Abort early if TMPDIR is non-writable or non-executable

Fixes #148

bin/ruby-build

@@ -841,6 +841,11 @@ else
   TMP="${TMPDIR%/}"
 fi
 
+if [ ! -w "$TMP" ] || [ ! -x "$TMP" ]; then
+  echo "ruby-build: TMPDIR=$TMP is set to a non-accessible location" >&2
+  exit 1
+fi
+
 # Work around warnings building Ruby 2.0 on Clang 2.x:
 # pass -Wno-error=shorten-64-to-32 if the compiler accepts it.
 #

test/build.bats

@@ -234,3 +234,21 @@ rubinius-2.0.0: --prefix=$INSTALL_ROOT
 bundle exec rake install
 OUT
 }
+
+@test "non-writable TMPDIR aborts build" {
+  export TMPDIR="${TMP}/build"
+  mkdir -p "$TMPDIR"
+  chmod -w "$TMPDIR"
+
+  run_inline_definition <<<""
+  assert_failure "ruby-build: TMPDIR=$TMPDIR is set to a non-accessible location"
+}
+
+@test "non-executable TMPDIR aborts build" {
+  export TMPDIR="${TMP}/build"
+  mkdir -p "$TMPDIR"
+  chmod -x "$TMPDIR"
+
+  run_inline_definition <<<""
+  assert_failure "ruby-build: TMPDIR=$TMPDIR is set to a non-accessible location"
+}