When I'm compiling GHC, and I get a type error, Hadrian helpfully tells me the command line that broke. I often copy/paste that command line to re-run it, for two reasons: * It is much much faster than running Hadrian from scratch, as I repeatedly try to compile the same source file. * More important, when building libraries or the stage2 compiler, I often want to add lots of debug or tracing flags to the command line, so I can find what is wrong with the stage1 compiler. This is utterly essential. * Indeed I often make a deliberate syntax error in (say) a library module, run Hadrian, watch it fall over with that syntax error, *so I get the command line*. Then I fix the deliberate error and repeatedly compile that one file with lots of tracing. But a recent change to Hadrian had broken this plan. Now the command line that appears looks like this: ``` simonpj@PF55P26D:~/code/HEAD-31$ /home/simonpj/.ghcup/bin/ghc -Wall -hisuf hi -osuf o -hcsuf hc -static -hide-all-packages -no-user-package-db '-package-env -' '-package-db _build/stage0/inplace/package.conf.d' '-this-unit-id ghc-10.1-inplace' '-this-package-name ghc' '-package-id array-0.5.8.0-9044' '-package-id base-4.21.0.0-ae91' '-package-id binary-0.8.9.3-25e5' '-package-id bytestring-0.12.2.0-7dd0' '-package-id containers-0.7-5a8f' '-package-id deepseq-1.5.1.0-6837' '-package-id directory-1.3.10.1-inplace' '-package-id exceptions-0.10.9-4d2e' '-package-id filepath-1.5.4.0-inplace' '-package-id ghc-boot-10.1-inplace' '-package-id ghc-boot-th-next-10.1-inplace' '-package-id ghc-heap-9.12.2-4363' '-package-id ghc-toolchain-0.1.0.0-inplace' '-package-id ghci-10.1-inplace' '-package-id hpc-0.7.0.2-inplace' '-package-id os-string-2.0.8-inplace' '-package-id process-1.6.26.1-inplace' '-package-id rts-1.0.2' '-package-id semaphore-compat-1.0.0-inplace' '-package-id stm-2.5.3.1-d35b' '-package-id text-2.1.2-ecdb' '-package-id time-1.15-inplace' '-package-id transformers-0.6.1.2-38b1' '-package-id unix-2.8.8.0-inplace' -i -i/home/simonpj/code/HEAD-31/_build/stage0/compiler/build -i/home/simonpj/code/HEAD-31/_build/stage0/compiler/build/autogen -i/home/simonpj/code/HEAD-31/compiler/ -I_build/stage0/compiler/build -I_build/stage0/compiler/build/. -Icompiler/. -I/home/simonpj/code/HEAD-31/libraries/process/include -I/home/simonpj/code/HEAD-31/_build/stage0/libraries/process/build/include -I/home/simonpj/code/HEAD-31/libraries/directory -I/home/simonpj/code/HEAD-31/_build/stage0/libraries/directory/build -I/home/simonpj/code/HEAD-31/libraries/unix/include -I/home/simonpj/code/HEAD-31/_build/stage0/libraries/unix/build/include -I/home/simonpj/code/HEAD-31/libraries/time/lib/include -I/home/simonpj/code/HEAD-31/_build/stage0/libraries/time/build/lib/include -I/home/simonpj/.ghcup/ghc/9.12.2/lib/ghc-9.12.2/lib/x86_64-linux-ghc-9.12.2-a828/bytestring-0.12.2.0-7dd0/include -I/home/simonpj/.ghcup/ghc/9.12.2/lib/ghc-9.12.2/lib/x86_64-linux-ghc-9.12.2-a828/ghc-internal-9.1202.0-1465/include -I/home/simonpj/.ghcup/ghc/9.12.2/lib/ghc-9.12.2/lib/x86_64-linux-ghc-9.12.2-a828/ghc-bignum-1.3-6db4/include -I/home/simonpj/.ghcup/ghc/9.12.2/lib/ghc-9.12.2/lib/x86_64-linux-ghc-9.12.2-a828/rts-1.0.2/include -optP-include -optP_build/stage0/compiler/build/autogen/cabal_macros.h -optP-DCAN_LOAD_DLL -outputdir _build/stage0/compiler/build -fdiagnostics-color=always -Wall -Wno-name-shadowing -Wnoncanonical-monad-instances -Wnoncanonical-monoid-instances -XGHC2024 -XNoImplicitPrelude -optc-Wno-error=inline -c -o _build/stage0/compiler/build/GHC/Core.o -DDEBUG -haddock -fno-warn-deprecated-flags -O +RTS -O64M -RTS -O2 @/tmp/extra-file-9558430904709-115211-0 ``` That `@/tmp/extra-file-9558430904709-115211-0` at the end points to a "response file" which contains... just the string `compiler/GHC/Core`. But Hadrian deletes the response file, so I cannot re-run the command. I can add `-r` to the Hadrian command `hadrian/build -r`. But then I a response file kept for every GHC invocation, so my root-directory fills up with tens of thousands of response files. I'm sure there is a good reason for the change, which is [this commit](https://gitlab.haskell.org/ghc/ghc/-/merge_requests/15891). But it would be helpful to find another way to solve the problem.