docs: add script to download mdbook (#8351)

We add a bash script to download and install mdbook. For
linux or mac x86_64, we download prebuilts from github.
Otherwise, we use `cargo install` to build it with rust.

docs_src/build/install_mdbook.sh

@@ -0,0 +1,87 @@
+#!/usr/bin/bash
+
+# Copyright (C) 2025 The Android Open Source Project
+#
+# Licensed 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.
+
+DARWIN_X86=1
+LINUX_X86=2
+DARWIN_ARM=3
+LINUX_ARM=4
+
+function add_cargo_path() {
+    local BASH_P="${HOME}/.bashrc"
+    local PATH_LINE='export PATH=${PATH}:~/.cargo/bin'
+    local TYPE=$1
+    if [ ${TYPE} == ${DARWIN_ARM} ] || [ ${TYPE} == ${DARWIN_X86} ]; then
+        BASH_P="${HOME}/.bash_profile"
+    fi
+    if ! (grep "${PATH_LINE}" ${BASH_P}); then
+        echo "${PATH_LINE}" >> ${BASH_P}
+    fi
+    source ${BASH_P}
+}
+
+function download_mdbook() {
+    if command -v mdbook >/dev/null 2>&1; then
+        echo "mdbook already installed"
+        exit 0
+    fi
+
+    local CHECK_UNAME="
+import sys;
+parts=[a.lower() for a in sys.stdin.read().strip().split(' ')];
+def get_type():
+  if 'darwin' in parts:
+    if 'x86_64' in parts:
+      return ${DARWIN_X86}
+    elif 'aarch' in parts:
+      return ${DARWIN_ARM}
+  elif 'linux' in parts:
+    if 'x86_64' in parts:
+      return ${LINUX_X86}
+    elif 'aarch' in parts:
+      return ${LINUX_ARM}
+  return 0
+print(get_type())
+"
+    local TYPE=`uname -a | python3 -c "${CHECK_UNAME}"`
+    if [ ${TYPE} == ${DARWIN_ARM} ] || [ ${TYPE} == ${LINUX_ARM} ]; then
+        # No github prebuilts are available, we build it with rust from source.
+        # First, need to install rust and cargo
+        if ! (command -v rustc >/dev/null 2>&1) || ! (command -v cargo >/dev/null 2>&1); then
+            echo "*** Need to install Rust ***"
+            curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
+        fi
+        if ! (command -v cargo >/dev/null 2>&1); then
+            echo "*** Still cannot find `cargo` ***"
+            exit 1
+        fi
+        cargo install mdbook
+    else
+        # Download prebuilts from github
+        mkdir -p ${HOME}/.cargo/bin
+        echo "*** Downloading mdbook from github release ***"
+        DL_URL='https://github.com/rust-lang/mdBook/releases/download/v0.4.43/mdbook-v0.4.43-x86_64-apple-darwin.tar.gz '
+        if [ ${TYPE} == ${LINUX_X86} ]; then
+            DL_URL='https://github.com/rust-lang/mdBook/releases/download/v0.4.43/mdbook-v0.4.43-x86_64-unknown-linux-gnu.tar.gz'
+        fi
+        curl -L -o ~/Downloads/mdbook.tar.gz ${DL_URL}
+        mkdir -p /tmp/mdbook
+        tar -xvzf ~/Downloads/mdbook.tar.gz -C /tmp/mdbook >/dev/null 2>&1
+        mv /tmp/mdbook/mdbook ~/.cargo/bin/
+    fi
+    add_cargo_path ${TYPE}
+}
+
+download_mdbook