clingo error with versions of virtual packages

[mwkrentel]

Steps to reproduce

This is a bug with clingo and versions of virtual packages.

For hpcviewer, old versions require java exactly version 8, new
versions use java >= 11, so we have:

depends_on('java@11:', type=('build', 'run'), when='@2021.0:')
depends_on('java@8', type=('build', 'run'), when='@:2020')

Note that the two when regions are disjoint, so for a given version,
only one can be correct. But with clingo, an old spec
hpcviewer@2019.12 concretizes as:

hpcviewer@2019.12%gcc@8.4.1 arch=linux-rhel8-x86_64
    ^openjdk@11.0.12_7%gcc@8.4.1 arch=linux-rhel8-x86_64

This is incorrect. Version 2019.12 satisfies @:2020 and
should require java 8, so openjdk 1.8.

The problem is with the combination of clingo and java as a virtual
package. The original concretizer correctly picks openjdk@1.8.0_265-b01

Or, if I change depends_on('java') to a concrete package openjdk
(version 1.8), then clingo correctly picks 1.8.0_265-b01.

ping @tgamblin @alalazo @becker33
anyone else ?

Error message

$ spack -d spec hpcviewer@2019.12

spack-spec.txt

Information on your system

$ spack debug report

• Spack: 0.11.2-14795-81c272fcb7
• Python: 3.6.8
• Platform: linux-rhel8-zen2
• Concretizer: clingo

General information

• I have run spack debug report and reported the version of Spack/Python/Platform
• I have searched the issues of this repo and believe this is not a duplicate
• I have run the failing commands in debug mode and reported the output

[alalazo]

Bug confirmed. This is due to the fact that we don't have a "version uniqueness" rule for virtual packages. This diff:

diff --git a/lib/spack/spack/solver/concretize.lp b/lib/spack/spack/solver/concretize.lp
index e444faffec..a05c062071 100644
--- a/lib/spack/spack/solver/concretize.lp
+++ b/lib/spack/spack/solver/concretize.lp
@@ -28,6 +28,8 @@ version_declared(Package, Version) :- version_declared(Package, Version, _).
 1 { version(Package, Version) : version_declared(Package, Version) } 1
  :- node(Package).
 
+:- virtual_node(Package), 2 { version(Package, _) }.
+
 % If we select a deprecated version, mark the package as deprecated
 deprecated(Package, Version) :- version(Package, Version), deprecated_version(Package, Version).

solves the bug for me. Currently checking if any test is failing and trying to add a regression test.

[alalazo]

For reference, the current answer set contains 2 versions of java:

version_satisfies("hpcviewer","2019.12") version_satisfies("hpcviewer",":2020") version("hpcviewer","2019.12") virtual_node("java") version_satisfies("java","8") version_satisfies("java","11:") version_satisfies("java","11") version("java","11") version("java","8") version_satisfies("openjdk","11.0:11") version("openjdk","11.0.12_7")

[alalazo]

Hi @mwkrentel thanks for the report! Fix is in #26740 In general if you encounter issues like this one with clingo, feel free to report them on Github and assign to me.