Commits on Apr 9, 2024

1. Warn if outdated JSX transform is detected …

   We want to warn if we detect that an app is using an outdated JSX
   transform. We can't just warn if `createElement` is called because we
   still support `createElement` when it's called manually. We only want
   to warn if `createElement` is output by the compiler.
   
   The heuristic is to check for a `__self` prop, which is an optional,
   internal prop that older transforms used to pass to `createElement` for
   better debugging in development mode.
   
   If `__self` is present, we `console.warn` once with advice to upgrade
   to the modern JSX transform. Subsequent elements will not warn.
   
   There's a special case we have to account for: when a static "key" prop
   is defined _after_ a spread, the modern JSX transform outputs
   `createElement` instead of `jsx`. (This is because with `jsx`, a spread
   key always takes precedence over a static key, regardless of the order,
   whereas `createElement` respects the order.) To avoid a false positive
   warning, we skip the warning whenever a `key` prop is present.

   

   acdlite committed Apr 9, 2024
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