End-to-end sync against a fake switch and a fake driver. The driver stands
in for odoc_driver_opam: it logs the order it was called in and creates the
package's doc directory.

  $ mkpkg() { mkdir -p "prefix/.opam-switch/packages/$1.$2"; cat > "prefix/.opam-switch/packages/$1.$2/opam"; }
  $ mkpkg a 1 <<EOF
  > opam-version: "2.0"
  > EOF
  $ mkpkg b 1 <<EOF
  > opam-version: "2.0"
  > depends: [ "a" ]
  > EOF
  $ cat > driver.sh <<'EOF'
  > #!/bin/sh
  > pkg="$1"
  > [ "$pkg" = "bad" ] && { echo "boom" >&2; exit 1; }
  > echo "$pkg" >> "$OPAM_SWITCH_PREFIX/build-order"
  > mkdir -p "$OPAM_SWITCH_PREFIX/odoc/$pkg"
  > echo ok > "$OPAM_SWITCH_PREFIX/odoc/$pkg/index.html"
  > EOF
  $ chmod +x driver.sh

The post-install hook marks a package stale by touching a marker file; the
post-remove hook just deletes the package's doc directory. Stand in for them:

  $ stale() { mkdir -p "prefix/odoc/$1"; touch "prefix/odoc/$1/.odd-stale"; }
  $ removed() { rm -rf "prefix/odoc/$1"; }

No stale markers is a no-op with no output:

  $ odd sync --prefix prefix --driver ./driver.sh

Marked packages are rebuilt in dependency order, regardless of the order they
were marked in (b was marked first but depends on a):

  $ stale b
  $ stale a
  $ odd sync --prefix prefix --driver ./driver.sh
  odd: 2 built, 0 failed
  $ cat prefix/build-order
  a
  b

A successful build clears the marker, and a landing page lists the documented
packages:

  $ test -e prefix/odoc/a/.odd-stale || echo consumed
  consumed
  $ grep -o '<li>.*</li>' prefix/odoc/index.html | sed 's/<[^>]*>//g'
  a 1
  b 1

A failing package stays marked for the next session; others still build:

  $ mkpkg bad 1 <<EOF
  > opam-version: "2.0"
  > EOF
  $ stale bad
  $ stale a
  $ odd sync --prefix prefix --driver ./driver.sh
  odd: 1 built, 1 failed
  odd: see $TESTCASE_ROOT/prefix/var/cache/odd/log
  $ test -e prefix/odoc/bad/.odd-stale && echo still-marked
  still-marked

A removal deletes the package's docs (post-remove hook); the landing page
drops it the next time sync runs. Note that bad, still marked from the previous
run, is retried (and fails again) — the designed retry behaviour:

  $ test -d prefix/odoc/b && echo present
  present
  $ rm -r prefix/.opam-switch/packages/b.1
  $ removed b
  $ odd sync --prefix prefix --driver ./driver.sh
  odd: 0 built, 1 failed
  odd: see $TESTCASE_ROOT/prefix/var/cache/odd/log
  $ test -d prefix/odoc/b || echo gone
  gone
  $ grep -o '<li>.*</li>' prefix/odoc/index.html | sed 's/<[^>]*>//g'
  a 1

A missing driver leaves marked packages stale and is reported via the summary
(sync still exits 0 — it is hook-facing):

  $ stale a
  $ odd sync --prefix prefix --driver ./no-such-driver
  odd: 0 built, 2 failed
  odd: see $TESTCASE_ROOT/prefix/var/cache/odd/log
  $ ls prefix/odoc/a/.odd-stale prefix/odoc/bad/.odd-stale
  prefix/odoc/a/.odd-stale
  prefix/odoc/bad/.odd-stale

rebuild is the user-facing equivalent: it marks packages stale itself and
fails loudly:

  $ odd rebuild --prefix prefix --driver ./driver.sh a bad
  odd: 1 built, 1 failed
  odd: see $TESTCASE_ROOT/prefix/var/cache/odd/log
  [1]
  $ odd rebuild --prefix prefix --driver ./driver.sh nosuchpkg
  odd: not installed in this switch: nosuchpkg
  [124]