Add `nvm_ensure_default_set`

nvm.sh

@@ -873,6 +873,25 @@ nvm_get_arch() {
   echo "$NVM_ARCH"
 }
 
+nvm_ensure_default_set() {
+  local VERSION
+  VERSION="$1"
+  if [ -z "$VERSION" ]; then
+    echo 'nvm_ensure_default_set: a version is required' >&2
+    return 1
+  fi
+  if nvm_alias default >/dev/null 2>&1; then
+    # default already set
+    return 0
+  fi
+  local OUTPUT
+  OUTPUT="$(nvm alias default "$VERSION")"
+  local EXIT_CODE
+  EXIT_CODE="$?"
+  echo "Creating default alias: $OUTPUT"
+  return $EXIT_CODE
+}
+
 nvm_install_iojs_binary() {
   local PREFIXED_VERSION
   PREFIXED_VERSION="$1"

test/fast/Aliases/nvm_ensure_default_set

@@ -0,0 +1,18 @@
+#!/bin/sh
+
+die () { echo $@ ; exit 1; }
+
+. ../../../nvm.sh
+
+nvm alias default 0.1 >/dev/null || die "'nvm alias default 0.1' failed"
+
+nvm_ensure_default_set 0.3 || die "'nvm_ensure_default_set' with an existing default alias exits 0"
+
+nvm unalias default || die "'nvm unalias default' failed"
+
+OUTPUT="$(nvm_ensure_default_set 0.2)"
+EXPECTED_OUTPUT="Creating default alias: default -> 0.2 (-> iojs-v0.2.10)"
+EXIT_CODE="$?"
+
+[ "_$OUTPUT" = "_$EXPECTED_OUTPUT" ] || die "'nvm_ensure_default_set 0.2' did not output '$EXPECTED_OUTPUT', got '$OUTPUT'"
+[ "_$EXIT_CODE" = "_0" ] || die "'nvm_ensure_default_set 0.2' did not exit with 0, got $EXIT_CODE"

test/fast/Aliases/teardown

@@ -14,3 +14,4 @@ rm -f "../../../alias/stable"
 rm -f "../../../alias/unstable"
 rm -f "../../../alias/node"
 rm -f "../../../alias/iojs"
+rm -f "../../../alias/default"

test/fast/Unit tests/nvm_ensure_default_set

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+die () { echo $@ ; exit 1; }
+
+. ../../../nvm.sh
+
+EXPECTED_OUTPUT="nvm_ensure_default_set: a version is required"
+OUTPUT="$(nvm_ensure_default_set 2>&1 >/dev/null)"
+EXIT_CODE="$?"
+[ "_$OUTPUT" = "_$EXPECTED_OUTPUT" ] || die "'nvm_ensure_default_set' did not output "$EXPECTED_OUTPUT", got "$OUTPUT""
+[ "_$EXIT_CODE" = "_1" ] || die "'nvm_ensure_default_set' did not exit with 1, got "$EXIT_CODE""
+
+# see test/fast/Aliases for remaining nvm_ensure_default_set tests