Error compiling Unreal Engine 4.25 on ubuntu focal

Question

I have been following the linux setup guide for UE4.

Everything worked out fine until the call to make (Last step of "3 - Building UE4 on Linux").

The output for the build is the following:

Performing 37 actions (10 in parallel)
[4/37] Compile Module.TraceLog.cpp
[1/37] Compile PCH.Core.h
[6/37] Compile Module.UnrealHeaderTool.cpp
[2/37] Compile PCH.CoreUObject.h
[3/37] Compile BuildSettings.cpp
[5/37] Compile SharedPCH.Core.ShadowErrors.h
[7/37] Link (lld) libUnrealHeaderTool-BuildSettings.so
[8/37] Compile Module.Json.cpp
[9/37] Compile Module.Projects.cpp
[10/37] Compile Module.Core.1_of_13.cpp
[11/37] Compile Module.Core.2_of_13.cpp
[12/37] Compile Module.Core.3_of_13.cpp
[13/37] Compile Module.Core.4_of_13.cpp
[14/37] Compile Module.Core.10_of_13.cpp
[15/37] Compile Module.Core.6_of_13.cpp
[16/37] Compile Module.Core.8_of_13.cpp
[17/37] Compile Module.Core.5_of_13.cpp
[18/37] Compile Module.Core.9_of_13.cpp
[19/37] Compile Module.Core.11_of_13.cpp
[20/37] Compile Module.Core.13_of_13.cpp
[21/37] Compile Module.Core.12_of_13.cpp
[22/37] Compile Module.Core.7_of_13.cpp
[23/37] Link (lld) libUnrealHeaderTool-TraceLog.so
[24/37] Compile Module.CoreUObject.7_of_8.cpp
[25/37] Compile Module.CoreUObject.5_of_8.cpp
[26/37] Compile Module.CoreUObject.4_of_8.cpp
[27/37] Compile Module.CoreUObject.3_of_8.cpp
[28/37] Compile Module.CoreUObject.2_of_8.cpp
[29/37] Compile Module.CoreUObject.1_of_8.cpp
[30/37] Compile Module.CoreUObject.8_of_8.cpp
[31/37] Compile Module.CoreUObject.6_of_8.cpp
[32/37] Link (lld) libUnrealHeaderTool-Core.so
[33/37] Link (lld) libUnrealHeaderTool-Json.so
[34/37] Link (lld) libUnrealHeaderTool-Projects.so
[35/37] Link (lld) libUnrealHeaderTool-CoreUObject.so
[36/37] Link (lld) UnrealHeaderTool
[37/37] UnrealBuildTool.exe UnrealHeaderTool.target
Total time in Local executor: 107.91 seconds
Parsing headers for CrashReportClient
  Running UnrealHeaderTool CrashReportClient "/d/dev/UnrealEngine/Engine/Intermediate/Build/Linux/B4D820EA/CrashReportClient/Shipping/CrashReportClient.uhtmanifest" -LogCmds="loginit warning, logexit warning, logdatabase error" -Unattended -WarningsAsErrors -abslog="/d/dev/UnrealEngine/Engine/Programs/UnrealBuildTool/Log_UHT.txt"
Assertion failed: IsValidIndex(Index) [File:Runtime/Core/Public/Containers/UnrealString.h] [Line: 207] 
String index out of bounds: Index 1 from a string with a length of 1
LogCore: Error: appError called: Assertion failed: IsValidIndex(Index) [File:Runtime/Core/Public/Containers/UnrealString.h] [Line: 207]
String index out of bounds: Index 1 from a string with a length of 1
make: *** [Makefile:297: CrashReportClient-Linux-Shipping] Error 1

I have tried different branches (release, 4.25, 4.24), resetting fully the git repository and rebuilding, but it doesn't go any further as the error is not very explicit.

Any pointer would be appreciated.

Answer 1

The issue is due to a bug in the FPaths::MakePathRelativeTo implementation.

It is looking at the second character in the root folder (to see if it is a ':') but my disk is mounted under a single letter path. This can be fixed by re-mounting the disk in a folder with 2 or more characters.

Also, depending on your locale, you may want to force it to English to avoid some encoding and number format issues: export LC_ALL=en_US.utf8