[william-xue]

Fixes #6474.

What changes

src/traces/bar/plot.js returned early for every blank bar when textposition was *auto* or *inside*, so a bar of zero length never drew its text. The early return now covers *inside* placement and bars that have no position at all (null values). Text with *auto* placement falls through to the existing fit check, which finds no room inside a zero-length bar and places the text outside.

*outside* text already drew for zero-length bars, so *auto* and *outside* now agree.

On the behavior change

Issue #6474 reports this same behaviour, and the maintainer record on it is split. alexcjohnson (collaborator) wrote on 2023-02-09 that it "does look like a bug to me, and certainly a zero-size bar is different from no bar", and that the fix "may be as simple as removing that textPosition === 'auto' || line (and adding this situation to a test image)". This branch does exactly that removal, and the moved baselines are the test image.

The other reading is on record too: in the equivalent plotly.py report (plotly/plotly.py#4686) archmoj wrote on 2024-07-24 "I'm not sure we should consider this a bug", pointing at explicit textposition as the way to choose the placement, and gvwilson agreed it was "a feature rather than a bug".

The attribute description in src/traces/bar/attributes.js states the contract for *auto* as well: the text is moved outside when the bar is too small and nothing is stacked on it. A zero-length bar is the extreme case of too small, and *outside* already draws its text today, so before this change the two documented placements disagreed with each other.

Bars that carry no value at all keep their current behaviour: a null value still produces no text, and the new test asserts that.

Validation

plotly-4.1.1.min.js from the CDN, loaded in headless Chrome. One page holds two figures; the .barlayer .bartext nodes come from the DOM after newPlot.

trace	before	after
y: [0, 5, 10], textposition: 'auto', text: ['ZERO', 'FIVE', 'TEN']	FIVE, TEN	ZERO (bartext-outside, translate(96.66, 334)), FIVE, TEN
y: [null, 5, 10], textposition: 'auto', text: ['NULLPT', 'FIVE', 'TEN']	FIVE, TEN	FIVE, TEN (unchanged)

The right column comes from the same page with the change applied to the bundle copy.

Tests

• test/jasmine/tests/bar_test.js: new case inside the A bar plot describe, should draw *auto* text of zero-length bars outside. It fails before the change, because no ZERO node exists, and it asserts that a null value keeps its text hidden.

Baselines

Thirteen baselines move. They are the baselines-default-diff artifact of the test-baselines job from the CI run on 07834db0 (ubuntu-latest), so they carry the renderer the job uses rather than a local machine.

Every one keeps its dimensions, and diffing each updated image against the previous baseline shows label-sized deltas only — 0.02% to 0.38% of the pixels, with the largest change in blank-bar-outsidetext.png:

• bar mocks, whose text is laid out by the code path that changed: bar_attrs_relative.png, round-bar_attrs_relative.png, bar_display_height_zero.png, bar_display_height_zero_no_line_width.png, bar_display_height_zero_only_line_width.png, rounded-bar_display_height_zero_no_line_width.png, bar_hide_nulls.png, bar-marker-line-colorscales.png, blank-bar-outsidetext.png
• funnel mocks, which plot through src/traces/funnel/plot.js → barPlot.plot and therefore use the same text placement: funnel-grouping-vs-defaults.png, funnel-offsetgroups.png, funnel_horizontal_stack_basic.png, funnel_nonnumeric_sizes.png

map_* and scattermap_dynamic_defaults are deliberately left alone: those mocks cannot render without a Mapbox token.

I did not run the karma suites locally.

The draft log follows in a second commit, since its filename needs this PR number.

[camdecoster]

Thanks for the PR. This changes behavior that might be considered a feature, so I'm going to pause on reviewing until I discuss this with my team.

[william-xue]

Understood — no rush on the review.

For the discussion, both sides of the record are now in the description:

• alexcjohnson on bar chart: textposition='auto' not working for 0 values #6474 (2023-02-09): "does look like a bug to me, and certainly a zero-size bar is different from no bar"
• archmoj on plotly.py#4686 (2024-07-24), with gvwilson agreeing: not a bug / a feature, with explicit textposition as the way to pick the placement

What tipped it for me was consistency rather than preference: the textposition description in src/traces/bar/attributes.js says *auto* moves the text outside when the bar is too small, and *outside* already draws the label on a zero-length bar today — so the two documented placements disagreed before this change. The scope is zero-length bars only; a null bar still gets no text, and there is a test for that.

If the team lands on the current behaviour being intended, say so and I'll close this.