fix(jj): detect renamed files correctly

[jakubbortlik]

I've been trying out diffview+ with jj and I've run into an issue with renamed files where the apparently default format for jj diff --summary for renamed files factors out common path components as follows: R common/{a.txt => b.txt}. The present parse with local from_path, to_path = path:match("^(.-)%s+=>%s+(.-)$") doesn't handle this format correctly which results in renamed file paths containing stray braces and being in general broken.

This PR fixes this issue by using a template for jj diff instead of the --summary option, that always emits the new and old paths separately. The implementation follows the pattern of other templates (e.g., the FH_TEMPLATE) and covers the functionality with tests.

[Copilot]

Pull request overview

This PR fixes incorrect rename/copy detection in the Jujutsu (jj) adapter. Previously, tracked_files ran jj diff --summary and parsed lines like R common/{a.txt => b.txt} with a regex. jj's --summary renders renames/copies through display_diff_path(), which factors out common path prefixes/suffixes into a lossy, unparseable form (stray braces, and genuinely ambiguous output when paths contain {, }, or =>). The PR replaces --summary with a jj diff -T <template> invocation that emits the status char, target path, and (for renames/copies) the source path as separate \x1f-delimited fields, then parses each line deterministically. This aligns with the existing FH_TEMPLATE approach already used for jj log.

I verified against jj's official template docs and CHANGELOG that every method used (TreeDiffEntry.status_char(), .path(), .status(), .source().path()) is valid and available by jj 0.37.0, which is below the project's documented minimum of jj ≥ 0.38.0 — so there is no version-compatibility regression. This is the only jj diff --summary call site.

Changes:

• Add TRACKED_FILES_TEMPLATE and parse_tracked_files_line, and switch tracked_files from --summary to -T <template> parsing.
• Simplify the file-collection loop to consume the new parser's status/path/oldpath return values.
• Add unit tests for parse_tracked_files_line and integration tests covering renames with common suffixes, literal {/}, and => in names.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
lua/diffview/vcs/adapters/jj/init.lua	Adds the diff template + line parser, rewires tracked_files, and exports both via _test.
lua/diffview/tests/functional/jj_adapter_spec.lua	Adds unit tests for the parser and integration tests for tricky rename path shapes.

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[dlyongemallo]

I think this isn't necessary to export?

[jakubbortlik]

Oh, you're right. I didn't double check. I believe the same applies to FH_TEMPLATE, as it isn't used anywhere either. So I guess I can remove both, right?

[jakubbortlik]

Removed both.