Replace ubuntu:18.04 with ubuntu:20.04 as base image for clang-format

scripts/docker/Dockerfile.clang

@@ -1,49 +1,13 @@
-FROM ubuntu:18.04
+FROM ubuntu:20.04
 
 RUN apt-get update && apt-get install -y \
         bc \
         git \
         build-essential \
+        clang-format-8 \
         wget \
-        ccache \
         && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/*
 
-RUN KEYDUMP_URL=https://cloud.cees.ornl.gov/download && \
-    KEYDUMP_FILE=keydump && \
-    wget --quiet ${KEYDUMP_URL}/${KEYDUMP_FILE} && \
-    wget --quiet ${KEYDUMP_URL}/${KEYDUMP_FILE}.sig && \
-    gpg --import ${KEYDUMP_FILE} && \
-    gpg --verify ${KEYDUMP_FILE}.sig ${KEYDUMP_FILE} && \
-    rm ${KEYDUMP_FILE}*
-
-ARG CMAKE_VERSION=3.16.8
-ENV CMAKE_DIR=/opt/cmake
-RUN CMAKE_URL=https://github.com/Kitware/CMake/releases/download/v${CMAKE_VERSION} && \
-    CMAKE_SCRIPT=cmake-${CMAKE_VERSION}-Linux-x86_64.sh && \
-    CMAKE_SHA256=cmake-${CMAKE_VERSION}-SHA-256.txt && \
-    wget --quiet ${CMAKE_URL}/${CMAKE_SHA256} && \
-    wget --quiet ${CMAKE_URL}/${CMAKE_SHA256}.asc && \
-    wget --quiet ${CMAKE_URL}/${CMAKE_SCRIPT} && \
-    gpg --verify ${CMAKE_SHA256}.asc ${CMAKE_SHA256} && \
-    grep -i ${CMAKE_SCRIPT} ${CMAKE_SHA256} | sed -e s/linux/Linux/ | sha256sum --check && \
-    mkdir -p ${CMAKE_DIR} && \
-    sh ${CMAKE_SCRIPT} --skip-license --prefix=${CMAKE_DIR} && \
-    rm cmake*
-ENV PATH=${CMAKE_DIR}/bin:$PATH
-
-ENV LLVM_DIR=/opt/llvm
-RUN LLVM_VERSION=8.0.0 && \
-    LLVM_URL=https://releases.llvm.org/${LLVM_VERSION}/clang+llvm-${LLVM_VERSION}-x86_64-linux-gnu-ubuntu-18.04.tar.xz && \
-    LLVM_ARCHIVE=llvm-${LLVM_VERSION}.tar.xz && \
-    SCRATCH_DIR=/scratch && mkdir -p ${SCRATCH_DIR} && cd ${SCRATCH_DIR} && \
-    wget --quiet ${LLVM_URL} --output-document=${LLVM_ARCHIVE} && \
-    wget --quiet ${LLVM_URL}.sig --output-document=${LLVM_ARCHIVE}.sig && \
-    gpg --verify ${LLVM_ARCHIVE}.sig ${LLVM_ARCHIVE} && \
-    mkdir -p ${LLVM_DIR} && \
-    tar -xvf ${LLVM_ARCHIVE} -C ${LLVM_DIR} --strip-components=1 && \
-    echo "${LLVM_DIR}/lib" > /etc/ld.so.conf.d/llvm.conf && ldconfig && \
-    rm -rf /root/.gnupg && \
-    rm -rf ${SCRATCH_DIR}
-ENV PATH=${LLVM_DIR}/bin:$PATH
+ENV CLANG_FORMAT_EXE=clang-format-8