ci: Dont stamp Envoy binary in Pull Requests (#26776)

Fix #26632

Signed-off-by: Ryan Northey <ryan@synca.io>

.azure-pipelines/bazel.yml

@@ -98,6 +98,9 @@ steps:
       AZP_TARGET_BRANCH: "origin/$(System.PullRequest.TargetBranch)"
     ${{ if ne(variables['Build.Reason'], 'PullRequest') }}:
       AZP_TARGET_BRANCH: "origin/$(Build.SourceBranchName)"
+    ${{ if eq(variables['Build.Reason'], 'PullRequest') }}:
+      # sha1sum of `ENVOY_PULL_REQUEST`
+      BAZEL_FAKE_SCM_REVISION: e3b4a6e9570da15ac1caffdded17a8bebdc7dfc9
     ${{ if parameters.rbe }}:
       GCP_SERVICE_ACCOUNT_KEY: $(GcpServiceAccountKey)
       ENVOY_RBE: "1"

.bazelrc

@@ -33,6 +33,10 @@ build --action_env=PATH --host_action_env=PATH
 # Requires setting `BAZEL_VOLATILE_DIRTY` in the env.
 build --action_env=BAZEL_VOLATILE_DIRTY --host_action_env=BAZEL_VOLATILE_DIRTY
 
+# Prevent stamped caches from busting (eg in PRs)
+# Requires setting `BAZEL_FAKE_SCM_REVISION` in the env.
+build --action_env=BAZEL_FAKE_SCM_REVISION --host_action_env=BAZEL_FAKE_SCM_REVISION
+
 build --enable_platform_specific_config
 build --test_summary=terse
 

bazel/get_workspace_status

@@ -28,10 +28,15 @@ then
     exit 0
 fi
 
-# The code below presents an implementation that works for git repository
-git_rev=$(git rev-parse HEAD) || exit 1
-echo "BUILD_SCM_REVISION ${git_rev}"
-echo "STABLE_BUILD_SCM_REVISION ${git_rev}"
+if [[ -n "$BAZEL_FAKE_SCM_REVISION" ]]; then
+    echo "BUILD_SCM_REVISION $BAZEL_FAKE_SCM_REVISION"
+    echo "STABLE_BUILD_SCM_REVISION $BAZEL_FAKE_SCM_REVISION"
+else
+    # The code below presents an implementation that works for git repository
+    git_rev=$(git rev-parse HEAD) || exit 1
+    echo "BUILD_SCM_REVISION ${git_rev}"
+    echo "STABLE_BUILD_SCM_REVISION ${git_rev}"
+fi
 
 # If BAZEL_VOLATILE_DIRTY is set then stamped builds will rebuild uncached when
 # either a tracked file changes or an untracked file is added or removed.

ci/run_envoy_docker.sh

@@ -103,6 +103,7 @@ docker run --rm \
        -e BAZEL_STARTUP_OPTIONS \
        -e BAZEL_BUILD_EXTRA_OPTIONS \
        -e BAZEL_EXTRA_TEST_OPTIONS \
+       -e BAZEL_FAKE_SCM_REVISION \
        -e BAZEL_REMOTE_CACHE \
        -e ENVOY_STDLIB \
        -e BUILD_REASON \