hadrian source-dist target looks suspicious

Has anyone verified that the source-dist target implemented in hadrian produces the correct output?

When I run the target, it quickly fails because the iserv directory doens't exist.

Error when running Shake build system:
  at want, called at src/Main.hs:75:30 in main:Main
* Depends on: source-dist
  at need, called at src/Rules/SourceDist.hs:18:9 in main:Rules.SourceDist
* Depends on: sdistprep/ghc-8.9.0.20190612-src.tar.xz
  at apply1, called at src/Development/Shake/Internal/Rules/Oracle.hs:159:32 in shake-0.18.2-0392a442bcb46d33094c35faa3fdf1bf54150a9904de548fd5d2d9310226ffad:Development.Shake.Internal.Rules.Oracle
* Depends on: OracleQ (DirectoryContents (Not (Or [Test "//.*",Test "//#*",Test "//*-SAVE",Test "//*.orig",Test "//*.rej",Test "//*~",Test "//autom4te*",Test "//dist",Test "//dist-install",Test "//log",Test "//stage0",Test "//stage1",Test "//stage2",Test "//stage3",Test "hadrian/.cabal-sandbox",Test "hadrian/.stack-work",Test "hadrian/UserSettings.hs",Test "hadrian/cabal.sandbox.config",Test "hadrian/cfg/system.config",Test "hadrian/bin",Test "hadrian/dist",Test "hadrian/dist-newstyle",Test "libraries//*.buildinfo",Test "libraries//GNUmakefile",Test "libraries//config.log",Test "libraries//config.status",Test "libraries//configure",Test "libraries//ghc.mk",Test "libraries//include/Hs*Config.h",Test "libraries/dph",Test "libraries/primitive",Test "libraries/random",Test "libraries/stm",Test "libraries/vector",Test "mk/build.mk"]),"iserv"))
* Raised the exception:
iserv: getDirectoryContents:openDirStream: does not exist (No such file or directory)

It seems to blindly copy all the files in certain directories so in the likely situation where I have a dirty build tree the target will produce a tarball with these dirty files.

Thinking about #16860 (closed), there doens't appear to be any logic to generate Lexer.hs or Happy.hs.