[fnaji]

Follow-up to #25 (1.0.18).

Problem

1.0.18 draws a cell as one stacked bar only when there is no x axis. With an x axis that gives each value of a cell its own position, stack and fill still draw separate bars, the same as dodge. A common case is the colour factor on x, which is what the customer did on tercen.com. There, no x position holds more than one value, so ggplot has nothing to stack.

Fix (utils.R, ChartBar)

• Stack / fill. When no x position in a layer holds more than one value in its cell, the cell is drawn as one bar. The bar is stacked or filled in x-axis order, first position at the bottom. With no x axis, the order is still the crosstab order (Bar chart without x axis: crosstab order, and stack/fill really stack #25).
• Values sharing an x. When values share an x position, for example a numeric x with a colour per x, ggplot stacks per x position as before.
• Dodge. Unchanged.

Verification

Each case ran on local Tercen Studio in dodge, stack and fill. Each was compared with the released 1.0.18 image, once as released and once with this utils.R mounted.

Projection	Result
Customer data, x = label (text, also the colour)	stack and fill: one bar per cell, in x/legend order. dodge: identical to 1.0.18.
Customer data, no x	identical to 1.0.18
Synthetic data, numeric x (Day), 3 colours per x	identical to 1.0.18, still stacked per x
Synthetic data, no x	identical to 1.0.18

Unit tests (new)

• Refactor. utils.R moves the bar placement into pure functions: crosstab_x_position, collapse_bars, stack_cells and bar_layer. They can be tested without a Tercen context. The output is unchanged: 12 Studio projections are pixel-identical before and after.
• unit_tests/run.R. 24 base-R checks, with no testthat added to the image. Each builds the bar layer and reads back what ggplot computes:
  • one bar per cell, and its stack order: crosstab order without x, x order with the colour on x;
  • fill reaching 1;
  • plain ggplot behaviour when values share an x.
• The checks catch real regressions. They fail on the 1.0.17 read order (4 failures), the 1.0.18 rule that only merges without an x axis (5 failures), and an upside-down stack (6 failures).
• .github/workflows/unit-tests.yml. Builds the image and runs the tests in it on every pull request and on pushes to master. It is green on this PR.
• Location. The tests live in unit_tests/, not tests/, which Tercen's installer and the library scan treat as platform golden tests.

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