Refactor iwyu build into docker install script.

ci/docker_install_iwyu.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+set -eu
+
+: ${IWYU_REPO:="https://github.com/include-what-you-use/include-what-you-use.git"}
+: ${IWYU_BRANCH:="clang_7.0"}
+: ${IWYU_SRC:="/tmp/iwyu"}
+: ${IWYU_HOME:="/opt/iwyu"}
+
+git clone "${IWYU_REPO}" "${IWYU_SRC}"
+git -C "${IWYU_SRC}" checkout ${IWYU_BRANCH}
+
+mkdir -p "${IWYU_HOME}"
+pushd "${IWYU_HOME}"
+
+# Build IWYU for current Clang
+export CC=clang-7
+export CXX=clang++-7
+
+cmake -DCMAKE_PREFIX_PATH=/usr/lib/llvm-7 "${IWYU_SRC}"
+make -j4
+
+popd

dev/lint/Dockerfile

@@ -18,7 +18,7 @@
 FROM arrow:python-3.6
 
 RUN apt-get install -y -q gnupg && \
-    apt update && \
+    apt-get update && \
     apt-get install -y -q \
       clang-7 \
       libclang-7-dev \
@@ -28,3 +28,7 @@ RUN apt-get install -y -q gnupg && \
 
 RUN conda install flake8 && \
     conda clean --all -y
+
+ENV PATH=/opt/iwyu/bin:$PATH
+ADD ci/docker_install_iwyu.sh /arrow/ci/
+RUN arrow/ci/docker_install_iwyu.sh

dev/lint/run_iwyu.sh

@@ -16,6 +16,8 @@
 # limitations under the License.
 #
 
+set -eux
+
 export ARROW_BUILD_TOOLCHAIN=$CONDA_PREFIX
 
 mkdir -p /build/lint
@@ -32,24 +34,5 @@ cmake -GNinja \
 
 popd
 
-# Build IWYU for current Clang
-git clone https://github.com/include-what-you-use/include-what-you-use.git
-pushd include-what-you-use
-git checkout clang_7.0
-popd
-
-export CC=clang-7
-export CXX=clang++-7
-
-mkdir -p iwyu
-pushd iwyu
-cmake -G "Unix Makefiles" \
-      -DCMAKE_PREFIX_PATH=/usr/lib/llvm-7 \
-      ../include-what-you-use
-make -j4
-popd
-
-export PATH=`pwd`/iwyu/bin:$PATH
-
 export IWYU_COMPILATION_DATABASE_PATH=/build/lint
 /arrow/cpp/build-support/iwyu/iwyu.sh all