Xcode failed to emit precompiled header?

问题

thanks in advance for the help you will give me.

I have searched this for half a day over the internet yesterday and two hours now and I haven't found anything (more than those two links that did not help FMDatabase.h not found when using route-me library & Failed to emit precompiled header for bridging header)

So here is my problem : I just had in hands a project that a previous developer has been working on, and when I try to launch it, here I have two errors :

failed to emit precompiled header '/Users/me/Library/Developer/Xcode/DerivedData/Alavoc-arfzuirebtfstncdztyvgvtpcbgw/Build/Intermediates.noindex/PrecompiledHeaders/Alavoc-Bridging-Header-swift_1I75NH5N40QPS-clang_30E4RG2TSVLXF.pch' for bridging header '/Users/me/Downloads/Alavoc-ios-master/Alavoc/bridge/Alavoc-Bridging-Header.h'

/Users/me/Downloads/Alavoc-ios-master/Alavoc/externalLib/customClass/customClassViewController.h:13:9: error: 'FMDB/FMDB.h' file not found

There is also one fatal error wroten like this (even if I only have two errors counted, this one appears in the log above the two other ones previously described)

fatal error: module file '/Users/me/Library/Developer/Xcode/DerivedData/ModuleCache/30E4RG2TSVLXF/Foundation-3DFYNEBRQSXST.pcm' is out of date and needs to be rebuilt: signature mismatch note: imported by '/Users/me/Library/Developer/Xcode/DerivedData/Alavoc-arfzuirebtfstncdztyvgvtpcbgw/Build/Intermediates.noindex/PrecompiledHeaders/Alavoc-Bridging-Header-swift_1I75NH5N40QPS-clang_30E4RG2TSVLXF.pch' /Users/me/Downloads/Alavoc-ios-master/Alavoc/bridge/Alavoc-Bridging-Header.h:13:9: note: in file included from /Users/me/Downloads/Alavoc-ios-master/Alavoc/bridge/Alavoc-Bridging-Header.h:13: #import "customClassViewController.h"

customClassViewController.h line 13 :

#import <FMDB/FMDB.h>

I guess those errors are linked. Do you have any idea where it could come from ?

Thanks in advance for your help guys, I really appreciate it!

Edit for battlmonster (new errors) :

Here are the two errros (file not found (in Alavoc-Bridging-Header.h FMDB.h not found)) and failed to emit precompiled header :

fatal error: file '/Users/me/Downloads/Alavoc-ios-master/Alavoc/bridge/Alavoc-Bridging-Header.h' has been modified since the precompiled header '/Users/me/Library/Developer/Xcode/DerivedData/Alavoc-arfzuirebtfstncdztyvgvtpcbgw/Build/Intermediates.noindex/PrecompiledHeaders/Alavoc-Bridging-Header-swift_1I75NH5N40QPS-clang_30E4RG2TSVLXF.pch' was built note: please rebuild precompiled header '/Users/me/Library/Developer/Xcode/DerivedData/Alavoc-arfzuirebtfstncdztyvgvtpcbgw/Build/Intermediates.noindex/PrecompiledHeaders/Alavoc-Bridging-Header-swift_1I75NH5N40QPS-clang_30E4RG2TSVLXF.pch' /Users/me/Downloads/Alavoc-ios-master/Alavoc/bridge/Alavoc-Bridging-Header.h:29:9: error: 'FMDB/FMDB.h' file not found

import
    ^ 1 error generated. <unknown>:0: error: failed to emit precompiled header
'/Users/me/Library/Developer/Xcode/DerivedData/Alavoc-arfzuirebtfstncdztyvgvtpcbgw/Build/Intermediates.noindex/PrecompiledHeaders/Alavoc-Bridging-Header-swift_1I75NH5N40QPS-clang_30E4RG2TSVLXF.pch' for bridging header '/Users/me/Downloads/Alavoc-ios-master/Alavoc/bridge/Alavoc-Bridging-Header.h'

回答1:

This error is about a malformed bridging header. The bridging header is a special header file which lists all Objective-C header files with classes that must be accessible from Swift code. All the bridging header definitions are precompiled in a way to be ready to use from Swift. In your case the bridging header is "Alavoc/bridge/Alavoc-Bridging-Header.h", and it includes a header for customClassViewController.h (from Alavoc/externalLib/customClass), which indicates that your fellow developer wants that customClassViewController is accessible in Swift code.

Now the confusing thing about the bridging header is that it is not recursively including everything, i.e. it just looks on the first level of definitions, and if you import something in your import that you want in Swift, you have to add it to the bridging header explicitly, or else you'll probably get a warning (or an error sometimes). Say you have #import "A.h" in the bridging header, and you have #import "B.h" inside "A.h", then you likely would have to add "B.h" to the bridging header as well.

Now in your example A = customClassViewController, and B = FMDB, and normally you would need to add FMDB to the bridging header, but the thing is that you most likely don't want exporting FMDB to Swift via your bridging header, because it is not meant for this (it is for your own objc code and not for 3rd party libs).

The solution would be to remove line 13 from your "customClassViewController.h". This would likely fix the bridging header compilation, but probably break the customClassViewController, so you need to include FMDB in "customClassViewController.m" and most likely adapt the "customClassViewController.h" to not have anything related to FMDB (or forward-declare those usages with @class X;).

If you move #import <FMDB/FMDB.h> to your implementation (.m) files and still get error: 'FMDB/FMDB.h' file not found, it is likely about FMDB path not being listed in your header search paths.

To solve the last one just include the right path in your "Header Search Paths" in Xcode build settings. Let's say FMDB is located at /Users/me/Downloads/Alavoc-ios-master/Alavoc/ASDASD/FMDB (and you have /Users/me/Downloads/Alavoc-ios-master/Alavoc/ASDASD/FMDB/FMDB.h inside), Then you need to open Xcode project settings - select your target on the left - select "Build Settings" on the top - find "Header Search Paths" setting and add /Users/me/Downloads/Alavoc-ios-master/Alavoc/ASDASD path