fix(deck.gl): restore legend display for Polygon charts with linear palette and fixed color schemes

[sadpandajoe]

SUMMARY

• Fixed critical regression where legends disappeared in deck.gl Polygon charts between Superset 5.0 and 6.0
• Affected charts using linear_palette (default) and fixed_color schemes when displaying metrics
• Single-line conditional logic fix with comprehensive test coverage

Root Cause

The bucket generation logic incorrectly treated any truthy colorSchemeType as requiring color breakpoints:

before:

const buckets = colorSchemeType
? getColorBreakpointsBuckets(formData.color_breakpoints)
: getBuckets(formData, payload.data.features, accessor);

after:

const buckets = colorSchemeType === COLOR_SCHEME_TYPES.color_breakpoints
? getColorBreakpointsBuckets(formData.color_breakpoints)
: getBuckets(formData, payload.data.features, accessor);

When colorSchemeType was "linear_palette" or "fixed_color", it incorrectly called getColorBreakpointsBuckets() with undefined color_breakpoints, returning empty buckets and causing legends to disappear.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

11 comprehensive tests covering all scenarios:

• Bucket generation logic for all color scheme types
• Error handling and edge cases
• Legend integration testing
• Utility function validation

Manual test:

1. open up a workspace
2. go to the polygon chart
3. verify legend shows up

ADDITIONAL INFORMATION

• Has associated issue: fixes Disappeared features in the representations of deck.gl in the version of Superset 6.0.0 #34822
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[korbit-ai]

I've completed my review and didn't find any issues.

Files scanned

​

File Path	Reviewed
superset-frontend/plugins/legacy-preset-chart-deckgl/src/layers/Polygon/Polygon.tsx	✅

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