Add command-line option "latest"

Allow the user to install the latest available version without
having to hardcode and pass the exact number.

Author: emaxx-google

llvm.sh

@@ -158,17 +158,18 @@ LLVM_VERSION_PATTERNS[18]="-18"
 LLVM_VERSION_PATTERNS[19]="-19"
 LLVM_VERSION_PATTERNS[20]="-20"
 LLVM_VERSION_PATTERNS[21]=""
+LLVM_VERSION_PATTERNS["latest"]=""
 
 if [ ! ${LLVM_VERSION_PATTERNS[$LLVM_VERSION]+_} ]; then
     echo "This script does not support LLVM version $LLVM_VERSION"
     exit 3
 fi
 
-LLVM_VERSION_STRING=${LLVM_VERSION_PATTERNS[$LLVM_VERSION]}
+LLVM_REPO_SUFFIX=${LLVM_VERSION_PATTERNS[$LLVM_VERSION]}
 
 # join the repository name
 if [[ -n "${CODENAME}" ]]; then
-    REPO_NAME="deb ${BASE_URL}/${CODENAME}/  llvm-toolchain${LINKNAME}${LLVM_VERSION_STRING} main"
+    REPO_NAME="deb ${BASE_URL}/${CODENAME}/  llvm-toolchain${LINKNAME}${LLVM_REPO_SUFFIX} main"
     # check if the repository exists for the distro and version
     if ! wget -q --method=HEAD ${BASE_URL}/${CODENAME} &> /dev/null && \
       ! curl -sSLI -XHEAD ${BASE_URL}/${CODENAME} &> /dev/null; then
@@ -212,14 +213,20 @@ elif [[ $is_new_debian -eq 1 ]]; then
 Architectures: amd64 arm64
 Signed-By: /etc/apt/trusted.gpg.d/apt.llvm.org.asc
 URIs: ${BASE_URL}/${CODENAME}/
-Suites: llvm-toolchain${LINKNAME}${LLVM_VERSION_STRING}
+Suites: llvm-toolchain${LINKNAME}${LLVM_REPO_SUFFIX}
 Components: main"
     echo "$TEXT_TO_ADD" | tee -a "$SOURCES_FILE" > /dev/null
 else
     add-apt-repository -y "${REPO_NAME}"
 fi
 
 apt-get update
+
+if [[ "$LLVM_VERSION" == "latest" ]]; then
+    LLVM_VERSION=$(apt-cache search '^llvm-[0-9]+$' | awk '{print $1}' | sed "s/llvm-//" | sort -n | tail -n 1)
+    echo "Installing version=$LLVM_VERSION"
+fi
+
 PKG="clang-$LLVM_VERSION lldb-$LLVM_VERSION lld-$LLVM_VERSION clangd-$LLVM_VERSION"
 if [[ $ALL -eq 1 ]]; then
     # same as in test-install.sh