client/webconsole/new-console-output/components/console-output.js:22:40 requireHook@resource://devtools/client/shared/browser-loader.js:132:14 @resource://devtools/client/webconsole/new-console-output/new-console-output-wrapper.js:16:43 requireHook@resource://devtools/client/shared/browser-loader.js:132:14 this.NewConsoleOutput@resource://devtools/client/webconsole/new-console-output/main.js:17:33 _initUI@resource://devtools/client/webconsole/new-webconsole.js:229:29 init@resource://devtools/client/webconsole/new-webconsole.js:80:5 WC_init@resource://devtools/client/webconsole/hudservice.js:369:12 HS_openWebConsole@resource://devtools/client/webconsole/hudservice.js:98:12 open/<@resource://devtools/client/webconsole/panel.js:79:16 process@resource://gre/modules/Promise-backend.js:922:23 walkerLoop@resource://gre/modules/Promise-backend.js:806:7 Promise*scheduleWalkerLoop@resource://gre/modules/Promise-backend.js:739:11 schedulePromise@resource://gre/modules/Promise-backend.js:770:7 completePromise@resource://gre/modules/Promise-backend.js:707:7 promise callback*completePromise@resource://gre/modules/Promise-backend.js:698:7 process@resource://gre/modules/Promise-backend.js:958:5 walkerLoop@resource://gre/modules/Promise-backend.js:806:7 Promise*scheduleWalkerLoop@resource://gre/modules/Promise-backend.js:739:11 schedulePromise@resource://gre/modules/Promise-backend.js:770:7 completePromise@resource://gre/modules/Promise-backend.js:707:7 open/<@resource://devtools/client/webconsole/panel.js:57:9 EventListener.handleEvent*open@resource://devtools/client/webconsole/panel.js:56:7 onLoad@resource://devtools/client/framework/toolbox.js:1665:19 ************************* A coding exception was thrown in a Promise resolution callback. See https://developer.mozilla.org/Mozilla/JavaScript_code_modules/Promise.jsm/Promise Full message: TypeError: panel is undefined Full stack: onLoad/<@resource://devtools/shared/base-loader.js -> resource://devtools/client/framework/toolbox.js:1681:13 process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:922:23 walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:806:7 Promise*scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:739:11 schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:770:7 completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:707:7 promise callback*completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:698:7 process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:958:5 walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:806:7 Promise*scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:739:11 schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:770:7 completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:707:7 open/<@resource://devtools/shared/base-loader.js -> resource://devtools/client/webconsole/panel.js:57:9 EventListener.handleEvent*open@resource://devtools/shared/base-loader.js -> resource://devtools/client/webconsole/panel.js:56:7 onLoad@resource://devtools/shared/base-loader.js -> resource://devtools/client/framework/toolbox.js:1665:19 *************************

I can't reproduce this on Nightly, but I think that's because I'm on 58.0a1 (2017-09-29) and not being offered another update. I do see this on a local build though, I'm not sure how the integration tests are passing

This looks like a require path error - it is probably related to Bug 1402394

Confirmed that backing out Bug 1402394 fixes the problem for me. But other folks in the devtools channel are not seeing this problem locally.

Alastor, just to double check - you are seeing this on a Nightly build and not a local build of mozilla-central? And if so, can you try running Nightly with the `-purgecaches` argument and see if it fixes the problem? This was fixed for me locally with a clobber build - although I don't think that a clobber should have been required as a result of https://hg.mozilla.org/mozilla-central/rev/941327d5a29b

Gregory, I can't find guidelines for when a clobber should be required but I don't think it should have been in this case - the changeset is only renaming some js files (https://hg.mozilla.org/mozilla-central/rev/941327d5a29b). Is that correct, or should we be clobbering in cases like this? I confirmed that backing out 941327d5a29b locally allowed devtools to open again, as did a clobber.

I use my own mozilla-central build, and `-purgecaches` doesn't help anymore. However, after doing '$./mach clobber' again, the issue is gone! Thanks for help!

(In reply to Alastor Wu [:alwu][please needinfo me][GMT+8] from comment #6) > I use my own mozilla-central build, and `-purgecaches` doesn't help anymore. > > However, after doing '$./mach clobber' again, the issue is gone! Thanks for > help! No problem - moving this into the build module as per Comment 5

I haven't looked at this in extreme detail. But my money is on a case-only rename. e.g. devtools/client/shared/components/splitter/draggable.js -> devtools/client/shared/components/splitter/Draggable.js, devtools/client/shared/components/tabs/tabs.css -> devtools/client/shared/components/tabs/Tabs.css, devtools/client/shared/components/frame.js -> devtools/client/shared/components/Frame.js. Case-only renames are a bit dangerous because not all filesystems are case sensitive or case preserving. So when a case-only rename is encountered, it can wreck havoc on tools, like build systems. There's not much we can do about case-only renames from the build system level. The best we can do is prevent them via a VCS hook. Bug 797962 tracks that. I don't see much value in keeping this bug open (it would likely linger indefinitely). So marking resolved.