test: opam constraint generation

This generalizes the test for ocaml#3431 and actually reveals that nested ors
are incorrectly translated at the moment: in `p_or3`, `(or :a :b :c)`
gets converted to `{a | b & c}`.

It also adds a test for `(and)` and `(or)` with no argument, which
should fail cleanly.

Signed-off-by: Etienne Millon <me@emillon.org>

test/blackbox-tests/test-cases/opam-constraints.t

@@ -0,0 +1,95 @@
+This tests the dune-project -> opam file generation with different kinds of
+constraints.
+
+  $ cat > dune-project << EOF
+  > (lang dune 2.1)
+  > (generate_opam_files)
+  > (package
+  >  (name p)
+  >  (depends
+  >   ; unary ops
+  >   (p_eq (= v))
+  >   (p_lt (< v))
+  >   (p_gt (> v))
+  >   (p_ge (>= v))
+  >   (p_le (<= v))
+  >   (p_ne (<> v))
+  >   ; binary ops
+  >   (p_bin (<> :os win32))
+  >   ; and
+  >   (p_and2 (and :a :b))
+  >   (p_and1 (and :a))
+  >   (p_and3 (and :a :b :c))
+  >   ; or
+  >   (p_or2 (or :a :b))
+  >   (p_or1 (or :a))
+  >   (p_or3 (or :a :b :c)) ; buggy output
+  >   ; mixed operations
+  >   (p_and_in_or (or :a (and :b :c))) ; buggy output, see #3431
+  >   (p_or_in_and (and :a (or :b :c)))
+  >   ))
+  > EOF
+
+  $ dune build
+
+  $ cat p.opam
+  # This file is generated by dune, edit dune-project instead
+  opam-version: "2.0"
+  depends: [
+    "dune" {>= "2.1"}
+    "p_eq" {= "v"}
+    "p_lt" {< "v"}
+    "p_gt" {> "v"}
+    "p_ge" {>= "v"}
+    "p_le" {<= "v"}
+    "p_ne" {!= "v"}
+    "p_bin" {os != "win32"}
+    "p_and2" {a & b}
+    "p_and1" {a}
+    "p_and3" {a & b & c}
+    "p_or2" {a | b}
+    "p_or1" {a}
+    "p_or3" {a | b & c}
+    "p_and_in_or" {a | b & c}
+    "p_or_in_and" {a & b | c}
+  ]
+  build: [
+    ["dune" "subst"] {pinned}
+    [
+      "dune"
+      "build"
+      "-p"
+      name
+      "-j"
+      jobs
+      "@install"
+      "@runtest" {with-test}
+      "@doc" {with-doc}
+    ]
+  ]
+
+`(and)`/`(or)` with no argument should get rejected.
+
+  $ cat > dune-project << EOF
+  > (lang dune 2.1)
+  > (generate_opam_files)
+  > (package
+  >  (name p)
+  >  (depends
+  >   (p (and))))
+  > EOF
+
+  $ dune build 2>&1 | grep 'Internal error'
+  Internal error, please report upstream including the contents of _build/log.
+
+  $ cat > dune-project << EOF
+  > (lang dune 2.1)
+  > (generate_opam_files)
+  > (package
+  >  (name p)
+  >  (depends
+  >   (p (or))))
+  > EOF
+
+  $ dune build 2>&1 | grep 'Internal error'
+  Internal error, please report upstream including the contents of _build/log.