doc/bugs/Build_failure__58___language-javascript-0.7.1.0.mdwn

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+### Please describe the problem.
+
+Building the latest version from source, whatever method I use eventually fails on the language-javascript-0.7.1.0 dependency. The error (stack output):
+
+language-javascript              > Configuring language-javascript-0.7.1.0...
+language-javascript              > build
+language-javascript              > Preprocessing library for language-javascript-0.7.1.0..
+language-javascript              > happy: src/Language/JavaScript/Parser/Grammar7.y: hGetContents: invalid argument (invalid byte sequence)
+unordered-containers             > [6 of 9] Compiling Data.HashSet.Internal
+
+### What steps will reproduce the problem?
+
+1. Install ghc 8.10.7 via ghcup
+2. Check out latest source
+3. Issue any of the supported build commands, watch the failure eventually happen
+
+### What version of git-annex are you using? On what operating system?
+
+git master (tag 8.20211123 has the same issue)
+
+### Please provide any additional information below.
+
+[[!format sh """
+# If you can, paste a complete transcript of the problem occurring here.
+# If the problem is with the git-annex assistant, paste in .git/annex/daemon.log
+
+
+# End of transcript or log.
+"""]]
+
+### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)
+
+Yes, it's wonderful.