From cdc263621ec7c462040e6b66c9caa4a49e9585f1 Mon Sep 17 00:00:00 2001
From: Andy Gocke <andy@commentout.net>
Date: Fri, 2 Oct 2026 14:36:58 -0700
Subject: [PATCH] Seed Debug Roslyn caches in rolling builds

Add rolling-only Debug CoreCLR builds for cache-enabled Unix PR legs and isolate their Roslyn cache entries from Release builds.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 6b47078d-4fe1-4db0-93fd-264f9a651be7
---
 .../coreclr/templates/setup-roslyn-cache.yml  | 10 ++++++----
 eng/pipelines/runtime.yml                     | 19 +++++++++++++++++++
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/eng/pipelines/coreclr/templates/setup-roslyn-cache.yml b/eng/pipelines/coreclr/templates/setup-roslyn-cache.yml
index dcc5e6152ec062..091e8dcbc9f8cc 100644
--- a/eng/pipelines/coreclr/templates/setup-roslyn-cache.yml
+++ b/eng/pipelines/coreclr/templates/setup-roslyn-cache.yml
@@ -9,16 +9,18 @@ steps:
   # request itself or its target branch. This lets rolling builds seed the
   # cache without allowing pull requests to modify caches used by main.
   #
-  # The managed configuration is intentionally excluded. Roslyn's
-  # deterministic key includes the compilation options, and some pipeline
-  # legs override the matrix configuration in their build arguments.
+  # Keep Debug and Release entries separate so rolling builds can seed both
+  # configurations without competing for the same immutable cache key.
+  # Roslyn's own deterministic key accounts for legs that override the
+  # matrix configuration in their build arguments.
   - task: Cache@2
     displayName: Roslyn compiler cache
     continueOnError: true
     inputs:
-      key: roslyn | v1 | ${{ parameters.osGroup }}${{ parameters.osSubgroup }} | ${{ parameters.archType }} | ${{ parameters.nameSuffix }} | "$(Build.BuildId)"
+      key: roslyn | v2 | ${{ parameters.osGroup }}${{ parameters.osSubgroup }} | ${{ parameters.archType }} | ${{ parameters.nameSuffix }} | "$(buildConfigUpper)" | "$(Build.BuildId)"
       path: $(Pipeline.Workspace)/.roslyn-cache
       restoreKeys: |
+        roslyn | v2 | ${{ parameters.osGroup }}${{ parameters.osSubgroup }} | ${{ parameters.archType }} | ${{ parameters.nameSuffix }} | "$(buildConfigUpper)"
         roslyn | v1 | ${{ parameters.osGroup }}${{ parameters.osSubgroup }} | ${{ parameters.archType }} | ${{ parameters.nameSuffix }}
 
   - script: |
diff --git a/eng/pipelines/runtime.yml b/eng/pipelines/runtime.yml
index 9fabe16d48fd80..1dd60140236382 100644
--- a/eng/pipelines/runtime.yml
+++ b/eng/pipelines/runtime.yml
@@ -351,6 +351,25 @@ extends:
                 eq(stageDependencies.EvaluatePaths.evaluate_paths.outputs['SetPathVars_libraries.containsChange'], true),
                 eq(variables['isRollingBuild'], true))
 
+      # Seed the Debug compiler cache used by the CoreCLR_AllSubsets PR builds.
+      - ${{ if eq(variables.isRollingBuild, true) }}:
+        - template: /eng/pipelines/common/platform-matrix.yml
+          parameters:
+            jobTemplate: /eng/pipelines/common/global-build-job.yml
+            buildConfig: debug
+            platforms:
+            - linux_x64
+            - linux_musl_x64
+            - osx_arm64
+            jobParameters:
+              nameSuffix: CoreCLR_AllSubsets
+              buildArgs: -s clr+libs+libs.tests+host+packs -rc Release -c $(_BuildConfig) /p:ArchiveTests=true
+              timeoutInMinutes: 180
+              preBuildSteps:
+                - template: /eng/pipelines/coreclr/templates/setup-sccache.yml
+              postBuildSteps:
+                - template: /eng/pipelines/coreclr/templates/sccache-stats.yml
+
       - template: /eng/pipelines/common/platform-matrix.yml
         parameters:
           jobTemplate: /eng/pipelines/common/global-build-job.yml