[Bug] updateSpec: background is not re-rendered when spec.background and spec.theme change in the same call

[chendaxin-tk]

Version

2.1.6 (also reproduces on 2.1.5)

Link to Minimal Reproduction

https://gist.github.com/chendaxin-tk/dfb94e188970055a1ddadc2332194c23

Self-contained HTML — save it and open in a browser, it loads vchart 2.1.6 from unpkg and prints the result on the page.

Steps to Reproduce

1. Render a chart whose spec.background is the mark form { fill: <gradient> }, with spec.theme.background = 'transparent' (the canvas base color has to be transparent, otherwise the gradient's alpha composites against it).
2. Call updateSpec() with a spec where background is a color string ('#4e83fd') and theme.background is back to an opaque color ('#ffffff').
3. Look at the canvas.

A plain updateSpec(spec) is enough — no extra arguments needed.

Current Behavior

The canvas still paints the old gradient. Sampling the bottom-right pixel:

after render : pixel=255,159,67   stage.background=transparent
after update : pixel=255,159,67   stage.background=#4e83fd     <-- still the gradient

Note stage.background is updated correctly to #4e83fd. The problem is that the background mark created from the previous { fill } spec is never rebuilt or removed, and it covers the whole viewBox — so the corrected canvas base color is invisible and nothing changes on screen.

Isolating it — same repro, only what changes in the update spec varies:

#	changed in updateSpec	result
A	background and theme	❌ old gradient stays
B	background only, theme untouched	✅ blue
C	background and theme, called as updateSpec(spec, false, { reuse: false, morph: false }, { change: true, reMake: true })	✅ blue

Expected Behavior

Case A should behave like case B — the new background should be painted.

Probable Cause

In core/vchart.js, updateSpec only compares background when the theme is unchanged:

isEqual(lastSpec.theme, this._spec.theme)
  ? (isEqual(this._spec.background, lastSpec.background) || (result.reMake = !0, result.changeBackground = !0))
  : result.changeTheme = !0;

When both change in the same call, the ternary takes the changeTheme branch, so reMake / changeBackground are never set and the background mark is not rebuilt. setBackground() still runs indirectly via _setCurrentTheme() → _updateCurrentTheme(), which is why stage.background looks right while the canvas does not change.

This looks like a remaining gap in the fix for #3054, which covered the case where only background changes.

Forcing reMake: true (case C above) is a workaround, but it rebuilds the whole chart.

Additional observation (could not minimize — treat as a lead, not a confirmed repro)

In a larger application the same gradient → solid transition throws instead of silently keeping the old background:

TypeError: Cannot read properties of undefined (reading 'group')
    at GroupMark._compileProduct (...)

which aborts the entire updateSpec. In mark/base/base-mark.js, _compileProduct guards option on two lines but dereferences it bare on a third:

_compileProduct(option) {
    this.commit(), this._context = null == option ? void 0 : option.context;   // guarded
    const product = this.getProduct();
    if (this._visible) {
        if (isValid(product)) option.group && product.parent !== option.group && option.group.appendChild(product);   // NOT guarded
        else {
            if (!this.getCompiler().isInited) return;
            this._initProduct(null == option ? void 0 : option.group);         // guarded
        }

I was not able to reproduce this one in isolation, so I am reporting it only as a pointer — the inconsistent guarding is visible statically and may or may not be related to the main issue above.

Environment

• @visactor/vchart 2.1.6 (UMD build from unpkg) and 2.1.5
• Chromium (Playwright), Linux