Update CI

Signed-off-by: FedericoBruzzone <federico.bruzzone.i@gmail.com>

Author: FedericoBruzzone

.github/workflows/ubuntu-x86.yml

@@ -24,19 +24,35 @@ jobs:
           CC: ${{ matrix.compiler.CC }}
           CXX: ${{ matrix.compiler.CXX }}
         run: |
-          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo gpg --dearmor -o /usr/share/keyrings/llvm-keyring.gpg
+          set -euxo pipefail
 
-          echo "deb [signed-by=/usr/share/keyrings/llvm-keyring.gpg] http://apt.llvm.org/jammy/ llvm-toolchain-jammy-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
+          sudo apt-get update -y
+          sudo apt-get install -y --no-install-recommends ca-certificates wget python3-pip python3-setuptools
 
-          sudo apt-get update
-          sudo apt-get install -y --fix-missing \
-            llvm-21 \
-            llvm-21-dev \
-            llvm-21-tools \
-            clang-21 \
-            python3-setuptools
+          # Install LLVM repo via the official apt.llvm.org helper
+          wget -q https://apt.llvm.org/llvm.sh
+          chmod +x llvm.sh
+          sudo ./llvm.sh 21
 
-          sudo pip3 install lit
+          # apt.llvm.org is snapshot-based; indexes can briefly reference .debs that rotate away (404).
+          # Harden install: force fresh indexes, clean partial downloads, use --fix-missing, and retry multiple times.
+          sudo apt-get clean
+          sudo rm -rf /var/lib/apt/lists/*
+          sudo rm -rf /var/cache/apt/archives/partial || true
+
+          for i in 1 2 3 4 5; do
+            sudo apt-get update -y
+            if sudo apt-get -o Acquire::Retries=5 install -y --no-install-recommends --fix-missing llvm-21 llvm-21-dev llvm-21-tools clang-21; then
+              break
+            fi
+            # reset state before next attempt
+            sudo apt-get clean
+            sudo rm -rf /var/lib/apt/lists/*
+            sudo rm -rf /var/cache/apt/archives/partial || true
+            sleep $((i * 5))
+          done
+
+          sudo pip3 install --no-cache-dir lit
       - name: Build `llvm-pass-template`
         run: |
           cd $GITHUB_WORKSPACE