From f1f6a97bd01b5dff54ccba446d1afa010a89c527 Mon Sep 17 00:00:00 2001
From: Liam Murphy <liampm32@gmail.com>
Date: Sat, 14 Feb 2026 12:45:32 +1100
Subject: [PATCH] isabelle: don't use `/tmp` as a temp directory

Isabelle uses `/tmp` no matter what on Unix platforms, apparently
because using an arbitrary `$TMPDIR` can cause "path too long" errors on
macOS (https://isabelle.in.tum.de/repos/isabelle/rev/ff92d6edff2c).

However, when not using the sandbox (i.e. on Darwin), this causes the
build to fail if its temp directory (`/tmp/isabelle-`) has already been
created by a previous build using a different build user. For example,
this is the cause of https://hydra.nixos.org/build/321069301.

So, this PR changes it to use `$TMPDIR` during the build of Isabelle
itself (but still use `/tmp` when using Isabelle normally). I had
initially hoped this would also enable Isabelle to build within the
Darwin sandbox, but something else seems to be wrong (I get an opaque
`I/O error: Operation not permitted`).
---
 pkgs/applications/science/logic/tlaplus/tlaps.nix | 7 ++++++-
 pkgs/by-name/is/isabelle/package.nix              | 5 +++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/pkgs/applications/science/logic/tlaplus/tlaps.nix b/pkgs/applications/science/logic/tlaplus/tlaps.nix
index fd5f62b5177a..acf4903a4787 100644
--- a/pkgs/applications/science/logic/tlaplus/tlaps.nix
+++ b/pkgs/applications/science/logic/tlaplus/tlaps.nix
@@ -31,9 +31,14 @@ stdenv.mkDerivation rec {
 
   installPhase = ''
     mkdir -pv "$out"
-    export HOME="$out"
+    export HOME="$TMPDIR"
     export PATH=$out/bin:$PATH
 
+    # Stop Isabelle trying to use `/tmp`.
+    user_home="$(isabelle getenv -b ISABELLE_HOME_USER)"
+    mkdir -p "$user_home/etc"
+    echo 'ISABELLE_TMP_PREFIX="$TMPDIR/isabelle"' > "$user_home/etc/settings"
+
     pushd zenon
     ./configure --prefix $out
     make
diff --git a/pkgs/by-name/is/isabelle/package.nix b/pkgs/by-name/is/isabelle/package.nix
index 297fb7c15a3d..05c1c1eeabb9 100644
--- a/pkgs/by-name/is/isabelle/package.nix
+++ b/pkgs/by-name/is/isabelle/package.nix
@@ -266,6 +266,11 @@ stdenv.mkDerivation (finalAttrs: {
     export HOME=$TMP # The build fails if home is not set
     setup_name=$(basename contrib/isabelle_setup*)
 
+    # Stop Isabelle trying to use `/tmp`.
+    user_home="$(bin/isabelle getenv -b ISABELLE_HOME_USER)"
+    mkdir -p "$user_home/etc"
+    echo 'ISABELLE_TMP_PREFIX="$TMPDIR/isabelle"' > "$user_home/etc/settings"
+
     #The following is adapted from https://isabelle.sketis.net/repos/isabelle/file/Isabelle2021-1/Admin/lib/Tools/build_setup
     TARGET_DIR="contrib/$setup_name/lib"
     rm -rf "$TARGET_DIR"