From 311f2b24331ec1d8ef0244807379f38b69b982ce Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Shixiang=20Wang=20=28=E7=8E=8B=E8=AF=97=E7=BF=94=29?=
 <wangshx@csu.edu.cn>
Date: Sun, 11 Oct 2026 18:37:47 +0800
Subject: [PATCH] ci: shallow checkout with on-demand base fetch in deploy
 workflow

B5 of issue #306: change detection only needs the base commit, so
fetch-depth: 0 (full ~5 GB history clone) is unnecessary in
quarto-publish.yml.

- fetch-depth: 1 in the build-deploy checkout
- Detect changed QMD files fetches the base SHA on demand with
  `git fetch --no-tags --depth=1 origin "$BASE_SHA"` before diffing;
  on fetch failure it falls back to a full build (need_julia=true,
  need_python=true, has_changes=false), matching the existing
  no-base-SHA path - so a missing base commit degrades to today's
  behaviour instead of failing.

Verified safe:
- date-modified: last-modified does NOT depend on git history: a local
  render of a file with mtime 2020-01-01 (git log saying 2026) renders
  "January 1, 2020" - Quarto uses the file mtime, which actions/checkout
  preserves on shallow clones. So displayed dates are unaffected.
- git diff --name-only $BASE_SHA HEAD works after the on-demand fetch
  (tested against a real shallow clone in /tmp).
- Commit-and-push from shallow checkouts (the "Commit updated dependency
  files" step) works: tested commit+push from a depth-1 clone.
- ci-benchmark.yml keeps fetch-depth: 0 (cold-cache benchmark renders
  legitimately need full history); quarto-publish-update-cache.yml also
  keeps it - it pushes dependency-update commits to main and those are
  safest from a full clone.

Co-Authored-By: Claude Code <noreply@anthropic.com>
---
 .github/workflows/quarto-publish.yml | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/quarto-publish.yml b/.github/workflows/quarto-publish.yml
index 59e2cd5a3..859fed68e 100644
--- a/.github/workflows/quarto-publish.yml
+++ b/.github/workflows/quarto-publish.yml
@@ -79,7 +79,10 @@ jobs:
       - name: Checkout repo
         uses: actions/checkout@v7
         with:
-          fetch-depth: 0
+          # Shallow checkout (issue #306, B5): the change-detection step
+          # below needs only the base commit, which it fetches on demand.
+          # Full history costs ~1 min of checkout against a ~5 GB .git.
+          fetch-depth: 1
 
       # ── Detect changed files ─────────────────────────────────
       # Determines which QMDs changed so we can:
@@ -106,6 +109,18 @@ jobs:
             exit 0
           fi
 
+          # Shallow checkout (issue #306, B5): fetch just the base commit so
+          # the diff below has both endpoints. Fails soft – on error (e.g.
+          # the base commit was force-pushed away) fall back to a full build.
+          if ! git fetch --no-tags --depth=1 origin "$BASE_SHA"; then
+            echo "⚠️ Could not fetch base $BASE_SHA – treating as full build"
+            echo "changed_qmds=" >> "$GITHUB_OUTPUT"
+            echo "has_changes=false" >> "$GITHUB_OUTPUT"
+            echo "need_julia=true" >> "$GITHUB_OUTPUT"
+            echo "need_python=true" >> "$GITHUB_OUTPUT"
+            exit 0
+          fi
+
           CHANGED_QMDS=$(git diff --name-only --diff-filter=ACMR "$BASE_SHA" HEAD -- '*.qmd' 2>/dev/null | tr '\n' ' ' || echo "")
           echo "changed_qmds=$CHANGED_QMDS" >> "$GITHUB_OUTPUT"