profiles: Do not repeat entries in 'manifest' file.

Fixes <https://issues.guix.gnu.org/55499>.
Reported by Ricardo Wurmus <rekado@elephly.net>.

With this change, the manifest file created for:

  guix install r r-seurat r-cistopic r-monocle3 r-cicero-monocle3 r-assertthat

goes from 5.7M to 176K.  Likewise, on this profile, wall-clock time of:

  GUIX_PROFILING=gc guix package -I

goes from 0.7s to 0.1s, with heap usage going from 55M to 9M.

* guix/profiles.scm (manifest->gexp)[optional]: New procedure.
[entry->gexp]: Turn into a monadic procedure.  Return a 'repeated' sexp
if ENTRY was already visited before.
Adjust caller accordingly.  Bump manifest version.
(sexp->manifest)[sexp->manifest-entry]: Turn into a monadic procedure.
Add case for 'repeated' nodes.  Add each entry to the current state
vhash.
Add clause for version 4 manifests.
[sexp->manifest-entry/v3]: New procedure, with former
'sexp->manifest-entry' code.
* tests/profiles.scm ("deduplication of repeated entries"): New test.
* guix/build/profiles.scm (manifest-sexp->inputs+search-paths)[let-fields]:
New macro.
Use it.  Expect version 4.  Add clause for 'repeated' nodes.

0 files changed, 0 insertions, 0 deletions