From b6fa56820c6fe5b8eb3370411d6738a3f3148b4c Mon Sep 17 00:00:00 2001
From: tannevaled <tannevaled@users.noreply.github.com>
Date: Sun, 25 Oct 2026 18:56:57 +0100
Subject: [PATCH] ci: install qemu-user, not the virtual qemu-user-static
 (Ubuntu 26.04)
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`ubuntu-latest` became Ubuntu 26.04 on 2026-10-19. There `qemu-user-static` is
a VIRTUAL package and apt refuses to choose between its two providers:

    E: Package 'qemu-user-static' has no installation candidate
    Package qemu-user-static is a virtual package provided by:
      qemu-user-binfmt-hwe 1:10.2.1+ds-1ubuntu4.4
      qemu-user-binfmt     1:10.2.1+ds-1ubuntu3.3

The step exits 100 in about twenty seconds, so this lane went red between a
green main and the next push with nothing committed here.

⚠ Installing a PROVIDER is not the fix: `qemu-user-binfmt` registers binfmt
handlers, it does not ship the `qemu-<arch>-static` binaries this lane invokes.
A lane given only a provider takes its `command -v` branch and goes GREEN while
testing nothing, which is worse than red. `qemu-user` ships the dynamic
`qemu-<arch>`, which is all `go test -exec` needs, so both packages are
installed and BOTH binary names are accepted at run time.

⛔ And a missing emulator now FAILS this lane, which PRINTS which emulator it
ran (`running ppc64le under qemu-ppc64le`). Without that line, "ran under
emulation" and "skipped" are indistinguishable from a green tick.

Written by `qemufix` v0.37.0 (go-fleettools/fleettools#128), which recognises
four shapes, refuses by name anything else rather than guessing, and is
idempotent. Nothing else in the lane changed: the retry loop, `CGO_ENABLED=0`,
the test timeouts and the package lists are carried through verbatim.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---
 .github/workflows/arch-qemu-nightly.yml | 37 +++++++++++++++++++++----
 1 file changed, 32 insertions(+), 5 deletions(-)

diff --git a/.github/workflows/arch-qemu-nightly.yml b/.github/workflows/arch-qemu-nightly.yml
index 869f2e94..43ada205 100644
--- a/.github/workflows/arch-qemu-nightly.yml
+++ b/.github/workflows/arch-qemu-nightly.yml
@@ -60,10 +60,21 @@ jobs:
       # first, and they are only refreshed if that was not enough. apt is also
       # told to give up on a stuck mirror rather than sit on it, which is what
       # made the outer timeout the only thing stopping it.
-      - name: Install qemu-user-static
+      # ⛔ `qemu-user-static` is a VIRTUAL package on Ubuntu 26.04, which
+      # `ubuntu-latest` became on 2026-10-19, and apt refuses to choose between its
+      # two providers:
+      #
+      #   E: Package 'qemu-user-static' has no installation candidate
+      #
+      # ⚠ Installing a provider is NOT the fix: `qemu-user-binfmt` registers binfmt
+      # handlers, it does not ship the `qemu-<arch>-static` binaries this lane
+      # invokes. `qemu-user` ships the dynamic `qemu-<arch>`, which is all that
+      # `go test -exec` needs, so both are installed and BOTH NAMES are accepted
+      # below. go-tex/engine#645 has the full account.
+      - name: Install qemu user-mode emulators
         run: |
           apt=(-y -qq -o Acquire::Retries=3 -o Acquire::http::Timeout=30 -o Acquire::https::Timeout=30)
-          if timeout 240 sudo apt-get install "${apt[@]}" qemu-user-static; then
+          if timeout 240 sudo apt-get install "${apt[@]}" qemu-user qemu-user-binfmt; then
             exit 0
           fi
           for attempt in 1 2; do
@@ -71,11 +82,11 @@ jobs:
             timeout 240 sudo apt-get update "${apt[@]}" || true
             sudo rm -f /var/lib/apt/lists/lock /var/cache/apt/archives/lock /var/lib/dpkg/lock*
             sudo dpkg --configure -a || true
-            if timeout 240 sudo apt-get install "${apt[@]}" qemu-user-static; then
+            if timeout 240 sudo apt-get install "${apt[@]}" qemu-user qemu-user-binfmt; then
               exit 0
             fi
           done
-          echo "::error::qemu-user-static could not be installed"
+          echo "::error::qemu-user qemu-user-binfmt could not be installed"
           exit 1
       - name: Test under qemu (${{ matrix.goarch }})
         # qemu-user emulation is ~50-100x slower than native, so the wall here is
@@ -92,4 +103,20 @@ jobs:
         # margin, which ordinary runner variance crosses. 60m puts s390x at
         # about half the wall, which is what "generous headroom" was meant to
         # say. (On real s390x silicon the same suite runs natively in seconds.)
-        run: GOARCH=${{ matrix.goarch }} go test -timeout=60m -exec=${{ matrix.qemu }} ./...
+        run: |
+          base="${{ matrix.qemu }}"
+          q=""
+          for cand in "$base" "${base%-static}"; do
+            command -v "$cand" >/dev/null 2>&1 && q="$cand" && break
+          done
+          # ⛔ A missing emulator FAILS this lane. A lane that reports success for
+          # an architecture it never ran is the one outcome this matrix exists to
+          # rule out.
+          if [ -z "$q" ]; then
+            echo "::error::no qemu user emulator for ${{ matrix.goarch }} (looked for $base and ${base%-static})"
+            exit 1
+          fi
+          # Printed on purpose: without it, "ran under emulation" and "skipped" are
+          # indistinguishable from a green tick.
+          echo "running ${{ matrix.goarch }} under $q"
+          GOARCH=${{ matrix.goarch }} go test -timeout=60m -exec="$q" ./...