adding spack diff command (#22283)

A `spack diff` will take two specs, and then use the spack.solver.asp.SpackSolverSetup to generate
lists of facts about each (e.g., nodes, variants, etc.) and then take a set difference between the
two to show the user the differences.

Example output:

    $ spack diff python@2.7.8 python@3.8.11
     ==> Warning: This interface is subject to change.

     --- python@2.7.8/tsxdi6gl4lihp25qrm4d6nys3nypufbf
     +++ python@3.8.11/yjtseru4nbpllbaxb46q7wfkyxbuvzxx
     @@ variant_value @@
     -  python patches a8c52415a8b03c0e5f28b5d52ae498f7a7e602007db2b9554df28cd5685839b8
     +  python patches 0d98e93189bc278fbc37a50ed7f183bd8aaf249a8e1670a465f0db6bb4f8cf87
     @@ version @@
     -  openssl Version(1.0.2u)
     +  openssl Version(1.1.1k)
     -  python Version(2.7.8)
     +  python Version(3.8.11)

Currently this uses diff-like output but we will attempt to improve on this in the future.

One use case for `spack diff` is whenever a user has a disambiguate situation and cannot 
remember how two different installs are different. The command can also output `--json` in
the case of a more analysis type use case where we want to save complete data with all
diffs and the intersection. However, the command is really more intended for a command
line use case, and we likely will have an analyzer more suited to saving data

Signed-off-by: vsoch <vsoch@users.noreply.github.com>

Co-authored-by: vsoch <vsoch@users.noreply.github.com>
Co-authored-by: Tamara Dahlgren <35777542+tldahlgren@users.noreply.github.com>
Co-authored-by: Todd Gamblin <tgamblin@llnl.gov>

1 files changed, 10 insertions, 1 deletions

diff --git a/share/spack/spack-completion.bash b/share/spack/spack-completion.bash
index bf2a488a85..03e9770c37 100755
--- a/share/spack/spack-completion.bash
+++ b/share/spack/spack-completion.bash
@@ -333,7 +333,7 @@ _spack() {
     then
         SPACK_COMPREPLY="-h --help -H --all-help --color -c --config -C --config-scope -d --debug --timestamp --pdb -e --env -D --env-dir -E --no-env --use-env-repo -k --insecure -l --enable-locks -L --disable-locks -m --mock -p --profile --sorted-profile --lines -v --verbose --stacktrace -V --version --print-shell-vars"
     else
-        SPACK_COMPREPLY="activate add analyze arch audit blame bootstrap build-env buildcache cd checksum ci clean clone commands compiler compilers concretize config containerize create deactivate debug dependencies dependents deprecate dev-build develop docs edit env extensions external fetch find flake8 gc gpg graph help info install license list load location log-parse maintainers mark mirror module monitor patch pkg providers pydoc python reindex remove rm repo resource restage solve spec stage style test test-env tutorial undevelop uninstall unit-test unload url verify versions view"
+        SPACK_COMPREPLY="activate add analyze arch audit blame bootstrap build-env buildcache cd checksum ci clean clone commands compiler compilers concretize config containerize create deactivate debug dependencies dependents deprecate dev-build develop diff docs edit env extensions external fetch find flake8 gc gpg graph help info install license list load location log-parse maintainers mark mirror module monitor patch pkg providers pydoc python reindex remove rm repo resource restage solve spec stage style test test-env tutorial undevelop uninstall unit-test unload url verify versions view"
     fi
 }
 
@@ -842,6 +842,15 @@ _spack_develop() {
     fi
 }
 
+_spack_diff() {
+    if $list_options
+    then
+        SPACK_COMPREPLY="-h --help --json --first -a --attribute"
+    else
+        _all_packages
+    fi
+}
+
 _spack_docs() {
     SPACK_COMPREPLY="-h --help"
 }