[Perf] nvm_echo: use the printf shell builtin under zsh

In zsh, `command printf` skips the builtin and forks `/usr/bin/printf`.

nvm.sh

@@ -22,11 +22,22 @@ nvm_stdout_is_terminal() {
 }
 
 nvm_echo() {
-  command printf %s\\n "$*" 2>/dev/null
+  # in zsh, `command printf` skips the builtin and runs `/usr/bin/printf`
+  if [ -n "${ZSH_VERSION-}" ]; then
+    # shellcheck disable=SC3044
+    builtin printf %s\\n "$*" 2>/dev/null
+  else
+    command printf %s\\n "$*" 2>/dev/null
+  fi
 }
 
 nvm_echo_with_colors() {
-  command printf %b\\n "$*" 2>/dev/null
+  if [ -n "${ZSH_VERSION-}" ]; then
+    # shellcheck disable=SC3044
+    builtin printf %b\\n "$*" 2>/dev/null
+  else
+    command printf %b\\n "$*" 2>/dev/null
+  fi
 }
 
 nvm_cd() {

test/fast/Unit tests/nvm_echo

@@ -0,0 +1,38 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+cleanup() {
+  rm -rf "${TEST_DIR}"
+}
+
+: nvm.sh
+\. ../../../nvm.sh
+
+TEST_DIR="$(pwd)/nvm_echo_tmp"
+[ ! -e "${TEST_DIR}" ] && mkdir "${TEST_DIR}"
+
+# a `printf` that reports that it ran: `nvm_echo` must use a shell builtin
+# rather than resolving `printf` through `PATH` (zsh's `command` skips the
+# builtin and runs `/usr/bin/printf` on every call)
+MOCK_BIN="${TEST_DIR}/bin"
+mkdir -p "${MOCK_BIN}"
+{
+  echo '#!/bin/sh'
+  echo "echo 'MOCKED-PRINTF'"
+} > "${MOCK_BIN}/printf"
+chmod +x "${MOCK_BIN}/printf"
+
+OUTPUT="$(nvm_echo 'hello world')"
+[ "${OUTPUT}" = 'hello world' ] || die "expected 'hello world', got '${OUTPUT}'"
+
+OUTPUT="$(nvm_echo)"
+[ -z "${OUTPUT}" ] || die "expected no output, got '${OUTPUT}'"
+
+OUTPUT="$(PATH="${MOCK_BIN}:${PATH}" nvm_echo 'no fork, please' 2>&1)"
+[ "${OUTPUT}" = 'no fork, please' ] || die "for nvm_echo, expected 'no fork, please', got '${OUTPUT}'"
+
+OUTPUT="$(PATH="${MOCK_BIN}:${PATH}" nvm_echo_with_colors 'no fork, please' 2>&1)"
+[ "${OUTPUT}" = 'no fork, please' ] || die "for nvm_echo_with_colors, expected 'no fork, please', got '${OUTPUT}'"
+
+cleanup