build: Set os_release_id="(...)" in build.rs

This enables us to add specific flags known to work on platforms on which
we control the toolchain build-time options.

Currently, the logic is working well enough that compilation doesn't stop
working if you're not on Solus.

Tested on fedora.

Signed-off-by: Rune Morling <[email protected]>

Author: ermo

.cargo/config.toml

@@ -1,17 +1,3 @@
-[build]
-# - On systems that do not use lld as the system linker (such as Solus) using
-#   lld directly saves about a second  of build time for incremental compiles
-#   for building boulder (from 2.191s to 1.198s on Reilly's machine).
-# - The new symbol mangling format[1] improves the backtrace shown by
-#   RUST_BACKTRACE=1 and other debug utilities. It should also be helpful once
-#   we have ABI reports. Upstream hasn't switched to it yet by default due to
-#   stable distros not having new enough tools, but that doesn't matter for us
-#   [1]:  https://doc.rust-lang.org/rustc/symbol-mangling/v0.html
-rustflags = [
-    "-Clink-arg=-fuse-ld=lld",
-    "-Csymbol-mangling-version=v0",
-]
-
 [profile.release]
 lto = "thin"
 
@@ -20,7 +6,7 @@ lto = "thin"
 # and full backtraces. Hyperfine tests shows opt-level = 1 to be a good
 # compromise between compile speed and runtime speed.
 # During testing, opt-level = 2 caused a non-trivial slowdown in compilation
-# iteration speed, but also sped up execution times commensurably.
+# iteration speed, but also sped up execution times commensurably. /ermo
 [profile.onboarding]
 inherits = "dev"
 opt-level = 1
@@ -37,29 +23,49 @@ opt-level = 3
 strip = "none"
 debug = true
 
-# This build profile is for packaging on Serpent, where we control the toolchain.
-# Hence, we can get away with adding rustflags here that we know are present
-# in the Serpent toolchain builds.
+# Having a way to detect on which system we are compiled means we can get
+# away with adding rustflags here that we know are present in the Serpent
+# toolchain builds.
 #
 # We can set these extra flags via matching on a target cfg() expression.
 #
-# This requires that we set a custom cfg value for the Serpent rustc at compile time,
-# which the cfg() expression can then match against, so that this target is _only_
-# selected for Serpent-native builds
+# This requires that we set a custom cfg value for the Serpent rustc at
+# compile time, which the cfg() expression can then match against, so that
+# this target is _only_ selected for Serpent-native builds
 #
-# Note that target rustflags take precedence over the build.rustflags specified above.
+# - On systems that do not use lld as the system linker (such as Solus) using
+#   lld directly saves about a second  of build time for incremental compiles
+#   for building boulder (from 2.191s to 1.198s on Reilly's machine).
 #
-# So in addition to the above [build] settings:
-# - Add compression of debug symbols with zstd, which shrinks the dev profile
+# - In testing, compression of debug symbols with zstd shrinks the dev profile
 #   boulder binary from 206.03MB to 81.44MB, a 124.59MB or ~60% savings.
 #   It doesn't affect the binary size for packaging builds since we strip those,
 #   but the debug symbols are reduced in size from 113.16MB to 34.63MB.
 #   It adds about ~152ms to the build times which is less than we gained by
-#   switching to lld.
+#   switching to lld. This feature requires a compiler compiled with support
+#   for zstd debug symbols.
 #
-# [target.'cfg(all(custom_value = "serpent"))']
-# rustflags = [
-#    "-Clink-arg=-fuse-ld=lld",
-#    "-Csymbol-mangling-version=v0",
-#    "-Clink-arg=-Wl,--compress-debug-sections=zstd",
-# ]
+# - The new symbol mangling format[1] improves the backtrace shown by
+#   RUST_BACKTRACE=1 and other debug utilities. It should also be helpful once
+#   we have ABI reports. Upstream hasn't switched to it yet by default due to
+#   stable distros not having new enough tools, but that doesn't matter for us
+#   [1]:  https://doc.rust-lang.org/rustc/symbol-mangling/v0.html
+#
+
+# NB: os_release patterns need to be added to both target configs for this to
+#     work...
+#
+# The Solus toolchain supports zstd debug sections currently (Serpent doesn't)
+[target.'cfg(any(os_release_id = "solus"))']
+rustflags = [
+"-Clink-arg=-fuse-ld=lld",
+"-Clink-arg=-Wl,--compress-debug-sections=zstd",
+"-Csymbol-mangling-version=v0",
+]
+
+# Default flags
+[target.'cfg(not(any(os_release_id = "solus")))']
+rustflags = [
+"-Clink-arg=-fuse-ld=lld",
+"-Csymbol-mangling-version=v0",
+]

Cargo.lock

@@ -27,6 +27,7 @@ diesel = { version = "2.2.1", features = ["sqlite", "returning_clauses_for_sqlit
 diesel_migrations = "2.2.0"
 dirs = "5.0.1"
 elf = "0.7.4"
+etc-os-release = "0.1.0"
 indicatif = "0.17.8"
 itertools = "0.13.0"
 futures = "0.3.30"

Cargo.toml

@@ -43,3 +43,6 @@ strum.workspace = true
 thiserror.workspace = true
 tokio.workspace = true
 url.workspace = true
+
+[build-dependencies]
+etc-os-release.workspace = true

boulder/Cargo.toml

@@ -0,0 +1,15 @@
+use etc_os_release::OsRelease;
+use std::error::Error;
+use std::path::PathBuf;
+
+/// Set cargo::rustc-cfg=os_release_id="whatever" when /etc/os-release warrants it
+fn main() -> Result<(), Box<dyn Error>> {
+    // only recompile when necessary
+    let top_level = PathBuf::from("..").canonicalize()?;
+    println!("cargo::rerun-if-changed={}/build.rs", top_level.display());
+    // if /etc/os-release doesn't exist, we have a problem big enough that it's OK to crash
+    let os_release = OsRelease::open()?;
+    println!("cargo::rustc-cfg=os_release_id=\"{}\"", os_release.id());
+
+    Ok(())
+}

boulder/build.rs

@@ -21,10 +21,10 @@ clap.workspace = true
 derive_more.workspace = true
 diesel.workspace = true
 diesel_migrations.workspace = true
-itertools.workspace = true
 fnmatch = { path = "../crates/fnmatch" }
 futures.workspace = true
 hex.workspace = true
+itertools.workspace = true
 libsqlite3-sys.workspace = true
 log.workspace = true
 nix.workspace = true
@@ -39,6 +39,9 @@ thiserror.workspace = true
 url.workspace = true
 xxhash-rust.workspace = true
 
+[build-dependencies]
+etc-os-release.workspace = true
+
 [package.metadata.cargo-machete]
 # Needed for unixepoch() in src/db/state/migrations/2024-03-04-201550_init/up.sql
 ignored = ["libsqlite3-sys"]

moss/Cargo.toml

@@ -0,0 +1,15 @@
+use etc_os_release::OsRelease;
+use std::error::Error;
+use std::path::PathBuf;
+
+/// Set cargo::rustc-cfg=os_release_id="whatever" when /etc/os-release warrants it
+fn main() -> Result<(), Box<dyn Error>> {
+    // only recompile when necessary
+    let top_level = PathBuf::from("..").canonicalize()?;
+    println!("cargo::rerun-if-changed={}/build.rs", top_level.display());
+    // if /etc/os-release doesn't exist, we have a problem big enough that it's OK to crash
+    let os_release = OsRelease::open()?;
+    println!("cargo::rustc-cfg=os_release_id=\"{}\"", os_release.id());
+
+    Ok(())
+}