swiftLanguageVersions contains non int element

[RLovelett]

When opening the Argo repository I am getting the following error.

Fatal error: swiftLanguageVersions contains non int element: file /home/rlovelett/Source/langserver-swift/.build/checkouts/swift-package-manager.git--2409619289911516842/Sources/PackageLoading/PackageDescription4Loader.swift, line 72
Current stack trace:
0    libswiftCore.so                    0x00007f7d3c58567d <unavailable> + 5518973
1    libswiftCore.so                    0x00007f7d3c5855e0 swift_reportError + 27
2    libswiftCore.so                    0x00007f7d3c65e5f0 _swift_stdlib_reportFatalErrorInFile + 191
3    libswiftCore.so                    0x00007f7d3c1c4d0d <unavailable> + 1584397
4    libswiftCore.so                    0x00007f7d3c56db32 <unavailable> + 5421874
5    libswiftCore.so                    0x00007f7d3c1c368c <unavailable> + 1578636
6    libswiftCore.so                    0x00007f7d3c56db71 <unavailable> + 5421937
7    libswiftCore.so                    0x00007f7d3c1c36a0 StaticString.withUTF8Buffer<A>(_:) + 1122
8    libswiftCore.so                    0x00007f7d3c1c4675 <unavailable> + 1582709
9    libswiftCore.so                    0x00007f7d3c56da7d <unavailable> + 5421693
10   libswiftCore.so                    0x00007f7d3c1c4d36 <unavailable> + 1584438
11   libswiftCore.so                    0x00007f7d3c56dace <unavailable> + 5421774
12   libswiftCore.so                    0x00007f7d3c1c4d80 String._withUnsafeBufferPointerToUTF8<A>(_:) + 335
13   libswiftCore.so                    0x00007f7d3c1c4491 <unavailable> + 1582225
14   libswiftCore.so                    0x00007f7d3c4bf5ba <unavailable> + 4707770
15   libswiftCore.so                    0x00007f7d3c1c368c <unavailable> + 1578636
16   libswiftCore.so                    0x00007f7d3c4bf601 <unavailable> + 4707841
17   libswiftCore.so                    0x00007f7d3c1c36a0 StaticString.withUTF8Buffer<A>(_:) + 1122
18   libswiftCore.so                    0x00007f7d3c1c1500 _assertionFailure(_:_:file:line:flags:) + 434
19   libSwiftPM.so                      0x00007f7d3b542803 <unavailable> + 2660355
20   libSwiftPM.so                      0x00007f7d3b54284c <unavailable> + 2660428
21   libSwiftPM.so                      0x00007f7d3b544a6b <unavailable> + 2669163
22   libswiftCore.so                    0x00007f7d3c1857e0 Collection.map<A>(_:) + 1972
23   libSwiftPM.so                      0x00007f7d3b53d726 <unavailable> + 2639654
24   libSwiftPM.so                      0x00007f7d3b53c060 loadPackageDescription4(_:baseURL:) + 134
25   libSwiftPM.so                      0x00007f7d3b50b0d0 ManifestLoader.loadFile(path:baseURL:version:manifestVersion:fileSystem:) + 3109
26   libSwiftPM.so                      0x00007f7d3b50ada0 ManifestLoader.load(packagePath:baseURL:version:manifestVersion:fileSystem:) + 589
27   libSwiftPM.so                      0x00007f7d3b50ef08 <unavailable> + 2449160
28   libSwiftPM.so                      0x00007f7d3b50a990 ManifestLoaderProtocol.load(package:baseURL:version:manifestVersion:fileSystem:) + 140
29   libSwiftPM.so                      0x00007f7d3b62d44e <unavailable> + 3621966
30   libSwiftPM.so                      0x00007f7d3b63c11e <unavailable> + 3682590
31   libSwiftPM.so                      0x00007f7d3b62d6fa <unavailable> + 3622650
32   libSwiftPM.so                      0x00007f7d3b63c16b <unavailable> + 3682667
33   libSwiftPM.so                      0x00007f7d3b5b06c0 DiagnosticsEngine.wrap<A>(with:_:) + 105
34   libSwiftPM.so                      0x00007f7d3b629654 <unavailable> + 3606100
35   libSwiftPM.so                      0x00007f7d3b6293d7 <unavailable> + 3605463
36   libSwiftPM.so                      0x00007f7d3b638701 <unavailable> + 3667713
37   libSwiftPM.so                      0x00007f7d3b6296d7 <unavailable> + 3606231
38   libSwiftPM.so                      0x00007f7d3b63874b <unavailable> + 3667787
39   libswiftCore.so                    0x00007f7d3c395890 Sequence._compactMap<A>(_:) + 911
40   libswiftCore.so                    0x00007f7d3c395790 Sequence.compactMap<A>(_:) + 145
41   libSwiftPM.so                      0x00007f7d3b625680 Workspace.loadRootManifests(packages:diagnostics:) + 348
42   libSwiftPM.so                      0x00007f7d3b622313 <unavailable> + 3576595
43   libSwiftPM.so                      0x00007f7d3b6283f0 Workspace.loadPackageGraph(root:createMultipleTestProducts:diagnostics:) + 200
44   (null)                             0x000056547302b7b9 <unavailable> + 878521
45   (null)                             0x000056547302ab6f <unavailable> + 875375
46   (null)                             0x000056547302a96c <unavailable> + 874860
47   (null)                             0x0000565472ffec24 <unavailable> + 695332
48   (null)                             0x00005654730027be <unavailable> + 710590
49   libdispatch.so                     0x00007f7d3d55455e <unavailable> + 263518
50   libdispatch.so                     0x00007f7d3d563877 <unavailable> + 325751
51   libdispatch.so                     0x00007f7d3d5545f4 <unavailable> + 263668
52   libdispatch.so                     0x00007f7d3d57f805 <unavailable> + 440325
53   libdispatch.so                     0x00007f7d3d573e69 <unavailable> + 392809
54   libdispatch.so                     0x00007f7d3d573ec7 <unavailable> + 392903
55   libdispatch.so                     0x00007f7d3d590a1a <unavailable> + 510490
56   libdispatch.so                     0x00007f7d3d592091 <unavailable> + 516241
57   libdispatch.so                     0x00007f7d3d594957 <unavailable> + 526679
58   libdispatch.so                     0x00007f7d3d593d06 <unavailable> + 523526
59   libdispatch.so                     0x00007f7d3d59078c <unavailable> + 509836
60   libdispatch.so                     0x00007f7d3d592091 <unavailable> + 516241
61   libdispatch.so                     0x00007f7d3d594957 <unavailable> + 526679
62   libdispatch.so                     0x00007f7d3d593d06 <unavailable> + 523526
63   libdispatch.so                     0x00007f7d3d59078c <unavailable> + 509836
64   libdispatch.so                     0x00007f7d3d59aeed <unavailable> + 552685
65   libdispatch.so                     0x00007f7d3d59a98c <unavailable> + 551308
66   libpthread.so.0                    0x00007f7d3be2a594 <unavailable> + 30100
67   libc.so.6                          0x00007f7d3a6b5fd0 clone + 63
[Info  - 9:07:46 AM] Connection to server got closed. Server will restart.