[stdlib] Start oil-polyfill.sh

Just an idea for now.  Not used anywhere.

design-docs/index.md

@@ -15,12 +15,13 @@ Index of Oil Enhancement Proposals
    - Status of command sub, assignments builtins, "bare" assignment, etc.
 - [0005-oil-word-eval](0005-oil-word-eval.md)
   - The "!QEFS" problem.
-  - `shopt -s oil-word-eval`
+  - `shopt -s oil-word-eval` or `shopt -s static-word-eval`
     - no splitting
     - static globbing
     - are these separate options or not?  maybe just make it one option
+    - keep `oil` out of the name so other shells can implement it
 - [0006-splicing-arrays](0006-splicing-arrays.md)
-  - `__syntax__ oil-splice` -- syntax hcange @a @f(x, y) syntax
+  - `__syntax__ oil-splice` -- syntax change @a @f(x, y) syntax
     - @(...) makes since in OSH but not Oil... doh.  I guess it's not used, so you
       can use it.
     - also add argv in addition to repr?  yeah I think that's a good addition

stdlib/oil-polyfill.sh

@@ -0,0 +1,33 @@
+# oil-polyfill.sh
+#
+# Portable shell for some of Oil's builtins.
+#
+# Usage:
+#   source oil-polyfill.sh
+#
+# TODO: Where to deploy this?  I think we want versioned copies in
+# ~/.local/lib/oil-0.7.0/stdlib/oil-polyfill.sh
+
+sh-strict() {
+  ### Turn on "legacy" shell strict modes.
+
+  # bash has this option, which is similar.
+  # use || true in case 
+  # Actually we don't need this because of static-word-eval subsumes it?
+  #shopt -s nullglob 2>/dev/null || true
+
+  # POSIX
+  set -o errexit -o nounset -o pipefail
+}
+
+log() {
+  ### Write a message to stderr.
+  echo "$@" 1>&2
+}
+
+die() {
+  ### Write a message to stderr and exit failure.
+  log 'fatal:' "$@"
+  exit 1
+}
+