Update docs following feedback from @Mort1, @hannesm and @cfcs

That list is becoming long and messy, might need to think of a better way to
organise it.

tmpl/wiki/package-hardening.md

@@ -8,48 +8,111 @@ $ opam list -a | grep mirage | wc -l
 ```
 
 We now have various libraries covering all aspect of the OS: from network to
-block device drivers -- at all levels of the stack: from virtual network cards
-to TLS or virtual block devices to virtual filesystem. These libraries also
-span multiple hypervisors such Xen as well as KVM (via solo5).
+block device drivers -- at all aspects of the stack: from virtual network cards
+to TLS or virtual block devices to virtual filesystems. These libraries also
+span multiple hypervisors including Xen and (via solo5) KVM.
 
 All of this is great: this means that as a MirageOS user, you can spend time
-developping your own application instead of spending time re-implementing
+developing your own application instead of spending time re-implementing
 something that the OS would usually do for you. There are of course still
-gaps in the ecosystem, but this is getting better that it used to be.
+gaps in the ecosystem, but things are getting better!
 
 The next problem is knowing the level of confidence to attribute to each of
 these libraries. Would be great to be able to answer questions such as:
-Does the library has a good test coverage? Was it formally verifired?
+Does the library has a good test coverage? Was it formally verified?
 Was it used in production? In order to do this, I would like to introduce
-the "MirageOS hardining process". Ideally this will live in a tool (e.g.
+the "MirageOS hardening process". Ideally this will live in a tool (e.g.
 `mirage lint`) but to start we list the criteria that such an hardened
 package should follow.
 
-### Project Linting
+### Project Paperwork
 
-- have well-identified maintainers
-- use the correct set of tags in opam metadata
-- use proper names: same name for ocaml and ocamlfind package, and also ideally
+- Have well-identified maintainers. GitHub recently
+  [introduced code owners](https://github.com/blog/2392-introducing-code-owners),
+  which may be worth to use for some (of our core) libraries.
+
+- Have a design document specifying the scope of the library (and esp. what is
+  out of scope)
+
+- Use the correct set of tags in opam metadata
+
+- Use proper names: same name for opam and ocamlfind package, and also ideally
   for the top-level module (see next point).
-- use module alias and proper namespaces (to avoid name-clashes)
-- have documentation
-- have a clear LICENSE file
-- use Jbuilder to build, in order to have short feedback loops when fixing bugs
-  spawning multiple packages
-- use topkg to release, in order to ease the task of the release manager
-- have proper indentation (usgin ocp-indent + checked-in ocp-indent file)
-- use at most 80 collumns
-- for binaries and packages: have a way to gather the licenses of all the
-  dependencies (so for example advertising clauses can be respected)
+
+- Use module alias instead of packs to define proper namespaces
+  (to avoid name-clashes)
+
+- Have documentation
+
+- Have a clear LICENSE file
+
+- Use [topkg](https://github.com/dbuenzli/topkg) to release, in order to ease
+  the task of the release manager(s).
+
+- Have proper indentation (using ocp-indent + checked-in ocp-indent file)
+
+- Use at most 80 columns (`ocp-indent` unfortunately doesn't check this)
+
+- Follow [OCaml programming guidelines](https://ocaml.org/learn/tutorials/guidelines.html)
+
+- Ideally, use [Jbuilder](https://github.com/janestreet/jbuilder) to build,
+  in order to have short feedback loops when fixing bugs spanning multiple
+  packages.
+
+### Code Good Practice
+
+- Provide pretty printers by using [fmt](http://erratique.ch/software/fmt/doc/Fmt.html)
+
+- Do not expose any exceptions in the public interface, but use the
+  [result](http://caml.inria.fr/pub/docs/manual-ocaml/libref/Pervasives.html#TYPEresult)
+  type and [rresult](http://erratique.ch/software/rresult/doc/Rresult.html)
+  combinators!
+
+- Use [logs](http://erratique.ch/software/logs/doc/Logs.html) for logging
+
+- Use [astring](http://erratique.ch/software/astring/doc/Astring.html) for
+  string processing
+
+- Use [bos](http://erratique.ch/software/bos/doc/Bos.html) for operating system
+  interaction
+
+- Use [fpath](http://erratique.ch/software/fpath/doc/Fpath.html) for file paths
+
+- Avoid integer overflows (basically every addition and subtraction, as well
+  as multiplication needs to be guarded unless you know that an overflow can
+  never happen (in this case, a comment should be suggested))
+
+- Work on 32bit (esp. in regards to the last point)
+
+- Avoid global mutable state
+
+- Be aware of non-tail recursive functions
+
+- Be aware of polymorphic equality drawbacks -- when possible define your own
+  specialized functions.
 
 ### Project Confidence
 
-- have unit tests (using alcotest) (ideally with coverage report)
-- have fuzz tests (using crowbar)
-- depends only on libraries released in opam
-- is released in opam
-- for binaries: have a way to reproduce the build at a later date (by vendoring
-  opam metadata?)
+- All direct dependencies are specified in the opam file (e.g. sometimes some
+  direct dependencies are included by transitivity -- this is not very stable
+  and could break the package in the future if one of a transitive dependency
+  is updated)
+
+- Use `-safe-string` (looks like this will be the default in 4.06)
+
+- Have unit tests (using alcotest) (ideally with coverage report)
+
+- Have fuzz tests (using crowbar)
+
+- Depends only on libraries released in opam
+
+- Is released in opam
+
+- For distributed binaries: have a way to reproduce the exact set of packages
+  needed to build the released version of the binary, for instance by vendoring
+  opam metadata.
+
 - have a clear indication if the library is used in production (and if yes by
   which project)
-- bonus: has been formally verified
+
+- bonus: has been formally verified