Contexts

dotc has almost no global state (with the exception of the name table, which hashes strings into unique names). Instead, all essential bits of information that can vary over a compiler run are collected in a Context (defined in Contexts).

Most methods in the compiler depend on an implicit anonymous Context parameter, and a typical definition looks like the following:

import dotty.tools.dotc.Contexts.{Context, ctx}

def doFoo(using Context): Unit =
  val current = ctx.run // access the Context parameter with `ctx`

Memory Leaks

Careful: Contexts can be heavy so beware of memory leaks

It is good practice to ensure that implicit contexts are not captured in closures or other long-lived objects, in order to avoid space leaks in the case where a closure can survive several compiler runs (e.g. a lazy completer for a library class that is never required). In that case, the convention is that the Context be an explicit parameter, to track its usage.

Context Properties