[Fix] nvm-exec: improve the no-version failure message

The message claimed "no .nvmrc file found" even when one was found and its version simply was not installed,
and it never mentioned that `NODE_VERSION=default` selects the `default` alias.

Refs #3810

nvm-exec

@@ -12,7 +12,9 @@ if [ -n "$NODE_VERSION" ]; then
 else
   { NVM_RC_VERSION="$(nvm_rc_version 3>&1 1>&4)"; } 4>&1 && nvm_ensure_version_installed "$NVM_RC_VERSION";
   if ! nvm use >/dev/null 2>&1; then
-    echo "No NODE_VERSION provided; no .nvmrc file found" >&2
+    nvm_err 'nvm-exec: unable to select a node version'
+    # shellcheck disable=SC2016
+    nvm_err '  Set `NODE_VERSION` (e.g. `NODE_VERSION=default`), or add an `.nvmrc` file.'
     exit 127
   fi
 fi

test/fast/Running 'nvm-exec' should display required node version

@@ -1,14 +1,28 @@
 #!/bin/bash
 
 set -x
+export NVM_DIR="$(cd ../.. && pwd)"
+
+# an ambient value would send nvm-exec down its `NODE_VERSION` branch
+unset NODE_VERSION
+
 : nvm.sh
 \. ../../nvm.sh
 
-cleanup() { rm -f .nvmrc; }
+ORIG_PWD="$(pwd)"
+
+cleanup() {
+  cd "${ORIG_PWD}" 2>/dev/null || true
+  rm -f .nvmrc
+  [ -n "${TMP_DIR-}" ] && rm -rf "${TMP_DIR}"
+}
 die () { echo "$@" ; cleanup ; exit 1; }
 
 NVM_TEST_VERSION=v0.42
 
+HINT="nvm-exec: unable to select a node version
+  Set \`NODE_VERSION\` (e.g. \`NODE_VERSION=default\`), or add an \`.nvmrc\` file."
+
 # Write it to nvmrc
 echo "$NVM_TEST_VERSION" > .nvmrc
 
@@ -17,9 +31,26 @@ EXPECTED="Found '$(pwd)/.nvmrc' with version <${NVM_TEST_VERSION}>
 N/A: version \"${NVM_TEST_VERSION}\" is not yet installed.
 
 You need to run \`nvm install ${NVM_TEST_VERSION}\` to install and use it.
-No NODE_VERSION provided; no .nvmrc file found";
+${HINT}";
 
 # Skip install, we want to test the error message
 [ "${EXPECTED}" = "${OUTPUT}" ] || die "expected >${EXPECTED}<, got >${OUTPUT}<"
 
+rm -f .nvmrc
+
+NVM_EXEC="$(cd ../.. && pwd)/nvm-exec"
+
+# Run from a fresh, empty directory so no ambient .nvmrc above the test dir
+# can satisfy the lookup and mask the hint.
+TMP_DIR="$(mktemp -d)"
+cd "${TMP_DIR}" || die "could not cd to temp dir"
+
+OUTPUT="$("${NVM_EXEC}" node </dev/null 2>&1)";
+EXIT_CODE=$?
+EXPECTED="No version provided and no .nvmrc file found
+${HINT}";
+
+[ "${EXPECTED}" = "${OUTPUT}" ] || die "expected >${EXPECTED}<, got >${OUTPUT}<"
+[ "${EXIT_CODE}" = 127 ] || die "expected exit code 127, got >${EXIT_CODE}<"
+
 cleanup