From 9c8cac4a2e701ec99edcdf6ad6c12bb6102b0102 Mon Sep 17 00:00:00 2001
From: Cassidy Marble <cassidy@marble.sh>
Date: Tue, 6 Oct 2026 18:01:38 -0300
Subject: [PATCH] [Perf] `nvm_is_valid_version`, `nvm_validate_implicit_alias`:
 avoid forks

---
 nvm.sh                                    | 30 +++++++++--------------
 test/fast/Unit tests/nvm_is_valid_version | 19 ++++++++++++++
 2 files changed, 30 insertions(+), 19 deletions(-)

diff --git a/nvm.sh b/nvm.sh
index 20d880ad..a1df0506 100755
--- a/nvm.sh
+++ b/nvm.sh
@@ -1061,17 +1061,14 @@ ${NVM_LS_REMOTE_POST_MERGED_OUTPUT}" | nvm_grep -v "N/A" | command sed '/^ *$/d'
 }
 
 nvm_is_valid_version() {
-  if nvm_validate_implicit_alias "${1-}" 2>/dev/null; then
-    return 0
-  fi
   case "${1-}" in
-    "$(nvm_iojs_prefix)" | \
-    "$(nvm_node_prefix)")
+    "stable" | "unstable" | "iojs" | "node")
       return 0
     ;;
     *)
       local VERSION
-      VERSION="$(nvm_strip_iojs_prefix "${1-}")"
+      VERSION="${1-}"
+      VERSION="${VERSION#iojs-}"
       local NVM_VERSION_CORE
       NVM_VERSION_CORE="${VERSION#v}"
       case "${NVM_VERSION_CORE}" in
@@ -1085,6 +1082,9 @@ nvm_is_valid_version() {
             *.*.*) ;;
             *) return 1 ;;
           esac
+          # a prerelease's `-` makes it unreachable for the pure-shell checks
+          # below, so do the full check now.
+          nvm_version_greater_than_or_equal_to "${VERSION}" 0 || return 1
         ;;
         *.)
           NVM_VERSION_CORE="${NVM_VERSION_CORE%.}"
@@ -1093,7 +1093,7 @@ nvm_is_valid_version() {
       case "${NVM_VERSION_CORE}" in
         '' | .* | *. | *..* | *.*.*.* | *[!0-9.]*) return 1 ;;
       esac
-      nvm_version_greater_than_or_equal_to "${VERSION}" 0
+      # every version that reaches this point is a number, and so `>= 0`
     ;;
   esac
 }
@@ -1741,12 +1741,9 @@ nvm_add_iojs_prefix() {
 }
 
 nvm_strip_iojs_prefix() {
-  local NVM_IOJS_PREFIX
-  NVM_IOJS_PREFIX="$(nvm_iojs_prefix)"
-
   case "${1-}" in
-    "${NVM_IOJS_PREFIX}") nvm_echo ;;
-    *) nvm_echo "${1#"${NVM_IOJS_PREFIX}"-}" ;;
+    "iojs") nvm_echo ;;
+    *) nvm_echo "${1#iojs-}" ;;
   esac
 }
 
@@ -2470,17 +2467,12 @@ BEGIN {
 }
 
 nvm_validate_implicit_alias() {
-  local NVM_IOJS_PREFIX
-  NVM_IOJS_PREFIX="$(nvm_iojs_prefix)"
-  local NVM_NODE_PREFIX
-  NVM_NODE_PREFIX="$(nvm_node_prefix)"
-
   case "$1" in
-    "stable" | "unstable" | "${NVM_IOJS_PREFIX}" | "${NVM_NODE_PREFIX}")
+    "stable" | "unstable" | "iojs" | "node")
       return
     ;;
     *)
-      nvm_err "Only implicit aliases 'stable', 'unstable', '${NVM_IOJS_PREFIX}', and '${NVM_NODE_PREFIX}' are supported."
+      nvm_err "Only implicit aliases 'stable', 'unstable', 'iojs', and 'node' are supported."
       return 1
     ;;
   esac
diff --git a/test/fast/Unit tests/nvm_is_valid_version b/test/fast/Unit tests/nvm_is_valid_version
index 8b03d14c..806b4fb3 100755
--- a/test/fast/Unit tests/nvm_is_valid_version	
+++ b/test/fast/Unit tests/nvm_is_valid_version	
@@ -41,3 +41,22 @@ nvm_is_valid_version v9.9.1-nightly201803256591d9f761 || die "nvm_is_valid_versi
 nvm_is_valid_version v9.0.0-v8-canary201710301f8f3dcf36 || die "nvm_is_valid_version v9.0.0-v8-canary201710301f8f3dcf36 did not return 0"
 nvm_is_valid_version v8.16.2-test201910293843c56739f || die "nvm_is_valid_version v8.16.2-test201910293843c56739f did not return 0"
 nvm_is_valid_version iojs-v3.2.1-nightly201508291a531b4e44 || die "nvm_is_valid_version iojs-v3.2.1-nightly201508291a531b4e44 did not return 0"
+
+# `nvm_is_valid_version` must not fork a command for a plain version: mock
+# `awk`, which the version comparisons used, and fail if it runs. (Prereleases
+# still reach the comparison, which is why this checks a release version.)
+TEST_DIR="$(pwd)/nvm_is_valid_version_tmp"
+[ ! -e "${TEST_DIR}" ] && mkdir "${TEST_DIR}"
+MOCK_BIN="${TEST_DIR}/bin"
+mkdir -p "${MOCK_BIN}"
+{
+  echo '#!/bin/sh'
+  echo 'echo "awk was called" >&2'
+  echo 'exit 1'
+} > "${MOCK_BIN}/awk"
+chmod +x "${MOCK_BIN}/awk"
+
+PATH="${MOCK_BIN}:${PATH}" nvm_is_valid_version v18.20.0 \
+  || die 'nvm_is_valid_version v18.20.0 forked a command'
+
+rm -rf "${TEST_DIR}"