diff #

Compare two versions of a VI: added/removed terminals, changed operations, and rewired connections. diff never requires primitive or vi.lib mappings, so it works on any two VIs out of the box. Useful in code review and CI to see what actually changed in a binary .vi file, not just that it changed.

Output is picked along two independent axes: --format selects the serialization (text, json, or html), and -v/--verbose selects the detail level within text. They compose independently — --format never implies a detail level, and --verbose has no effect on json or html.

Both text tiers, and json/html, project the SAME UID-keyed change map — diff matches nodes and structures by their stable LabVIEW UID (not by name), so an added or removed instance of a repeated node name is never confused with a rewire of an unrelated one, and a node merely wrapped in a new structure or handed a fresh UID never shows up as a phantom change. -v/--verbose only adds DEPTH to the same set of changes — it never shows a different diff.

Synopsis #

lvkit diff <vi_a> <vi_b> [options]

Arguments #

Options #

--format is becoming lvkit's house convention for output selection across subcommands (a single flag for mutually exclusive output projections, rather than one boolean per format); other commands' existing --json booleans will migrate to it over time, with --json kept as an alias.

Example #

text output is a single recursive containment tree, rendered as a netlist — the same node-first, named-port syntax describe --verbose's ## Netlist section uses (see Netlist). Every change reads inline as a change tag (+/-/~) in column 0, followed by netlist syntax at whatever depth its own containment puts it: a structure's own line reads case (selector): (or while (...):/for (...):/sequence:), and a node's own line reads name(port=net, ...) -> outNets — the node leads, each wired input bound to its source net by port name, never by position. A structure is a recursion point: its own scope line, then a quoted sub-header per affected frame ("Default":), with that frame's changes indented beneath it on their own lines, recursing into nested structures. An unchanged structure that merely CONTAINS a change still prints its own scope line (with a space gutter, not a change tag), so nested changes always show their enclosing case (...): context. There are no Operations:/Wiring:/Structures: sections. Siblings inside a container print in the VI's own dataflow order (the order the current/head version places them), not grouped by change kind — a genuinely new node can print before a genuinely removed one, or the reverse, depending on where each one falls.

lvkit diff "Convert File Extension (String)__ogtk.vi" "Convert File Extension (Path)__ogtk.vi" \
  --search-path samples/OpenG/extracted

+ Strip Path(path=file name) -> stripped path, name
+ Convert File Extension (String)__ogtk.vi(new ending (none)=new ending (none), file name=name) -> prev ending, new filename
+ Build Path(name or relative path=new filename, base path=stripped path) -> appended path
- Match Pattern#1(string=file name, regular expression='\\.[~\\.]*$') -> before substring, match substring, after substring, offset past match
- case (new ending (none)):
    "Default":
-     Match Pattern#2(string=new ending (none), regular expression='^\\.') -> before substring, match substring, after substring, offset past match
-     Less Than 0?(x=Match Pattern#2.offset past match) -> result
-     Select(f_value='%s', selector=Less Than 0?.result, t_value='.%s') -> result
-     Format String(0=Select.result, 1=Match Pattern#1.before substring, 5=new ending (none)) -> Format String.2, Format String.4
- = (unnamed str) = "'\\\\.[~\\\\.]*$'"

The renamed VI now calls the old one as a SubVI (+ Convert File Extension (String)__ogtk.vi(new ending (none)=new ending (none), file name=name) -> prev ending, new filename) instead of inlining its old case (new ending (none)): logic (- case (new ending (none)):) — everything the removed case used to contain (Match Pattern#2, Less Than 0?, Select, Format String) nests under its "Default": frame, indented beneath the structure's own line. The OTHER Match Pattern instance (Match Pattern#1) — the one that lived outside the case and is unrelated to it — sits at the top level instead, right alongside the genuinely new/removed nodes. Note the ordering: the three ADDED nodes print first — that's where the renamed VI's own dataflow places them — then the removed case and the removed Match Pattern#1, last because they exist only in the OLD version and have no position in the new one's order.

Pass -v/--verbose (or its back-compat alias --long) for the SAME tree, plus more depth:

lvkit diff "Convert File Extension (String)__ogtk.vi" "Convert File Extension (Path)__ogtk.vi" \
  --search-path samples/OpenG/extracted --verbose

Signature:
  ~ input: file name: str -> Path
  ~ output: new filename: str -> Path
 
+ Strip Path(path=file name) -> stripped path, name
+ Convert File Extension (String)__ogtk.vi(new ending (none)=new ending (none), file name=name) -> prev ending, new filename
+ Build Path(name or relative path=new filename, base path=stripped path) -> appended path
- Match Pattern#1(string=file name, regular expression='\\.[~\\.]*$') -> before substring, match substring, after substring, offset past match
- case (new ending (none)):
    "Default":
-     Match Pattern#2(string=new ending (none), regular expression='^\\.') -> before substring, match substring, after substring, offset past match
-     Less Than 0?(x=Match Pattern#2.offset past match) -> result
-     Select(f_value='%s', selector=Less Than 0?.result, t_value='.%s') -> result
-     Format String(0=Select.result, 1=Match Pattern#1.before substring, 5=new ending (none)) -> Format String.2, Format String.4
- = (unnamed str) = "'\\\\.[~\\\\.]*$'"

--verbose doesn't change WHICH changes are reported, or how they're nested — it's the exact same containment tree either way. It only adds: a Signature section BEFORE the tree (the VI's own connector-pane interface, a distinct concern the change map doesn't cover); old→new detail on a modified constant's value instead of just its name; and, when at least one other change is present, a trailing (N unchanged nodes) tally AFTER the tree. This pair happens to share no unchanged nodes at all, so no tally appears in either tier.

The +/-/~ gutter (column 0) is orthogonal to WHAT changed — the same tag prefixes a structure's case (...): line, a node's name(port=net, ...) -> outNets line, and a constant's = name = value line alike. A frame/value-kind change (a whole case/sequence frame added, removed, or reselected) has no line of its own: its tag folds straight onto the quoted frame header it decorates (e.g. + "4": for a brand-new case value with content added inside it) instead of appearing as a separate line — that line already says everything a repeated one would. A wire whose sink is otherwise unchanged but sits alongside an added/removed node at the same containment depth is suppressed outright — that node's own name(port=net, ...) -> outNets line already shows the net inline, so a standalone wire line would just repeat it. A wire change with no such sibling — an unchanged node losing or gaining a connection, with no node add/remove alongside it — still renders its own sink = source line, and a REMOVED wire always renders even when nothing else at that containment depth changed; see Netlist: Diff annotations for a worked example. (A constant edited IN PLACE — same UID, new value — reads as its own instance line like any other modified node, since it's tracked in the UID-keyed change map by its stable UID; only an ADDED or REMOVED constant, which has no UID of its own to key on, goes through the separate name/value-matched list and keeps the dedicated = marker, e.g. + = name = value.)

If the two VIs are identical, --format text (both the default and --verbose) prints a single line, No changes detected., instead of an empty diff/report. --format json and --format html still produce output when the VIs are identical — an empty changes list, or a viewer with nothing in the change list to select.

JSON output #

lvkit diff "Convert File Extension (String)__ogtk.vi" "Convert File Extension (Path)__ogtk.vi" \
  --search-path samples/OpenG/extracted --format json

Prints the diff engine's ChangeMap as JSON: a changes list — one entry per added/removed/modified node, wire, or structure, each with uid, full_id, kind, change (added/removed/modified), label, detail, and diagram geometry (bounds, path, and for a modified element the prior-version bounds_before/path_before) — plus common_nodes, the count of nodes matched unchanged across both VIs. This is the same change map --format html renders into the viewer below, and what an editor integration or AI agent should parse instead of scraping text output.

Interactive diff viewer #

lvkit diff "Convert File Extension (String)__ogtk.vi" "Convert File Extension (Path)__ogtk.vi" \
  --search-path samples/OpenG/extracted --open

This writes outputs/vi-diff/Convert File Extension (String)__ogtk__Convert File Extension (Path)__ogtk.html and opens it in the browser. The file is a single self-contained HTML page — no server, no external JS/CSS — so it works equally well opened locally, sent in a review, or hosted as a static CI artifact.

• Four view modes, switchable from the toolbar: overlay (the default — overlays both VIs with an opacity slider), before, after, and split (two panes — before above, after below — that pan and zoom together).
• A numbered change list in the sidebar covers every added/removed/modified node or wire; each entry's number is drawn as a badge on the diagram next to the element it correlates with.
• Clicking a change in the list (or its badge on the diagram) jumps to it; prev/next buttons, or the p/n keys, step through the list in order.
• Selecting a change spotlights it — the rest of the diagram dims — and zooms/centers on it. If the change lives inside a case or sequence frame that isn't the one currently showing, the viewer switches that frame into view first, in both panes, so a change never hides behind an unselected case.
• Independent zoom (toolbar buttons, +/- keys, or Ctrl/Cmd+scroll) is shared across all four view modes.
• The URL fragment encodes the selected change, view mode, change-list mode, and per-structure frame selection (#c=N&view=overlay&list=tree&frame=UID=VALUE), so a link into the viewer can deep-link straight to a specific change.

Flat vs. tree change list #

A Flat / Tree toggle sits above the change list. Flat (the default) is the numbered list in engine order, one row per change. Tree regroups the SAME list by containment — client-side, from the container_uid/ frame_path every entry already carries, no extra data and no second engine call — into exactly the structure the text containment tree above prints: a structure is a recursion point, its frames are quoted sub-headers, and contained changes nest beneath them. Every row keeps its number badge and click-to-select behavior in either mode — switching modes only changes how the list is grouped, never which change a click selects or what it does.

Exit codes #

diff exits 0 whenever it successfully compares the two VIs — including when they're identical. The exit code does not tell you whether the VIs differ; a CI step that needs to gate on "did this VI change" has to check the printed output (No changes detected. vs. a diff/report), or parse the json/html output, rather than the exit code.

diff exits 1 when vi_a or vi_b doesn't exist, when --open is combined with --format text/--format json, or when loading either VI raises a ValueError, FileNotFoundError, or KeyError (for example, a path that isn't a .vi file) — each of these prints a one-line Error: ... message to stderr. A .vi that pylabview itself can't parse (corrupt or truncated data) raises RuntimeError, which isn't one of the caught types: diff still exits 1, but stderr gets a full Python traceback instead of a clean Error: line.

Notes #

• diff compares two individual .vi files. To cover a change set in CI, invoke it once per changed VI from your pipeline.
• diff runs without a .lvkit/ resolution store — pass --project-root if one exists, but diff doesn't require setup to have been run first.
• If a SubVI referenced by either VI isn't found on --search-path, diff doesn't fail: that SubVI is recorded as an unresolved dependency and the comparison proceeds with what could be loaded.
• Because vi.lib auto-detection uses whatever LabVIEW is installed on the machine (see SubVI & vi.lib resolution), pass --no-auto-vilib for a diff that's identical across machines and in CI.

See also #

• Netlist — the node-first, named-port grammar this page's text output renders, documented in full (including the diff-specific gutter/suppression rules).
• describe — a snapshot of a single VI's signature and operations.
• render — a faithful diagram of a single VI, for visual comparison.
• structure — the same terminal/operation/wiring breakdown for .lvlib/.lvclass members.
• SubVI & vi.lib resolution — the resolution flags diff shares with the other commands.