From 29474acf2ea6ea038df9dd35e627bcd5b2ff3df6 Mon Sep 17 00:00:00 2001
From: jyn <github@jyn.dev>
Date: Wed, 31 May 2023 10:51:22 -0500
Subject: [PATCH] Use `download-rustc = "if-unchanged"` in PR CI and
 `x86_64-gnu`

This has two main benefits:

1. It tests that download-rustc doesn't regress. This doesn't reduce our test coverage, since we
   still never use `download-rustc` in a full bors merge, but it should make it a lot less likely that
   this breaks by accident.

2. It greatly speeds up CI when compiler/ and library/ haven't been modified. Once the changes in
   https://github.com/rust-lang/compiler-team/issues/619 land, this will also be faster for changes to
   library/, and only changes to compiler/ will have to rebuild.
---
 .github/workflows/ci.yml     | 4 +++-
 src/ci/docker/run.sh         | 1 +
 src/ci/github-actions/ci.yml | 3 +++
 src/ci/run.sh                | 4 ++++
 4 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2d7e03d1f007d..e2d94b0256157 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -38,6 +38,7 @@ jobs:
   pr:
     name: "PR - ${{ matrix.name }}"
     env:
+      DOWNLOAD_RUSTC: 1
       PR_CI_JOB: 1
       CI_JOB_NAME: "${{ matrix.name }}"
       CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
@@ -277,8 +278,9 @@ jobs:
             os: ubuntu-20.04-8core-32gb
             env: {}
           - name: x86_64-gnu
+            env:
+              DOWNLOAD_RUSTC: 1
             os: ubuntu-20.04-4core-16gb
-            env: {}
           - name: x86_64-gnu-stable
             env:
               IMAGE: x86_64-gnu
diff --git a/src/ci/docker/run.sh b/src/ci/docker/run.sh
index cedbc0390f8ff..8d1198614aa40 100755
--- a/src/ci/docker/run.sh
+++ b/src/ci/docker/run.sh
@@ -290,6 +290,7 @@ docker \
   --env DEPLOY \
   --env DEPLOY_ALT \
   --env CI \
+  --env DOWNLOAD_RUSTC \
   --env GITHUB_ACTIONS \
   --env GITHUB_REF \
   --env GITHUB_STEP_SUMMARY="/checkout/obj/${SUMMARY_FILE}" \
diff --git a/src/ci/github-actions/ci.yml b/src/ci/github-actions/ci.yml
index 2c21fa5493533..141d1bcd2e9f3 100644
--- a/src/ci/github-actions/ci.yml
+++ b/src/ci/github-actions/ci.yml
@@ -321,6 +321,7 @@ jobs:
     <<: *base-ci-job
     name: PR - ${{ matrix.name }}
     env:
+      DOWNLOAD_RUSTC: 1
       <<: [*shared-ci-variables, *public-variables]
       PR_CI_JOB: 1
     if: github.event_name == 'pull_request'
@@ -450,6 +451,8 @@ jobs:
             <<: *job-linux-8c
 
           - name: x86_64-gnu
+            env:
+              DOWNLOAD_RUSTC: 1
             <<: *job-linux-4c
 
           # This job ensures commits landing on nightly still pass the full
diff --git a/src/ci/run.sh b/src/ci/run.sh
index ce0dd6018af82..dcfea67569ee4 100755
--- a/src/ci/run.sh
+++ b/src/ci/run.sh
@@ -124,6 +124,10 @@ else
     RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --enable-llvm-assertions"
   fi
 
+  if [ "$DOWNLOAD_RUSTC" = 1 ]; then
+    RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.download-rustc=if-unchanged"
+  fi
+
   RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.verify-llvm-ir"
 
   # When running gcc backend tests, we need to install `libgccjit` and to not run llvm codegen