make an explicit change on compiler then run bootstrap test

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

src/ci/docker/host-x86_64/mingw-check/Dockerfile

@@ -46,7 +46,20 @@ ENV RUN_CHECK_WITH_PARALLEL_QUERIES 1
 # Check library crates on all tier 1 targets.
 # We disable optimized compiler built-ins because that requires a C toolchain for the target.
 # We also skip the x86_64-unknown-linux-gnu target as it is well-tested by other jobs.
-ENV SCRIPT python3 ../x.py check --stage 0 --set build.optimized-compiler-builtins=false core alloc std --target=aarch64-unknown-linux-gnu,i686-pc-windows-msvc,i686-unknown-linux-gnu,x86_64-apple-darwin,x86_64-pc-windows-gnu,x86_64-pc-windows-msvc && \
+ENV SCRIPT \
+           # `core::builder::tests::ci_rustc_if_unchanged_logic` bootstrap test covers the `rust.download-rustc=if-unchanged` logic.
+           # Here we are adding a dummy commit on compiler and running that test to ensure when there is a change on the compiler,
+           # we never download ci rustc with `rust.download-rustc=if-unchanged` option.
+           echo \"\" >> ../compiler/rustc/src/main.rs && \
+           git config --global user.email \"dummy@dummy.com\" && \
+           git config --global user.name \"dummy\" && \
+           git add ../compiler/rustc/src/main.rs && \
+           git commit -m \"test commit for rust.download-rustc=if-unchanged logic\" && \
+           python3 ../x.py test bootstrap -- core::builder::tests::ci_rustc_if_unchanged_logic && \
+           # Revert the dummy commit
+           git reset --hard HEAD~1 && \
+
+           python3 ../x.py check --stage 0 --set build.optimized-compiler-builtins=false core alloc std --target=aarch64-unknown-linux-gnu,i686-pc-windows-msvc,i686-unknown-linux-gnu,x86_64-apple-darwin,x86_64-pc-windows-gnu,x86_64-pc-windows-msvc && \
            /scripts/check-default-config-profiles.sh && \
            python3 ../x.py check --target=i686-pc-windows-gnu --host=i686-pc-windows-gnu && \
            python3 ../x.py clippy bootstrap -Dwarnings && \

src/ci/github-actions/jobs.yml

@@ -85,6 +85,9 @@ envs:
 # it in each job definition.
 pr:
   - image: mingw-check
+    env:
+      # We are adding (temporarily) a dummy commit on the compiler
+      READ_ONLY_SRC: "0"
     <<: *job-linux-4c
   - image: mingw-check-tidy
     continue_on_error: true