Re: [PR PATCH] [Updated] [RFC] Enable usage of rust-sccache for cargo builds

[icp1994 <icp1994@users.noreply.github.com>]

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There is an updated pull request by icp1994 against master on the void-packages repository

https://github.com/icp1994/void-packages enable-sccache
https://github.com/void-linux/void-packages/pull/41617

[RFC] Enable usage of rust-sccache for cargo builds
Reviving https://github.com/void-linux/void-packages/pull/30702 - I tested the changes in this PR: **YES**

I have been using this for almost a week and it has reduced build times for rust packages quite considerably in my laptop. I have addressed some of the questions/suggestions from the reviews of the previous PR.

Although not the most scientific benchmark, I noted the build times from the cargo output while packaging 4 templates across iterations. In the first two iterations, all of them ran without sccache with an older version of the template to get a baseline without the interference of the crates being downloaded. Third iteration was with same old versions but with sccache enabled which created the cache of all 4 packages combined. Finally, last iteration with the full cache and the latest version of the templates - a typical scenario while updating a package. The difference between the second and the fourth iterations are as follows:
```
rust-analyzer | 6m 13s | 4m 49s
gping         | 1m 44s | 40.81s
difftastic    | 1m 32s | 34.80s
streampager   | 1m 14s | 23.25s
```

I will add docs for README later if there is consensus to merge this eventually.

A patch file from https://github.com/void-linux/void-packages/pull/41617.patch is attached

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From ca7095b51bf3a60520268fbd3d4a10273c7a538c Mon Sep 17 00:00:00 2001
From: icp <pangolin@vivaldi.net>
Date: Fri, 13 Jan 2023 22:21:19 +0530
Subject: [PATCH] Enable usage of rust-sccache for cargo builds

---
 common/build-helper/rust.sh       | 7 +++++++
 common/xbps-src/shutils/chroot.sh | 4 ++--
 etc/defaults.conf                 | 6 ++++++
 xbps-src                          | 2 +-
 4 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/common/build-helper/rust.sh b/common/build-helper/rust.sh
index f689f7c7f9d96..7566e0f6c11f3 100644
--- a/common/build-helper/rust.sh
+++ b/common/build-helper/rust.sh
@@ -30,6 +30,13 @@ else
 	unset CARGO_BUILD_TARGET
 fi
 
+if [ -n "$XBPS_SCCACHE" ] && [ "$pkgname" != "rust-sccache" ]; then
+	hostmakedepends+=" rust-sccache"
+	export RUSTC_WRAPPER="/usr/bin/sccache"
+	export SCCACHE_DIR="${XBPS_HOSTDIR}/sccache"
+	export SCCACHE_IDLE_TIMEOUT=30
+fi
+
 # For cross-compiling rust -sys crates
 export PKG_CONFIG_ALLOW_CROSS=1
 
diff --git a/common/xbps-src/shutils/chroot.sh b/common/xbps-src/shutils/chroot.sh
index d65d8d7e30741..65d1f6d719780 100644
--- a/common/xbps-src/shutils/chroot.sh
+++ b/common/xbps-src/shutils/chroot.sh
@@ -88,8 +88,8 @@ PATH=/void-packages:/usr/bin
 
 exec env -i -- SHELL=/bin/sh PATH="\$PATH" DISTCC_HOSTS="\$XBPS_DISTCC_HOSTS" DISTCC_DIR="/host/distcc" \
     ${XBPS_ARCH+XBPS_ARCH=$XBPS_ARCH} ${XBPS_CHECK_PKGS+XBPS_CHECK_PKGS=$XBPS_CHECK_PKGS} \
-    CCACHE_DIR="/host/ccache" IN_CHROOT=1 LC_COLLATE=C LANG=en_US.UTF-8 TERM=linux HOME="/tmp" \
-    PS1="[\u@$XBPS_MASTERDIR \W]$ " /bin/bash +h "\$@"
+    CCACHE_DIR="/host/ccache" SCCACHE_DIR="/host/sccache" IN_CHROOT=1 LC_COLLATE=C LANG=en_US.UTF-8 \
+    TERM=linux HOME="/tmp" PS1="[\u@$XBPS_MASTERDIR \W]$ " /bin/bash +h "\$@"
 _EOF
 
     chmod 755 $XBPS_MASTERDIR/bin/xbps-shell
diff --git a/etc/defaults.conf b/etc/defaults.conf
index f70e4ea3d0067..422f851136258 100644
--- a/etc/defaults.conf
+++ b/etc/defaults.conf
@@ -55,6 +55,12 @@ XBPS_SUCMD="sudo /bin/sh -c"
 #
 #XBPS_CCACHE=yes
 
+# [OPTIONAL]
+# Enable or disable sccache when building packages. The sccache directory
+# is stored in the hostdir, i.e hostdir/sccache.
+#
+#XBPS_SCCACHE=yes
+
 # [OPTIONAL]
 # Enable or disable distcc when building packages. The distcc directory
 # is stored in the hostdir, i.e hostdir/distcc.
diff --git a/xbps-src b/xbps-src
index cdb5f8c6d643e..49ac4c9b4bd24 100755
--- a/xbps-src
+++ b/xbps-src
@@ -658,7 +658,7 @@ export XBPS_SHUTILSDIR XBPS_CROSSPFDIR XBPS_TRIGGERSDIR \
     XBPS_CMPVER_CMD XBPS_FETCH_CMD XBPS_VERSION XBPS_BUILDSTYLEDIR \
     XBPS_CPPFLAGS XBPS_CFLAGS XBPS_CXXFLAGS XBPS_FFLAGS XBPS_LDFLAGS \
     XBPS_MAKEJOBS XBPS_BUILD_FORCEMODE XBPS_USE_GIT_REVS XBPS_DEBUG_PKGS \
-    XBPS_CHECK_PKGS XBPS_CCACHE XBPS_DISTCC XBPS_DISTCC_HOSTS XBPS_SKIP_DEPS \
+    XBPS_CHECK_PKGS XBPS_SCCACHE XBPS_CCACHE XBPS_DISTCC XBPS_DISTCC_HOSTS XBPS_SKIP_DEPS \
     XBPS_SKIP_REMOTEREPOS XBPS_CROSS_BUILD XBPS_ARG_PKG_OPTIONS XBPS_CONFIG_FILE \
     XBPS_KEEP_ALL XBPS_HOSTDIR XBPS_MASTERDIR XBPS_SRC_VERSION \
     XBPS_DESTDIR XBPS_MACHINE XBPS_TEMP_MASTERDIR XBPS_BINPKG_EXISTS \