[New] add `lts/-1` etc, to point to an LTS line relative to "latest"

nvm.sh

@@ -855,8 +855,25 @@ nvm_alias() {
     return 1
   fi
 
+  local NVM_ALIAS_DIR
+  NVM_ALIAS_DIR="$(nvm_alias_path)"
+
+  if [ "$(expr "${ALIAS}" : '^lts/-[1-9][0-9]*$')" -gt 0 ]; then
+    local N
+    N="$(echo "${ALIAS}" | cut -d '-' -f 2)"
+    local RESULT
+    RESULT="$(command ls "${NVM_ALIAS_DIR}/lts" | command tail -n "${N}" | command head -n 1)"
+    if [ "${RESULT}" != '*' ]; then
+      nvm_alias "lts/${RESULT}"
+      return $?
+    else
+      nvm_err 'That many LTS releases do not exist yet.'
+      return 2
+    fi
+  fi
+
   local NVM_ALIAS_PATH
-  NVM_ALIAS_PATH="$(nvm_alias_path)/${ALIAS}"
+  NVM_ALIAS_PATH="${NVM_ALIAS_DIR}/${ALIAS}"
   if [ ! -f "${NVM_ALIAS_PATH}" ]; then
     nvm_err 'Alias does not exist.'
     return 2

test/fast/Unit tests/mocks/LTS_names.txt

@@ -0,0 +1,5 @@
+erbium
+dubnium
+carbon
+boron
+argon

test/fast/Unit tests/nvm_alias LTS-N

@@ -0,0 +1,34 @@
+#!/bin/sh
+
+die () { echo "$@" ; cleanup ; exit 1; }
+
+
+cleanup() {
+  unset -f nvm_download
+}
+
+\. ../../../nvm.sh
+
+set -ex
+
+MOCKS_DIR="${PWD}/mocks"
+
+# sample output at the time the test was written
+TAB_PATH="${MOCKS_DIR}/nodejs.org-dist-index.tab"
+nvm_download() {
+  cat "${TAB_PATH}"
+}
+
+nvm_ls_remote >/dev/null || die "nvm_ls_remote_failed?!"
+
+LTS_NAMES_PATH="${MOCKS_DIR}/LTS_names.txt"
+
+N=0
+while IFS= read -r LTS; do
+  N=$(($N+1))
+  EXPECTED="$(nvm_alias "lts/${LTS}")"
+  ACTUAL="$(nvm_alias "lts/-${N}")"
+  [ "${EXPECTED}" = "${ACTUAL}" ] || die "\`nvm_alias lts/-${N}\` was \`${ACTUAL}\`; expected \`${EXPECTED}\`"
+done < "${LTS_NAMES_PATH}"
+
+cleanup

update_test_mocks.sh

@@ -44,9 +44,14 @@ set -e
 
 ALIAS_PATH="$MOCKS_DIR/nvm_make_alias LTS alias calls.txt"
 : > "$ALIAS_PATH"
+LTS_NAMES_PATH="$MOCKS_DIR/LTS_names.txt"
+: > "$LTS_NAMES_PATH"
 nvm_make_alias() {
   # prevent local alias creation, and store arguments
   echo "${1}|${2}" >> "$ALIAS_PATH"
+  if [ "${1}" != 'lts/*' ]; then
+    echo "${1#lts/}" >> "$LTS_NAMES_PATH"
+  fi
 }
 nvm ls-remote --lts > /dev/null