NIFI-15853 - Support fetchable allowable values in the connector wizard. added searchable select component.

[rfellows]

Summary

NIFI-15853

This pull request fixes connector wizard properties whose allowable values must be loaded from the backend (allowableValuesFetchable === true with no static allowableValues). Previously those properties were rendered as a plain text control and never triggered the allowable-values request, so users could not pick from server-provided options.

The fix introduces a reusable SearchableSelect component (Material-based, ControlValueAccessor) and routes both static and dynamic allowable values through it. ConnectorPropertyInput now emits requestAllowableValues exactly once per fetchable control when the step loads (guarded by hasFetchedDynamicValues), and resets that guard when the bound descriptor's property.name changes so a rebound descriptor can refetch. Loading, error, and empty responses are handled with fallbacks so the field stays usable (text input or textarea as appropriate).

STRING_LIST properties now render as a multi-select when allowable values exist (static or dynamic), and as a comma-separated textarea when they do not — replacing the previous plain text input for that type.

Scope

• 14 files, all under nifi-frontend/src/main/frontend (~4800 insertions, ~77 deletions on squashed commit 75068da3e3).

New / updated shared UI

• SearchableSelect (libs/shared/src/components/searchable-select/): filterable overlay select with optional multi-select, sticky search with clear, optional async search and virtual scrolling, optional grouped options, loading/error/empty states, full keyboard navigation, and accessibility (role="combobox", aria-*). Spec file adds broad coverage (107 tests covering single/multi select, filter, keyboard navigation, focus management, virtual scrolling, async search, grouping, value-change deduplication, and disabled states).
• MultiSelectOption: extends MatOption for options inside the overlay; theming (min-height, padding, hover, selected, keyboard focus) is scoped under .multi-select-option so other mat-select usages are unaffected.
• ConnectorPropertyInput: template moved to connector-property-input.component.html; helpers for input kind and dynamic state (shouldUseSelect, shouldUseTextInput, shouldUseTextarea, isMultiSelect, isDynamicValuesFetchEmpty, isDynamicValuesFetchFailed); textarea branch aligned with text input for validation errors (required, pattern, verificationError, assetContentMissing where applicable).
• Exports: libs/shared/src/components/index.ts and libs/shared/src/types/index.ts updated for new components/types.

Visible UX (intentional)

• Static allowableValues dropdowns now use searchable-select instead of mat-select (search filter + clear control) so static and dynamic flows share one widget.
• STRING_LIST is multi-select or textarea as described above.
• Option row styling is isolated to searchable-select's option component; other selects in NiFi are not restyled globally.

Out of scope / follow-ups

• ASSET / ASSET_LIST handling (called out in component doc comment as deferred).
• SECRET dropdown and BOOLEAN slide-toggle alignment with the new patterns.
• Dependency-aware refetch when a parent property changes (dynamic allowable values are still fetched once per control lifecycle / descriptor identity as implemented here).

Screenshots

Fetched allowable values from the KafkaToS3 connector for topic names

Tracking

Please complete the following tracking steps prior to pull request creation.

Issue Tracking

• Apache NiFi Jira issue created

Pull Request Tracking

• Pull Request title starts with Apache NiFi Jira issue number, such as NIFI-15853
• Pull Request commit message starts with Apache NiFi Jira issue number, as such NIFI-15853
• Pull request contains commits signed with a registered key indicating Verified status

Pull Request Formatting

• Pull Request based on current revision of the main branch
• Pull request refers to a feature branch with one commit containing changes

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Verification

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Build

• Build completed using ./mvnw clean install -P contrib-check
  • JDK 21
  • JDK 25

(Frontend-only change under nifi-frontend; full root contrib-check should still be run per project norms before merge.)

Licensing

• New dependencies are compatible with the Apache License 2.0 according to the License Policy
• New dependencies are documented in applicable LICENSE and NOTICE files

Documentation

• Documentation formatting appears as expected in rendered files

[scottyaslan]

Reviewing...