From a2bbc12812cb3a012cc4af50ff918dca21795c9e Mon Sep 17 00:00:00 2001
From: Colin Walters <walters@verbum.org>
Date: Wed, 28 Oct 2020 20:06:26 +0000
Subject: [PATCH] rust: Enable lto by default

This avoids us leaking all of the Rust symbols as public
into our shared library.

Came up in team chat since one person tried to copy just `/usr/bin/rpm-ostree`
from the dev container into a target and got a linker crash; but
really we want to avoid all the duplicated symbols entirely.

(And we should investigate cross-language LTO because that's the
 only way to get full savings)
---
 configure.ac    | 15 +--------------
 rust/Cargo.toml |  7 +++----
 2 files changed, 4 insertions(+), 18 deletions(-)

diff --git a/configure.ac b/configure.ac
index 95411159..a9f91d6f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -236,19 +236,6 @@ AM_CONDITIONAL(RUST_DEBUG, [test "x$rust_debug_release" = "xdebug"])
 dnl Unconditional now.
 RPM_OSTREE_FEATURES="$RPM_OSTREE_FEATURES rust"
 
-dnl Only use this for package builds, as it will hackily edit Cargo.toml right now
-AC_ARG_ENABLE(lto,
-AC_HELP_STRING([--enable-lto],
-               [Build code with Link Time Optimization [default=no]]))
-dnl https://github.com/rust-lang/cargo/issues/4349
-dnl https://bugzilla.mozilla.org/show_bug.cgi?id=1386371
-if test "${enable_lto}" = yes; then
-    if ! grep -q '^lto.*=true' rust/Cargo.toml 2>/dev/null; then
-        echo '# Inserted by configure --enable-lto' >> rust/Cargo.toml
-        echo "lto = true" >> rust/Cargo.toml
-    fi
-fi
-
 AC_ARG_ENABLE(rojig,
   AC_HELP_STRING([--enable-rojig],
     [Support for shipping ostree commits via RPMs [default=no]]))
@@ -303,6 +290,6 @@ echo "
     rojig:                                   ${enable_rojig:-no}
     bubblewrap:                              $with_bubblewrap
     gtk-doc:                                 $enable_gtk_doc
-    rust:                                    $rust_debug_release (lto: ${enable_lto:-no})
+    rust:                                    $rust_debug_release
     cbindgen:                                ${cbindgen:-internal}
 "
diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 4068884f..23300063 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -46,7 +46,6 @@ crate-type = ["staticlib"]
 panic = "abort"
 # We assume we're being delivered via e.g. RPM which supports split debuginfo
 debug = true
-# For true release builds, we do suggest you enable LTO via e.g.
-# env RUSTFLAGS='-C lto=true' as part of the outer build.  It's just
-# off by default because it's quite slow and the default is more oriented
-# towards local development.
+# We need this to avoid leaking symbols, see
+# https://internals.rust-lang.org/t/rust-staticlibs-and-optimizing-for-size/5746
+lto = true