nf-core/tools: EDAM ontology map covers 61 of 728 format concepts, and a failed download is indistinguishable from "no term exists"

Summary

Two defects in nf_core/modules/modules_utils.py::load_edam() and its caller
nf_core/modules/lint/__init__.py::_add_edam_ontologies() cause
nf-core modules lint --fix to write ontologies: [] onto channel elements
that do have an EDAM term.

1. The map is built from one sparsely-populated column.
load_edam() keys the extension map on EDAM.tsv column 14, "File extension":

if fields[0].split("/")[-1].startswith("format") and fields[14]:

EDAM 1.25 populates that column for 61 of 728 format_* concepts. So BAM
(format_2572), FASTA (format_1929), VCF (format_3016), BED (format_3003)
and CRAM (format_3462) — the formats nf-core modules mostly emit — are absent
from the map, and every channel element carrying them gets an empty ontology list.

2. A failed download is silently indistinguishable from an empty answer.
On RequestException, load_edam() logs a warning and returns {}. The caller
cannot tell that apart from a successful load, so it still runs the annotation pass
and writes, for every file-typed element (lint/__init__.py:598-599):

elif "type" in section and section["type"] == "file":
    section["ontologies"] = []

An explicit empty list in committed YAML reads as "EDAM has no term for this
format" — a claim the tool is not in a position to make when it never loaded the
ontology.

Measurement

Over the 184 modules used by nf-core/rnaseq and nf-core/sarek
(1,893 file-typed channel elements):

Of those 1,538, the most frequent extensions are
bam (108), fasta (64), txt (57), bai (56), cram (49), bed (33), vcf (32).

Also keying the map on each concept's lowercased preferred label and its
single-token exact synonyms takes it from 67 to 798 keys
and makes 513 of the 1,538 elements annotatable. Tokens claimed by
more than one format concept (7 shown in the analysis output) are dropped rather
than guessed — a wrong ontology term is worse than a missing one.

The remainder stays unmapped, led by *. (370 — a wildcard with no extension),
tbi (63), fai (42), crai (38), csi (21). Index-file suffixes look like a
separate question and are out of scope here.

Reproduction

reproduce_bug.py runs against nf-core/tools 4.1.0 and checks both behaviours by
calling the real functions. For the caller branch it extracts the
_add_edam_ontologies closure's own source from the installed package via ast
and executes that, rather than re-implementing it — the function under test is
upstream's own bytes. Driving ModuleLint.update_meta_yml_file() end-to-end was
attempted first but needs a nextflow binary and a clonable git remote, neither
available in this sandbox.

$ nfvenv/bin/python reproduce_bug.py
  nf-core 4.1.0
  [PASS] A1 load_edam() returns empty dict when the download fails
  [PASS] A2 the failure is not signalled to the caller (no exception, no sentinel)
  extracted upstream closure: 42 lines
  [PASS] A3 real closure + empty map writes an explicit empty ontologies list
  load_edam() with a real EDAM.tsv: 67 extensions
  [PASS] B 'bam' is absent from the map built by load_edam()
  [PASS] B 'fasta' is absent    [PASS] B 'vcf' is absent
  [PASS] B 'bed' is absent      [PASS] B 'cram' is absent
  [PASS] B 'fastq' IS present
  EDAM 1.25: 61/728 format concepts carry a File extension value

Proposed fix

patch/load_edam_proposed.py — returns (mapping, ok) so the caller can skip
annotation instead of writing empty lists, and widens the key set as measured. The
curated "File extension" column always wins on conflict; obsolete/deprecated
concepts are skipped. 12 tests in test_patch.py cover both claims plus the
properties a reviewer would want guarded: no ambiguous token is emitted, widening
never drops an existing key, the curated mapping is never overridden, a failed load
is distinguishable from a successful one, and every emitted URI appears verbatim in
EDAM.tsv.

Note on a related finding

81 modules in the same set have tools[].identifier empty in meta.yml, which the
bio.tools registry would populate. I could not fill those: bio.tools resolves into a
private address range from this environment, and writing identifiers I could not
verify against the registry would be fabrication. The list is available if useful.

Start with nf_core/modules/modules_utils.py::load_edam() and nf_core/modules/lint/init.py::_add_edam_ontologies(), then run reproduce_bug.py to observe both failures. Use the proposed behavior in patch/load_edam_proposed.py as a guide and run test_patch.py; done means failed downloads skip annotation, valid EDAM terms are mapped without ambiguous tokens, and existing curated mappings remain intact.