FilledAreaPlot rejects valid charts due to a likely typo (`X_values`) in `performTableCheck()`

[kz930]

What happened?

FilledAreaPlotOpDesc has a check (performTableCheck()) that decides, when a Line
Group is set, whether the groups share the same x-axis. If they don't, it shows an
error page instead of drawing the chart.

That check has one line that writes to X_values (capital X), while every other line in
the block uses lowercase x_values:

File: common/workflow-operator/src/main/scala/org/apache/texera/amber/operator/visualization/filledAreaPlot/FilledAreaPlotOpDesc.scala (in performTableCheck(), ~line 124)

for _, group in grouped:
    if x_values == None:
        x_values = set(group[x].unique())
    elif set(group[x].unique()).intersection(x_values):
        X_values = x_values.union(set(group[x].unique()))   # <-- capital X: result is never used
    elif not set(group[x].unique()).intersection(x_values):
        count += 1
        if count > tolerance:
            error = "X attributes not shared across groups"

X_values is assigned once and never read (not in this file, not anywhere in the
repo), so the union(...) is thrown away. Because of this, x_values never grows, and
the check compares each group only against the first group — instead of against all
groups seen so far.

Why this is a bug: it rejects inputs that plotly can render perfectly well.
px.area draws each line group as a stacked area and stacks them over the union of
all x-values (missing points filled with 0, stackgaps="infer zero" by default). So the
"compare against everything so far" (union) reading is the one that matches how the
chart actually works — the current code is both a dead store and too strict.

I confirmed this by running the check logic and px.area on the sample data below:
current code → error = "X attributes not shared across groups"; with X_values
changed to x_values → error = ""; and px.area renders the data fine (3 traces).

The line has been here since the operator was first added in #2086, and later PRs
(#2994, #3111) carried it over unchanged.

Suggested fix (low priority): please confirm the intent. If groups should be
compared against all x-values seen so far, this is a one-character fix
(X_values → x_values). If comparing only to the first group was intended, the dead
line should be removed.

How to reproduce?

Add a Filled Area Plot with Line Group set, and give it groups that overlap in a
chain but where the last group shares no x with the first:

x	y	grp
1	10	A
2	10	A
2	10	B
3	10	B
3	10	C
4	10	C

(A = {1,2}, B = {2,3}, C = {3,4}: A–B share 2, B–C share 3, but C shares nothing
with A.)

Config: X = x, Y = y, Line Group = grp.

• Expected: a stacked area chart (plotly renders this fine).
• Actual: no chart — an error page: "X attribute is not shared across all line groups."

Version/Branch

1.3.0-incubating-SNAPSHOT (main)

Commit Hash (Optional)

No response

What browsers are you seeing the problem on?

No response

Relevant log output

[VuMartin]

/take

[chenlica]

@kz930 As you created the issue, please make sure to coordinate with @VuMartin who took it.

[kz930]

Hi @VuMartin, thanks for taking this issue. I suspect the fix is changing X_values to x_values. I included a reproduction case and can help test the PR.

[VuMartin]

Hi @kz930, thanks for helping. I tested the reproduction case you provided, and the fix resolves the issue. It’s shown in the screenshot in the PR. Let me know if you’d like me to test any additional cases.

[kz930]

It looks good to me.