Chain class Null safety

A chain of stack traces.

A stack chain is a collection of one or more stack traces that collectively represent the path from main through nested function calls to a particular code location, usually where an error was thrown. Multiple stack traces are necessary when using asynchronous functions, since the program's stack is reset before each asynchronous callback is run.

Stack chains can be automatically tracked using Chain.capture. This sets up a new Zone in which the current stack chain is tracked and can be accessed using new Chain.current. Any errors that would be top-leveled in the zone can be handled, along with their associated chains, with the onError callback. For example:

Chain.capture(() {
  // ...
}, onError: (error, stackChain) {
  print("Caught error $error\n"
        "$stackChain");
});