From 63432ec02271507c5fe53a8f5d531eafd2174a0d Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Fri, 16 Oct 2026 13:03:49 +0200
Subject: [PATCH 1/4] Enable ccache, with its cache outside the build env

Install ccache in the build env, which activates the existing gcc/g++
symlinks, and point it at a ccache/ directory next to envs/. The build
env's path contains the GAP version, so a cache inside it would never be
reused; outside it, CI can persist it across builds.

Building the packages takes 40-70 of the 55-90 minutes the gap-system/gap
CI job needs, almost all of it in libsemigroups, semigroups, Normaliz and
CARAT, which change rarely.

Assisted-by: Claude Code (Opus 5.5)
---
 .gitignore            |  1 +
 cygwin-gap-build.list |  1 +
 release_gap.sh        | 23 +++++++++++++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/.gitignore b/.gitignore
index d290454..4762d87 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,6 +2,7 @@
 .*.sw[po]
 
 # Directories created during the build, containing build artifacts
+ccache
 dist
 download
 envs
diff --git a/cygwin-gap-build.list b/cygwin-gap-build.list
index fb3b417..fc5f1da 100644
--- a/cygwin-gap-build.list
+++ b/cygwin-gap-build.list
@@ -1,5 +1,6 @@
 autoconf
 automake
+ccache
 cddlib-devel
 gcc-core
 gcc-core
diff --git a/release_gap.sh b/release_gap.sh
index b7ee9ad..f9fdfe5 100755
--- a/release_gap.sh
+++ b/release_gap.sh
@@ -40,6 +40,23 @@ download/setup-x86_64.exe --site ${CYGWIN_MIRROR} \
 if [ -x envs/build-${GAP_VERSION}-x86_64/usr/bin/ccache ]; then
     ln -s /usr/bin/ccache envs/build-${GAP_VERSION}-x86_64/usr/local/bin/gcc
     ln -s /usr/bin/ccache envs/build-${GAP_VERSION}-x86_64/usr/local/bin/g++
+
+    # The cache lives outside the build env, whose path contains the GAP
+    # version, so that CI can keep it across builds. subcyg clears the
+    # environment, hence a profile script; it receives a Windows path because
+    # a POSIX path means something else in the build env's Cygwin.
+    # CCACHE_BASEDIR makes the versioned paths below /opt relative, and the
+    # compiler is reinstalled for every build, so check its content, not its
+    # mtime.
+    mkdir -p ccache
+    cat > envs/build-${GAP_VERSION}-x86_64/etc/profile.d/ccache.sh <<EOF
+export CCACHE_DIR="\$(cygpath -u '$(cygpath -w -a ccache)')"
+export CCACHE_BASEDIR=/opt
+export CCACHE_COMPILERCHECK=content
+export CCACHE_COMPRESS=1
+EOF
+    tools/subcyg "${ENV_BUILD_DIR}" "ccache -M 2G && ccache -z"
+    USE_CCACHE=yes
 fi
 # A bit of cleanup
 rm -f envs/build-${GAP_VERSION}-x86_64/Cygwin*.{bat,ico}
@@ -89,6 +106,12 @@ echo "::group::Build Packages"
 tools/subcyg "${ENV_BUILD_DIR}" "cd ${GAP_ROOT}/pkg && (../bin/BuildPackages.sh --parallel || true)"
 echo "::endgroup::"
 
+if [ "${USE_CCACHE}" = yes ]; then
+    echo "::group::ccache statistics"
+    tools/subcyg "${ENV_BUILD_DIR}" "ccache -s"
+    echo "::endgroup::"
+fi
+
 # gap-prep-runtime
 echo "::group::gap-prep-runtime"
 mkdir -p $(dirname ${GAP_ROOT_RUNTIME})

From d23ae18b767bfb61ef274c81553c88fdb4435278 Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Sat, 17 Oct 2026 19:33:32 +0200
Subject: [PATCH 2/4] Detect ccache in the build env by its .exe name

From the host Cygwin, `[ -x .../usr/bin/ccache ]` is false although
setup installed ccache there, so the ccache setup never ran. Test for
ccache.exe instead, and create /usr/local/bin before linking into it.

Assisted-by: Generative AI
---
 release_gap.sh | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/release_gap.sh b/release_gap.sh
index f9fdfe5..1c03fca 100755
--- a/release_gap.sh
+++ b/release_gap.sh
@@ -37,7 +37,9 @@ download/setup-x86_64.exe --site ${CYGWIN_MIRROR} \
     --arch x86_64 --no-admin --no-shortcuts --quiet-mode
 
 # Install symlinks for CCACHE
-if [ -x envs/build-${GAP_VERSION}-x86_64/usr/bin/ccache ]; then
+# (test the real file name: `-x .../ccache` fails from the host Cygwin)
+if [ -f envs/build-${GAP_VERSION}-x86_64/usr/bin/ccache.exe ]; then
+    mkdir -p envs/build-${GAP_VERSION}-x86_64/usr/local/bin
     ln -s /usr/bin/ccache envs/build-${GAP_VERSION}-x86_64/usr/local/bin/gcc
     ln -s /usr/bin/ccache envs/build-${GAP_VERSION}-x86_64/usr/local/bin/g++
 

From a235b801f7b30b1bc13622a6af6488efe0a97e69 Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Sat, 17 Oct 2026 21:10:27 +0200
Subject: [PATCH 3/4] Look for ccache where setup installs it

The build env mounts its bin/ directory as /usr/bin, so setup installs
ccache.exe into envs/build-*/bin. The test on envs/build-*/usr/bin never
succeeded, whatever the file name, and the ccache setup never ran.

Assisted-by: Generative AI
---
 release_gap.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/release_gap.sh b/release_gap.sh
index 1c03fca..82f3e18 100755
--- a/release_gap.sh
+++ b/release_gap.sh
@@ -37,8 +37,8 @@ download/setup-x86_64.exe --site ${CYGWIN_MIRROR} \
     --arch x86_64 --no-admin --no-shortcuts --quiet-mode
 
 # Install symlinks for CCACHE
-# (test the real file name: `-x .../ccache` fails from the host Cygwin)
-if [ -f envs/build-${GAP_VERSION}-x86_64/usr/bin/ccache.exe ]; then
+# (the build env mounts its bin/ as /usr/bin, so that is where setup puts it)
+if [ -f envs/build-${GAP_VERSION}-x86_64/bin/ccache.exe ]; then
     mkdir -p envs/build-${GAP_VERSION}-x86_64/usr/local/bin
     ln -s /usr/bin/ccache envs/build-${GAP_VERSION}-x86_64/usr/local/bin/gcc
     ln -s /usr/bin/ccache envs/build-${GAP_VERSION}-x86_64/usr/local/bin/g++

From 46a0f857e46ba77c22df6305aead7154f56fa4a6 Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Sat, 17 Oct 2026 22:39:23 +0200
Subject: [PATCH 4/4] Show all output of commands run by subcyg

subcyg follows the command's output file with tail -F, which starts at
its last 10 lines. Whatever a command prints before tail starts, a
second after the command, was cut to those 10 lines, such as the hit
and miss counts of `ccache -s`. Start at the first line instead.

Assisted-by: Generative AI
---
 tools/subcyg | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/subcyg b/tools/subcyg
index d41f583..93b18bf 100755
--- a/tools/subcyg
+++ b/tools/subcyg
@@ -53,7 +53,7 @@ pid=$!
 # sometimes there can be a delay.
 sleep 1
 if [ -f "$subcyg_root$outtmp" ]; then
-    tail -F --pid=$pid "$subcyg_root$outtmp" 2>/dev/null
+    tail -n +1 -F --pid=$pid "$subcyg_root$outtmp" 2>/dev/null
     if [ $? -eq 130 ]; then
         # tail was interrupted by Ctrl-C, so treat this as though the
         # wrapped command were terminated as well.