JSX uses mixed signatures and union sigs use subtype on partial match #28141
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Jessidhia
reviewed
Oct 26, 2018
| function checkJsxReturnAssignableToAppropriateBound(isSFC: boolean, elemInstanceType: Type, openingLikeElement: Node) { | ||
| if (isSFC) { | ||
| function checkJsxReturnAssignableToAppropriateBound(refKind: JsxReferenceKind, elemInstanceType: Type, openingLikeElement: Node) { | ||
| if (refKind === JsxReferenceKind.Function) { | ||
| const sfcReturnConstraint = getJsxStatelessElementTypeAt(openingLikeElement); | ||
| if (sfcReturnConstraint) { | ||
| checkTypeRelatedTo(elemInstanceType, sfcReturnConstraint, assignableRelation, openingLikeElement, Diagnostics.JSX_element_type_0_is_not_a_constructor_function_for_JSX_elements); |
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(note) as of React 16, components are also allowed to return number / string / boolean (in other words, anything other than undefined, symbol or a non-Element, non-Array object), but at least TS@latest will reject SFC which include those return types. It does validate with classes, just not functions.
If fixed this probably goes in another PR though.
ahejlsberg
approved these changes
Oct 26, 2018
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Fixes #27948 in the general case where the union elements are like
ComponentType- very similar signatures in each union member.