[Refactor] nvm_alias, nvm_resolve_alias: use builtins

[Tests] `nvm_alias`, `nvm_resolve_alias`: add edge-case tests

nvm_alias() used a sed/awk pipeline to strip comments and blank lines from alias files that almost always contain a single word.
A while-read loop with parameter expansion does the same filtering more directly.

nvm_resolve_alias() piped nvm_alias through head and tail to extract one line, and used printf/grep for cycle detection.
Parameter expansion and a case statement replace both without the extra plumbing.

All replacements are POSIX (read -r, case, IFS=, parameter expansion).
As a side effect, this also removes 4 external process invocations during shell init.

[Fix] `nvm_resolve_alias`: detect cycles via newline-anchored `case`

The original commit referenced above changed SEEN_ALIASES from `\n`-delimited
storage (interpreted by `printf '%b' | nvm_grep -e "^${name}$"`) to space-
delimited but left the line-anchored grep in place — without newlines in
the haystack the anchored pattern can never match, so cycles never break.

Switch to literal-newline storage and a `case` pattern anchored on those
newlines. Newline anchoring also handles alias names containing spaces,
which token-based patterns false-positive on (e.g. lookup of `bar` matches
substring " bar " inside " foo bar midway " when the chain visits the
multi-token alias `foo bar`).

New test file covers self-loop, multi-hop loop, cycle through a
space-bearing alias name, and a non-cycle through a space-bearing
alias name. Existing `test/fast/Aliases/circular/` fixtures continue
to pass.

nvm.sh

@@ -1370,7 +1370,22 @@ nvm_alias() {
     return 0
   fi
 
-  command sed 's/#.*//; s/[[:space:]]*$//' "${NVM_ALIAS_PATH}" | command awk 'NF'
+  local NVM_ALIAS_LINE
+  while IFS= read -r NVM_ALIAS_LINE || [ -n "${NVM_ALIAS_LINE}" ]; do
+    NVM_ALIAS_LINE="${NVM_ALIAS_LINE%%#*}"
+    case "${NVM_ALIAS_LINE}" in
+      *[!\ \	]*) ;;
+      *) continue ;;
+    esac
+    while : ; do
+      case "${NVM_ALIAS_LINE}" in
+        *' ') NVM_ALIAS_LINE="${NVM_ALIAS_LINE% }" ;;
+        *'	') NVM_ALIAS_LINE="${NVM_ALIAS_LINE%	}" ;;
+        *) break ;;
+      esac
+    done
+    nvm_echo "${NVM_ALIAS_LINE}"
+  done < "${NVM_ALIAS_PATH}"
 }
 
 nvm_ls_current() {
@@ -1403,24 +1418,32 @@ nvm_resolve_alias() {
   local ALIAS
   ALIAS="${PATTERN}"
   local ALIAS_TEMP
+  local ALIAS_OUTPUT
 
   local SEEN_ALIASES
-  SEEN_ALIASES="${ALIAS}"
+  SEEN_ALIASES="
-  local NVM_ALIAS_INDEX
+${ALIAS}
-  NVM_ALIAS_INDEX=1
+"
   while true; do
-    ALIAS_TEMP="$( (nvm_alias "${ALIAS}" 2>/dev/null | command head -n "${NVM_ALIAS_INDEX}" | command tail -n 1) || nvm_echo)"
+    ALIAS_OUTPUT="$(nvm_alias "${ALIAS}" 2>/dev/null)" || ALIAS_OUTPUT=''
+    ALIAS_TEMP="${ALIAS_OUTPUT%%
+*}"
 
     if [ -z "${ALIAS_TEMP}" ]; then
       break
     fi
 
-    if command printf '%b' "${SEEN_ALIASES}" | nvm_grep -q -e "^${ALIAS_TEMP}$"; then
+    case "${SEEN_ALIASES}" in
+      *"
+${ALIAS_TEMP}
+"*)
         ALIAS="∞"
         break
-    fi
+      ;;
+    esac
 
-    SEEN_ALIASES="${SEEN_ALIASES}\\n${ALIAS_TEMP}"
+    SEEN_ALIASES="${SEEN_ALIASES}${ALIAS_TEMP}
+"
     ALIAS="${ALIAS_TEMP}"
   done
 

test/fast/Aliases/nvm_alias handles comment-only alias file

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../../.. && pwd)"
+
+: nvm.sh
+\. "${NVM_DIR}/nvm.sh"
+
+# Create an alias file containing only comments
+printf '# this is a comment\n# another comment\n' > ../../../alias/test-edge-comments
+ACTUAL="$(nvm_alias test-edge-comments 2>/dev/null)"
+EXIT_CODE="$(nvm_alias test-edge-comments 2>/dev/null; echo $?)"
+[ -z "${ACTUAL}" ] || die "expected empty output for comment-only alias file, got >${ACTUAL}<"
+[ "${EXIT_CODE}" = '0' ] || die "expected exit code 0, got ${EXIT_CODE}"
+
+rm -f ../../../alias/test-edge-comments

test/fast/Aliases/nvm_alias handles empty alias file

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../../.. && pwd)"
+
+: nvm.sh
+\. "${NVM_DIR}/nvm.sh"
+
+# Create an empty alias file
+printf '' > ../../../alias/test-edge-empty
+ACTUAL="$(nvm_alias test-edge-empty 2>/dev/null)"
+EXIT_CODE="$(nvm_alias test-edge-empty 2>/dev/null; echo $?)"
+[ -z "${ACTUAL}" ] || die "expected empty output for empty alias file, got >${ACTUAL}<"
+[ "${EXIT_CODE}" = '0' ] || die "expected exit code 0, got ${EXIT_CODE}"
+
+rm -f ../../../alias/test-edge-empty

test/fast/Aliases/nvm_alias strips trailing whitespace

@@ -0,0 +1,16 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../../.. && pwd)"
+
+: nvm.sh
+\. "${NVM_DIR}/nvm.sh"
+
+# Create an alias file with trailing spaces and tabs
+printf '22.1.0   \t \n' > ../../../alias/test-edge-trailing-ws
+ACTUAL="$(nvm_alias test-edge-trailing-ws)"
+EXPECTED='22.1.0'
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}<, got >${ACTUAL}<"
+
+rm -f ../../../alias/test-edge-trailing-ws

test/fast/Aliases/nvm_resolve_alias handles cycles

@@ -0,0 +1,52 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../../.. && pwd)"
+
+: nvm.sh
+\. "${NVM_DIR}/nvm.sh"
+
+# 1-hop self-reference: alias points to itself
+echo 'self' > '../../../alias/self'
+
+ACTUAL="$(nvm_resolve_alias self)"
+EXPECTED='∞'
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}< for self-reference, got >${ACTUAL}<"
+
+rm -f '../../../alias/self'
+
+# Multi-hop loop: link1 -> link2 -> link3 -> link1
+echo 'link2' > '../../../alias/link1'
+echo 'link3' > '../../../alias/link2'
+echo 'link1' > '../../../alias/link3'
+
+ACTUAL="$(nvm_resolve_alias link1)"
+EXPECTED='∞'
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}< for 3-hop cycle, got >${ACTUAL}<"
+
+rm -f '../../../alias/link1' '../../../alias/link2' '../../../alias/link3'
+
+# Cycle through an alias name containing a space
+echo 'midway' > '../../../alias/foo bar'
+echo 'foo bar' > '../../../alias/midway'
+
+ACTUAL="$(nvm_resolve_alias 'foo bar')"
+EXPECTED='∞'
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}< for space-name cycle, got >${ACTUAL}<"
+
+rm -f '../../../alias/foo bar' '../../../alias/midway'
+
+# Non-cycle through an alias name containing a space.
+# Token-based cycle detection would false-positive on this chain because
+# 'bar' appears as a substring of the multi-token alias name 'foo bar'.
+# Resolves: 'foo bar' -> 'midway' -> 'bar' -> 0.0.99
+echo 'midway' > '../../../alias/foo bar'
+echo 'bar' > '../../../alias/midway'
+echo '0.0.99' > '../../../alias/bar'
+
+ACTUAL="$(nvm_resolve_alias 'foo bar')"
+EXPECTED='v0.0.99'
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}< for space-name chain, got >${ACTUAL}<"
+
+rm -f '../../../alias/foo bar' '../../../alias/midway' '../../../alias/bar'

test/fast/Aliases/nvm_resolve_alias handles deep chain

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../../.. && pwd)"
+
+: nvm.sh
+\. "${NVM_DIR}/nvm.sh"
+
+# Create a 4-deep alias chain: hop1 -> hop2 -> hop3 -> hop4 -> 0.0.99
+echo 'hop2' > ../../../alias/hop1
+echo 'hop3' > ../../../alias/hop2
+echo 'hop4' > ../../../alias/hop3
+echo '0.0.99' > ../../../alias/hop4
+
+ACTUAL="$(nvm_resolve_alias hop1)"
+EXPECTED='v0.0.99'
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}< for 4-deep chain, got >${ACTUAL}<"
+
+rm -f ../../../alias/hop1 ../../../alias/hop2 ../../../alias/hop3 ../../../alias/hop4

test/fast/Aliases/nvm_resolve_alias with nonexistent target

@@ -0,0 +1,19 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../../.. && pwd)"
+
+: nvm.sh
+\. "${NVM_DIR}/nvm.sh"
+
+# Create an alias pointing to a version that does not exist as an alias
+echo '99.99.99' > ../../../alias/test-edge-noexist
+
+ACTUAL="$(nvm_resolve_alias test-edge-noexist)"
+EXPECTED='v99.99.99'
+EXIT_CODE="$(nvm_resolve_alias test-edge-noexist >/dev/null 2>&1; echo $?)"
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}<, got >${ACTUAL}<"
+[ "${EXIT_CODE}" = '0' ] || die "expected exit code 0, got ${EXIT_CODE}"
+
+rm -f ../../../alias/test-edge-noexist