From 9dea2c8f397c004d3f3288bac3c0df9c842fe713 Mon Sep 17 00:00:00 2001
From: Ha Thach <thach@tinyusb.org>
Date: Fri, 5 Jun 2026 14:34:27 +0700
Subject: ci: carry metrics baseline forward on no-code-change pushes (#3678)

* ci: carry metrics baseline forward on no-code-change pushes

The code-metrics job is gated on code_changed and only uploads the
metrics-tinyusb artifact on push, so a workflow/docs-only push to master (e.g.
removing an unrelated workflow) leaves the latest master Build run without a
baseline. PRs download the baseline from the latest master run, so the size
comparison then finds nothing and silently falls back to absolute sizes.

Add a small metrics-carry-forward job that, on a non-code-change push, downloads
the previous metrics-tinyusb artifact and re-publishes it, so the latest run
always carries a usable baseline. Carry-forward runs re-upload too, so the
baseline chains across consecutive no-code pushes (bounded by artifact retention).
---
 .github/workflows/build.yml | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index af0191149..e5075f46f 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -192,6 +192,36 @@ jobs:
           header: code-metrics
           path: metrics_compare.md
 
+  # ---------------------------------------
+  # Keep the metrics baseline available on no-code-change pushes
+  # The code-metrics job only runs (and uploads metrics-tinyusb) when code changed, so a
+  # workflow/docs-only push to master would leave the latest run without a baseline for PRs
+  # to compare against. Carry the previous artifact forward so the baseline is never missing.
+  # ---------------------------------------
+  metrics-carry-forward:
+    needs: [ check-paths ]
+    if: github.event_name == 'push' && needs.check-paths.outputs.code_changed != 'true'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Download previous metrics baseline from this branch
+        uses: dawidd6/action-download-artifact@v11
+        with:
+          workflow: build.yml
+          workflow_conclusion: ''      # any conclusion, matching the PR-side baseline download
+          search_artifacts: true       # scan back past runs that lack the artifact (e.g. earlier no-code pushes)
+          branch: ${{ github.ref_name }}
+          name: metrics-tinyusb
+          path: .
+          if_no_artifact_found: warn
+        continue-on-error: true        # best-effort: never make a no-code push red
+
+      - name: Re-publish baseline so the latest run keeps it
+        if: hashFiles('metrics.json') != ''
+        uses: actions/upload-artifact@v7
+        with:
+          name: metrics-tinyusb
+          path: metrics.json
+
   # ---------------------------------------
   # Build Make/CMake on Windows/MacOS
   # ---------------------------------------
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