unikernel/duniverse/dune_/test/blackbox-tests/test-cases/pkg/solve-compiler-dependency.t

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+Creates some packages that simulate some of the ocaml compiler
+packages and test solving a project that depends on "ocaml".
+
+  $ . ./helpers.sh
+  $ mkrepo
+
+  $ CURRENT=5.2.0
+  $ NEXT=5.3.0
+  $ NEXT_NEXT=5.3.1
+
+The vanilla compiler package, intended to be the default compiler package.
+  $ mkpkg ocaml-base-compiler $CURRENT
+
+A configurable compiler. It's marked as avoid-version with the intention that
+packages explicitly opt into using it.
+  $ mkpkg ocaml-variants $CURRENT+trunk << EOF
+  > flags: [avoid-version]
+  > EOF
+
+A meta package which depends on a disjunction of different compiler
+implementations.
+  $ mkpkg ocaml $CURRENT << EOF
+  > depends: [
+  >   "ocaml-base-compiler" {>= "$CURRENT~" & < "$NEXT~" } |
+  >   "ocaml-variants" {>= "$CURRENT~" & < "$NEXT~" }
+  > ]
+  > EOF
+
+When the latest version of all packages is the same, the ocaml-base-compiler
+package is chosen, which is what we want.
+  $ solve ocaml
+  Solution for dune.lock:
+  - ocaml.5.2.0
+  - ocaml-base-compiler.5.2.0
+
+Now pretend that there was an alpha release of the current version of the
+compiler also in the repo.
+  $ mkpkg ocaml-base-compiler $CURRENT+alpha1 << EOF
+  > flags: [avoid-version]
+  > EOF
+
+The alpha version of the compiler is not chosen here because dune's
+solver respects the avoid-version flag between multiple versions of
+the same package.
+  $ solve ocaml
+  Solution for dune.lock:
+  - ocaml.5.2.0
+  - ocaml-base-compiler.5.2.0
+
+Now release a new version of ocaml-variants and a new version of ocaml that
+uses it. The dependency specification for ocaml is based on how the package is
+organized in the wild.
+  $ mkpkg ocaml-variants $NEXT+trunk << EOF
+  > flags: [avoid-version]
+  > EOF
+  $ mkpkg ocaml $NEXT << EOF
+  > depends: [
+  >   "ocaml-base-compiler" {= "$NEXT" } |
+  >   "ocaml-variants" {>= "$NEXT~" & < "$NEXT_NEXT~" }
+  > ]
+  > EOF
+
+Note that dune didn't change the solution to include the newest
+release of the "ocaml" package, as doing so would cause a dependency
+on an unstable version of the compiler. Dune assumes that any version
+of compiler packages with a higher version number than the latest
+version of ocaml-base-compiler without the avoid-version flag is
+unstable.
+  $ solve ocaml
+  Solution for dune.lock:
+  - ocaml.5.2.0
+  - ocaml-base-compiler.5.2.0
+
+A package can still force an unstable version of the compiler by leaving no
+other choices:
+
+  $ mkpkg edgy 1.0 << EOF
+  > depends: [ "ocaml" {> "$CURRENT" } ]
+  > EOF
+  $ solve edgy
+  Solution for dune.lock:
+  - edgy.1.0
+  - ocaml.5.3.0
+  - ocaml-variants.5.3.0+trunk (this version should be avoided)
+
+  $ mkpkg edgy 1.0 << EOF
+  > depends: [ "ocaml" "ocaml-base-compiler" {> "$CURRENT" } ]
+  > EOF
+  $ solve edgy
+  Solution for dune.lock:
+  - edgy.1.0
+  - ocaml.5.2.0
+  - ocaml-base-compiler.5.2.0+alpha1 (this version should be avoided)