Andrew Trick 6823b100a7 Diagnose exclusivity in the presence of coroutines. ...

Potentially source breaking: SR-11700 Diagnose exclusivity violations
with Dictionary.subscript._modify:

  Exclusivity violations within code that computes the `default`
  argument during Dictionary access are now diagnosed.

  ```swift
  struct Container {
     static let defaultKey = 0

     var dictionary = [defaultKey:0]

     mutating func incrementValue(at key: Int) {
       dictionary[key, default: dictionary[Container.defaultKey]!] += 1
     }
  }
  error: overlapping accesses to 'self.dictionary', but modification requires exclusive access; consider copying to a local variable
       dictionary[key, default: dictionary[Container.defaultKey]!] += 1
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  note: conflicting access is here
       dictionary[key, default: dictionary[Container.defaultKey]!] += 1
                                ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
  ```

This reworks the logic so that four problems end up being fixed:

Fixes three problems related to coroutines:

(1) DiagnoseStaticExclusivity must consider begin_apply as a user of accessed variables. This was an undefined behavior hole in the diagnostics.

(2) AccessedSummaryAnalysis should consider begin_apply as a user of accessed arguments. This does not show up in practice because coroutines don't capture things.

(3) AccessedSummaryAnalysis must consider begin_apply a valid user of
    noescape closures.

And fixes one problem related to resilience:

(4) AccessedSummaryAnalysis must conservatively consider arguments to external functions.

Fixes <rdar://problem/56378713> Investigate why AccessSummaryAnalysis is crashing

2020-04-28 10:57:40 -07:00

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