analyze: add --json output, fixes #9992

[MannXo]

Adds --json to borg analyze, as proposed in #9992.

The numbers are emitted as raw byte values, for the default mode as well as for --by-name. Output goes to stdout as one JSON object, like the other --json commands.

$ borg analyze -a 'sh:alpha*' --json
{
    "dedup_size": {
        "considered_archives": 2,
        "deduplicated": {"source_size": 3000, "stored_size": 3794},
        "exclusive": {"source_size": 1000, "stored_size": 3398},
        "missing_chunks": 0,
        "total_archives": 3,
        "total_chunks": 13,
        "unreferenced": {"chunks": 0, "stored_size": 0},
        "whole_repository": false
    },
    "encryption": {"encryption": "aes256-ocb", "id_hash": "sha256"},
    "hotspots": [{"path": "home/user/src/sub", "size": 1000}],
    "repository": {"id": "...", "last_modified": "...", "location": "..."}
}

(Reformatted to fit: the real output puts one key per line. The numbers are from the fixture repository described under Testing, with the repository id and paths genericized.)

Decisions worth a second opinion

• No compression factor. The text report shows stored / source, but in JSON that is derivable, and the "n/a" the text uses where there is no source size is not a useful JSON value. Say the word and I will add it.
• hotspots is null, not [], when fewer than two archives matched. The hot spots were then not computed at all, which is different from having computed them and found no churn. --by-name omits the key entirely, as it does no hot-spot analysis.
• exclusive is absent when whole_repository is true. That mirrors the text report, which suppresses the line because every referenced chunk is then trivially exclusive to the set.
• missing_chunks is included although the text report only logs it as a warning. Monitoring wants it, and dropping it would leave a JSON consumer unable to see that the numbers are based on an incomplete index.
• Key names follow the text report's column names: source_size and stored_size.

Refactor

The analysis methods now return their numbers, and printing moved into report_dedup_size(), report_by_name() and report_hotspots(), so the text report and the JSON come from one source of truth rather than two.

The text output is unchanged, byte for byte. I checked that. I built a fixture repository (2 archives named alpha, 1 named beta, sharing one file, with churn in a subdirectory), captured analyze in six variants such as: whole repository, a matching set, a single archive, --by-name, the --by-name + filter error, and the no-match error — on master and on this branch, and diffed the captured stdout and stderr:

$ diff -r before/ after/ && echo "TEXT OUTPUT IDENTICAL"
TEXT OUTPUT IDENTICAL

Testing

4 new tests in analyze_cmd_test.py, covering the default mode, the whole-repository case, hot spots (both computed and not computed), and --by-name.

$ pytest --benchmark-skip -q -n auto src/borg/testsuite/archiver/analyze_cmd_test.py
11 passed in 2.98s

$ pytest --benchmark-skip -q -n auto          # this branch
2201 passed, 616 skipped in 112.44s (0:01:52)

$ pytest --benchmark-skip -q -n auto          # master, for comparison
2197 passed, 616 skipped in 105.44s (0:01:45)

Exactly the 4 new tests, no new skips. The skips are the fakeroot, FUSE and Linux-only ones; I ran this on macOS, so CI covers those.

Each new test was checked by reverting the behaviour it covers, one sabotage at a time, and confirming the intended test fails and then passes again:

Sabotage	Test that failed
always emit exclusive, also for the whole repository	test_analyze_json_whole_repository
hotspots = [] instead of null when not computed	test_analyze_json_hotspots
emit formatted sizes instead of raw byte values	test_analyze_json (+ 6 text-report tests)
sort the --by-name rows smallest first	test_analyze_json_by_name
count shared chunks against the first name	test_analyze_by_name, test_analyze_json_by_name
add the shared size to the total a second time	test_analyze_by_name, test_analyze_json_by_name
print the text report in JSON mode too	test_analyze_json, and 2 more
put the --by-name result under the dedup_size key	test_analyze_json_by_name

The dedup-size test does not hardcode the compression-dependent stored sizes. It asserts that both columns of the corresponding text row are format_file_size() of the JSON values, which pins the "same numbers the text report is rendered from" property directly.

black --check, ruff check and pre-commit run are clean on the changed files. cd docs && make html builds, and the new :ref: resolves (href="../internals/frontends.html#json-output").

Docs

• docs/internals/frontends.rst gains an Archive Analysis subsection describing every key, plus an example. The example is real captured output with the repository id and paths genericized.
• The epilog gains a short JSON output paragraph and a :ref: to that section, with a plain-text substitution in rst_plain_text_references so borg analyze --help renders it as a sentence rather than leaking markup.
• docs/usage/analyze.rst.inc is regenerated (python scripts/make.py build_usage).

I did not regenerate docs/man/borg-analyze.1. It is stale from an earlier change (t still documents only the hot spots and none of the dedup-size report) so regenerating it would fold an unrelated docs catch-up into this PR. Happy to add it here, or in a separate commit, whichever you prefer.

I also have not touched CHANGES.rst, since recent feature commits do not.

---

Claude Code assisted with this change(Opus 5). I verified every change including the byte-for-byte text-output comparison, the per-test sabotage table and the docs build above are the evidence, and the JSON examples are captured output, not written by hand.

[ThomasWaldmann]

Opus being dramatic as usual. Sabotage! :-)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.12%. Comparing base (a293a67) to head (0550944).
⚠️ Report is 79 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10001      +/-   ##
==========================================
+ Coverage   85.88%   86.12%   +0.23%     
==========================================
  Files          95       96       +1     
  Lines       17088    17354     +266     
  Branches     2616     2655      +39     
==========================================
+ Hits        14676    14946     +270     
+ Misses       1674     1667       -7     
- Partials      738      741       +3     

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[ThomasWaldmann]

Windows CI is failing due to path normalization.

[MannXo]

Windows CI is failing due to path normalization.

reflected