In reply to @p14:matrix.org
I want to try and debug the lack of an $AR variable set while building a package without incurring a full rebuild. Is there a good way to turn on tracing (set -x) while all the setup scripts run for nix develop? (context: https://github.com/NixOS/nixpkgs/pull/246577#issuecomment-1672980907)

My repro is to insert NIX_DEBUG = if bintoolsName == "llvm-binutils" then 6 else null; onto pkgs/build-support/bintools-wrapper/default.nix and then build for example pkgsLLVM.llvmPackages_15.compiler-rt-no-libc.stdenv.cc. It results in:

x86_64-unknown-linux-gnu-clang-wrapper> /nix/store/mldrk9c17hjsqjv938hp1192i7f56844-x86_64-unknown-linux-gnu-llvm-binutils-wrapper-15.0.7/nix-support/setup-hook: line 1: /nix/store/yl01rd58vp4m8bbhkihpk132cprfmx6f-expand-response-params/bin/expand-response-params: Permission denied

And the first line of setup-hook reads:

@expandResponseParams@ -> /nix/store/yl01rd58vp4m8bbhkihpk132cprfmx6f-expand-response-params/bin/expand-response-params

Wow, this is unfortunate. If I build:

nix build --rebuild pkgsLLVM.llvmPackages_15.compiler-rt-no-libc.stdenv.cc.bintools

I get:

-r--r--r-- 1 root root 0 Jan  1  1970 result/nix-support/setup-hook

Now if I try to determine why setup-hook is empty by setting the preHook to include 'set -x', then, it's non-empty and works correctly:

preHook = if bintoolsName == "llvm-binutils" then "set -x" else null;

What's going on?

Wow, this is unfortunate. If I build:

nix build --rebuild pkgsLLVM.llvmPackages_15.compiler-rt-no-libc.stdenv.cc.bintools

I get:

-r--r--r-- 1 root root 0 Jan  1  1970 result/nix-support/setup-hook

Now if I try to determine why setup-hook is empty by setting the preHook to include 'set -x', then, it's non-empty and works correctly:

preHook = if bintoolsName == "llvm-binutils" then "set -x" else null;

I end up with:

-r--r--r-- 1 root root 4781 Jan  1  1970 result/nix-support/setup-hook


What's going on?

Wow, this is unfortunate. If I build:

nix build --rebuild pkgsLLVM.llvmPackages_15.compiler-rt-no-libc.stdenv.cc.bintools

I get:

-r--r--r-- 1 root root 0 Jan  1  1970 result/nix-support/setup-hook

Now if I try to determine why setup-hook is empty by setting the preHook to include 'set -x', then, it's non-empty and works correctly:

preHook = if bintoolsName == "llvm-binutils" then "set -x" else null;

I end up with:

-r--r--r-- 1 root root 4781 Jan  1  1970 result/nix-support/setup-hook

What's going on?

Wow, this is unfortunate. If I build:

nix build --rebuild pkgsLLVM.llvmPackages_15.compiler-rt-no-libc.stdenv.cc.bintools```

I get:

-r--r--r-- 1 root root 0 Jan 1 1970 result/nix-support/setup-hook

Now if I try to determine _why_ setup-hook is empty by setting the preHook to include 'set -x', then, it's non-empty and works correctly:

preHook = if bintoolsName == "llvm-binutils" then "set -x" else null;

I end up with:

-r--r--r-- 1 root root 4781 Jan 1 1970 result/nix-support/setup-hook

What's going on?

Wow, this is unfortunate. If I build:

nix build --rebuild pkgsLLVM.llvmPackages_15.compiler-rt-no-libc.stdenv.cc.bintools
```
I get:

-r--r--r-- 1 root root 0 Jan 1 1970 result/nix-support/setup-hook

Now if I try to determine _why_ setup-hook is empty by setting the preHook to include 'set -x', then, it's non-empty and works correctly:

preHook = if bintoolsName == "llvm-binutils" then "set -x" else null;

I end up with:

-r--r--r-- 1 root root 4781 Jan 1 1970 result/nix-support/setup-hook

What's going on?

Wow, this is unfortunate. If I build:

nix build --rebuild pkgsLLVM.llvmPackages_15.compiler-rt-no-libc.stdenv.cc.bintools

I get:

-r--r--r-- 1 root root 0 Jan  1  1970 result/nix-support/setup-hook

Now if I try to determine why setup-hook is empty by setting the preHook to include 'set -x', then, it's non-empty and works correctly:

preHook = if bintoolsName == "llvm-binutils" then "set -x" else null;

I end up with:

-r--r--r-- 1 root root 4781 Jan  1  1970 result/nix-support/setup-hook

What's going on?

In reply to @p14:matrix.org
I guess I'm seeing: https://github.com/NixOS/nixpkgs/blob/2283bf968f3b6a2f100d81fb43db6d91f6aea706/pkgs/stdenv/generic/setup.sh#L936

On my machine,

nix build --rebuild nixpkgs/73f18ca8b33ad1281958193e7e35f63b6ef47e52#pkgsLLVM.llvmPackages_15.compiler-rt-no-libc.stdenv.cc.bintools
stat -c%s result/nix-support/setup-hook
``
Apparently, with --rebuild, reproducibly gives me a zero-byte setup-hook. But not on another machine. So, nondeterminism lurking somewhere nasty?

On my machine,

nix build --rebuild nixpkgs/73f18ca8b33ad1281958193e7e35f63b6ef47e52#pkgsLLVM.llvmPackages_15.compiler-rt-no-libc.stdenv.cc.bintools
stat -c%s result/nix-support/setup-hook

Apparently, with --rebuild, reproducibly gives me a zero-byte setup-hook. But not on another machine. So, nondeterminism lurking somewhere nasty?

I'm afraid that if I simply delete the bad paths I won't be able to reproduce this. Though I dare say that keeping the bad outputs doesn't help me much either.

That said, I'm doing a --rebuild, that shouldn't keep corrupted paths on disk would it? This means surely that I'm repeatably generating the bad file, (I hope, tell me if I'm wrong?)