FieldGridDropdown: recomputeAriaContext() throws when the field has no DOM element

[microbit-robert]

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Component

FieldGridDropdown

Description

recomputeAriaContext() in FieldGridDropdown ignores the boolean returned by super.recomputeAriaContext() and then unconditionally calls getFocusableElement(), which throws. This can be observed when using the zelos renderer.

It should probably follow the pattern in core:

const shouldCustomize = super.recomputeAriaContext();
if (!shouldCustomize) return false;

Reproduction steps

1. Running this repo locally, edit the test file for the field-grid-dropdown plugin (test/index.ts) by setting the renderer to zelos
2. npm start
3. Observe the following output:

Stack trace

field currently has no representative DOM element.
    at FieldGridDropdown.getFocusableElement (webpack-internal:///../../node_modules/blockly/blockly_compressed.js:1084:175)
    at FieldGridDropdown.recomputeAriaContext (webpack-internal:///./src/index.ts:98:76)
    at hi.recomputeAriaContext (webpack-internal:///../../node_modules/blockly/blockly_compressed.js:1349:462)
    at hi.setShadow (webpack-internal:///../../node_modules/blockly/blockly_compressed.js:1330:184)
    at ee (webpack-internal:///../../node_modules/blockly/blockly_compressed.js:83:115)
    at ce (webpack-internal:///../../node_modules/blockly/blockly_compressed.js:82:168)
    at Li.createShadowBlock (webpack-internal:///../../node_modules/blockly/blockly_compressed.js:1214:245)
    at Li.respawnShadow_ (webpack-internal:///../../node_modules/blockly/blockly_compressed.js:1209:291)
    at Li.respawnShadow_ (webpack-internal:///../../node_modules/blockly/blockly_compressed.js:1224:169)
    at Li.setShadowStateInternal (webpack-internal:///../../node_modules/blockly/blockly_compressed.js:1213:502)

Screenshots

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