Move disabling incr comp and denying warnings to the CI config

.cirrus.yml

@@ -13,4 +13,7 @@ task:
     - ./y.sh prepare
   test_script:
     - . $HOME/.cargo/env
+    # Disabling incr comp reduces cache size and incr comp doesn't save as much
+    # on CI anyway.
+    - export CARGO_BUILD_INCREMENTAL=false
     - ./y.sh test

.github/workflows/main.yml

@@ -10,6 +10,14 @@ defaults:
 
 permissions: {}
 
+env:
+  # Disabling incr comp reduces cache size and incr comp doesn't save as much
+  # on CI anyway.
+  CARGO_BUILD_INCREMENTAL: false
+  # Rust's CI denies warnings. Deny them here too to ensure subtree syncs don't
+  # fail because of warnings.
+  RUSTFLAGS: "-Dwarnings"
+
 jobs:
   rustfmt:
     runs-on: ubuntu-latest

build_system/build_backend.rs

@@ -3,7 +3,7 @@
 use crate::path::{Dirs, RelPath};
 use crate::rustc_info::get_file_name;
 use crate::shared_utils::{rustflags_from_env, rustflags_to_cmd_env};
-use crate::utils::{is_ci, is_ci_opt, maybe_incremental, CargoProject, Compiler, LogGroup};
+use crate::utils::{is_ci, is_ci_opt, CargoProject, Compiler, LogGroup};
 
 pub(crate) static CG_CLIF: CargoProject = CargoProject::new(&RelPath::SOURCE, "cg_clif");
 
@@ -16,16 +16,12 @@ pub(crate) fn build_backend(
     let _group = LogGroup::guard("Build backend");
 
     let mut cmd = CG_CLIF.build(&bootstrap_host_compiler, dirs);
-    maybe_incremental(&mut cmd);
 
     let mut rustflags = rustflags_from_env("RUSTFLAGS");
 
     rustflags.push("-Zallow-features=rustc_private".to_owned());
 
     if is_ci() {
-        // Deny warnings on CI
-        rustflags.push("-Dwarnings".to_owned());
-
         if !is_ci_opt() {
             cmd.env("CARGO_PROFILE_RELEASE_DEBUG_ASSERTIONS", "true");
             cmd.env("CARGO_PROFILE_RELEASE_OVERFLOW_CHECKS", "true");

build_system/build_sysroot.rs

@@ -6,8 +6,7 @@
 use crate::path::{Dirs, RelPath};
 use crate::rustc_info::get_file_name;
 use crate::utils::{
-    maybe_incremental, remove_dir_if_exists, spawn_and_wait, try_hard_link, CargoProject, Compiler,
-    LogGroup,
+    remove_dir_if_exists, spawn_and_wait, try_hard_link, CargoProject, Compiler, LogGroup,
 };
 use crate::{config, CodegenBackend, SysrootKind};
 
@@ -270,7 +269,6 @@ fn build_clif_sysroot_for_triple(
     }
     compiler.rustflags.extend(rustflags);
     let mut build_cmd = STANDARD_LIBRARY.build(&compiler, dirs);
-    maybe_incremental(&mut build_cmd);
     if channel == "release" {
         build_cmd.arg("--release");
     }

build_system/main.rs

@@ -61,15 +61,17 @@ fn main() {
     env::set_var("CG_CLIF_DISABLE_INCR_CACHE", "1");
 
     if is_ci() {
-        // Disabling incr comp reduces cache size and incr comp doesn't save as much on CI anyway
-        env::set_var("CARGO_BUILD_INCREMENTAL", "false");
-
         if !is_ci_opt() {
             // Enable the Cranelift verifier
             env::set_var("CG_CLIF_ENABLE_VERIFIER", "1");
         }
     }
 
+    // Force incr comp even in release mode unless in CI or incremental builds are explicitly disabled
+    if env::var_os("CARGO_BUILD_INCREMENTAL").is_none() {
+        env::set_var("CARGO_BUILD_INCREMENTAL", "true");
+    }
+
     let mut args = env::args().skip(1);
     let command = match args.next().as_deref() {
         Some("prepare") => Command::Prepare,

build_system/utils.rs

@@ -288,13 +288,3 @@ fn drop(&mut self) {
         IN_GROUP.store(false, Ordering::SeqCst);
     }
 }
-
-pub(crate) fn maybe_incremental(cmd: &mut Command) {
-    if is_ci() || std::env::var("CARGO_BUILD_INCREMENTAL").map_or(false, |val| val == "false") {
-        // Disabling incr comp reduces cache size and incr comp doesn't save as much on CI anyway
-        cmd.env("CARGO_BUILD_INCREMENTAL", "false");
-    } else {
-        // Force incr comp even in release mode unless in CI or incremental builds are explicitly disabled
-        cmd.env("CARGO_BUILD_INCREMENTAL", "true");
-    }
-}